Category: CBSE Class 8

On this page, you will find Reaching the Age of Adolescence Class 8 Notes Science Chapter 10 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 10 Reaching the Age of Adolescence will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 10 Reaching the Age of Adolescence

Reaching the Age of Adolescence Class 8 Notes Understanding the Lesson

1. The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. It begins around the age of eleven and lasts upto eighteen or nineteen years of age. Hence adolescence occurs between childhood and adulthood.

2. The human body undergoes several changes during adolescence such as change in body shape, voice change, development of sex organs, etc.

3. The phase wherein the bodily changes occurs in terms of sexual growth, is known as puberty. Therefore puberty is defined as the onset of reproductive maturity, starting at the age of 11 years and lasts till the age of 18 years. It starts earlier in females than in males.

4. During adolescence, in girls, the region below the waist becomes wider whereas in boys, shoulders broaden and the muscles of the body grow more prominently than girls.

5. At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes and produce hoarse voice whereas girls have a high pitched or shrilled voice. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

6. There is a sudden change in height of human beings during puberty. The height increases faster in girls than boys and both reach their maximum height at the age of 18.

7. During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases which results in development of acne and pimples on the face of boys and girls.

8. In the period of adolescence, a person reaches the maturity level of mental, intellectual and emotional thinking.

9. During puberty, breasts begins to develop in girls; facial hair, i.e., moustache and beard in boys. These features which distinguish the male from female are called secondary sexual characters.

10. The changes which occur at adolescence are controlled by hormones which are chemical substances. They are secreted from endocrine glands, or endocrine system.

11. The male hormone or testosterone is released by the testes and the female hormone or estrogen is produced by ovaries are responsible for secondary sexual characters in both of them. The production of these hormones are under the control of pituitary gland.

12. Hormones from pituitary stimulate testes and ovaries to release male (testosterone) and female (estrogen) hormone into the blood stream which reach a particular body part called target site. The target site responds to the hormones. The testes and ovaries secrete sex hormones which are responsible in the male and female secondary characters.

13. Reproductive phase of life in humans start when their testes and ovaries begin to produce gametes. In male, the reproductive phase begins at puberty at the ages 14 – 15 and lasts, as long as he is healthy whereas in female it begins at the ages 10-12 and lasts until the age of 45-50 years.

14. The uterine wall in females prepare itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down along with blood. This is called menstruation.

15. The first menstrual flow begins at puberty is termed as menarche.

16. Stoppage of menstruation at the age of 45-50 is termed as menopause.

17. Sex of unborn child depends on whether the egg is fertilised with sperm having X or Y chromosome.

18. The thyroid gland produces the thyroxine hormone which prevents from ‘goitre’ disease. Similarly, the pancreas produces the insulin hormone which checks the disease ‘diabetes’. The adrenals produce hormone 1 adrenaline which helps the body to adjust to stress when one is very angry, embarrassed or worried.

19. The adrenals and thyroid secrete their hormone when they receive orders from the pituitary through its I hormones. The pituitary also secretes growth hormone which is necessary for the normal growth of a person.

20. Hormones play a vital role in completing life cycle in insects and frogs. For example, metamorphosis (changing of larva into adult) in insects is controlled by insect hormones. In a frog, it is controlled by thyroxine, the hormone produced by thyroid. The production of thyroxine needs the presence of iodine in water.

21. Nutritional needs of the adolescents: At the stage of adolescence, the human body grows at an extremely fast rate and requires adequate intake of a balanced diet which should contain proportionate I amount of proteins, carbohydrates, fats, vitamins and minerals, etc. They can be obtained from green vegetables, normal Indian meal of roti/dal/rice, milk, fruits, etc.

21. Maintaining personal hygiene and doing physical exercise is of utmost important to stay fit and healthy.

22. We should avoid drug to avoid physical, mental and emotional ailments.

Class 8 Science Chapter 10 Notes Important Terms

Adam’s apple: At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

Adolescence: The period of life, when the body undergoes changes, which leads to reproductive maturity, is called adolescence. It starts around the age of 11 and lasts upto 18 or 19 years of age.

