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On this page, you will find Electricity Class 10 Notes Science Chapter 12 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 12 Electricity will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 12 Notes Electricity

Electricity Class 10 Notes Understanding the Lesson

1. Current electricity: The branch of physics which deals with the study of charge in motion is called current electricity.

2. Electric charge: Charge is the property of matter due to which it produces and experiences electric and magnetic effects.

• SI unit of charge is coulomb (C).
• There exists two types of charges in nature.

(i) positive charge
(ii) negative charge

• Smallest stable charged particles are protons and electrons.
• Charge on an electron is negative and that on a proton is positive but both are equal in magnitude
  i. e., 1.6 x 10^-19C

Properties of charge

• Like charges repel each other and unlike charges attract each other.
• Charge can neither be created nor destroyed but it can be transferred from one body to another
  i. e., charge is conserved.

3. Electric current (I): Electric current is defined as the total amount of charge flowing through a particular area in unit time. It is denoted by T. \(I=\frac{Q}{t}\)

where, Q = amount of charge, t = time interval

• Electric current is a scalar quantity.
• SI unit of current is ampere (A).
• 1 Ampere

One ampere is constituted by the flow of one coulomb of charge per second.
\(I=\frac{Q}{t} \mid \text { If } Q=1 C \text { and } t=1 s, \text { then } I=\frac{1 C}{1 S}=1 A\)

• Small quantities of current are expressed in milliampere or in microampere.
  1 mA = 10^-3 A (Here ‘m’ is a prefix used to express milli)
  10 μA = 10^-6 A (‘μ’ is symbol of micro)

4. Direction of current:

• Electric current flows in the circuit from positive terminal of cell to the negative terminal of cell.
• In metals flow of electron constitutes current. Conventionally the direction of current is taken as opposite to the direction of motion of electrons.

5. Electric potential difference: Electric potential difference between two points in an electric circuit, carrying current can be defined as the amount of work done to move a unit charge from one point to another.
\(\text { Potential difference }(\mathrm{V})=\frac{\text { Work done }(\mathrm{W})}{\text { Charge }(\mathrm{Q})}\)
\(V=\frac{W}{Q}\)

• SI unit of potential difference is volt (V).
• The electron moves in a wire due to potential difference. The potential difference may be produced by chemical reaction occurring in a battery.
• 1 volt (1 V)

One volt is the potential difference between two points in a current carrying conductor, when 1 Joule of work is done to move a charge of 1 coulomb from one point to the other.
\(\text { Therefore, } 1 \text { volt }=\frac{1 \text { Joule }}{1 \text { Coulomb }}\)
IV = 1JC^-1

6. Electric circuit: A continuous and closed path of electric current is called an electric circuit.

7. Circuit diagram: A circuit is a simplified systematic representation of the components of an electrical circuit.
Table 12.1 Symbols of some commonly used components in circuit diagrams

8. Measuring Instruments:

• Ammeter: It is used to measure the magnitude of electric current through any wire of a circuit.
• It is always connected in series.
• It should have low resistance.

Voltmeter: It measures the potential difference between two points of the circuit.

• The voltmeter is always connected in parallel across the points between which the potential difference to be measured.
• It should have high resistance.

9. Ohm’s law: According to ohm’s law, the potential difference, v, across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing.

Here, R is constant for a given metallic wire at a given temperature and is called resistance.

10. V-I graph of ohm’s law and its experimental setup:
1. Circuit diagram

2. Variation of current with potential difference

Slope of V-I curve gives resistance
\(R=\text { slope }=\frac{\Delta \mathrm{V}}{\Delta \mathrm{I}}\)
I-V curve of Ohm’s law

Slope of I-V curve =\(\frac{1}{\mathrm{R}}\)
\(\frac{1}{\mathrm{R}}=\text { Slope }=\frac{\Delta \mathrm{I}}{\Delta \mathrm{V}}\)

11. Resistance:

• It is the property of a conductor to resist the flow of charges through it.
• SI unit of resistance is ohm, represented by Greek letter Ω (omega).

(i) One ohm
If the potential difference across the two ends of a conductor is IV and the current through it is 1A, then the resistance, R, of the conductor is 1 Ω.
\(1 \mathrm{ohm}=\frac{1 \text { volt }}{1 \mathrm{ampere}}\)

• The current through a resistor is inversely proportional to its resistance keeping voltage constant.
• Resistance in a circuit arises due to retardation in motion of electrons as they are restrained by attraction of atom among which they move.

(ii) Rheostat
Rheostat is a component or device used to regulate current without changing the voltage source, it is also called variable resistance.

12. Factors affecting resistance of a conductor

• Resistance of a uniform metallic conductor is directly proportional to its length (l)
  R α Z …………(1)
• Resistance is inversely proportional to area of cross-section (A).
  

where, ρ(rho) is constant of proportionality and it is called electric resistivity of the material of the conductor.

• Resistance of a metallic conductor also depends on temperature.
• It also depends on the nature of the material.

13. Electric resistivity (ρ)
(i) Resistivity depends on the nature of the material and temperature. It is independent of the length and area of cross-section of the conductor.

(ii) where, R = resistance
A = Area of cross-section
l = length of conductor

(iii) SI unit of resistivity is ‘Ωm’.

14. Classification of Elements on the basis of resistivity

• Metals and alloys have very low resistivity in the range of 10^-8 O m to 10^-6 Q m. They are good conductors of electricity.
• Insulators have resistivity of the order of 10¹² to 10¹⁷ Q m. They are bad conductors of electricity.

15. Use of elements on the basis of resistivity.

• Copper and aluminium are used for electric transmission lines because both posses low resistivity.
• Alloys are commonly used in electric heating appliances.

Resistivity of an alloy is generally higher than that of its constituent metals. Alloy do not oxidise readily at high temperatures. For this reason, they are commonly used in electric heating devices.

16. Combination of Resistors

17. Special Case

Resistance in Series	Resistance in Parallel
When ‘n’ number of identical resistors having resistance ‘R’ is connected in series then equivalent resistance becomes \(R_{e q}=n \mathrm{R}\)	When ‘n’ number of identical resistors having resistance ‘R’ is connected in parallel then equivalent resistance becomes\(\mathrm{R}_{e q}=\frac{\mathrm{R}}{n}\)

18. Some Important points for series and parallel combination

• For getting maximum equivalent resistance, all resistors should be connected in series and for getting minimum equivalent resistance, all resistors should be connected in parallel.
• In domestic circuits, parallel combination is used because in series arrangement, if any one of appliances fails or is switched off, all the other appliances stop working.

19. Electric power (P): The rate at which electric energy is consumed or dissipated is called electric power.
Electric power
\(P=V I=I^{2} R=\frac{V^{2}}{R}\)

• One watt (1 W)
  One watt is the power consumed by a device that carries 1 A of current when operated at a potential difference of 1 V.
  Thus, 1 W = 1 volt x 1 ampere = 1 V A
• Larger unit of power
  1 kW = 1000 W (1 kW = one kilowatt)

• Commercial unit of electric energy (kWh) (units)
  1 KWh = 1000 watt x 3600 seconds
  1 unit = 1 kWh = 3.6 x 10⁶ J

One kilowatt hour is the energy consumed when 1 kilowatt of power is used for one hour.

Heating effect of electric current

• Heating effect: When an electric current passes through a wire, the wire gets heated and its temperature rises. This is known as heating effect of electric current.

Joule’s law of heating: Heat produced in a conductor is directly proportional to

• square of current for a given resistor (H α I²)
• the resistance for a given current (H α R)
• the time for which the current flows through the resistor (H α t) H = I²Rf

20. Practical applications of heating effect of electric current

1. Incandescent electric lamp: The heating effect of electric current is also used to produce light, like in a electric bulb. The filament of the bulb is made up of tungsten with high melting point (3380°C). It is thermally isolated using insulated support. Presence of chemically inactive gases like argon and nitrogen prolong the life of the filament. When voltage is applied across the filament of the bulb, the current starts passing through it. The filament gets heated to a very high temperature (2700°C). It becomes white hot and starts radiating heat and light.

2. Fuse: Fuse is a device which is based on the principal of heating effect of electric current. It protects circuits and appliances by stopping the flow of any unduly high current. It consists a piece of wire made of a metal or an alloy of appropriate melting point. If a current larger than the specified value flows through the circuit, the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit.

Class 10 Science Chapter 12 Notes Important Terms

Current (I): The rate of flow of charge is called current.

Potential Difference (V): Work done to move a unit charge from one point to another.

Volt: When 1 joule work is done in carrying one coulomb charge then potential difference is called 1 volt. Voltmeter: Instrument used to measure potential difference.

Ammeter: Instrument used to measure electric current.

Ohm’s Law: Potential difference across two points of a metallic conductor is directly proportional to current passing through the circuit provided that temperature remains constant.

Resistance (R): It is the property of a conductor to resist the flow of charges through it.

Rheostat: Variable resistance is a component used to regulate current without changing the source of voltage.

Resistivity (ρ): It is defined as the resistance offered by a cube of a material of side 1 m when current flows perpendicular to its opposite faces.

Electric Fuse: It is a safety device that protects our electrical appliances in case of short circuit or overloading

Electric Power: The rate at which electric energy is consumed or dissipated in an electric circuit.

Heating Effect of Electric Circuit: If an electric circuit is purely resistive, the source of energy continually gets dissipated entirely in form of heat. This is known as heating effect of electric current.

On this page, you will find Human Eye and Colourful World Class 10 Notes Science Chapter 11 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 11 Human Eye and Colourful World will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 11 Notes Human Eye and Colourful World

Human Eye and Colourful World Class 10 Notes Understanding the Lesson

1. The human eye: The human eye an extremely valuable and a sensitive sense organ, which enables us to see objects and colours around us.

2. Parts of the human eye:

• Cornea: A thin membrane through which light enters the eye, maximum refraction occurs at the outer surface of cornea.
• Iris: A dark muscular membrane which controls size of pupil.
• Pupil: Regulates and controls the amount of light entering the eye.
• Eye lens: Composed of fibrous, jelly-like material, with adjustable curvature, forms an inverted and real image of object on retina.
• Retina: It is a light sensitive screen on which image is formed.

3. Power of Accommodation:

• The ability of the eye lens to adjust its focal length is called accommodation.
• Least distance of distinct vision: Minimum distance at which object can be seen distinctly without any strain from normal eye, i.e, 25 cm for normal vision.
• Far point of the eye: The farthest point upto which the eye can see objects clearly is called far point of the eye. It is infinity for normal eye.

4. Defects of Vision:
(i) Cataract: Crystalline lens of people at old age becomes milky and cloudy. This condition is called cataract. It is possible to restore vision through cataract surgery.
(ii) Myopia: (Near sightedness)

A person with myopia can see nearby objects clearly but cannot see distant objects clearly. Cause

• Due to excessive curvature of the eye lens.
• Elongation of the eyeball.

(iii) Hypermetropia (far-sightedness)
A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.
Cause

• The focal length of the eye lens is too long.
• The eyeball has become too small.

Correction
Convex lens of suitable power.

(iv) Presbyopia
The power of accommodation of the eye usually decreases with ageing. In this eye defect it is difficult to see nearby objects comfortably and distinctly without corrective eye glasses.

Cause:Weakening of cilary muscles and diminishing flexibility of eye lens.

Correction: By using bifocal lens. Upper portion consists of concave lens and lower part is convex lens.

5. Refraction of Light through Prism

(i) The refraction of light takes place at two surfaces firstly when light enters from air to prism and j secondly when light emerges from prism.
(ii) Angle of prism: The angle between the two lateral faces of the prism is called angle of prism.
(iii) Angle of deviation: The angle between incident ray (produced forward) and emergent ray I (produced backward).

6. Dispersion of White Light by a Glass Prism
Dispersion:

• The splitting of light into its component colours is called dispersion.
• Red light bends the least while violet bends the most.

Spectrum: The band of the coloured components of a light beam is called spectrum, i.e., VIBGYOR

When an inverted prism is kept a little distance away from the prism causing dispersion or basically in the path of splitted beam, the spectrum recombines to form white light.

7. Rainbow Formation
A rainbow is a natural spectrum appearing in the sky after rain shower. It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. The water droplet act like small prism. They refract and disperse the incident sunlight, then reflect it internally and finally refract it again.

Due to dispersion of light and internal reflection different colours appears.

8. Atmospheric Refraction
If physical conditions of the refracting medium (air) are not stationary, the apparent position of the object fluctuates.

Twinkling of stars

• The twinkling of stars is due to atmospheric refraction of starlight.
• When starlight enters the earth’s atmosphere, it suffers refraction continuously. Since the physical conditions of the earth’s atmosphere are not stationary the stars appear twinkling.

Advance sunrise and delayed sunset

Advance sunrise and delayed sunset is due to atmospheric refraction.
When the sun is slightly below the horizon, the sunlight coming from the less dense (vacuum) to the more dense (air) medium is refracted downwards. Therefore the Sun appears to be above the horizon. Similarly, even after sunset, the Sun can be seen for sometime due to refraction of sunlight.

9. Tyndall Effect

The phenomenon of scattering of light by colloidal particle gives rise to Tyndall effect.
Tyndall effect can be observed when sunlight passes through a canopy of a dense forest. Here tiny droplets in mist scatters light.
The colour of the scattered light depends on the size of the scattering particles. Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths.

