Category: CBSE Notes

By going through these CBSE Class 12 Chemistry Notes Chapter 1 The Solid State, students can recall all the concepts quickly.

The Solid State Notes Class 12 Chemistry Chapter 1

A solid is defined as that form of matter which possesses rigidity and hence possesses a definite shape and a definite volume.

The following are the characteristic properties of the solid-state:

1. They have definite mass, volume, and shape.
2. Intermolecular distances are short.
3. Intermolecular forces are strong.
4. Their constituent particles (atoms, molecules, or ions) have fixed positions and can only oscillate about their mean positions.
5. They are incompressible and rigid.

Solids can be classified into two classes:
1. Crystalline Solids: The substances whose constituents are arranged in a definite orderly arrangement are called crystalline solids. For example, NaCl, S, diamond, sugar, etc. The crystalline substances have sharp melting points and have physical properties different in different directions, i.e., crystalline substances are ANISOTROPIC. They have long-range and short-range orders.

2. Amorphous Substances: The substances whose constituents are not arranged in an orderly arrangement are called amorphous substances. For example, glass, rubber, fused silica, plastics, etc. They do not have sharp melting points and their physical properties are the same in all directions, i.e., there are ISOTROPIC. They have short-range orders.

The difference in their characteristics are:

Crystalline Solids	Amorphous Solids
1. Arrangement of constituents: Crystalline solids have an orderly arrangement of constituents. Thus they have definite regular geometry.	1. Amorphous substances do not possess an orderly arrangement.
2. Interfacial angles: Crystals are always bounded by planes so that a definite angle between two planes exists.	2. Amorphous substances are not bound by plane faces; so do not possess interfacial angles.
3. Anisotropy: Crystalline solids exhibit anisotropy i.e. their physical properties are different in different directions.	3. Amorphous substances like liquids have the properties same in all directions. Therefore, they are called to be isotropic.
4. Melting points: Melting points in crystalline solids are sharp and distinct.	4. These do not have sharp melting points e.g., glass on heating softens and starts flowing
5. Heat of fusion: These have definite heat of fusion.	5. Amorphous solids do not have definite heat of fusion.
6. Nature: They are true solids.	6. Pseudo solids or supercooled liquids.
7. Order in the arrangement of constituent particles: Long-range order	7. Only short-range order.

Classification of Crystalline Solids:
1. Molecular solids: These solids have molecules as constituent particles.

They are further subdivided into.
→ Non-polar molecular solids: They comprise either atoms, e.g., argon and helium, or the molecules formed by non-polar covalent bonds, for example, -H₂, Cl₂, and I₂. They are held by weak dispersion forces or London forces. These solids are soft and non-conductors of electricity. They have low melting points and are usually liquids or gases at room temperature and pressure.

→ Polar molecular solids: The molecules of substances like HCl and SO₂ etc. are formed by polar covalent bonds. The molecules in such solids are held together by relatively stronger dipole-dipole interactions. They are soft solids and non-conductors of electricity. Their melting points are higher than non-polar molecular solids. They are mostly liquids and gases at room temperature and pressure. Solid SO₂ and solid NH₃, are some of the examples of such solids.

→ Hydrogen bonded molecular solids: The molecules of such solids contain polar-covalent bonds between H and F, O or N atoms. Strong hydrogen bonds bind the molecules of such solids like H₂O (ice). They are non-conductors of electricity. Generally, they are volatile liquids or soft solids under room temperature and pressure.

2. Ionic Solids: They comprise ions. They are formed by three-dimensional arrangements of cations and anions bound by strong Coulombic forces. These solids are hard and brittle. They have high melting and boiling points. Since ions are not free to move they are electrical insulators in the solid-state. These ions become mobile in molten or aqueous states. Hence they conduct electricity in their molten or aqueous state.

3. Metallic Solids: Metals are an orderly collection of positive ions (kernels) surrounded by and held together by a sea of mobile or free electrons. These mobile electrons are responsible for the high electrical and thermal conductivity of metals. They are also responsible for the color and luster of metals. Metals are highly malleable and ductile.