Adrenaline: The hormone produced by adrenals is called adrenaline. It helps the body to adjust to stress when one is very angry, embarrassed and worried.

Balanced diet: A balanced diet or meal is one which includes proteins, vitamins, fats, carbohydrates, minerals, etc., in adequate quantity and proportion.

Chromosomes: These are thread-like structures present inside the nucleus of a cell and helps in for carrying genetic information from one generation to next generation.

Endocrine glands: Different types of hormones are secreted from particular glands called endocrine glands or endocrine system.

Female hormone or estrogen: The female hormone is secreted by ovaries at the onset on puberty and causes development of secondary sexual characters in female.

Growth hormones: Pituitary gland secretes growth hormones which is necessary for the normal growth of a person.

Hormones: Hormones are chemical substances secreted from endocrine glands. They are responsible for regulating metabolic and other activities of the body.

Insulin: The hormone produced by pancreas is called insulin.

Male hormone or testosterone: The male hormone is released by the testes at the onset of puberty and causes changes in secondary sexual characters.

Menarche: The first menstrual flow begins at puberty is known as menarche.

Menopause: When the menstruation ceases, the stage is called menopause.

Menstruation: The process in a woman of discharging blood and other material from the lining of uterus at intervals of about 28-30 days is called menstruation.

Pituitary gland: A pea-sized body attached to the base of the brain that is important in controlling growth and development and functioning of the other endocrine gland.

Puberty: The period of life, during which the human body undergoes several changes and reaches sexual maturity and the human beings become capable of reproduction, is called puberty.

Reproductive health: Good health is essential for adolescence and for reproductive phase of life. For good health one should have a balanced diet, do physical exercises, avoid smoking, drinking and drugs, maintain hygiene and take proper sleep and rest.

Secondary sexual characters: In adolescence period, there are several changes including growth of facial hair, i.e., moustaches and beard on boys’ face, development of breast in girls, etc. These features or characters that help to distinguish the male from the female are called secondary sexual characters.

Sex chromosomes: All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chro-mosomes out of these are the sex chrmosomes named X and Y. A male has one X and one Y chromosome while a female has two X chromosomes.

Thyroxine: The hormone produced by the thyroid gland is called thyroxine.

 

On this page, you will find Reproduction in Animals Class 8 Notes Science Chapter 9 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 9 Reproduction in Animals will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 9 Reproduction in Animals

Reproduction in Animals Class 8 Notes Understanding the Lesson

1. Reproduction is the process of continuation of similar kinds of individuals, generation after generation. In this process, all living beings produce their young ones for continuity of life on the planet earth.

2. There are two modes by which animals reproduce. These are:

• Sexual reproduction and
• Asexual reproduction.

3. Reproduction resulting from the fusion of male and female gametes is called sexual reproduction; e.g., frog, fish, cow, human beings, etc., reproduce by sexual reproduction.

4. Reproduction in which young ones are formed from the cells of a single parent and are identical copies of their parents is called asexual reproduction. This type of reproduction is seen in Amoeba, yeast, worms, etc.

5. There are different reproductive organs in male and female. The main reproductive organs in males are testes, sperm ducts, urethra and penis , whereas those in females are ovaries, oviducts, uterus and vagina

6. In male, the testes produce the male gametes called sperms , whereas in female, the ovary produces female gametes called ova (eggs)
In human beings, a single matured egg is released into the oviduct by one of the ovaries every month.

7. Uterus is the part where development of the baby takes place.

8. When sperms come in contact with an egg, one of them may fuse with the egg. Such fusion of egg and the sperm is called fertilisation

9. The nuclei of the sperm and the egg fuse to form a single nucleus forming a fertilised egg called zygote

10. Fertilisation which takes place inside the female body is called internal fertilisation and that in which the fusion of a male and a female gametes takes place outside the female body is called external fertilisation. Internal fertilisation occurs in many animals including humans, cows, dogs and hens whereas external fertilisation is very common in aquatic animals like fish, frogs, starfish, etc.