Colour of the clear sky is blue: The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. When sunlight passes through the atmosphere, the fine particles in air scatter the blue colour more strongly than red.

Danger signal lights are red in colour: Because red colour is least scattered by fog or smoke.

Sun appears reddish early in the morning: In the morning and evening, the Sun lies near the horizon. Sunlight travels through a larger distance in the atmosphere and most of the blue light and shorter wavelengths are scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelength. This gives rise to the reddish appearance of the Sun.

Class 10 Science Chapter 11 Notes Important Terms

Eye: The human eye is an extremely valuable and sensitive sense organ, which enables us to see objects and colours around us.

Power of accommodation: The ability of the eye lens to adjust its focal length is called accommodation.

Myopia: A person with myopia can see nearby objects clearly but cannot see distant objects clearly.

Cataract: Crystalline lens of people at old age becomes milky and cloudy. This condition is called cataract.

Hypermetropia: A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.

Presbyopia: The power of accommodation of the eye usually decreases with ageing. In this eye defect, it is difficult to see nearby objects comfortably and distinctly without corrective eye glasses.

Dispersion: The splitting of light into its component colours is called dispersion.

Atmospheric refraction: Refraction of light by the constituent particles of the atmosphere. Tyndall effect: The phenomenon of scattering of light by colloidal particles gives rise to Tyndall effect.

On this page, you will find Light Reflection and Refraction Class 10 Notes Science Chapter 10 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 10 Light Reflection and Refraction will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 10 Notes Light Reflection and Refraction

Light Reflection and Refraction Class 10 Notes Understanding the Lesson

1. Light: It is a form of energy which produces the sensation of sight.

• Light exhibits dual nature i.e. wave as well as particle nature.
• It travels with a speed of 3 x 10⁸ m/s in vacuum. However speed is inversely proportional to optical density of the medium.

2. Reflection: When light falls on a surface, it bounces back to the medium. The phenomena is called reflection.

3. Beam: A beam is a bundle of rays, which originates from a common source and travels in the same direction.

4. Laws of Reflection:
Terminology

• Incident ray: Ray of light coming from a source towards the reflecting surface.
• Reflected ray: Ray of light which is reflected back by a reflection surface.
• Normal: Perpendicular drawn to the reflecting surface.
• Angle of incidence: The angle between incident ray and normal at the point of incidence.
• Angle of reflection: The angle between reflected ray and normal at the point of reflection

Laws:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, the normal to the mirror at the point of incidence and reflected ray, all lie in the same plane.
  These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces.

5. Types of mirror
1. Plane mirror
2. Spherical mirror

• Concave mirror
• Convex mirror

Concave Mirror: A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of sphere, is called a concave mirror.
Convex Mirror: A spherical mirror whose reflecting surface is curved outwards, is called a convex mirror.

6. Basic terms of Spherical Mirrors:

• Centre of curvature: The centre of a hollow sphere of which the curved or spherical mirror forms a part is called centre of curvature.
• Radius of curvature (R): The radius of sphere of which the reflecting surface of a spherical mirror forms a part is called the radius of curvature of the mirror.
• Pole: The centre of the reflecting surface of spherical mirror. The pole is usually represented by the letter P.
• Principal axis: Its an imaginary line passing through the centre of curvature and pole.
• Aperture: The diameter of the reflecting surface of the spherical mirror is called its aperture.
• Principal focus: A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appear to meet after reflection from the spherical mirror is called principal focus.
• Focal length (f): The distance between the pole and principal focus (F) of a spherical mirror is called the focal length of the mirror. It is denoted by f.
• \(f=\frac{\mathrm{R}}{2}\)

7. Type of image

Real image	Virtual image
1. When rays of light after reflection meets at a point, real image is formed.	1. When rays of light do not actually meet but appear to meet at a point after reflection, virtual image is formed.
2. Real image can be obtained on screen.	2. Virtual image cannot be obtained on screen.
3. Real image is formed in front of mirror.	3. Virtual image is formed behind the mirror.
4. Real image is always inverted.	4. Virtual image is always erect.

Representation of images formed by spherical mirror using ray diagrams:

• In order to locate the image of an object, an arbitrarily large number of rays emanating from a point could be considered.
• The intersection of reflected ray gives the position of image.

8. Rules for obtaining image:
(i) A ray parallel to the principal axis, after reflection, will pass through the principal focus in case of concave mirror or appear to diverge from the principal focus in case of a convex mirror.

(ii) A ray passing through principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror after reflection will emerge parallel to the principal axis.

(iii) A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of curvature of a convex mirror after reflection, is reflected back along the same path.

(iv) A ray incident obliquely to the principal axis, towards point P (pole of the mirror) on the concave or convex mirror is reflected obliquely.

9. Formation of image by concave mirror
Image formation by a concave mirror for different positions of the object

S. No.	Position of the object	Position of the image	Size of the image	Nature of the image
(a)	At infinity	At the focus F	Highly diminished, point-sized	Real and inverted
(b)	Beyond C	Between F and C	Diminished	Real and inverted
(c)	At C	At bc	Same size	Real and inverted
(d)	Between C and F	Beyond C	Enlarged	Real and inverted
(e)	At F	At infinity	Highly enlarged	Real and inverted
(f)	Between P and F	Behind the mirror	Enlarged	Virtual and erect

Ray diagram for the image formation by a concave mirror

10. Formation of image by convex mirror

S. No.	Position of the object	Position of the image	Size of the image	Nature of the image
(a)	At infinity	At the focus F, behind the mirror	Highly diminished, point-sized	Virtual and erect
(b)	Between infinity and the pole P of the mirror	Between P and F, behind the mirror	Diminished	Virtual and erect

Ray diagram for image formation by convex mirror

11. Uses of mirrors
(a) Uses of concave mirrors:

• Concave mirrors are commonly used in torches, search lights and vehicles headlights to get powerful beam of light.
• It is used in shaving mirrors to see large image of the face.
• The dentists use concave mirror to see large images of the teeth of patients.
• Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

(b) Uses of convex mirrors:

• Convex mirrors are used as rear-view (wing) mirrors in vehicles.
• Convex mirrors are used as street reflectors because they are able to spread light over a bigger area.

12. Sign convention for reflection by spherical mirrors:

• The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.
• All distances parallel to the principal axis are measured from the pole of the mirror.
• All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.
• Distances measured perpendicular to and above the principal axis (along +y-axis) are taken as positive, (u)

13. Mirror formula and Magnification
Mirror formula
\(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)

Refractive index:
Refractive index: The ratio of speed of light in vacuum (c) to the speed of light in any medium (v) is called refractive index of the medium.

Relative refractive index:
The relative refractive index of a medium with respect to other medium is the ratio of speed of light in the second

Here, n₂₁ = Relative refractive index of medium 1 with respect to medium 2.

14. Some applications of refraction:

• Bottom of a tank or a pond containing water appears to be raised due to refraction.
• When a thick glass slab is placed over some printed matter, the letters appear raised when viewed through the glass slab.
• When a pencil is partly immersed in water, it appears to be displaced at the interface of air and water.
• A lemon kept in water in a glass tumbler appears to be bigger than its actual size, when viewed from sides.
  Lens: A transparent medium bound by two surfaces, of which one or both surfaces are spherical.

15. Convex lens: A lens may have two spherical surfaces, bulging outwards. Such a lens is called a double convex lens or convex lens.

• It is thicker at the middle as compared to the edges.
• Convex lens converges light as shown in Figure above.

Hence, convex lenses are called converging lens.

16. Concave lens: A double concave lens is bounded by two spherical surface curved inwards.

• It is thicker at the edges than in the middle.
• Concave lens diverges light and is called diverging lens.

17. Basic terms of spherical lens:

• Principal axis: A line joining the centre of curvatures of two spherical surfaces forming a lens is called principal axis. The line joining C₁ and C₂ is the principal axis (see figure below).
• Principal focus: A point on the principal axis of a lens where all rays of light parallel to the principal axis meet (figure a) or appears to meet (figure b) after passing through the lens is called principal focus of the lens.
• Optical centre: The central point of a lens (O) through which a ray of light pass undeviated is called optical
  
• Focal length: The distance between the principal focus and optical centre of a lens is called focal length of lens. It is denoted by f.
• Aperture of lens: The effective diameter of circular outline of a spherical lens is called its apperture.

18. Rules for making ray diagram

1. A ray of light from the object, parallel to the principal axis, after refraction from a lens passes through the principal focus or appears to diverge from the principal focus

2. A ray of light passing through the principal focus or appearing to meet at the principal focus after refraction, will emerge parallel to the principal axis.

3. A ray of light passing through the optical centre of lens will emerge without any deviation.

19. Image formation by convex lens. Nature, position and relative size of the image formed by a convex lens for various positions of the object.

S. No.	Position of the object	Position of the image	Relative size of the image	Nature of the image
(a)	At infinity	At focus F2	Highly diminished, point-sized	Real and inverted
(6)	Beyond 2F1	Between F2 and 2F2	Diminished	Real and inverted
(c)	At 2FX	At 2F2	Same size	Real and inverted
(d)	Between F1 and 2F1	Beyond 2F2	Enlarged	Real and inverted
(e)	At focus F1	At infinity	Infinitely large or highly enlarged	Real and inverted
(f)	Between focus F1 and optical centre 0	On the same side of the lens as the object	Enlarged	Virtual and erect

20. Ray diagram for the image formation by convex lens:

21. Image formation by concave lens:

Position of the objectPosition of the imageRelative size of the imageNature of the imageAt infinityAt focus F₁ Highly diminished, point-sizedVirtual and erectBetween infinity and optical 1 centre 0 of the lensBetween focus F₁ and optical centre 0DiminishedVirtual and erect

22. Sign convention of spherical lens:

• Sign conventions of lens is same as sign convention of mirrors
• The focal length of convex lens is positive and concave lens is taken as negative.

23. Lens formula and magnification:
\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

u = object distance
v = image distance
f= focal length

24. Magnification (m)
Magnification is defined as the ratio of the height of image to the height of object.
\(m=\frac{\text { Height of the image }}{\text { Height of the object }}=\frac{h^{\prime}}{h}=\frac{v}{u}\)
h’ = height of image
h = height of object

25. Power of a lens
The power of a lens is defined as reciprocal of its focal length.
\(P=\frac{1}{f}\)
f = focal length (in metre)

• The SI unit of power is ‘dioptre’. It is denoted by the letter D.
• 1 dioptre is the power of a lens whose focal length is 1 metre, 1 D = 1 m^-1
• Power of convex lens is positive and concave lens is negative.

26. Combination of lens
\(\frac{1}{f_{\text {net}}}=\frac{1}{f_{1}}+\frac{1}{f_{2}}\)
f_net ⁼ Net focal length f_x = focal length of lens 1 f₂ = focal length of lens 2
P net = Power of combination
P₁ = Power of lens 1
P₂ = Power of lens 2.

Class 10 Science Chapter 10 Notes Important Terms

Reflection: When light falls on a surface and bounces back to the medium, the phenomenon is called reflection.

Concave mirror: A spherical mirror, whose reflecting surface is curved inwards.

Convex mirror: A spherical mirror, whose reflecting surface is curved outwards.

Magnification: Magnification is expressed as a ratio of the height of image to the height of object.

Refraction: The deviation of light rays from its path when it travels from one transparent medium to another transparent medium is called refraction of light.

Lens: A transparent medium bound by two surfaces, of which one or both surfaces are spherical, forms a lens.

On this page, you will find Improvement in Food Resources Class 9 Notes Science Chapter 15 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 15 Improvement in Food Resources will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Science Chapter 15 Notes Improvement in Food Resources

Improvement in Food Resources Class 9 Notes Understanding the Lesson

1. The population of India is more than one billion people, and it is still growing. So, the need of the hour is to increase the food production. This can be done by farming on more land. India is already intensively cultivated, so the only way out is to increase our production efficiency for both crops and livestock.

2. There is a need for sustainable practices in agriculture and animal husbandry to increase food production without degrading our environment and disturbing the balances maintaining it.

3. Types of Revolutions Related to Increase in Food Production

• Green revolution: increase in food grain production.
• White revolution: increase in milk production.
• Blue revolution: increase in fish production.
• Yellow revolution: increase in oilseed crops production.
• Golden revolution: increase in pulse production.

4. Kharif season crops: These are grown in rainy season from the month of June to October. Paddy, soyabean, pigeon pea, maize, cotton, green gram and black gram are kharif crops.

5. Rabi season crops: These are grown in winter season from November to April. Wheat, gram, peas, mustard and linseed are Rabi crops.

6. Msyor groups of activities for improving crop yields

• Crop variety improvement
• Crop production improvement
• Crop protection management

7. Hybridisation: A crossing between genetically dissimilar plants is called hybridisation.

8. Types of hybridisation

• Intervarietal: crossing between different varieties.
• Interspecific: crossing between two different species of the same genus.
• Intergeneric: crossing between different genera.

9. Ways of improving crop: Hybridisation, polyploidy, recombinant DNA technology, genetic manipulation, mutation breeding, etc.