4. Covalent or Network Solids: A wide variety of crystalline solids of non-metals results from the formation of covalent bonds between adjacent atoms throughout the crystal. They are giant-sized molecules. Covalent bonds are strong and directional in nature. Such solids are hard and brittle. They have extremely high melting points and even decompose before melting. They are insulators and do not conduct electricity. Diamond and silicon carbide (SiC) are typical examples of such solids. Graphite is soft and conductor of electricity.

The different properties of the four types of solids are listed in the table below:
Crystal Lattices and Unit Cells: A regular three-dimensional arrangement of points in space is called a Crystal Lattice.

There are only 14 possible three-dimensional lattices. These are called Bra Vais Lattices.

Characteristics of a crystal lattice

1. Each point in a lattice is called a lattice point or lattice site.
2. Each point in a crystal lattice represents one constituent particle which may be an atom, molecule, or ion.
3. Lattice points are joined by straight lines to bring out the geometry of the lattices.

Unit Cell is the smallest portion of a crystal lattice which, when repeated in different directions venerates the entire lattice.

Table: Different Types Of Solids:

A unit cell is characterized by

1. Its dimensions along the three edges a, b and c. These edges may or may not be mutually perpendicular.
2. Angles between the edges, α (between b and c), β (between a and c), and γ (between a and b). Thus a unit cell is characterized by 6 parameters: a, b, c, α, β and γ.

These parameters of a typical unit cell are shown in the figure below:

Illustration of parameters of a unit cell

Primitive And Centered Unit Cells:
Unit cells can be broadly divided into two categories, primitive and centered unit cells.
1. Primitive Unit Cells: When constituent particles are present only on the corner positions of a unit cell, it is called a primitive unit cell.

2. Centered Unit Cells: When a unit cell contains one or more constituent particles present at positions other than corners in addition to those at comers, it is called a centered unit cell.

Centered unit cells are of three types:
(a) Body-Centered Unit Cells: Such a unit cell contains one constituent particle (atom, molecules, or ion) at its body center beside the ones that are at its corners.

(b) Face-Centered Unit Cells: Such a unit cell contains one constituent particle present at the center of its face, besides the ones that are at its corners

(c) End-Centered Unit Cells: In such a unit cell, one constituent particle is present at the center of any two opposite faces besides the ones present at its corners.

In all, there are seven types of primitive unit cells.

Table 1.2: Seven primitive unit cells and their possible variations as centered units

Unit Cells Of 14 Types Of Bra Vais Lattices:

→ The three cubic lattices: all sides of name length angles between faces all 90°

→ The two tetragonal: one side different in length to the other two angles between faces all 90°

→ The four orthorhombic lattices: unequal sides; angles between faces all 90°

→ The two monoclinic lattice: unequal sides; two faces have angles different to 90°

Number Of Atoms In A Unit Cell:
1. Primitive Cubic Unit Cell: Primitive cubic unit cell has atoms only at its corner. Each atom at a comer is shared between eight adjacent unit cells as shown in the figure below, four-unit cells in the same layer and four-unit cells of the upper (or lower) layer. Therefore only l /8th of an atom (molecule or ion) actually belongs to a particular unit cell.

In all, since each cubic unit cell has 8 atoms on its corners, the total number of atoms in one unit cell is 8 × \(\frac{1}{8}\) = 1 atom.

In a simple cubic unit cell, each corner atom is shared between 8 unit cells.

2. Body-Centered Cubic Unit Cell: A body-centered cubic (bcc) unit cell has an atom at each of its corners and also one atom at its body center. Fig. depicts such a structure.

(a) open structure
(b) space-filling model and
(c) the unit cell with portions of atoms actually belonging to it.

It can be seen that the atom at the body center wholly belongs to the unit cell in which it is present. Thus in a body-centered cubic (bcc) unit cell:

1. 8 corners × \(\frac{1}{8}\) per corner atom = 8 × \(\frac{1}{8}\) = 1 atom
2. 1 body centre atom = 1 × 1 = 1 atom
   ∴ Total number of atoms per unit cell = 2 atoms

3. Face Centered Cubic unit cell: A face-centered cubic (fee) unit cell contains atoms at all the comers and at the center of all the faces of the cube. Each atom located at the face-center is shared between two adjacent unit cells and only \(\frac{1}{2}\) of each atom belong. to a unit cell. The figure below depicts such a structure.

(a) open structure
(b) space-filling model and
(c) the unit cell with portions of atoms actually belonging to it.