11. The zygote formed after fertilisation begins to develop into an embryo . The zygote divides repeatedly to give rise to a ball of cells which then begin to form groups that develop into different tissues and organs of the body termed as embryo.

12. The embryo gets embedded in the wall of the uterus for further development.

13. The stage of the embryo in which all the body parts can be identified is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby.

14. The animals which give birth to their young ones are called viviparous animals and those which lay eggs to reproduce are called oviparous animals.

15. The immature free-living form of most invertebrates (animals lacking a backbone) and amphibians and fish which at hatching from the egg is fundamentally unlike its parent and must metamorphose is called larva.

16. The transformation of the larva into an adult through drastic changes is called metamorphosis.

17. In Hydra, new individuals develop from buds. This method of asexual reproduction is called budding.

18. Amoeba reproduces by dividing itself into two. This type of asexual reproduction is called binary fission.

Class 8 Science Chapter 9 Notes Important Terms

Asexual reproduction: The mode of reproduction in which a single organism is able to produce one or more of its kind by itself is known as asexual reproduction; e.g., Amoeba, yeast, Hydra, etc., undergo asexual reproduction.

Binary fission: The type of reproduction in which an animal reproduces by dividing into two individuals is called binary fission; e.g., Amoeba reproduces by dividing itself into two.

Budding: This kind of reproduction is seen in Hydra and yeast. It is the process of reproduction in which new individuals develop as outgrowths from a single parent. The outgrowths developed on parent body is called buds and the process of reproduction is known as budding.

Embryo: When cells produced by the division of the zygote begin to form groups that develop into different tissues and organs of the body is called embryo.

External fertilisation: The fusion of male and female gametes takes place outside the female body. This is called external fertilisation. Most of the aquatic animals undergo this type of fertilisation.

Fertilisation: The process of union of male gametes or sperms and female gametes or ova (egg) is called fertilisation.

Foetus: The stage of the development of embryo in which the development and emergence of the various body parts like the hands, the feet and eyes, etc., can be identified is called the foetus.

Internal fertilisation: The fusion of male and female gametes or fertilisation that takes place inside the female body is called internal fertilisation. All insects, birds and mammals including human beings undergo this type of fertilisation.

Metamorphosis: A biological process in which larva drastically changes into an adult in an invertebrate or amphibian during their life cycle is known as metamorphosis.

Ova or Eggs: Female gametes produced by ovary in female are called ova or eggs.

Oviparous animals: The animals which lay eggs and hatch them to produce their young ones are called oviparous animals; e.g., frog, butterflies, hen, crow, etc.

Reproduction: The process of producing the offspring of one’s own kind for continuity of life in the earth is known as reproduction.

Sexual reproduction: The type of reproduction which involves fusion of male and female gametes is called sexual reproduction.

Sperms: Sperms are the male gametes produced by the testes in male.

Viviparous animals: The animals which give birth to their young ones are called viviparous animals; e.g., cow, buffalo, cat, dog, human beings, etc.

Zygote: The nucleus of the sperms and the egg fuse to form a single nucleus during the process of fertilisation. The fertilised egg is called zygote.

On this page, you will find Playing with Numbers Class 8 Notes Maths Chapter 16 Pdf free download. CBSE NCERT Class 8 Maths Notes Chapter 16 Playing with Numbers will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Maths Chapter 16 Notes Playing with Numbers

Playing with Numbers Class 8 Notes Conceptual Facts

1. Generalised form of a two-digit number if a is ten place digit and 6 is unit place digit.
a x 10 + b x 1 = 10a + b

2. Generalised form of a three-digit number if a is ten place digit and b is unit place digit.
a x 100 + b x 10 + c x 1 = 100a + 10b+ c

3. Two-digit original numbers = 10a + b
Number obtained by reversing the digits = 10b + a
Sum = 10a + b + 10b + a
= 11a + 11b – 11(a + b)

which is divisible by 11.
Difference = (10a + b) – (10b + a)
= 10a + 6 – 106 – a
= 9a -9b – 9(a – b)
which is divisible by 9.