10. Some of the factors for which variety improvement is done are

• Higher yield
• Improved quality
• Biotic and abiotic resistance
• Change in maturity duration
• Wider adaptability
• Desirable agronomic characteristics
• Higher yield
• Improved quality
• Biotic and abiotic resistance
• Change in maturity duration
• Wider adaptability
• Desirable agronomic characteristics

11. Nutrients
There are sixteen nutrients which are essential for plants. Carbon and oxygen supplied by air, hydrogen comes from water, and the other thirteen nutrients supplied by soil to plants.

12. Types of Nutrients:

• Macronutrients: The nutrients which are required in large quantities. They are six.
• Micronutrients: The nutrients which are required in small quantities. They are seven.

13. Manure
Manure is prepared by the decomposition of animal excreta and plant waste and contains a lot of organic matter which helps in enriching soil with nutrients and increasing soil fertility. It is classified on the basis of kind of biological material used as:

• Compost: Compost is prepared by decomposition of the farm waste material like livestock excreta (cow dung etc.), vegetable waste, animal refuse, domestic waste, sewage waste, straw, eradicated weeds, etc., in pits.
• Vermi-compost: The compost is called as vermicompost if it is prepared by using earthworms to hasten the process of decomposition of plant and animal refuse.
• Green manure: Green plants like sun hemp or guar are grown and then mulched by ploughing them into the soil prior to the sowing of the crop seeds to enrich the soil in nitrogen and phosphorus.

14. Fertilisers: They are commercially produced plant nutrients which supply nitrogen, phosphorus and potassium to soil in order to increase the crop yield.

15. Organic farming: It is a farming system which focuses on the minimal or no use of chemicals like fertilisers, herbicides, pesticides, etc., and with a maximum input of organic manures, recycled farm-wastes (straw and livestock excreta), use of bio-agents, etc.

16. Irrigation systems
Wells, canals, river lift system, tank, etc., are used for irrigation. Some new initiatives like rainwater harvesting and watershed management are being used. For this small check-dams are constructed to stop the rainwater from flowing and lead to an increase in ground water levels.

17. Cropping Patterns

• Mixed cropping: Growing two or more crops simultaneously on the same piece of land.
• Inter-cropping: Growing two or more crops simultaneously on the same field in a definite pattern.
• Crop rotation: Growing two or more crops on a piece of land in a pre-planned succession.

18. Crop Protection Management

Weeds: The unwanted plants in the cultivated field which compete for food, space and light with the crop plant and reduce the growth of the crop. For example, Xanthium (gokhroo), Parthenium (gajar ghas), Cyperinus rotundus (motha).

Weed control methods: Mechanical removal, spray of chemicals called weedicides and preventive methods like proper seed bed preparation, timely sowing of crops, intercropping and crop rotation.

Three ways in which insect pests attack the plants

• They cut the root, stem and leaf,
• They suck the cell sap from various parts of the plant, and
• They bore into stem and fruits.

19. Insect and Pest control methods: Spray of chemicals like insecticides, pesticides, use of resistant varieties and summer ploughing in which fields are ploughed deep in summers to destroy weeds and pests, crop rotation and cropping systems.

Ways to reduce loss during storage of grains

• Proper treatment and systematic management of warehouses.
• They include strict cleaning of the produce before storage,
• Proper drying of the produce first in sunlight and then in shade
• Fumigation using chemicals that can kill pests.

Animal Husbandry

• The scientific management of animal livestock is called animal husbandry.
  Cattle husbandry is done for two purposes: milk and draught labour for agricultural work.
• Two species of Indian cattle: Bos indicus of cows and Bos bubalis of buffaloes.
• Milch animals: Milk-producing females of cattle are called milch animals (dairy animals).
• Draught animals: Animals used for farm labour are called draught animals.
• Lactation period: The period of milk production after the birth of a calf is called lactation period. Milk
• production can be increased by increasing the lactation period.
• Exotic or foreign breeds of cow: Jersey, Brown Swiss are selected for long lactation periods while Local breeds of cow: Red Sindhi, Sahiwal show excellent resistance to diseases.

Food requirements of dairy animals:
Their food requirements are of two types:

• Maintenance requirement, which is the food required to support the animal to live a healthy life.
• Milk producing requirement, which is the type of food required during the lactation period.

Two types of feed for animals are

• Roughage, which is largely fibre.
• Concentrates, which are low in fibre and have high levels of proteins and other nutrients.

20. Poultry farming: It is undertaken to raise domestic fowl called layers for egg production and the broilers for chicken meat.

21. Indigenous breed: Aseel; Exotic or foreign breed: Leghorn

Desirable traits of poultry

• number and quality of chicks;
• dwarf broiler parent for commercial chick production;
• summer adaptation capacity/tolerance to high temperature;
• low maintenance requirements;
• reduction in the size of the egg-laying bird with ability to utilise more fibrous cheaper diets formulated using agricultural by-products.

22. Fish production: It includes the finned true fish as well as shellfish such as prawns and molluscs.

23. Two ways of obtaining fish

• Capture fishery: Fish are obtained from natural resources in capture fishery.
• Culture fishery: Fish farming is called culture fishery.

24. Types of fish: The fish can be classified according to the water source from which they are obtained as Freshwater fishery and Marine fishery.

25. Inland or freshwater fisheries: Fresh water resources include canals, ponds, reservoirs and rivers. Example- Catla, Rohu, etc.

26. Marine fisheries: Marine fishery resources include 7500 km coastline and the deep seas beyond it. Some marine fish varieties are pomphret, mackerel, tuna, sardines and Bombay duck. Fishes like mullets, bhetki and pearl spots; shellfish such as prawns, mussels and oysters as well as seaweed are of high economic value.

27. Composite fish culture systems: A combination of five or six fish species is used in a single fish pond in the composite fish culture system. The selected species do not compete for food among them as they have different types of food habits.

28. The types of fishes used are:
Catlas are surface feeders, Rohus feed in the middle-zone of the pond, Mrigals and Common Carps are bottom feeders, and Grass Carps feed on the weeds. As a result, the food available in all the parts of the pond is used.

29. Bee Keeping: It is done for obtaining honey which is used in many medicinal preparations and bee wax which is used in cosmetics.

30. Local variety of bee: Apis cerana indica, commonly known as the Indian bee, Apis dorsata, the rock bee and Apis florae, the little bee.

31. Italian bee variety: Apis mellifera is the Italian variety of bee. It has the following advantages:

• They have high honey collection capacity.
• They sting somewhat less.
• They stay in a given beehive for long periods, and breed very well.

Class 9 Science Chapter 15 Notes Important Terms

Green revolution: The increase in food grain production is called green revolution.

White revolution: The increase in milk production is called white revolution.

Blue revolution: The increase in fish production is called as blue revolution.

Yellow revolution: The increase in oilseed crops production is called yellow revolution.

Golden revolution: The increase in pulse production is called golden revolution.

Kharif season crops: These crops are grown in rainy season from the month of June to October. Rabi season crops: These crops are grown in winter season from November to April.

Hybridisation: A crossing between genetically dissimilar plants is called as hybridisation. Macronutrients: The nutrients which are required in large quantities.

Micronutrients: The nutrients which are required in small quantities.

Manure: Manure is prepared by the decomposition of animal excreta and plant waste and helps in increasing soil fertility.

Vermi-compost: The compost prepared by using earthworms to hasten the process of decomposition of plant and animal refuse.

Fertilisers: They are commercially produced plant nutrients which supply nitrogen, phosphorus and potassium to soil in order to increase the crop yield.

Organic farming: The farming system which focuses on the minimal or no use of chemicals like fertilisers, herbicides, pesticides etc. and with a maximum input of organic manures, recycled farm- wastes (straw and livestock excreta), use of bio-agents, etc.

Mixed cropping: Growing two or more crops simultaneously on the same piece of land.

Inter-cropping: Growing two or more crops simultaneously on the same field in a definite pattern.

Crop rotation: Growing two or more crops on a piece of land in a pre-planned succession.

Weeds: The unwanted plants in the cultivated field which compete for food, space and light with the crop plant and reduce the growth of the crop.

Animal husbandry: The scientific management of animal livestock is called animal husbandry. Milch animals: Milk-producing females are called milch animals (dairy animals).

Draught animals: Animals used for farm labour are called draught animals.

Lactation period: The period of milk production after the birth of a calf is called lactation period. Capture fishing: Fish obtained from natural resources is capture fishing.

Culture fishery: Fish farming is called culture fishery.

Composite fish culture systems: A combination of five or six fish species is used in a single fish pond in the composite fish culture system.

On this page, you will find Heredity and Evolution Class 10 Notes Science Chapter 9 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 9 Heredity and Evolution will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 9 Notes Heredity and Evolution

Heredity and Evolution Class 10 Notes Understanding the Lesson

1. Heredity: Transmission of characters/traits from parents to their offspring. Variation: The degree by which progeny differ from their parents.

2. Genetics: The branch of science which deals with the study of heredity and variation.

3. Inheritance: It is the process by which characters are passed on from parent to progeny.

4. Gregor Mendel and his Contributions: Mendel is called as the Father of genetics. Mendel used a number of contrasting characters for garden pea. The seven pairs of contrasting characters taken by Mendel in garden pea are given in the figure.

5. Monohybrid Cross: Cross between two pea plants for one pair of contrasting trait of a character. Example: Tall/Short Plants for Stem height. Results of Monohybrid Cross for the character Height

6. In monohybrid cross for character height; Mendel crossed a homozygous tall pea plant (TT) with a homozygous dwarf pea plant (tt) to obtain all heterozygous tall pea plants (Tt) in the F₁ generation. On selfing the heterozygous pea plants (Tt) obtained in the F₁ generation, he obtained F₂ progeny which showed a phenotypic ratio of 3 : 1 for tall and dwarf plants respectively and a genotypic ratio of 1: 2 : 1 for TT : Tt: tt pea plants respectively.

7. Conclusions:

• TT and Tt both are tall plants while tt is a short plant.
• A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.
• Characters/Traits like T are called dominant trait (because it express itself) ‘t’ are recessive trait (because it is not expressed in the presence of the dominant trait)

8. Dihybrid Cross: A cross made between two plants having two pairs of contrasting characters is called dihybrid cross.

9. Observations:

• When pea plant with round-yellow seeds (RRYY) was crossed with wrinkled-green seeds (rryy), all the progeny obtained in F₁ generation was RrYy (round and yellow seeds).
• Self pollination of F₁ plants (RrYy) gave the phenotypic ratio of 9 : 3 : 3 : 1 for round-yellow, round- j green, wrinkled-yellow and wrinkled-green pea seeds respectively.

10. Conclusions:

• Round and yellow seeds are dominant characters.
• Occurrence of new phenotypic combinations shows that genes for round and yellow seeds are inherited independently of each other.

11. Sex Determination
Sex is determined either by environmental factors or by the genetic factors.
Determination of sex due to environmental factors: In some animals, the temperature at which fertilised eggs are kept determines whether the animals developing in the eggs will be male or female. For example, Turtle.
In other animals, such as snails, individuals can change sex, indicating that sex is not genetically determined.

Determination of sex due to genetical factors:
In human beings, the sex of the individual is largely genetically determined. The genes inherited from parents decide the sex of the child. Sex is determined by a pair of chromosome called sex chromosome.

In human beings there are 23 pairs of chromosomes.
Out of these 22 pairs are called autosomes and the last pair of chromosomes that help in deciding gender of that individual are called sex chromosome. Females have XX as sex chromosome while males have XY as sex chromosome.

A cross between a male with XY sex chromosomes and a female with XX as sex chromosome shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother.

12. Evolution
The process by which different kinds of living organism have developed from earlier life forms during the history of the Earth is called evolution. The essence of idea of evolution is the change in the frequency of certain genes in a population over generations.

Situation I shows Natural Selection: A group of twelve red beetles living in bushes with green leaves are easily spotted by their predator crows. So, red colour does not have any selective advantage in bushes with green beetles than red ones in the beetle population. Hence due to natural selection, the green beetles have better survival chances in green colour bushes. Thus natural selection directs evolution in this case.

Situation II shows Genetic Drift: In the second situation also red coloured beetle live in bushes with leaves. Variations arise as the beetles reproduce sexually and one beetle that is green in colour is produced which has selective advantage in green coloured bushes as crows cannot spot it easily. This beetle passes the colour on to its progeny, so that all its progeny beetles are green. The progeny of green beetles is not eaten, while the progeny of red beetles continues to be eaten. As a result, there are more and more green

which kill the red beetles but leaves the blue beetles. The blue beetles which survive increase in numbers. Though blue colour does not have survival advantage in green coloured bushes, still it survives accidentally or by chance. Such situation where change in the frequency of some genes arises accidentally or by chance without any survival advantage is called genetic drift.

green coloured leaves, are easily spotted and eaten by crows. A colour variation arises during reproduction i and results in a beetle that is blue in colour. This beetle passes the blue colour on to its progeny, so that all its progeny beetles are blue which are again easily spotted in the green coloured bushes by the crows like the red ones. There are a few blue beetles, but most are red. An elephant comes by and stamps on the bushes

the bushes start suffering from a plant disease due to which the beetles are poorly nourished as the amount of leaf material for the beetles is reduced. No genetic change occurs but the average weight of the beetles.

Situation III shows the effect of availability of resources: The beetle population begins to expand but gets decreased. After a few years when the plant disease gets eliminated the average weight of the beetle increases again as lot of leaf food is available.