Thus in a face-centered cubic face unit cell.

1. 8 corners × \(\frac{1}{8}\) per corner atom = 8 × \(\frac{1}{8}\) = 1 atom
2. 6 face-centered atoms × \(\frac{1}{2}\) atom per unit cell = 6 × \(\frac{1}{2}\) = 3 atoms
   ∴ Total number of atoms per unit cell = 4 atoms

Close Packing Of Particles:
There are two common types of close packing of particles in a crystalline substance.
→ Hexagonal Close-Packing: This type of packing is referred to as the ABABA arrangement.

→ Cubic Close-Packing: This type of packing is referred to as

ABC ABC arrangement. In both types of packing, 74% of the available space is occupied by spheres.

Interstitial Sites: Two important interstitial sites are:
1. Tetrahedral Sites: When a sphere in the second layer is placed above three spheres that are touching each other, a tetrahedral site is formed. There are two tetrahedral sites for each sphere.

2. Octahedral Site: This type of site is formed at the center of six spheres and is produced by two sets of equilateral triangles which point in opposite directions. There is one octahedral site for each sphere.

Coordination Number And Radius Ratio: The ratio of the radius of the cation to the radius of an anion is called the Radius Ratio.
Radius ratio =\(\frac{\gamma_{+}}{\gamma}\); where γ+: radius of cation
γ-: radius of anion

→ It is very important to determine the structure of IONIC SOLIDS like Na⁺ Cl^–, Cs₄Cl^–, etc.

→ The number of spheres that are touching a given sphere is called the Coordination Number.

→ It may be remembered that coordination numbers of 4,6,8 and 12 are very common in various types of crystals.

Radius’Ratios in Crystals

It may be mentioned here that, although a large number of ionic substances obey this rule, there are many exceptions to this rule.

Structure of Sodium Chloride (NaCl) Rock-Salt Structure: It has a cubic closed packed structure i.e. face-centered cubic.

1. The Na⁺ ions (represented by o) occupy the octahedral holes in the ccp lattice of Cl^– ions (represented by •)
2. Each Na⁺ is surrounded by 6 Cl^– and vice-versa.
3. Na⁺ and Cl^– have 6: 6 fold coordination.

Table 1.3: Some Cubic Ionic Solids

Caesium Chloride (CsCl) Structure

1. In this structure, the Cl^– ions are at the comers of a cube whereas Cs₄ ion is at the center of the cube or vice versa as shown.
2. This structure has 8: 8 coordination, i.e., each Cs⁺ ion is touching eight Cl^– ions, and each Cl^– ion is touching eight Cs⁺ ions.
3. For exact fitting of Cs ions in, the cubic voids the ratio \(\frac{\mathrm{r}_{\mathrm{Cs}^{+}}}{\mathrm{r}_{\mathrm{Cl}^{-}}}\) should he equal to 0.732, however, actually the ratio is slightly larger (0.932). Therefore, packing of C1 ions slightly opens up to accommodate Cs4 ions.
4. The unit cell of caesium chloride has one Cs+ ion and one Cl~ ion as calculated below:
   .No. of Cl- ions = 8 (At corners) × \(\frac{1}{8}\) = 1
   No. of Cs+ ions = 1 (At the body centre) × 1 = 1
   Thus, no. of CsCl units per unit cell is 1.

Examples of the compounds having this type of structure are CsBr, Csl, TICl, and TIBr.

Cesium chloride structure

It may be mentioned here that temperature and pressure also affect the structure of an ionic solid. For example, at ordinary temperatures and pressures, chlorides, bromides, and iodides of lithium, sodium, potassium, and rubidium possess the NaCl structure with 6: 6 coordination.

It is observed that on the application of high pressure they transform to the CsCl structure with 8: 8 coordination. Thus, high pressure increases the coordination number. Ort the other hand, CsCl on heating transforms to the NaCl structure at 760 K. Thus, at higher temperature coordination number decreases.

Point Defects in Crystals: Ideal crystals with the perfect arrangement of constituents are found only at 0°K. Above this temperature, all crystalline solids have some defects in the arrangement of their unit. An ideal crystal of A⁺ B^– type may be represented as shown in Fig.