4. Three-digit original number if a is hundred place digit and 6 is ten place digit and c is unit place digit.
= 100a + 10b + c
The number obtained by reversing the digits = 100c + 10b + a
Difference = (100a + 10b + c) – (100c + 10b + a)
= 100a + 10b + c – 100c – 10b – a
= 99a – 99c = 99(a – c)
which is divisible by 99.

5. Divisibility test by 2 – A number is divisible by 2 if its unit place is even.
For example: 24, 48, 56 and 76 etc.

6. Divisibility test by 3 – A number is divisible by 3 if the sum of all digits of the given number is also divisible by 3.
For example: 123 = 1 + 2 + 3 = 6÷3 = 2
528 = 5 + 2 + 8 = 15 ÷ 3 = 5

7. Divisibility test by 5 – If the unit place digit is either 0 or 5 then it is divisible by 5.

8. Divisibility test by 9 – A number is divisible by 9 if the sum of its digits is also divisible by 9.
For example:
225 =2+2+5=9÷ 9=1
684 = 6 + 8 + 4 = 18 ÷ 9 = 2

9. Letters for digits – There are two rules followed while doing such puzzles.

• The first digit cannot be zero.
• Each letter in the puzzle must stand for just one digit.

On this page, you will find Introduction to Graphs Class 8 Notes Maths Chapter 15 Pdf free download. CBSE NCERT Class 8 Maths Notes Chapter 15 Introduction to Graphs will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Maths Chapter 15 Notes Introduction to Graphs

Introduction to Graphs Class 8 Notes Conceptual Facts

• XOX’ and YOY’ taken together are called coordinate axes.
• The plane containing the coordinate axes is called cartesian plane.
• The point of intersection of the coordinate axes is called origin.
• The x-coordinate is always written before y-coordinate e.g., if 2 is x-coordinate and 3 is y-coordinate, then the coordinates are (2, 3).
  
• The x-coordinate of a point lying on y-axis is zero.
• The y-coordinate of a point lying on x-axis is zero.
• The x-coordinate is also called abscissa and y-coordinate ordinate.

 

 

On this page, you will find Factorisation Class 8 Notes Maths Chapter 14 Pdf free download. CBSE NCERT Class 8 Maths Notes Chapter 14 Factorisation will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Maths Chapter 14 Notes Factorisation

Factorisation Class 8 Notes Conceptual Facts

• Prime factors of 30 (say) = 2 x 3 x 5
• Factors of algebraic expression 4xy = 4 x x x y
• 1 is a factor of every expression.
• Method of common factors
• 4x + 24 = 4(x + 6)
• Method of factorisation by regrouping terms
  6xy + 3y = 2 x 3 x x x y + xy = 3 xy (2x + 1) = 3y (2x + 1)

Factorisation using identities
a² + 2ab + b²– (a + b)²
a² – 2ab + b²= (a-b)²
a² – b² = (a + b) (a – b)

On this page, you will find Direct and Indirect Proportions Class 8 Notes Maths Chapter 13 Pdf free download. CBSE NCERT Class 8 Maths Notes Chapter 13 Direct and Indirect Proportions will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Maths Chapter 13 Notes Direct and Indirect Proportions

Direct and Indirect Proportions Class 8 Notes Conceptual Facts

1. The two quantities are said to be directly proportional if

• an increase in one leads to a corresponding increase in the other.
• a decrease in one leads to a corresponding decrease in the other.

2. If x varies directly as y then the ratio \(\frac{x}{y}=k\) (constant) symbolically, x α y, where α is symbol of
proportionality or x = ky \(\frac{x_{1}}{y_{1}}=\frac{x_{2}}{y_{2}}=\frac{x_{3}}{y_{3}}=k\)

3. The two quantities are said to be inversely proportional if

• an increase in one leads to a corresponding decrease in the other.
• a decrease in one leads to a corresponding increase in the other.