Mechanism of heredity: A section of DNA called genes present on chromosome provides information for the synthesis of proteins. Proteins control the formation of a character.

Acquired and Inherited Traits
Inherited traits: The traits which are passed on from the parents to their progeny by transfer of genes. For example, Eye colour.
Acquired traits: The traits acquired by individual during its lifetime. For example, Riding a bicycle, playing cricket, etc.

13. Speciation
The process of formation of new species from the existing species is called speciation. The factors which lead to the formation of new species are:
(i) Reproductive Isolation:

• Allopatric speciation: Caused by the various types of barriers like mountain ranges, rivers, seas, etc. It leads to reproductive isolation between members of the species and this is also called geographical isolation.
• Sympatric speciation: It occurs when populations of a species that share the same habitat become reproductively isolated from each other.

(ii) Genetic drift: It is caused by change in the frequency of particular genes by accident or by chance alone.
(iii) Natural selection: The process by which a group of organisms adopts to fit their environment in a better way.
(iv) Migration: When movement of a section of population to another place and population occurs.
(v) Mutation: Sudden changes in the sequence of DNA.

14. Evidences for Evolution
Homologous organs: Organs having the same basic structure but different functions are called homologous organs. They have a common origin (common ancestor). Example: Forelimbs of man, a lizard, a frog, elephant tusk and a bird have the same basic structure and design but perform different functions.

15. Analogous organs: Organs which perform the same function but have different basic structure are called as analogous organs. They have a different origin (different ancestors).
Example: the wings of insect and the wings of bird have different structure but perform the same function of flying.

16. Fossils: The remains or impressions of the dead animals or plants that lived in the remote past are called fossils.

17. Estimation of age of Fossils: There are two ways to estimate the age of the fossils:

18. Relative method: On digging the Earth, the fossils we find closer to the surface are more recent than the fossils we find in deeper layers.

19. Carbon-dating method: By detecting radioactivity of Carbon-14 isotope left in the fossil.

20. Evolution by Stages
Evolution of eye: The complex body designs have been created in stages over many generations. The flatworm named Planaria has very simple ‘eyes’ that are just eye-spots which detect light. But later on more complex eyes evolved in various organisms from them.

(i) Evolution of feathers: Evolutionary change produced in an organism for one purpose became more useful for a different function. Feathers first arose for insulation in cold weather but later they became more useful for flying.

(ii) Evolution by artificial selection: Evolution of wild cabbage is an example of evolution by artificial selection. Humans, cultivated wild cabbage as a food plant, and generated different vegetables from it by artificial selection.

Character Selected	Variety Selected
Very shot distances between leaves	Cabbage
Arrested flower development	Broccoli
Sterile flowers	Cauliflower
Swollen parts	Kohlrabi
Slightly larger leaves	Kale

21. Evolution should not be equated with ‘progress’: Natural selection and genetic drift cause evolution but that does not mean that

• one species is eliminated to form the new one, or
• the new species is better than the older one. So, evolution should not be equated with progress as multiple branches are possible at each and every stage of evolution.

Example: Human beings have not evolved from chimpanzees. Both have evolved in their own separate ways from a common ancestor a long time ago.

Only progressive trend in evolution: More and more complex body designs have emerged overtime. The older forms still survive along with the newer forms. Example: Bacteria are most primitive forms which are able to survive even in harsh habitats like hot springs or polar ice caps.

22. Human Evolution
Tools for tracing evolutionary relationships: Excavating, time-dating, studying fossils and determining DNA sequences. These tools have been used to study human evolution. Due to different forms and features of human were distinguished on the basis of skin colours into various races. But evidence points out that all human beings are a single species and there is no biological notion of human races.

Earliest members of human species (Homo sapiens) came from Africa. Some of our ancestors stayed back in Africa while others moved and spread across to West Asia, Central Asia, Eurasia, South Asia, and East Asia. They moved from the islands of Indonesia and the Philippines to Australia, and some crossed the Bering land bridge to reach the Americas. They did not go in a single line but went forwards and backwards, with groups sometimes separating from each other, sometimes coming back to mix with each other, even moving in and out of Africa.

Class 10 Science Chapter 9 Notes Important Terms

Heredity: Transmission of characters/traits from parents to their offspring, either through asexual reproduction or sexual reproduction.

Variation: The degree by which progeny differ from their parents.

Inheritance: It is the process by which characters are passed on from parent to progeny. Monohybrid cross: Cross between two pea plants for one pair of contrasting trait of a character.

Dihybrid cross: A cross made between two plants having two pairs of contrasting characters is called dihybrid cross.

Evolution: The process by which different kinds of living organism have developed from earlier life forms during the history of the Earth.

Inherited traits: The traits which are passed on from the parents to their progeny by transfer of genes. For example, Eye colour.

Acquired traits: The traits acquired by individual during its lifetime. For example, Riding a bicycle, playing cricket, etc.

Speciation: The process of formation of new species from the existing species is called speciation. Homologous organs: Organs having the same basic structure but different functions are called as homologous organs. They have a common origin (common ancestor).
Example: Forelimbs of man, a lizard, a frog and a bird have the same basic structure and design but perform different functions.

Analogous organs: Organs which perform the same function but have different basic structure are called as analogous organs. They have a different origin (different ancestors).
Example: The wings of insect and the wings of bird have different structure but perform the same function of flying.

Mutation: Sudden changes in the sequence of DNA.

Sympatric speciation: It occurs when populations of a species that share the same habitat become reproductively isolated from each other.

Allopatric speciation: Speciation caused by the various types of barriers like mountain ranges, rivers, seas, etc.

Fossils: The remains or impressions of the dead animals or plants that lived in the remote past are called as fossils.

On this page, you will find Natural Resources Class 9 Notes Science Chapter 14 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 11 Natural Resources will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Science Chapter 14 Notes Natural Resources

Natural Resources Class 9 Notes Understanding the Lesson

1. Natural resource: Any substance or material derived from nature that humans can use for their benefit. The resources on the Earth are land, water and air.

2. The outer crust and the upper mantle of the Earth is called lithosphere.

3. All the water on, under and above the surface of the Earth comprises the hydrosphere.

4. The blanket of air that covers the whole of the Earth is called atmosphere.

5. The atmosphere, the hydrosphere and the lithosphere interact to constitute biosphere which is the life-supporting zone of the Earth i.e., living things are found where these three exist.

6. The two components of the biosphere are

• Biotic component: comprises of living things.
• Abiotic component: comprises of non-living things like air, water and soil.

7. Air is a mixture of gases like nitrogen, oxygen, carbon dioxide and water vapour.

8. Carbon dioxide constitutes up to 95-97% of the atmosphere on planets—Venus and Mars.

9. Carbon dioxide is produced by activities like:

• Respiration in eukaryotic cells and prokaryotic cells.
• Combustion (it includes burning of fuels to get energy and forest fires).

10. Carbon dioxide is ‘fixed’ in two ways:

• By green plants during photosynthesis to make glucose.
• Carbonates dissolved in sea water are used by many marine animals to make their shells.

11. Role of atmosphere:

• It keeps the average temperature of the Earth fairly constant.
• It prevents the sudden increase in temperature during the daylight hours.
•  It slows down the escape of heat into outer space during night.

12. The temperature ranges from -190°C to 110°C in the moon as it does not have atmosphere.

13. Changes occur in the atmosphere due to:

• Heating of air
• The formation of water vapour.

14. Convection currents are set up in air when the atmosphere gets heated from below by the radiation that is reflected back by the land or water bodies.

15. During the day in the coastal regions, the air above the land gets heated faster and warm air being lighter rises up thereby creating a region of low pressure. The air over the sea then moves towards the area of low pressure. The movement of air from one region to the other creates winds. At night, water cools down slower than the land, so the air above water would be warmer than the air above the land. This causes air over the land to move towards the region of low pressure over water.

16. Two main factors which influence winds:

• the rotation of the Earth
• the presence of mountain ranges in the paths of wind

17. Heating of water bodies and the activities of living organisms result in evaporation of water and formation of water vapour.

18. As the air containing water vapour rises up, it expands and cools to condense in the form of tiny droplets. This condensation of water is facilitated if particles like dust and other suspended particles act as the ‘nucleus’ for these drops to form around. Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. These drops grow big and heavy and then fall down in the form of rain.

19. If the temperature of air is low, then precipitation may occur in the form of snow, sleet or hail.

20. The prevailing wind patterns in an area decide the rainfall patterns there.

21. The rains in India are mostly brought by the southwest or north-east monsoons.

22. The burning of fossil fuels like coal and petroleum releases:

• Oxides of nitrogen and sulphur which dissolve in rain to give rise to acid rain.
• Suspended particles which are unburnt carbon particles or substances called hydrocarbons. In cold weather conditions, high levels of these pollutants cause visibility to be lowered when water condenses out of air. This phenomenon is known as smog.

23. Most of the water on the Earth’s surface is found in seas and oceans and is saline.

24. Fresh water is found frozen in the ice-caps at the two poles and on snow covered mountains.

25. The underground water and the water in rivers, lakes and ponds is also fresh.

26. Water is essential for the various metabolic and the biochemical processes taking place in a living organism.

27. Water pollution is caused due to:

• Addition of undesirable substances (like pesticides, fertilisers, disease causing organisms)
• removal of desirable substances (like dissolved oxygen)
• Change in temperature of water (e.g., addition of hot water released from industries into rivers or the water released from dams into rivers which would be colder than water on the surface).

28. The outermost layer of our Earth is called the crust and the minerals found in this layer supply a variety of nutrients to life-forms.

29. Soil is a mixture of minerals, organic matter, gases, liquids, and various organisms that together support life on Earth.

30. Soil is formed due to various physical, chemical and biological processes which result in breakdown of rocks into fine particles of soil over millions of years. The formation of soil occurs due to factors and processes like Sun, water, wind, living organisms and lichens.

31. Removal of useful components from the soil and addition of undesirable substances into it which adversely affect the fertility of the soil and kill the diversity of organisms that live in it, is called soil pollution.

32. Constant recycling of nutrients and materials occurs between the biotic and the abiotic components in an ecosystem. The pathway by which a chemical substance moves through biotic and abiotic components of the Earth is called biogeochemical cycle.

33. Nitrogen gas constitutes 78% of our atmosphere and is a part of many molecules like proteins, nucleic acids (DNA and RNA) and some vitamins which are essential for life.

34. Legumes (like pulses) have nitrogen-fixing bacteria in their root nodules which convert the nitrogen molecules into nitrites and nitrates.

35. The high temperatures and pressures created in the air during lightning convert nitrogen into oxides of nitrogen which dissolve in water to give nitric and nitrous acids. They can be utilised by various living organisms when they fall on land along with rain.

36. The phenomenon in which the incoming sunlight is allowed to pass through the atmosphere but heat radiated back from the planet’s surface is trapped by the gases like carbon dioxide, water vapour and methane present in the atmosphere is called as greenhouse effect.

37. Increase in percentage of the gases like carbon dioxide and methane prevents escape of heat from the Earth. Greenhouse effect is responsible for the increase in average temperature worldwide and is causing global wanning.

38. Ozone is a molecule containing three atoms of oxygen with a formula of 03 and contains three atoms of oxygen. It is a poisonous gas but does not harm us as it is present in the upper reaches of the atmosphere. It plays an important role as it absorbs harmful radiations from the Sun which can harm living organisms.

39. Ozone layer is getting depleted due to the use of CFCs. CFCs are carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process. These react with the ozone molecules and result in its reduction.

40. An ozone hole caused due to the reduction of ozone molecules has been discovered above the Antarctica.

Class 9 Science Chapter 14 Notes Important Terms

Natural resource: Anything that comes from nature and can be used by humans for various purposes is called a natural resource.

Lithosphere: The outer crust and the upper mantle part of the Earth is called the lithosphere.

Hydrosphere: All the water on, under and above the surface of the earth comprises the hydrosphere.

Atmosphere: The blanket of air that covers the whole of the Earth is called atmosphere.

Biosphere: The region comprising of lithosphere, hydrosphere and the atmosphere which can sustain life or living organisms is called biosphere.

Components of biosphere: The two components of biosphere are biotic (living) component and abiotic (non living) component.

Wind: Moving air is called wind.

Air pollution: The addition of undesirable substances in air which adversely affect its physical, chemical or biological characteristics is called air pollution.

Pollutant: The undesirable substances added to air, water or land which pollutes them is called pollutant.

Biodiversity: The variety of life forms present on Earth constitutes its biodiversity.

Water pollution: The addition of undesirable substances in water which adversely affect its physical, chemical or biological characteristics is called water pollution.

Biogeochemical cycle: The pathway by which a chemical substance moves through biotic and abiotic components of the Earth is called biogeochemical cycle.

Greenhouse effect: The phenomenon in which the incoming sunlight is allowed to pass through the atmosphere but heat radiated back from the planet’s surface is trapped by the gases like carbon dioxide, water vapour and methane present in the atmosphere is called greenhouse effect.

Ozone: The triatomic molecule of oxygen with formula 03 which prevents the harmful UV radiation of the Sun from reaching the earth’s surface.

On this page, you will find Sound Class 9 Notes Science Chapter 12 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 12 Sound will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Science Chapter 12 Notes Sound

Sound Class 9 Notes Understanding the Lesson

1. Sound
Sound is a form of energy which produces a sensation of hearing in our ears.

2. Production of sound
Sound is produced by vibration of objects.

• The sound of human voice is produced due to vibration in the vocal chord.