Ideal Crystal A⁺ B^–

Defects in the crystals may give rise to
(A) Stoichiometric and
(B) Nonstoichiometric structures

(A) Stoichiometric structures: The compound A⁺ B^– is stoichiometric if it contains an equal number of ions A⁺ and B^– as suggested by the chemical formula of the compound. There are three types of defects in stoichiometric structures:
1. Schottky Defect. This defect consists of vacancies at cation sites and an equal number of vacancies at anion sites. It is predominant in compounds with high coordination numbers and where the ions are of similar size. ‘

2. Frenkel Defect. This defect consists of vacancies at cation sites in which the cation moves to another position in between two layers called interstitial sites. This defect is most predominant in compounds which have low coordination number and ions of different sizes.

3. Interstitial Defect: When some constituent particles occupy an interstitial site the crystal is said to have an interstitial defect. This defect increases the density of the substance.

(B) Nonstoichiometric Compounds: The compounds in which the ratio of the number of atoms of A⁺ to the number of atoms of B^– does not correspond to a simple whole number as suggested by the formula, are called nonstoichiometric compounds.

The nonstoichiometric defects are of two types:
1. Metal excess defects. In these defects, positive ions are in excess and arise due to.
(a) Anion vacancies: Vacancies at anion sites and their electrons remain trapped.

(b) Cation occupying Interstitial sites: Excess cations are present in interstitial sites and an equal number of electrons trapped.

2. Metal deficient defects. This arises due to
(a) Cation vacancies: Vacancies at cation sites and the extra negative charge is balanced by extra charge (higher oxidation state) of an equal number of some cations.

(b) Anion occupying Interstitial sites: Excess anions are present in interstitial sites and the corresponding increase in negative charge is balanced by oxidation of an equal number of cations to higher oxidation states.

1. Anion vacancy and electron remain trapped.
2. Cation occupying the interstitial site and electron trapped

2. (i) Cation vacancy and one A⁺ changes to A²⁺ . 2. (ii) Anion occupying the intertidal site and one A⁺ changes to A²⁺

Non-Stoichiometric Structures:
The examples of non-stoichiometric defects are in the crystals of FeO where the composition is Fe_0.93O to Fe_0.96O. This behavior is mostly found in Transition metals compounds. Electrons trapped in anionic vacancies are referred to as F-CENTRES [from the farbe-the German word for color]

It may be mentioned here that metal excess compounds and metal deficient compounds both act as semiconductors. Metal excess compounds conduct electricity through normal electron conduction mechanisms and are therefore n-type semiconductors. Metal deficient compounds conduct electricity through a positive hole conduction mechanism and are therefore p-type semiconductors.

Point Defects due to the Presence of Foreign Atoms:
So far we have discussed point defects where there are no foreign atoms. Foreign atoms can occupy interstitial or substitutional sites in a crystal. Solid solutions of group 13 or group 15 impurities with group 14 elements such as silicon or germanium are of great interest in the electronic industry as they are used to make transistors.

The group 13 elements such as AI and Ga and the group 15 elements such as P and As form substitutional solid solutions with Si and Ge. The group 15 elements have five valence electrons. After forming the four covalent bonds with the group 14 elements, one excess electron is left on them. The excess electrons give rise to electronic conduction (n-type conduction).

The group 13 elements have only three valence electrons. They combine with group 14 elements resulting in the formation of an electron-deficient bond or a hole. These holes give rise to positive hole conduction (p-type conduction). Silicon and germanium doped with group 13 or group, 15 elements impurities act as semi-conductors and have fairly high electrical conductivity. This type of conduction is known as extrinsic / conduction.

Introduction of a cation vacancy in NaCl by substitution of Na⁺ with Sr²⁺ ion.

Defects in the ionic solids may be introduced by adding impurity ions. If the impurity ions have a different valence state than that of the host ions, vacancies are created. For example, the addition of SrCl₂ to NaCl yields solid solutions where the divalent cation occupies Na⁺ sites and produces cation vacancies equal to the number of the divalent ions occupying substitutional sites. Similarly, AgCl crystals can be doped with CdCl₂ to produce impurity defects in a like-wise manner.

Electrical Properties: Solids exhibit an amazing range of electrical conductivities, extending over 27 orders of magnitude ranging from 10^-20 to 10⁷ ohm^-1 m^-1. Solids can be classified into three types on the basis of their conductivities.