4. If x varies inversely with y, then x α \(\frac{1}{y}\) ⇒ xy = k(constant) or xy – x₁y₁ = x₂y₂ = k.

5. Speed =\(\frac{\text { Distance }}{\text { Time }} \) or Distance = Speed x time or time =\(\frac{\text { Distance }}{\text { Speed }}\)

On this page, you will find Exponents and Powers Class 8 Notes Maths Chapter 12 Pdf free download. CBSE NCERT Class 8 Maths Notes Chapter 12 Exponents and Powers will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Maths Chapter 12 Notes Exponents and Powers

Exponents and Powers Class 8 Notes Conceptual Facts

• A numeral (a)ⁿ is called an exponential expression where a is called base and n the exponent or power.
  aⁿ = a x a x a x a……… x a (n times)
• A negative rational number raised to an even power is always positive, \(\text { e.g. },\left(-\frac{1}{2}\right)^{4}=\frac{1}{16}\)
• A negative rational number raised to an odd power is always negative, i.e., \(=\left(-\frac{1}{2}\right)^{3}=-\frac{1}{8}\)

Laws of exponents:

On this page, you will find Cell Structure and Function Class 8 Notes Science Chapter 8 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 8 Cell Structure and Function will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 8 Cell Structure and Function

Cell Structure and Function Class 8 Notes Understanding the Lesson

1. The basic structural and functional units of all the organs of the living organisms is called cell.

2. Cells were first discovered by Robert Hooke in 1665.

3. Cells of living organisms could be observed only after the discovery of improved microscopes.

4. Cells exhibit a variety of shapes and sizes.

5. Number of cells also varies from organism to organism.

6. Organisms made of more than one cell are called multicellular organisms while organisms made up of single cell are called unicellular organisms.

7. A single-celled organism, e.g., Amoeba captures and digests food, respires, excretes, grows and reproduces. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues.

8. A white blood cell (WBC) in human blood is an example of a single cell which can change its shape.

9. The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.

10. The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest cell measuring 170 mm x 130 mm, is the egg of an ostrich.

11. Each organ is further made up of smaller parts called tissues.

12. A tissue is a group of similar cells performing a specific function.

13. The basic components of a cell are cell membrane, cytoplasm and nucleus.

14. Cell membrane is also called plasma membrane or cytoplasmic membrane. The cell membrane separates cells from one another and also the cell from the surrounding medium. It is porous and allows the movement of substances or materials both inward and outward.

15. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to these cells.

16. The jelly-like substance between the nucleus and the cell membrane is called cytoplasm. Various components or organelles, like mitochondria, golgi bodies, ribosomes, etc., are present in cytoplasm.

17. The central dense round body in the centre is called the nucleus.

18. The membrane which separates nucleus from the cytoplasm is called the nuclear membrane.

19. Cells without well-organised nucleus, i.e., lacking nuclear membrane, are called prokaryotic cells.

20. The smaller spherical body in the nucleus is called the nucleolus.

21. Chromosomes are the thread-like structures which carry genes and help in inheritance or transfer of characters from the parents to the offspring.

22. Plant cell differs from animal cell in having a central large vacuole, cell wall and plastids.

23. The blank-looking structures in the cytoplasm are called vacuole.

24. Plastids are the coloured organelles, that are found in plant cells only.

25. Green coloured plastids are called chloroplasts.

Class 8 Science Chapter 8 Notes Important Terms

Cell: Cell is the basic structural and functional unit of all living organisms.

Cell membrane: The membrane around the cell is called cell membrane. It is also called plasma membrane or cytoplasmic membrane.

Cell wall: The hard and rigid covering of plasma membrane which are found in plant cells only is called cell wall.

Chloroplasts: The green coloured plastids having chlorophyll, which is essential for photosynthesis is called chloroplasts.

Chromosomes: The thread like structures found in the nucleus which carry genes are called chromosomes.

Eukaryotes: Organisms which have eukaryotic cells, i.e., which contains a well developed nucleus are called eukaryotes.

Gene: Genes are located in chromosomes. It is a unit of inheritance in living organisms.

Multicellular: The category of organism like plants and animals which contains a large number of cells are called multicellular organisms.

Nuclear membrane: Nuclear membrane separates nucleus from cytoplasm.