3. Propagation of sound
Sound propagates in the form of longitudinal waves and these waves require material medium to propagate. Hence sound waves are mechanical waves.

• A wave is a disturbance that moves through a medium when the particles of the medium set neighbouring particles into motion.
• The longitudinal wave of sound travels in the form of compression and rarefaction. Compression is the region of high pressure and rarefaction is the region of low pressure.
• The propagation of sound can be visualised as propagation of density variations or pressure variation in the medium.

4. Sound needs a medium to travel
Sound is a mechanical wave and need a material medium for its propagation.

• Longitudinal wave
  A wave in which the particles of the medium oscillate to and fro in the same direction in which the wave is moving is called longitudinal wave.
• Transversal wave
  A wave motion is said to transverse if the particles of the medium through which the wave propagates vibrate in the direction perpendicular to the direction of propagation of the wave.

5. Some important terms and Relations for longitudinal wave
Frequency: The frequency of wave is defined as the number of waves produced per second.
Or
The frequency of a sound wave is defined as the number of complete oscillations made by the particle of medium in one second.

• It is denoted by greek letter u (nu). Its SI unit is hertz (Hz).

(ii) Wavelength: The distance between two consecutive compressions or two consecutive rarefactions is called wavelength.

• It is usually represented by X (Greek letter lambda). Its SI units is metre (m).

(iii) Time period: The time taken by two consecutive compressions or rarefactions to cross a fixed point is called time period of wave.
Or

• Time taken by particle of medium to complete one oscillation is known as time period.
• It is represented by the symbol T. Its SI unit is second (s).

8. Amplitude: The magnitude of the maximum disturbance in the medium on either side of the mean value is called amplitude of wave. It is usually represented by the letter A. For sound its unit will be that of density or pressure.

9. Speed: The speed of sound is defined as the distance which a point on a wave, such as a compression or a rarefraction, travels per unit time.

10. Relations

• Relation between time period (T) and frequency (u)
  \(T=\frac{1}{v}\)
• Relation between speed of wave (υ), wavelength (λ) time period (T) and frequency (υ)
  υ = υλ

Sound propagates as density or pressure variations as shown in (a), (b) and (c) represents graphically the density and pressure variations.

11. Characteristics of a sound wave
We can describe a sound wave by

• Frequency
• Amplitude
• Speed

12. Frequency-pitch:

• How the brain interprets the frequency of an emitted sound is called its pitch. The faster the vibration of the source, the higher is the frequency and the higher is the pitch.
• The pitch of sound produced by an object of low frequency is low and the source described as flat sound.
• The pitch of sound produced by an object vibrating with high frequency is high and the sound is described as shrill sound.

13. Amplitude-loudness:

• The loudness or softness of a sound is determined by its amplitude. Greater the amplitude of vibration of source, greater is the loudness of sound.
• Loud sound can travel a larger distance as it is associated with high energy.
• A sound wave moves away from the source, its amplitude as well as its loudness decreases.

14. Quality-timber:

• The quality or timber of sound is that characteristics which enables us to distinguish one sound from an¬other having same loudness and pitch.
• A sound of single frequency is called a tone. The sound which is produced due to a mixture of several fre¬quencies is called a note and is pleasant to listen to.
• Quality of sound is represented by waveform.
• Noice is unpleasant to ear. Music is pleasant to hear and is of rich quantity.

15. Speed of sound in different media

• Speed of sound in a medium depends on inertia and elasticity of the medium.
• Speed of sound increases with increase in temperature.
• The speed of sound decreases when we go from solid to gaseous state.
  Speed of sound in solids > Speed of sound in liquids > Speed of sound in gases
• Speed of sound in air is 331 ms-1 at 0°C and 344 ms^-1 at 22°C.

16. Reflection of sound
Sound is reflected in same way as light. Incident and reflected ray make equal angles with the normal to the reflecting surface at the point of incidence and three are in the same plane.

17. Echo
An echo is the phenomenon of repetition of sound by reflection from an obstacle.

• The sensation of sound lasts in brain for (1/10) of a second. This property is called persistence of hearing. To hear a distinct echo the time interval between the original sound and the reflected one must be at least
  0. 1 second.
• For hearing a distinct echo, the minimum distance of the obstacle from the source of sound should be 17.2 m.

Take speed of sound = 344 m/s
(at temperature 20°C)
2d = v x t
v = 344 m/s
\(t=\frac{1}{10} \mathrm{s}\)
d=17.2m

18. Reverberation
A sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no longer audible. The repeated reflection that results in the persistence of sound is called reveberation.

Excessive reveberation is highly undesirable. To reduce reverberation, the roof and walls of the auditorium are generally covered with sound absorbent materials like compressed fibre board, rough plaster or draperies. The seat materials are also selected on the basis of their sound absorbing properties.

Reflection of sound
d – distance of person from obstacle
v = velocity of sound
t = time after echo is heard
2d = v x t
t = 2 dlv and d = vt/2

19. Uses of multiple reflection of sound
(i) Megaphones, horns, musical instruments such as trumpets and shehnais are all designed to send sound in a particular direction. In these instruments, a tube followed by a conical opening reflects sound successively to guide most of sound successively to guide most of sound from the source in the forward direction towards the audience.

2. Stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or lungs

In stethoscopes the sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflection of sound.

3. Generally the ceiling of concert halls, conference halls and cinema halls are curved so that sound after reflection reaches all corners of the hall.
Sometimes curved sound board may be placed behind of the stage so that the sound after reflecting from the sound board, spreads evenly across the width of the hall.

20. Range of Hearing

• Audible range: The sound whose frequency lies between 20 Hz and 20,000 Hz which we are able to hear is called audible sound.
  Inaudible range
• Infrasonic sound: Sound of frequencies below 20 Hz is called infrasonic sound or infra sound.
• Ultrasonic sound: Frequency higher than 20 KHz is called ultrasonic sound or ultrasound.

21. Uses of Ultrasound in Communication
Sonar
The acronym sonar stands for sound navigation and ranging.
Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

22. Components of sonar system
Sonar consists of a transmitter and a detector and is installed in a boat or a ship.

23. Working
The transmitter produces and transmits ultrasound waves. These waves travel through water and after striking the object on the sea bed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted.

24. Calculation of distance : The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound

Let the time intervel between transmission and reception of ultrasound signal be t and speed of sound through sea water be υ. The total distance, 2d, travelled by the ultrasound.

• Rhinoceroses communicate using infra sound of frequency as low as 5 Hz.
• Whales and elephants produce sound in infrasonic wave.
• Children under five and some animals, such as dogs can hear infrasonic sound.

Earthquake produces infrasonic waves.

• Ultrasound is produced by dolphines, bats and porpoises. R
• Moths of certain families can hear high frequency waves.

25. Application of Ultrasound
Industrial uses of ultrasound

(i) Cleaning instruments and electronic components
Ultrasound is generally used to clean parts located in hard to reach places, for example, spiral tube, odd shaped parts, electronic component, etc. Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to the high frequency, the particles of dust, grease and dirt get detached and drop out. The objects are thus thoroughly cleaned.

(ii) Detecting flaw and cracks in metal blocks
Ultrasounds can be used to detect crack and flaws in metal blocks. Metallic components are generally used in the construction of big structures like buildings, bridges, machines and also scientific equipments. The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure. Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of flaws or defect.

Medical uses of ultrasound
(i) Ultrasonography: The technique of obtaining of images of internal organs of the body by using ultrasonic waves is called ultrasonography. An ultrasound scanner is a medical instrument which is used by doctors to detect abnormalities such as stones in gall bladder and kidney or tumours in different organs. In this technique, the ultrasound scanner produces ultrasounds which travel through the tissues of the body, and if there are stones in the gall bladder or kidney or there is tumour in any internal organ, then the ultrasound waves get reflected from these regions due to the change in tissue density. These reflected ultrasound waves are converted into electrical signals and fed to the computer generating a three dimension images of the organ on the monitor of the computer.

(ii) Echocardiography: The technique of obtaining images of the heart by using reflection of ultrasonic waves from various parts of the heart is called echocardiography.

(iii) Breaking of kidney stones: Ultrasound can be used to break small stones formed in the kidney into fine grains. These grains later get flushed out of with urine.
2d = v x t

(iv) Use of ultrasound by bats for determining distance
Bats search out prey and fly in dark night by emitting and detecting reflections of ultrasonic waves. The high pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to bat’s ear. The nature of reflection tells the bat where the obstacle or pray is and what it is like.

26. Structure of the Human Ear
Introduction
The outer ear is called ‘pinna’. It collects the sound from the surroundings. The collected sound passes through the auditory canal. At the end of the auditory canal there is a thin membrane called the eardrum or tympanic membrane. When compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward.

Similarly, the eardrum moves outward when a rarefraction reaches it. In this way the eardrum vibrates. The vibrations are amplified several times by three bones (the hammer, anvil and stirrup) in the middle ear. The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear. In the inner ear, the pressure variations are turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.

Parts	Function
1. Pinna	Collects sound from surroundings
2. Hammer, anvil and stirrup	Amplifies vibration or pressure wave
3. Cochlea	Converts pressure variation into electrical signal
4. Eardrum	Thin membrane vibrates when sound reaches inside ear
5. Auditory nerve	Electrical signals are sent to brain from cochlea via auditory nerve.

Class 9 Science Chapter 12 Notes Important Terms

Sound: Sound is a form of energy which produces a sensation of hearing in our ears.

Longitudinal wave: A wave in which the particles of the medium oscillate to and fro in the same direction in which the wave is moving is called longitudinal wave.

Transverse wave: A wave in which particles of the medium vibrate at right angles to the direction of the propagation of the the wave.

Echo: The repetition of sound caused by the reflection of sound waves is called an echo.

Reverberation: The persistence of sound in a big hall due to repeated reflection of sound from the walls, ceiling and floor of the hall is called reverberation.

Stethoscope: Stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or lungs.

Sonar: Sonar is a device that uses ultrasonic wave to measure the distance, direction and speed of underwater object.

ultrasonography: The technique of obtaining images of internal organs of the body by using echoes of ultrasound wave is called ultrasonography.

Echo cardiography: The technique of obtaining images of the heart by using reflection of ultrasonic waves from various parts of the heart is called echo cardiography.

On this page, you will find How do Organisms Reproduce Class 10 Notes Science Chapter 8 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 8 How do Organisms Reproduce will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 8 Notes How do Organisms Reproduce

How do Organisms Reproduce Class 10 Notes Understanding the Lesson

1. Reproduction: It is the process by which organisms produce their own kind.

2. Importance of Reproduction: Reproduction enables the continuity of the species, generation after generation.

3. Basic Event in Reproduction for transmission of hereditary information: Copying of DNA
(Deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell.

4. DNA copying is accompanied by the creation of an additional cellular apparatus: As keeping one copy of DNA in the original cell and simply pushing the other one out would not work, because the copy pushed out would not have any organised cellular structure for maintaining life processes.

5. Importance of Variation: Process of copying the DNA is not completely accurate every time, so variations occur. The useful variations are retained while the harmful ones are eliminated. So, the variations enable the organism to survive under unfavourable conditions. This inbuilt tendency for variation during reproduction is the basis for evolution.

6. Difference between Sexual reproduction and Asexual Reproduction

Asexual Reproduction	Sexual Reproduction
Single parent is involved.	Two parents are involved.
No fusion of gametes.	Fusion of gametes occurs.
Progeny is genetically identical to the parent. For example, Fission in Amoeba	Variations occur in the progeny. For example, Human beings

6. Different Types of Asexual Reproduction
Fission

• Binary fission: The parent cell divides/splits equally into two daughter cells. For example, Amoeba
• Multiple fission: The parent cell splits into many cells. For example, Plasmodium (Malarial parasite)
• Binary fission: The splitting of the two cells into two equal halves during division can take place in any plane; it occurs in Amoeba.

Binary fission in Leishmania (which cause kala-azar), occurs in definite orientation/plane due to presence of whip-like structure at one of the cell

7. Fragmentation:
The process by which the broken pieces of an organism (fragments) grow into a complete organism. For example, Spirogyra

8. Regeneration: Some simple animals can develop into a new individual from their broken older parts by a process called regeneration. For example, Planaria, Hydra, Starfish.

9. Budding: In this process a new organism is produced as an outgrowth of the parent body part. For example, Hydra, Yeast.

10. Spore Formation: Small, bulb-like structures called spores develop at the top of the erect hyphae of the fungus. Spores released into the air, germinate into new individuals

11. Vegetative Propagation: A mode of reproduction in which the vegetative parts of the plant like the stem, root and leaves develop into new plant under favourable conditions.
Advantages of Vegetative Propagation

• Plants can bear flowers, fruits earlier than those produced from seeds.
• Enables us to grow banana, orange, rose, jasmine that have lost the capacity to produce seeds.
• Maintains genetical similarity in the plants.

Example: Layering or grafting done in sugarcane, rose and grapes; buds produced in the notches along the leaf margin of Bryophyllum which fall on the soil and develop into new plants.

Disadvantages of Vegetative Propagation

• Plants gradually lose their genetic variation.
• Since many plants are produced, it results in overcrowding and lack of nutrients.