1. Conductors: The solids with conductivities ranging between 10⁴ to 10⁷ ohm^-1 m^-1 are called conductors. Metals have conductivities in the order of 107 ohm’m1 and are good conductors.
2. Insulators: These are the solids with very low conductivities ranging between 10^-20 to 10^-10 ohm^-1 m^-1.
3. Semiconductors: These are the solids with conductivities in the intermediate range from 10^-6 to 10⁴ ohm^-1 m^-1.

Conduction of Electricity in Metals: A conductor may conduct electricity through the movement of electrons or ions. Meta (lie conductors belong to the former category and electrolytes to the latter.

Metals conduct electricity in solid as well as in the molten state. The conductivity of metals depends upon the number of valence electrons available per atom. The atomic orbitals of metal atoms from molecular orbitals are so close in energy to each other as to form a band. If this band is partially filled or it overlaps with a higher energy unoccupied conduction band, then electrons can flow easily under an applied electric field and the metal shows conductivity (Fig (a) below).

If the gap between the filled valence band and the next higher unoccupied band (conduction band) is large, electrons cannot jump to it and such a substance has very small conductivity and it behaves as an insulator. (Fig. (b) below)

Distinction among (a) metals, (b) insulators and (c) semi-conductors.
In each case, an unshaded area represents a conduction band.

Conduction of Electricity in semiconductors: In the case of semiconductors, the tire gap between the valence band and conduction band is small (Fig. c). Therefore, some electrons may jump to the conduction band and show some conductivity. The electrical conductivity of semiconductors increases with rising temperature since more electrons can jump to the conduction band. Substances like silicon and germanium show this type of behavior and are called intrinsic semiconductors.

The conductivity of these intrinsic semiconductors is too low to be of practical use. Their conductivity is increased by adding an appropriate amount of suitable impurity. This process is called doping. Doping can be done with an impurity that is electron-rich or electron deficit as compared to the intrinsic semiconductor silicon or germanium. Such impurities introduce electronic defects in them.

Magnetic Properties: Solids can be classified into different types depending upon their behavior towards magnetic fields. The substances which are weakly repelled by a magnetic field are called diamagnetic substances. For example, TiO₂ and NaCl. Diamagnetic substances have all their electrons paired.

The substances which are weakly attracted by a magnetic field are called paramagnetic substances. These substances have permanent magnetic dipoles due to the presence of some species (atoms, ions, or molecules) with unpaired electrons. The paramagnetic substances lose their magnetism in the absence of a magnetic field. For example, TiO, VO, and CuO.

The substances which are strongly attracted by a magnetic field are called ferromagnetic substances. These substances show permanent magnetism even in the absence of a magnetic field. Some examples of ferromagnetic solids are iron, cobalt, nickel, and CEO.

Ferromagnetism arises due to the spontaneous alignment of magnetic moments of ions or atoms in the same direction. Alignment of magnetic moments in opposite direction in a compensatory manner and resulting in a zero magnetic moment (due to an equal number of parallel and antiparallel magnetic dipoles) give rise to antiferromagnetism.

For example, MnO, Mn₂O₃, and MnO₂ are antiferromagnetic. Alignment of magnetic moments in opposite directions resulting in a net magnetic moment (due to an unequal number of parallel and antiparallel magnetic dipoles) gives rise to ferrimagnetism.

For example, FeX > 4 is ferrimagnetic.

Alignment of magnetic dipoles in (a) ferromagnetic, (b) anti-ferromagnetic, and (c) ferrimagnetic substances.

Ferromagnetism and paramagnetic substances change into I paramagnetic substances at higher temperatures due to the randomization of spins. Fe₃O₄ which is ferrimagnetic at room temperature becomes paramagnetic at 850 K.

By going through these CBSE Class 12 Biology Notes Chapter 16 Environmental Issues, students can recall all the concepts quickly.

Environmental Issues Notes Class 12 Biology Chapter 16

→ An increase in the human population is exerting tremendous pressure on our natural resources and is also contributing to pollution of air, water, and soil.

→ Pollution is referred to any undesirable change in physical, chemical, or biological characteristics of air, land, water, or soil. The agents that bring about such undesirable change are called pollutants. To control environmental pollution, the Government of India has passed the Environmental (Protection) Act, 1986. This Act is to protect the quality of the environment.