Nucleolus: The smaller, spherical and dense body inside the nucleus is called nucleolus.

Nucleus: The denser region of the cell that may be present at the centre of the cell is called nucleus.

Organ: The group of tissues, which are specialised to perform specific functions is called organ.

Organelle: One of the smaller component of cell is known as organelle.

Plasma membrane: The other name of cell membrane is plasma membrane. It is a membrane around the cell.

Plastids: The coloured organelles, that are found in plant cells only are called plastids.

Prokaryotes: The organisms which have prokaryotic cells, i.e., lack true nucleus are called prokaryotes, e.g., bacteria and blue green algae.

Protoplasm: The viscous fluid inside the cell which provides living nature to it is called protoplasm.

Pseudopodia: The temporary projections protruding out of the body of Amoeba for locomotion and taking food. These appear and disappear as Amoeba moves.

Tissue: A group of similar cells performing a specific function is called tissue.

Unicellular: The category of organisms containing single cell are called unicellular organisms.

Vacuoles: Vacuoles are the empty or blank looking structures in the cytoplasm.

White Blood Cell (WBC): It is the component of blood cells. It is an example of a single cell which can change its shape.

On this page, you will find Conservation of Plants and Animals Class 8 Notes Science Chapter 7 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 7 Conservation of Plants and Animals will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 7 Conservation of Plants and Animals

Conservation of Plants and Animals Class 8 Notes Understanding the Lesson

1. There are a number of plants and animals that exist on earth.

2. Deforestation means cutting down of forests.

3. The chances of natural calamities like droughts and floods increase due to the deforestation.

4. An ecosystem is made of all the plants, animals and microorganisms in an area along with non-living components such as climate, soil, river, deltas, etc.

5. Plants and animals of a particular area are known as flora and fauna, respectively, of that area.

6. The conversion of fertile lands into deserts is known as desertification.

7. To protect our flora and fauna and their habitats, protected areas called sanctuaries, national parks and biosphere reserves have been earmarked. Activities like plantation, cultivation, grazing, felling trees, hunting and poaching are prohibited there.

8. Biosphere reserves are large areas of protected land for conservation of wildlife, plant and animal resources and traditional life of the tribals living in that area.

9. A sanctuary is an area where animals are kept protected from the disturbances to them and their habitats.

10. National Parks are areas reserved for wildlife where they can freely use the habitats and natural resources.

11. Those species of plants and animals which are found exclusively in a particular area are termed as ‘endemic species’.

12. Species is a group of population which are capable of interbreeding.

13. Project Tiger was launched by the government to protect tigers in the country.

14. Extinct species are those which have disappeared completely from the earth. Example, Dodo and passenger pigeon.

15. Critically endangered species are those which are under highest risk of extinction as their number has decreased drastically. Example, Andean catfish, Abe’s salamander.

16. Endangered animals are those whose numbers are diminishing to such a level that they might face I extinction. Example, great Indian bustard and blue whale.

17. Vulnerable species are those which are most likely to become endangered if not taken care of.

18. Near threatened species are found in small numbers and are scattered all over the world.

19. A sourcebook that keeps a record of all the endangered plants and animals is called ‘Red Data Book’.

20. Migration is the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for a specific purpose like breeding.

21. Reforestation is restocking of the destroyed forests by planting new trees.

Class 8 Science Chapter 7 Notes Important Terms

Biodiversity: It is the variety of different types of plant and animal life in a particular habitat (or in the world as a whole).

Biosphere reserve: A large; protected area of land meant for conserving wildlife, biodiversity, and the traditional lifestyle of the tribal people living in the area is known as a ‘biosphere reserve’.

Deforestation: The cutting down of trees on a large scale is called deforestation.

Desertification: The conversion of fertile lands into deserts is called desertification.

Ecosystem: It is a system formed by the interaction of a community of organisms with their physical environment.

Endangered species: Those species whose numbers are so small that the species are at risk of extinction are called endangered species.

Endemic species: They are the species of plants and animals which are found exclusively in a place.