12. Tissue culture: In this technique, the cells removed from the tip of the plant are placed in an artificial medium where they divide rapidly to form a small group of cells or callus which forms plantlets when placed in a medium containing hormones for growth and differentiation. The plantlets are then placed in the soil to grow into mature plants. This technique can be used to obtain disease free plants from virus infected plants.

13. Sexual Reproduction
The process of sexual reproduction involves the fusion of gametes called fertilisation. During sexual reproduction, exchange of chromosomal (genetic) fragments between homologous chromosomes occur causing genetic recombination which leads to variation.

14. Sexual Reproduction in Flowering Plants Stamen: Male reproductive part of the flower made of filament and anther. Pollen grains are produced inside anthers.

Carpel: Female reproductive part of the flower made of three parts—Stigma, style and ovary. Ovules are present inside ovary.

16. Types of flowers

• Unisexual flowers: Flowers bear either stamen or carpel. For example, papaya and Watermelon.
• Bisexual flower: Flowers bear both stamen and carpel. Example: Hibiscus, Mustard.
• Pollination: The transfer of pollen grains from the anther to the stigma of a flower. The transfer occurs by agents like wind, water or animals.

17. Types of pollination
(i) Self-pollination: Transfer of pollen grains to the stigma of the same flower.

(ii) Cross-pollination: Transfer of pollen grains to the stigma of another flower.
The ovary contains ovules and each ovule has an egg cell. After the pollen lands on a suitable stigma, a pollen tube grows out of the pollen grain which bears male germ cells and travels through the style to reach the ovary. Male germ cells reach female gamete and fuse with it by process of fertilisation to form zygote. The zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is converted into a seed which forms a seedling/new plant by the process of seed germination. Ovary develops into fruit. Ovules develop into seed. Petals, sepals, stamens, style and stigma may shrivel and fall off in most cases but sepals may persist in the case of brinjal, tomato, etc.

18. Reproduction in Human Beings: Humans use a sexual mode of reproduction. The period when the reproductive organs become mature and functional in humans is called puberty. Many changes occur during puberty:

19. Changes common to both boys and girls: Thick hair growing in armpits and the genital area between the thighs; Thinner hair appear on legs, arms and on the face; skin frequently becomes oily and might begin to develop pimples.

Changes different in boys and girls: In girls, breast size begins to increase, with darkening of the skin of the nipples at the tips of the breasts. Girls begin to menstruate at around this time.
Boys begin to have new thick hair growth on the face and Seminal vesicle their voices begin to crack. The penis occasionally begins to become enlarged and erect, either in daydreams or at night.

20. Male Reproductive System
The male germ cells (sperms) are formed in a pair of testes (male reproductive organ) which are located inside scrotum situated outside the abdominal cavity. It helps to keep relatively a low temperature needed for the production of sperms by testes.

Testes release a male sex hormone called testosterone whose function is to:

• Regulate the formation of sperms.
• Bring about changes in appearance seen in boys at the time of puberty.

The sperms formed in testes are delivered through the vas deferens which unites with a tube coming from the urinary bladder. Urethra is a common passage for both the sperms and urine. Glands like the prostate and the seminal vesicles add their secretions to make transport of sperms easier and provide nutrition to them.

21. Female Reproductive System
The female germ-cells or eggs are made in the ovaries. Some hormones are formed inside ovaries. Thousands of immature eggs are already present in the ovary of a newly born girl which start maturing on reaching puberty. Every month one egg produced by one of the ovaries is carried from the ovary to the womb through a thin oviduct or fallopian tube. The two oviducts unite into an elastic bag-like structure known as the uterus which opens into the vagina through the cervix.

23. Fertilisation: During sexual intercourse the sperms enter through the vaginal passage, travel upwards and reach the oviduct where they may fertilise the egg to form zygote. The process of fusion of male and female gamete to form a zygote is called as fertilisation. The zygote formed gets implanted in the lining of the uterus, and starts dividing. The uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo.

24. Placenta and its functions: A disc shaped structure embedded in the uterine wall called the placenta provides nutrition to the embryo from the mother’s blood. It contains villi on the embryo’s side of the tissue which are surrounded by blood spaces on the mother’s side.

Following are the roles of placenta:

• It provides a large surface area for glucose and oxygen to pass from the mother to the embryo.
• It removes waste substances produced by the developing embryo.

25. Gestation Period: The development of the child inside the mother’s body takes approximately nine months. This period is called as gestation period. The child is born as a result of rhythmic contractions of the muscles in the uterus.

26. Fate of Unfertilised egg: The ovary releases one egg every month, the lining of the uterus becomes thick and spongy every month to receive a fertilised egg and nourish the embryo. If the egg is not fertilised, it lives for about one day. But if it remains unfertilised then the lining of the uterus slowly breaks and comes out through the vagina as blood and mucous. This cycle is called menstruation which takes place every month and lasts for about two to eight days.

27. Menopause: The sexual cycle in a woman continues upto the age of 45 to 50 years after which eggs are not released by the ovary and menstruation gets stopped. This stage is called Menopause.

28. Reproductive Health: The total well-being in all aspects of reproduction, i.e., physical emotional, social and behavioural is called reproductive health.

29. Sexually transmitted diseases: Bacterial infections like gonorrhoea and syphilis; viral infections like warts and HIV-AIDS. Transmission of many sexually transmitted diseases can be prevented by condoms.

30. Contraceptive methods: The methods to avoid pregnancy are called as contraceptive methods. The different methods are:
Physical methods: Prevent union of sperm and egg. For example, condoms, diaphragm and cervical caps Chemical methods: Act by changing the hormonal balance of the body so, that eggs are not released and fertilisation cannot occur. They may have side-effects too.

For example, Oral pills Surgical methods:

• Vasectomy: The vas deferens of male is blocked to prevent sperm transfer.
• Tubectomy: The fallopian tube of female is blocked to prevent egg to reach uterus.
• Copper-T or loop is placed in uterus to prevent pregnancy.

31. Pre-natal sex determination: The determination of the sex of the child before birth is called as pre-natal sex determination. It is prohibited by law as it is a major cause of illegal sex-selective abortion of female foetuses. The female-male sex ratio must be maintained for a reproductively healthy society.

Class 10 Science Chapter 8 Notes Important Terms

Reproduction: It is the process by which organisms produce their own kind.

Binary Fission: The parent cell divides/splits equally into two daughter cells. For example, Amoeba

Multiple Fission: The parent cell splits, into many cells. For example, Plasmodium (Malarial parasite)

Vegetative Propagation: A mode of reproduction in which the vegetative parts of the plant like the stem, root and leaves develop into new plant under favourable conditions.

Statement: Male reproductive part of the flower made of filament and anther. Pollen grains are produced inside anthers.

Carpel: Female reproductive part of the flower made of three parts stigma, style and ovary.

Pollination: The transfer of pollen grains from the anther to stigma of a flower.

Testosterone: Male sex hormone released by the testes.

Estrogen and Progesterone: These are the sex hormones released by the ovaries in the human females.

Placenta: A disc shaped structure embedded in the uterine wall which provides nutrition to the embryo from the mother’s blood.

Menopause: The sexual cycle in a woman continues upto the age of 45 to 50 years after which eggs are not released by the ovary and menstruation stops. This stage is called Menopause.

Contraceptive Methods: The methods to avoid pregnancy are called as contraceptive methods.

Vasectomy: The process by which the vas deferens of male is blocked to prevent sperm transfer.

Tubectomy: The process by which the fallopian tube of female is blocked to prevent egg to reach the uterus.

Pre-natal sex determination: The determination of the sex of the child before birth is called pre-natal sex determination.

On this page, you will find Work, Power And Energy Class 9 Notes Science Chapter 11 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 11 Work, Power And Energy will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Science Chapter 11 Notes Work, Power And Energy

Work, Power And Energy Class 9 Notes Understanding the Lesson

1. Work done by a constant force
Work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force.
Work done = force x displacement

• Work done has only magnitude and no direction i.e., work is a scalar quantity.
• SI unit of work is joule (J).
• 1 joule (one joule)

W = Fs
If F = 1 N and s = 1 m
W= 1 N x 1 Nm
W =  1 Nm
1j =1 Nm
1 J is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.

2. Conditions that need to be satisfied for work to be done

• Force should act on an object.
• The object must be displaced.

3. Zero work, Positive and Negative work
(i) Zero work: If the angle between force and displacement is 90°, then work done is said to be zero work.
Example: When a man carries a load on his hand and moves on a level road, work done by the man on the load is zero.

(ii) Positive work: Work done is said to be positive if force applied on an object and displacement are in the same direction.

Example: Work done by the force of gravity on a falling body is positive.

(iii) Negative work: Work done is said to be negative if the applied force on an object and displacement are in opposite direction.
W = -Fs
Here displacement is taken to be negative (-s).

Example: Work done by friction force is usually negative on a moving body.

4. Energy
Energy of a body is defined as the capacity or ability of a body to do work.
The SI unit of energy is joule (J) (unit of energy and work is same).

5. Forms of energy
There are various forms of energy in the nature, few of them are mechanical energy (potential energy + kinetic energy) heat energy, chemical energy and light energy.

6. Mechanical energy
Mechanical energy includes kinetic energy and potential energy.

7. Kinetic energy
The energy possessed by a body by the virtue of its motion is called kinetic energy.
Kinetic energy possessed by a body can be calculated by
\(E_{K}=\frac{1}{2} m v^{2}\)
m = mass of body
V = velocity of body

8. Derivation of kinetic energy (work energy theorem)
Let us consider an object lying on a frictionless surface having mass ‘m’

A force of constant magnitude F is acting on the body. Here initial velocity of the body is u and final velocity is v. As there is no dissipative forces, work done on the body will be stored in the form of change in kinetic energy.
W=Fs

If the object is starting from a stationary position u = 0, then

9. Potential energy
The energy possessed by a body due to its position or configuration is called potential energy.

10. Gravitational potential energy
Potential energy at any height (h) from a reference can be calculated by formula
E_p = mgh
where, m = mass of object
v = height from reference
The gravitational potential energy of an object at a point above the ground is defined as the work done in raising it from the ground to that point against gravity.

11. Derivation of potential energy
When work is done on the body, the work is stored in the form of energy. Consider an object of mass, m. Let it be raised through a height, h from the ground. A force is required to do this. The minimum force required to raise the object is equal to the weight of the object, mg. The object gains energy equal to the work done on it. Let the work done on the object against gravity be W.

That is W = force x displacement
= mgh .
Since work done on the object is equal to mgh, an energy equal to mgh units is gained by the object. This is the potential energy (Ep) of the object.
E_p = mgh

12. Law of conservation of energy
Energy can neither be created nor be destroyed, it can only be transformed from one form to another. The total energy before and after the transformation always remains constant.

13. Transformation of energy in nature
The change of one form of energy into another form of energy is known as transformation of energy.
Example:

• Potential energy of water is converted into electricity in dams.
• Electricity is converted into heat energy in heaters.
• Chemical energy of fuel is converted into mechanical energy in engines.

14. Conservation of mechanical energy
Mechanical energy is the sum of kinetic energy and potential energy.
If there is no loss, then mechanical energy of a system is always constant.
Potential energy + kinetic energy = constant.
or
\(m g h+\frac{1}{2} m v^{2}=\text { constant }\)

15. Power (P)
Power is defined as the rate of doing work or rate of transfer of energy.
Power = work/time
P=W/T

• Unit of power is watt (W).

16. Watt

17. Commercial unit of energy
Kilowatt hour (kWh) or 1 unit
The energy used in households, industries and commercial establishments are usually expressed in kilowatt hour.
1 kWh is the energy used in one hour (1 h) at the rate of 1000 J/s or (1 kW).
∴1 kWh =lkWxU = 1000 W x 3600 s = 3600000 J
1 kWh = 3.6 x 10⁶ J = 1 unit

18. Power can also be represented as,
P = Fv
F = force applied
v = velocity of object
\(P=\frac{W}{t}=\frac{F s}{t}=F v\)

Class 9 Science Chapter 11 Notes Important Terms

Work done: Work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force.

Energy: Energy of a body is defined as the capacity or ability of the body to do work.

Mechanical energy: Mechanical energy of a body is the sum of its kinetic energy and potential energy. Kinetic energy: The energy possessed by a body by the virtue of its motion.

Potential energy: The energy possessed by a body due to its position or configuration.

Law of conservation of energy: Energy can neither be created nor be destroyed, it can only be transformed from one form to another.

Conservation of mechanical energy: If there is no loss of energy, then mechanical energy of a system is always constant.

Power: Power is defined as the rate of doing work or rate of transfer of energy.

Commercial unit of energy: The energy used in households, industries and commercial establishment are usually expressed, in kilowatt hour. 1 kWh = 1 unit = 3.6 x 10⁶

On this page, you will find Control and Coordination Class 10 Notes Science Chapter 7 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 7 Control and Coordination will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 7 Notes Control and Coordination

Control and Coordination Class 10 Notes Understanding the Lesson

1.Growth related movements: A seed germinates and grows and seedling comes out by pushing the soil aside. Such a movement is related to growth as these movements would not happen if growth of seedling is stopped.

2. Growth unrelated movements: A cat running, children playing on swings, buffaloes chewing cud – these are not movements caused by growth. These are growth independent movements. When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop. This movement of its leaves are independent of growth.