→ Air pollution primarily results from the burning of fossil fuel, e.g., coal and petroleum, in industries and in automobiles. Air pollution is harmful to both animals and plants. Strict measures should be taken to keep our air clean.

→ The most common source of pollution of water bodies is domestic sewage. It reduces dissolved oxygen but increases biochemical oxygen demand of receiving water.

→ Domestic sewage is rich in nitrogen and phosphorus. It causes eutrophication and nuisance algae bloom.

• Industrial water waste is rich in toxic chemicals such as heavy metals and organic compounds. It can harm living organisms.
• Municipal solid wastes also can create problems.

→ A few toxic substances often present in industrial wastewaters can undergo biological magnification in the aquatic food chain Increase in concentration of the toxicant at successive trophic levels refers to biomagnification. This is due to a toxic substance accumulated by an organism that cannot be metabolized or excreted, and thus, passes on the next higher trophic level. This phenomenon is well known for mercury arid DDT.

Biomagnification of DDT in an aquatic food chain

Eutrophication refers to the natural aging of a lake by the biological enrichment of its waters. Wastewater including sewage can be treated in an integrated manner, by utilizing a mix of artificial and natural processes. Disposal of hazardous waste like defunct ships, radioactive wastes, and e-wastes requires additional effort.

→ Soil pollution is due to agricultural chemicals such as pesticides, insecticides, etc., and leachates from solid wastes deposited over it.

→ The major environmental issue of global nature is the increasing greenhouse effect. It is a naturally occurring phenomenon that is responsible for heating of earth’s surface and atmosphere. Without the greenhouse effect, the average temperature at the surface of the earth would have been -18°C rather than the present average of 15°C. Increased pollution on the earth is increasing the greenhouse effect, which is warming the earth.

→ The enhanced greenhouse effect is mainly due to increased emission of carbon dioxide, methane, nitrous oxide, CFCs, and deforestation. These pollutants and depleting the ozone layer. The effects may be changed in rainfall pattern, increase in global temperature and besides deleteriously will affect living organisms. The ozone layer in the stratosphere is depleting due to the emission of CFCs. The ozone layer protects us from the harmful effects of the UV rays of the sun. The depletion of the ozone layer can increase the risk of skin cancer, mutation, and other disorders.

→ Pollution: Undesirable change in physical. chemical or biological characteristics of air, land, water, or salt.

→ Pollutants: Agents which bring undesirable change in the abiotic components of the environment.

→ CNG: Compressed Natural Gas.

→ Noise: Undesirable high level of sound.

→ BOD: Biochemical Oxygen Demand.

→ Biomagnification: Increase in the concentration of the toxicant at successive trophic levels.

→ Eutrophication: Refers to the natural aging of a lake by biological enrichment of its water.

→ Solid wastes: Everything that goes out ¡n trash.

→ Municipal solid waste: Waste from homes, offices, hospitals, schools, etc. that are collected and disposed of by the municipality.

→ Electronic wastes: Irreparable computer and other electronic goods.

→ CFCs: Chlorofluorocarbons.

→ Snow blindness: Inflammation of the cornea.

→ Soil erosion: Removal of topsoil by natural agents such as wind, water, etc.

→ Reforestation: Process of restoring a forest.

By going through these CBSE Class 12 Biology Notes Chapter 15 Biodiversity and Conservation, students can recall all the concepts quickly.

Biodiversity and Conservation Notes Class 12 Biology Chapter 15

→ Biodiversity refers to the sum total of diversity that exists at all levels of biological organization.

→ Biodiversity is the term popularized by sociobiologist Edward Wilson to describe the combined diversity at all the levels of biological organization.

Some important are as follows:

• Genetic diversity
• Species diversity
• Ecological diversity

→ More than 1.5 million species have been recorded in the world, but there might still be more than 6 million species on earth waiting to be discovered and named. Of the named species >70 percent are animals of which 70 percent are insects. Among all the species, combined, the group fungi have more than all vertebrate species combined. In India, more than 45,000 species of plants and twice as many species of animals are found. Thus, it is one of the 12 mega diversity countries of the world.