Extinct animals: Animals which no more exist anywhere on the earth are known as extinct animals.

Fauna: The animals of a particular area are known as fauna of that area.

Flora: They are the plants of a particular area.

Migratory birds: Birds which move from one place to another for some reasons like breeding, climatic changes, etc., are known as migratory birds.

National park: The areas reserved for wildlife where they can freely use the habitats and natural resources are known as national parks.

Red Data Book: A source book that keeps a record of all the endangered animals, plants and other species.

Reforestation: The replanting or restoration of a forest that had been reduced by fire or cutting is called reforestation.

Sanctuary: The area where animals are kept protected from any disturbance to them or their habitat is known as a sanctuary.

On this page, you will find Combustion and Flame Class 8 Notes Science Chapter 6 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 6 Combustion and Flame will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 6 Combustion and Flame

Combustion and Flame Class 8 Notes Understanding the Lesson

1. Combustion is a chemical process in which a substance reacts with oxygen to give out heat energy.

2. All the substances that undergo combustion are said to be combustible.

3. A combustible substance may be solid, liquid or gaseous.

4. The presence of air is very necessary for combustion.

5. The lowest temperature at which a substance catches fire is known as its ignition temperature.

6. Some substances have very low ignition temperatures and they catch fire easily with a flame. They are known as inflammable substances; e.g., Petrol, LPG (Liquefied Petroleum Gas), alcohol, etc.

7. There are three significant requirements for producing fire fuel, air (for the supply of oxygen), and heat (to raise the temperature of the fuel above its ignition temperature).

8. When a substance burns rapidly and produces heat and light, the combustion is called rapid combustion.

9. When a material begins to burn suddenly without any external supply of heat or friction, the combustion is called spontaneous combustion; e.g., white phosphorus catches fire even at 25°C.

10. So, when the temperature goes beyond 25°C in summer, it catches fire automatically.

11. During combustion, when a large amount of heat and light is released with a bang or force, along with the production of gas, the combustion is called an explosion; e.g., bombs and fireworks, etc.

12. Flame is the region where combustion of gaseous substances or vapour goes on.

13. There are three distinct zones of a flame dark zone, luminous zone and non- luminous zone.

14. The amount of heat energy produced on burning 1 kg of a fuel completely is called the calorific value of that fuel.

15. The calorific value of a fuel is expressed in a unit called kilojoule per kilogram (kJ/kg).

16. A good fuel is one which is readily available, cheap, burns easily, produces large amount of heat and does not leave any undesirable substances.

17. The cutting down of trees is termed as ‘deforestation’.

18. The rise in temperature of the atmosphere of the earth is called global warming.

19. Water is commonly used to extinguish fire.

20. Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulphur dioxide and nitrogen oxides) combine with water is known as acid rain.

Class 8 Science Chapter 6 Notes Important Terms

Acid rain: Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulphur dioxide and nitrogen oxides) combine with water is known as acid rain. It harms trees, crops and buildings.

Calorific value: The amount of heat energy produced on combustion of 1 kg of fuel completely is called its calorific value.

Combustion: It is a chemical process in which a substance reacts with oxygen (in air) to emit heat and light.

Deforestation: The removal of trees on a large scale is termed as deforestation.

Explosion: A combustion reaction during which a large amount of heat and light energy is released, along with a bang or force with the production of gas, is called explosion.

Flame: It is a region where the combustion of gaseous substances or vapour goes on.

Fire extinguisher: A manually operated device used for extinguishing fire is known as a fire extinguisher.

Fuel: It is a material which is burn to produce heat.

Fuel efficiency: It is a parameter used to check the quality of fuel. It is expressed in term of its calorific value.

Global warming: An increase in the average temperature of the earth’s atmosphere, especially a sus-tained increase that causes climatic changes.

Ideal fuel: It is the fuel, that satisfies all the necessities of a fuel for specific uses.

Ignition temperature: The lowest temperature at which a substance catches fire is called its ignition temperature.

Inflammable substances: They are the substances that have a very low ignition temperature, and that can easily burn with a flame.