3. Movement is an attempt by living organisms to use changes in their environment to their advantage: Plants grow to get sunshine. Buffaloes chew cud to enable digestion of tough food. Swinging gives pleasure to the children. We try to protect ourselves by detecting the change in the environment and showing movement.

4. Control and coordination in animals is regulated by two systems: Nervous system and hormonal system.

5. Animals – Nervous System
The specialised tips of some nerve cells detect all information from our environment with help of receptors usually located in our sense organs, such as the inner ear, the nose, the tongue, etc. Gustatory receptors: Detect taste (present on tongue).

6. Olfactory receptors: Detect smell (present in nose).

7. Stimulus: Any agent, factor, chemical or change in external or internal environment which elicits reaction in an organism.

8. Response: A change in an organism (an action) resulting from a stimulus.

9. Mode of transmission of nerve impulse:

• An electrical impulse is generated when information is acquired at the end of the dendritic tip of a nerve cell.
• This impulse travels from the dendrite to the cell body, and then along the axon to its end.
• At the end of the axon, the electrical impulse sets off the release of some chemicals called neurotransmitters at synapse. Synapse is the junction between two neurons where axon ending of one neuron is placed close to dendrites of the next neuron.
• These chemicals (neurotransmitters) cross the synapse, and start a similar electrical impulse in a dendrite of the next neuron.
• A similar synapse finally allows delivery of such impulses from neurons to effectors.

10. Effectors are muscles, glands, tissues, cells, etc., which respond to the stimulus received from nervous system.

Nervous tissue is made up of an organised network of nerve cells or neurons, and is specialised for conducting information via electrical impulses from one part of the body to another. Neuron (Nerve cell) is the structural and functional unit of the nervous system.

11. Parts of a neuron

• where information is acquired—Dendrites
• through which information travels as an electrical impulse—Axon
• Impulse converted into a chemical signal for onward transmission—Synapse.

12. Reflex Action and Reflex Arc
(i) A reflex action is a spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain.

(ii) In such reactions we do something without thinking about it, or without feeling in control of our reactions. Reflex actions are very fast response of nervous system to dangerous situations. Example: We withdraw our hand immediately if we prick our finger or touch a hot object.

(iii) Reflex actions are involuntary actions as they cannot be controlled as per our will. They occur automatically.

(iv) The stimulus received by receptors present on sense organ is sent through sensory neuron to spinal cord. Spinal cord sends messages through motor neuron to muscles (effectors) to cause movement of the part and avoid damage. The arc formed in such case is called as the reflex arc.

13. Human Brain

• Brain is the main coordinating centre of the body.
• The brain and spinal cord constitute the central nervous system and are composed of nerves.
• They receive information from all parts of the body and integrate it.
• The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system.
• The nerves arising from the brain (cranial nerves) and nerves arising from spinal cord (spinal nerves) constitute the peripheral nervous system.
• The brain allows us to think and take actions based on that thinking.
• The actions based on our will are called voluntary actions. Example: Writing, talking, clapping at the end of a programme.
• Brain also sends messages to muscles. This is the second way in which nervous system communicates with muscles.

14. Parts of Brain:

• The brain has three major parts/regions: fore-brain, mid-brain and hind-brain.
• The fore-brain is the main thinking part of the brain. It has regions (sensory area) which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing (auditory area), smell (olfactory area), and sight (optic area) and so on.
• There are separate association areas where this sensory information is interpreted by putting it together with information from other receptors as well as with information that is already stored in brain.
• A separate part of fore-brain associated with hunger gives a sensation of feeling full.
• Many involuntary actions are controlled by mid-brain and hind-brain.
• Hind-brain comprises of cerebellum, pons and medulla oblongata.
• Cerebellum is responsible for precision of voluntary actions and maintaining the posture and balance of the body. Activities like walking in a straight line, riding a bicycle, picking up a pencil.
• Pons connects cerebellum and medulla oblongata and helps in regulation of respiration rate.
• Medulla controls the involuntary actions like blood pressure, salivation and vomiting.

15. Protection of Brain and spinal cord

• Human brain is present inside a bony box called skull or cranium.
• A fluid-filled inside the skull called cerebrospinal fluid, helps in shock absorption.
• The spinal cord is protected by the vertebral column.

16. How does the Nervous Tissue cause Action?
Muscle cells have contractile proteins, actin and myosin which change both their shape (by getting shortened) and their arrangement in the cell in response to nervous electrical impulses received by them. This results in movement of the part of the body.

17. Coordination in Plants
The touch-me-not plant moves its leaves in response to touch as its cells change shape by changing the amount of water in them, resulting in swelling or shrinking. Such movement is growth independent movement.

18. Movement Due to Growth: Pea plant climbs up by means of tendrils which are sensitive to touch. The part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.

19. Tropism/Tropic movements: Movements in plants which occur in direction of the stimulus. They are directional movements. These directional, or tropic, movements can be either towards the stimulus, or away from it.

20. Phototropism: Growth of plant in response to light. Shoots respond by bending towards light while roots respond by bending away from it.

21. Geotropism: Growth of plant in response to gravity. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the Earth.

22. Hydrotropism: Growth of plant in response to water. Roots always grow towards water and show hydrotropism.

23. Chemotropism: Growth of plant in response to chemicals. Example: Growth of pollen tubes towards ovules.

24. Thigmotropism: Growth of plant in response to touch. Example: Climbers coil around support.

25. Limitations to the use of electrical impulses
Firstly, they do not reach each and every cell in the animal body. They reach only those cells that are connected by nervous tissue.
Secondly, the cell takes some time to reset its mechanisms before it can generate and transmit a new impulse. They cannot continually create and transmit electrical impulses.

26. Way to overcome limitations to the use of electrical impulses
Most multicellular organisms use chemical communication to overcome the limitations of electrical impulse. Chemical compounds (hormones) released by stimulated cells diffuses all around it and is detected by other cells with help of special molecules on their surfaces.

27. How do Plants coordinate their activity?
Plants do not have nervous system. They respond to stimuli with help of chemicals called as plant growth regulators or plant hormones like auxin, gibberelin, cytokinin, abscissic acid, etc.

28. Auxin: It is synthesised at shoot tips and helps in bending of plant towards light. When light comes from one side of the plant, auxin diffuses towards the shady side of shoot. This higher concentration of auxin stimulates the cells to grow longer on the side of shoot which is away from light. Thus, plant appears to bend towards light.

29. Gibberellins: They help in the growth of the stem.

30. Cytokinins: This hormone promotes cell division. It occurs in higher concentration in areas of rapid cell division, such as in fruits and seeds.

31. Ethylene: It is a gaseous hormone which helps in ripening of fruits.

32. Abscissic acid: This hormone inhibits growth. Its effects include wilting of leaves. It is also called as stress hormone as it helps to overcome stress conditions.

33. Hormones in Animals
Hormones are non-nutrient chemicals which act as intercellular messengers, are produced in trace amounts, directly poured in the blood stream and act only on a specific target organ. They are secreted by endocrine glands (ductless glands).

34. Functions of Animal Hormones:
(i) Thyroxin hormone: Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck.

(ii) Adrenaline hormone: It is secreted by adrenal gland in response to stress of any kind and during emergency situations fear, joy, emotional stress, etc. Adrenaline increases breathing rate and the blood supply to heart and muscles. It constricts arterioles. Its target organ is heart and arteries. It is also called as emergency hormone or stress hormone.

(iii) Growth hormone is secreted by the anterior pituitary gland. If there is a deficiency of this hormone in childhood, it leads to dwarfism. Its excess causes gigantism.

(iv) Testosterone in males secreted by testis and oestrogen in females secreted by ovary causes changes in body of males and females during puberty.

(v) Insulin hormone is produced by the pancreas and helps in regulating blood sugar levels. Its deficiency causes diabetes due to increase in blood glucose level.

35. Feedback Mechanisms:
The timing and amount of hormone released are regulated by feedback mechanisms. For example, if the blood glucose level rises, it is detected by the cells of the pancreas which respond by producing more insulin to promote absorption of glucose and formation of glycogen in liver and muscles. When the blood sugar level falls and comes to normal, insulin secretion is stopped by the pancreas.

Class 10 Science Chapter 7 Notes Important Terms

Gustatory receptors: The receptors present in the tongue which help to detect taste.

Olfactory receptors: The receptors present in the nose which help to detect smell.

Neuron (Nerve cell): It is the structural and functional unit of the nervous system.

Synapse: The junction between the two neurons which helps to transmit the electrical or chemical signal to the next neuron.

Reflex action: A reflex action is a spontaneous, autonomic and mechanical response to a stimulus controlled by the spinal cord without the involvement of brain.

Tropism/Tropic movements: Tropism is a growth movement whose direction is determined by the direction from which the stimulus strikes the plant.

• Positive = Growth towards the stimulus
• Negative = growth away from the stimulus.

Phototropism: The response of a plant or its part to light. Roots are negatively phototropic while shoots are positively phototropic.

Geotropism: The response of a plant or its part to gravity. Roots are positively geotropic while shoots are negatively geotropic.

Hydrotropism: The response of a plant or its part to water. Roots always grow towards water and show positive hydrotropism.

Chemotropism: The response of a plant or its part to chemical stimulus. Pollen tubes grow towards ovule due to chemicals secreted by them.

Thigmotropism: The response of a plant or its part to stimulus of touch.

Hormones: Hormones are chemical messengers that are secreted directly into the blood, which carries them to the specific target organs and tissues of the body to exert their functions.

On this page, you will find Life Processes Class 10 Notes Science Chapter 6 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 6 Life Processes will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 6 Notes Life Processes

Life Processes Class 10 Notes Understanding the Lesson

1. Life Processes: All the processes like respiration, digestion, which together keep the living organisms alive and help in maintaining the functions of the body, are called life processes.

2. Nutrition: The process by which an organism obtains its food is called nutrition.
Modes of Nutrition:

• Autotrophic nutrition: Kind of nutrition in which inorganic materials like CO₂, water, etc. are utilised to prepare organic food by the process of photosynthesis. For example, green plants and some bacteria.
• Heterotrophic nutrition: Kind of nutrition in which organisms do not possess the ability to synthesise their own food. They depend on autotrophs for their food supply directly or indirectly. For example, animals, fungi.

3. Bio-catalysts: Enzymes are called bio-catalysts as they play an important role in chemical reactions taking place in living organisms.

4. Photosynthesis: Autotrophs take in CO₂ and H₂O and convert these into carbohydrates in the presence of chlorophyll and sunlight by the process called Photosynthesis.

5. Equation of Photosynthesis:

6. Raw Materials for Photosynthesis:

• Sunlight
• Chlorophyll-It helps to trap the energy of the Sun
• CO₂-It enters through Stomata
• Water-Water and dissolved minerals are taken up by the roots from soil

7. Products of Photosynthesis:

• Carbohydrates in the form of glucose
• Oxygen (O₂)-released as a by-product

8. Site of Photosynthesis:
Chloroplast is the site of photosynthesis. Chloroplast contains a green pigment called chlorophyll which helps to trap energy of sunlight.

9. Events of Photosynthesis:

• Absorption of light energy by chlorophyll.
• Conversion of light energy to chemical energy + splitting of water molecules into hydrogen and oxygen.
• Reduction of carbon dioxide to carbohydrates.

10. Structure of Leaf:
External structure of leaf comprises of

• Petiole: Stalk of leaf.
• Lamina: Flat, broad and expanded portion of leaf.
• Midrib: Midline which divides leaf into two equal halves.
• Veins: Supply water throughout surface of leaf.

11. Internal structure of leaf comprises of:

Epidermis: It has two parts:
(i) upper epidermis and
(ii) lower epidermis.

(i) Upper epidermis is usually covered by a waxy layer called cuticle which prevents water loss through transpiration.

(ii) Lower epidermis has stomata which help in gaseous exchange

Stomata: Tiny pores which are generally found in the lower epidermis and help in gaseous exchange and transpiration.

Guard cells: Bean-shaped cells which guard the opening of stomata. They have chloroplasts and have uneven thickening in their cell wall. Opening and closing of stomatal pore is done by guard cells. Movement of water into guard cells cause their swelling and open the stomatal pore. The shrinking of the guard cells when water moves out causes closing of stomatal pore.

12. Types of Heterotrophic Nutrition:

• Holozoic nutrition: The complex food material taken in by the organism is broken down into simpler and soluble molecules. For example, Human, Amoeba.
• Saprotrophic nutrition: The organisms feed on the dead and decaying matter. For example, Fungi.
• Parasitic nutrition: The organisms live either on or inside the organism to obtain its nutrition. For example, Lice, Cuscuta (amarbel).

13. Steps in Holozoic Nutrition:

• Ingestion
• Digestion
• Absorption
• Assimilation
• Egestion.

14. Nutrition in Amoeba
Temporary finger-like extensions of the cell surface called pseudopodia are used by Amoeba to engulf food. Pseudopodia fuse over the food particle forming a food vacuole in which complex substances are broken down into simpler ones and diffuse into the cytoplasm. The remaining undigested material moves to the surface of the cell and gets thrown out.

15. Nutrition in Paramoecium
In Paramoecium, food is moved to a specific spot by the movement of cilia which cover the entire surface of the cell.