Representing global biodiversity: proportional number of species of major taxa of plants. invertebrates and vertebrates

→ The diversity of plants and animals is not uniform throughout the world. For many groups of animals or plants, there are interesting patterns in diversity, the most well-known being th£ latitudinal gradient in diversity. Tropics harbor more species than temperate or polar areas. Colombia located near the equator has nearly 1,400 species of birds while New York at 41°N has 105 species and Greenland at 71°N only 56 species.

→ The relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola (Fig.).

Showing species-area relationship on a logarithmic scale. the relationship is a straight line described by the equation.
logS = log C + Z log A
where S = species richness
A = area
Z = slope of the line
C = Y-intercept

→ Species richness contributes to the well-being of an ecosystem. Rich biodiversity is hot only essential for ecosystem health but imperative for the very survival of the human race on this planet.

→ Conserving biodiversity is narrowly utilitarian, broadly utilitarian, and ethical. Besides the direct benefits (food, fiber, firewood, pharmaceuticals, etc.) there are many indirect benefits we receive through the ecosystem. Services such as pollination, pest control, climate moderation, and flood control. It is our moral responsibility to take good care of the earth’s biodiversity and pass it on in good order to our next generation.

→ There are four major causes of biodiversity losses.
There are:

• Habitat loss and fragmentation
• Over-exploitation
• Alien species invasions
• Co-extinctions

→ Biodiversity conservation can be taken in situ and ex-situ. In in. situ conservation, the endangered species are protected in their habitat so that the entire ecosystem is protected. Ex-situ conservation methods include protective maintenance of threatened species in zoological parks and botanical gardens, in vitro fertilization, cryopreservation of gametes, and tissue culture propagation.

→ Biodiversity: Totality of genes. species and ecosystems of a region.

→ Conservation: Preservation of biodiversity. It may be in situ or ex-situ.

→ Ecological diversity: Variation of habitats, community types, and abiotic environments present in a given area.

→ Extinction: The complete disappearance of any species from the biosphere by natural causes.

→ Exotic species: Species introduced into an ecosystem to which they are not native.

→ Fragmentation: The process of reduction of habitat into smaller scattered patches.

→ Genetic diversity: Total number of genetic characteristics either expressed or in all the individuals of a particular area.

→ Species diversity: The diversity at the species level.

→ Hot spots: Areas that are extremely rich in species, and under constant threat.

→ Endemism: Species confined to that region and not found anywhere else.

By going through these CBSE Class 12 Biology Notes Chapter 14 Ecosystem, students can recall all the concepts quickly.

Ecosystem Notes Class 12 Biology Chapter 14

→ An ecosystem is a structural and functional unit of the biosphere which consists of a community of living beings and the physical environment, both of them interacting and exchanging materials between them. In short, the ecosystem is a self-supporting, stable ecological unit that results from an interaction between the biotic community and its abiotic’ environment.

→ The ecosystem has two main components: an abiotic component that includes all plants, animals, and microorganisms, and an abiotic component that includes soil, water, minerals, CO_2, and oxygen. It receives energy in the form of sunlight.

→ The biotic component of the ecosystem contains all the living members. These are connected to each Other by food and energy. They are divided into producers (autotrophs) and consumers (herbivores and carnivores) and decomposers.

→ Food is manufactured from inorganic raw materials by autotrophs only so they are called producers. They are mainly photosynthetic plants that contain chlorophyll. Consumers are animals that feed on plants (herbivores) directly, are called primary consumers, and animals that feed on other organisms or their parts are called secondary or tertiary consumers (carnivores).

Microorganisms break the dead organic matter into simple substances which are returned to the environment for reuse, they are called decomposers. Based on the source of nutrition every organism occupies a place in an ecosystem. This place is called a trophic level of the organism.

→ Productivity, decomposition, energy flow, and nutrient cycling are the main functions of an ecosystem. The nutrients are used again and again in a cyclic manner but energy trapped from sunlight is lost as heat.

→ A food chain consists of various trophic levels which include a producer, various levels of consumers, and a decomposer.

→ Food chains are of three kinds viz. predator, parasitic and saprophytic chain. The food chains are interlinked to each other. The various food chains in a community form a food web.