On this page, you will find Coal and Petroleum Class 8 Notes Science Chapter 5 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 5 Coal and Petroleum will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 5 Coal and Petroleum

Coal and Petroleum Class 8 Notes Understanding the Lesson

1. All the things that are required to fulfil our needs are called resources.

2. Some resources like air, water, fuels, plants occur in nature. They are called natural resources.

3. Some resources like plastics, machines, etc., are man-made.

4. Natural resources are classified as:

• Inexhaustible natural resources and
• Exhaustible natural resources.

5. Inexhaustible natural resources are present in unlimited quantity in nature; e.g., sunlight, air, etc. Exhaustible natural resources are present in limited quantity in nature; e.g., petroleum, natural gas, wildlife, forest, etc.

6. Some of exhaustible resources are renewable while some are non-renewable.

7. Natural fuels that are made up by the dead remains of living organisms for over a long period of time, are called fossil fuels.

8. Fossil fuels may be divided into three categories:

• Solid – Coal
• Liquid – Petroleum
• Gas – Natural gas

9. Coal is black-coloured hard substance that mainly contains carbon.

10. Coal is one of the main sources of energy worldwide.

11. Coal is one of the fuels used to cook food, run engines, generate electricity and to run various industries. Millions of years ago, trees, plants, ferns and forests got buried below the rocks, soil and sand.

12. Under anaerobic condition high temperature and pressure, the carbon enriched organic matter of plants slowly got converted into coal.

13. This slow process of conversion of wood into coal is called carbonisation.

14. Destructive distillation of coal is done at 1000°C in absence of air to obtain many other useful organic and inorganic substances from it, such as coke, coal tar and coal gas.

15. Coke is a tough, porous and black substance. It is an almost pure form of carbon.

16. Coke is used in the manufacture of steel and in the extraction of many metals.

17. Coal tar is a black, thick liquid with an unpleasant smell. It is a mixture of about 200 substances.

18. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and industry like dyes, drugs, naphthalene balls, paints, plastics, etc.

19. Coal gas is produced during the processing of coal to get coke.

20. It is used as a fuel in many industries situated near the coal processing units.

21. The word ‘petroleum’ is derived from petra meaning ‘rock’ and oleum meaning ‘oil’.

22. Petroleum is a dark coloured viscous fluid and like all the other oils, it is lighter than water.

23. Petroleum was formed when organisms living in the sea are buried underneath sedimentary rock and subjected to intense heat and pressure under anaerobic condition.

24. Petroleum has such a great significance that it is named as ‘black gold’.

25. Separation of different constituents of petroleum through fractional distillation is called refining of petroleum.

26. Refining of petroleum is carried out in a petroleum refinery.

27. Natural gas is a very important fossil fuel because it is easy to transport through pipes.

28. Natural gas is stored under high pressure as compressed natural gas (CNG).

29. The great .advantage of CNG is that it can be used directly for burning in homes and factories.

30. We must use the fuels only when it is absolutely necessary.

31. In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/ diesel while driving.

32. To conclude, we can say that fossil fuels are our very important resources of energy. But as they are limited, we should use them judiciously.

Class 8 Science Chapter 5 Notes Important Terms

Coal: A fossil fuel, formed by the decay of vegetation which existed millions of years ago is called coal.

Coal gas: A mixture of gases produced during destructive distillation of coal is called coal gas.

Coal tar: Coal tar is a black coloured thick, viscous liquid which is obtained as byproduct when coal is carbonised to make coke.

Coke: On heating the coal strongly, the volatile impurities escape out from it and solid, pure carbon residue is left behind which is called coke.

Fossil fuel: Natural fuel that made up by burial of living organisms under deep down the earth for over a long period of time is called fossil fuel.

Natural gas: The gaseous mixture of lower hydrocarbon which occur deep inside the earth either alone or covering the crude oil in an oil field is called natural gas.

Petroleum: A dark coloured thick crude oil found deep below the ground is called petroleum.

Petroleum refinery: A place where process of separating the various constituents of petroleum is car-ried out is called petroleum refinery.