16. Nutrition in Human Beings
Human digestive system consists of alimentary canal and the associated glands. The alimentary canal is a long tube extending from the mouth to the anus.

17. Mouth – Helps in intake of whole food.

18. Teeth – Helps in chewing and grinding of food.

19. Tongue – Helps in tasting food + rolling food + swallowing food.

20. Salivary glands – Secrete saliva and mucus. The enzyme called salivary amylase is present in saliva which breaks down the complex starch into sugar.

21. Oesophagus (food pipe) – Food moves towards stomach through oesophagus by rhythmic contraction of its muscles called peristaltic movements or peristalsis.

22. Stomach – Muscular walls of stomach help in mixing food thoroughly with digestive juices. Stomach has gastric glands which secrete gastric juice containing pepsin, hydrochloric acid and mucus.

• Pepsin helps in digestion of proteins.
• Hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin + kills germs present in food particles.
• Mucus protects the inner lining of the stomach from the action of the hydrochloric acid under normal conditions.

23. Small Intestine: A sphincter muscle regulates the exit of food from stomach into the highly coiled, longest part of the alimentary canal called the small intestine. Herbivores have a longer small intestine compared to the carnivores to allow the cellulose present in the grass to get digested. The digestive juices released in small intestine are:

(i) Bile juice: It is released from liver (stored in gall bladder). It helps to create alkaline medium in the small intestine for the pancreatic enzymes to act. Bile salts present in bile juice break down large fat globules into smaller globules (emulsification of fats) to increase the efficiency of enzyme action.

(ii) Pancreatic juice: It is released from pancreas and contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.

(iii) Intestinal juice: The walls of the small intestine contain glands which secrete intestinal juice. The enzymes present in it finally convert the proteins to amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol. Intestinal juice completes the process of digestion.

(iv) Role of Villi: The digested food is absorbed by the inner lining or wall of the intestine with the help of villi. Villi are finger-like projections richly supplied with blood vessels and help to increase the surface area for absorption. Absorbed nutrients reach the cells through blood and are utilised for obtaining energy, building up new tissues and the repair of old tissues.

(v) Large Intestine: The unabsorbed food is sent into the large intestine where more villi absorb water from this material and remove the wastes through the anus by egestion. The exit of this waste material is regulated by the anal sphincter.

24. Respiration: The breakdown of simple food material to release energy is called as respiration. Aerobic respiration takes place in the presence of air (oxygen) whereas the anaerobic respiration occurs in the absence of air (oxygen). More amount of energy is released in aerobic respiration.

25. Glycolysis: This is the first step which occurs in the cytoplasm and results in breakdown of glucose (six-carbon molecule) into a three-carbon molecule called pyruvate. Glycolysis occurs both in aerobic as well as anaerobic respiration.

26. Fate of pyruvic acid (pyruvate):

• The pyruvate is converted into ethanol and carbon dioxide by the process called fermentation in yeast due to anaerobic respiration.
• The pyruvate is converted into a three-carbon compound lactic acid during respiration in muscle cells due to anaerobic respiration. Accumulation of lactic acid causes cramps in muscles.
• The pyruvate is broken down into carbon dioxide and water in presence of oxygen inside the mitochondria. The energy released during cellular respiration is used to synthesise a molecule called ATP which is used to fuel all other activities in the cell.

27. Types of Respiration:
(i) Aerobic

• Anaerobic respiration
• Aerobic respiration: It takes place in the presence air (oxygen).

Anaerobic respiration: It takes place in the absence of air (oxygen).
Respiration in plants: Respiration in plants is simpler than the respiration in animals.

28. Gaseous exchange occurs through:

• Stomata in leaves
• Lenticels in stems
• General surface of the roots.

29. Respiration in terrestrial animals: They use atmospheric oxygen for respiration.

30. Respiration in aquatic animals: Aquatic animals use the oxygen dissolved in water. They breathe at a faster rate since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air. Fishes take water from mouth and send it to the gills where the dissolved oxygen is taken up by blood.

31. Human Respiratory System: Air enters the body after getting filtered by fine hairs and mucus in the nostrils. The air then passes through trachea (present in throat) into the lungs. Rings of cartilage present on trachea prevent it from collapsing during the passage of air.

The trachea divide into bronchi which enter the lungs and divide further into bronchioles which finally terminate in balloon-like structures called alveoli which have a rich supply of blood vessels and help in exchange of gases.

32. Mechanism of breathing: During inhalation (breathing in), the volume of the chest cavity becomes larger as the ribs get lifted and diaphragm gets flattened. Air gets sucked into the lungs and fills the expanded alveoli. The blood brings carbon dioxide from the rest of the body to the alveoli and exchanges it for oxygen to be transported to all the cells in the body.

During exhalation (breathing out), the volume of the chest cavity becomes smaller as the ribs get relaxed and diaphragm moves upward (relaxes). Air rich in carbon dioxide gets pushed out of the lungs to come out through the nostrils.

33. Residual volume: It is the volume of air left behind in the lungs even after forceful breathing out of air. This helps to provide sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

34. Respiratory pigment: The respiratory pigment called haemoglobin in human beings is present in the red blood corpuscles. Haemoglobin has a very high affinity for oxygen.

35. Transportation
Transportation in Human Beings: Circulatory system helps to transport blood to various parts of the body to ensure the supply of nutrients and oxygen to these parts and remove carbon dioxide and metabolic wastes.
The circulatory system in human beings consists of:

• A pumping organ—a muscular heart
• Blood vessels—Arteries and veins
• Circulating medium—Blood and lymph

36. Steps in circulation of blood:

• The relaxed thin-walled upper chamber of the heart on the left, the left atrium, receives oxygen- rich blood from the lungs through the pulmonary vein.
• The left atrium contracts and transfers blood to the left ventricle.
• The left ventricle contracts and sends the oxygen-rich blood through aorta to the various parts of the body.
• De-oxygenated blood from the various parts of the body is transported by vena cava to the relaxed right upper chamber of the heart called the right atrium.
• The right atrium contracts and transfers blood to the right ventricle.
• The right ventricle pumps de-oxygenated blood for oxygenation to the lungs through pulmonary vein.
• Ventricles have thicker muscular walls than atrium as they have to pump blood into various organs.

37. Role of valves: Valves ensure that blood does not flow backwards when the atria or ventricles contract.

Significance of separation of right and left side of the heart: It is useful to prevent mixing of oxygenated and de-oxygenated blood. It also allows a highly efficient supply of oxygen to the body. It is useful for animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature.

38. Types of heart:
Fishes have a two chambered heart. Blood pumped by heart gets oxygenated by gills and passes directly to the rest of the body. This is called single circulation. Amphibians and reptiles have three- chambered hearts and tolerate some mixing of the oxygenated and de-oxygenated blood. Birds and mammals have four chambered heart. Blood goes through the heart twice during each cycle in them. This is known as double circulation.

Types of Blood Vessels

Arteries	Veins
(i) Carry blood from heart to various organs of the body.	(i) Carry blood from various organs of body to the heart.
(ii) Carry oxygenated blood from the heart except the pulmonary artery.	(ii) Carry de-oxygenated blood from various organs except the pulmonary vein.
(iii) Have thick and elastic walls.	(iii) Have thin non-elastic walls.
(iv) Valves are absent.	(iv) Valves are present.
(v) Blood flows under high pressure.	(v) Blood flows under low pressure.

39. Capillaries: The smallest vessels have walls which are one-cell thick and are called capillaries. Their thin wall helps in exchange of material between the blood and surrounding cells. Veins are formed when the capillaries join together.

40. Role of blood platelets: Platelet cells circulate around the body in the blood and help in the clotting of blood when blood flows out during injury or cut.

41. Lymph or Tissue fluid: It is formed by the plasma, proteins and blood cells which escape into the intercellular spaces in the tissues through the pores present in the walls of the capillaries. Lymph is similar to the plasma of blood but colourless and contains less protein. It also carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood. Lymph enters the lymphatic capillaries which join to form large lymph vessels that finally open into larger veins.

42. Transportation in Plants: Two main conducting pathways in plants are:
(i) Xylem and
(ii) Phloem

(i) Xylem: It carries water and minerals from the roots to other parts of the plants.

(ii) Phloem: It carries products of photosynthesis from leaves to the other parts of the plant.

43. Transport of Water and Minerals
(i) By root pressure: The cells of root in contact with soil actively take up ions which creates a difference in ion concentration between the root and the soil. Water moves into the root from the soil to eliminate this difference, creating a column of water that is steadily pushed upwards.

(ii) By transpiration pull: Loss of water from stomata by transpiration gets replaced by the xylem vessels in the leaf which creates a suction to pull water from the xylem cells of the roots. This strategy is used during day time and helps to transport water to the highest points of the plant body.

44. Transpiration and its roles: The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.
It helps in
(i) absorption and upward movement of water and minerals.
(ii) temperature regulation by cooling the leaf surface.

45. Transport of food and other substances: Translocation is the transport of soluble products of photosynthesis through phloem.
Sucrose is transferred into sieve tubes of phloem via the companion cells using energy from ATP. This increases the osmotic pressure inside the sieve tubes which causes movement of water into the sieve tubes from the adjacent xylem. This pressure helps in translocation of material in the phloem to tissues which have less pressure.

46. Excretion: Removal of metabolic wastes from the body is called as excretion.

47. Excretion in Unicellular organisms: Many unicellular organisms remove metabolic wastes from the body surface into the surrounding water by simple diffusion.

48. Excretion in Human Beings: Excretory system of human beings includes:
(i) A pair of Kidneys
(ii) A Urinary Bladder
(iii) A pair of Ureters
(iv) A Urethra The purpose of making urine is to filter out waste product from the blood i.e., urea which is produced in the liver. Each kidney has large numbers of filtration units called nephrons. The urine formation involves three steps.

(i) Glomerular filtration: Nitrogenous wastes, glucose water, amino acid filter from the blood in blood capillaries into Bowman Capsule of the nephrons.

(ii) Selective reabsorption: Some substances in the initial filtrate, such as glucose, amino acids, salts and a major amount of water are selectively reabsorbed back by capillaries surrounding the nephrons.

(iii) Tubular secretion: Some ions like K⁺, H⁺, etc. are secreted into the tubule which opens up into the collecting duct.

Urine produced in the kidneys passes through collecting duct into the ureters. Ureters takes urine into the urinary bladder where it is stored until it is released through the urethra. Release of urine is under nervous control.

49. Excretion in Plants: Excess oxygen and carbon dioxide removed through stomata. Excess water removed by transpiration through stomata.
Plant waste products are also removed by:

• Storage in cellular vacuoles
• Storage in leaves that fall off
• Storing as resins and gums in old xylem
• By excreting into the soil around them.

Class 10 Science Chapter 6 Notes Important Terms

Autotrophs: The organisms which can prepare their own food from inorganic substances by using light or chemical energy. For example, Green plants and Bacteria.

Heterotrophs: Organisms which cannot synthesise their own food and depend oh other organisms for their nutrition. For example, Humans.

Bio-catalysts: Enzymes are called as bio-catalysts as they play an important role in chemical reactions taking place in living organisms.

Photosynthesis: The process by which the green plants make their own food in the presence of carbon dioxide, water, chlorophyll and sunlight. The site of photosynthesis is chloroplast present in plant cells.

Ingestion: The process of taking in food into body of an organism.

Digestion: It is the breakdown of large insoluble food molecules into simpler and small water- soluble food molecules so that they can be absorbed into the blood stream.

Absorption: The process of passing the nutrients from the digested food into the blood stream from the walls of the intestine.

Assimilation: The process by which the absorbed food is used by the various cells and tissues of the body for growth and repair.

Egestion: The act or process of throwing out the undigested material from a cell or an organism is called as egestion.

Peristalsis: It is a series of wave-like muscle contractions of the muscles of the oesophagus that moves food into the stomach.

Emulsification: The breakdown of large fat globules in the duodenum into smaller globules in order to provide a larger surface area for the enzyme lipase to act and digest the fats into fatty acids and glycerol.

Inhalation: The process by which we take in air is called as inhalation. During inhalation, rib cage is moved up, diaphragm contracts (tightens) and moves downward to increase volume of chest cavity.

Exhalation: The process by which the air flows out of lungs is called as exhalation. During exhalation, the ribs relax; diaphragm relaxes and moves upward to reduce the volume of chest cavity.

Residual volume: The volume of air remaining in the lungs even after forceful exhalation is called residual volume.

Respiration: It is the biochemical process in which the cells of an organism obtain energy by combining oxygen and glucose, resulting in the release of carbon dioxide, water, and energy in the form of ATP.

Fermentation: It is a metabolic process which occurs under anaerobic conditions in yeast and bacteria to convert sugar to acids, gases or alcohol.

Haemoglobin: The respiratory pigment which helps to transport oxygen to various cells and tissues of the body.

Blood pressure: The force exerted by blood against the wall of a vessel is called blood pressure. It is measured by sphygmomanometer.

Translocation: It is the movement of materials from leaves to other tissues throughout the plant.

Transpiration: It is the evaporative loss of water by plants.

Nephron: It is the functional unit of kidney. It has two parts—the glomerulus and the renal tubule.

Haemodialysis: This is a process which helps in purifying the blood of a patient suffering from kidney problem or failure, using an artificial kidney. It removes nitrogenous waste products from the blood through dialysis.