→ Primary productivity is the rate of capture of solar energy or biomass production of the producers. It can be, gross primary productivity (GPP) and net primary productivity (NPP). GPP is the rate of capture of solar energy or total production of organic matter. NPP is the remaining biomass or the energy left after the utilization of producers. Secondary productivity is the rate of assimilation of food energy by the consumers. Decomposition is the breakdown of complex organic compounds of detritus into CO₂, water, and inorganic nutrients. It involves three processes: fragmentation of detritus, leaching, and catabolism.

→ Energy flow is unidirectional. The number of materials and energy transferred as food through successive higher trophic levels progressively decreases.

→ The graphic representation of the relationship of food and energy between organisms at different trophic levels is called pyramids. The base of each pyramid represents the producers and the apex represents the tertiary consumer.

The ecological pyramids are of three types:

1. pyramid of number,
2. pyramid of biomass and
3. pyramid of energy.

Mostly the pyramid of number and biomass are upright but sometimes the pyramid of biomass may be of the inverted type, e.g. in a sea. The pyramid of energy is always upright.

The inverted pyramid of biomass. A small standing crop of phytoplankton supports a large standing crop of zooplankton.

→ Biosphere or ecosphere is the part of the earth inhabited by organisms and their living and non-living environment. The earth is a closed system regarding materials. The substances vital for life are limited and must be recycled to sustain life. The earth is an open system regarding energy. It receives energy from the Sun in the form of solar energy, a part of it is trapped by living organisms and the major part is radiated back to outer space. The biosphere consists of the atmosphere, lithosphere, and hydrosphere.

→ The storage and movement of nutrient elements through the various components of the ecosystem is called nutrient cycling or Biogeochemical cycle, bio: living organisms, geo: rocks, air, water.

Nutrient cycles are of two types:

1. Gaseous cycle: It has carbon, hydrogen, oxygen, and nitrogen as a reservoir and exists in the atmosphere and
2. Sedimentary cycle: It has phosphorus, sulfur, calcium, potassium, etc. as a reservoir and is located in the earth’s crust.

The gaseous cycles are more balanced than the sedimentary cycles. The reservoir compensates for the deficit which occurs due to an imbalance in the rate of influx and efflux.

→ Biomes are regional, integrated, natural biotic units, which can be identified by the forum of life of the climax vegetation. Biomes may also include developing and modified communities, within the same climatic region like forest biomes will include young successional forests and open grass-dominated tracts.

The three major biomes are:

1. forest biome,
2. grassland biome, and
3. desert biome.

Each biome has a characteristic array of plants and animal life. Climatic and edaphic factors, latitude, and barriers determine the extent of a biome.

→ Ecotones are the zones present between adjacent biomes, these support some organisms from each adjoining biome and some typical characters of their own.

→ Abiotic components: Consists of environmental factors. These are inorganic substances, organic substances, and climatic factors.

→ Biotic components: These comprise various kinds of organisms which are producers. consumers and decomposers.

→ Biome: Biomes are regional, integrated, natural biotic units, which are identified by the life form of the climax vegetation.

→ Biotics: Study of the functions of life.

→ Boreal forest: Another name of the taiga.

→ Biodegradation: Breakdown of organic and inorganic material by bacteria and fungi.

→ Consumers: Organisms that depend upon producers for food. These are herbivores and carnivores.

→ Canopy: Part of a woodland or forest community that ¡s formed by the trees.

→ Community retrogression: The reversal of ecological succession due to a disturbance in some serai stage like the destruction of grass by overgrazing.

→ Decom posers: Heterotrophic organisms like bacteria and fungi. They recycle the nutrients in the ecosýstem.

→ Epilimnion: tipper layer of warm water in a stratified lake.

→ Eutrophic: Water body rich in nutrients.

→ Edge effect: Tendency of ecotone to have a greater number of species and higher population density as compared to adjacent communities.

→ Forb: Any herbaceous plant other than grass.

→ Ecotone: Transitional zone between two vegetation regions.

→ Ecotype: The climate and edaphic factors of a place constitute ecotype.

→ Hygrometer: Instrument to measure the humidity of air or gas.

→ Incomplete ecosystem: Lacks one or more basic components e.g. deep sea, due to absence of light lacks producers.

→ Limnology: Study of freshwater bodies like lakes.

→ Meteorology: Study of atmospheric phenomena like forecasting weather.

→ Nutrient cycle: The movement of nutrient elements through the various components oían ecosystem.

→ Oiigatrohic: Water body poor in nutrients.

→ Productivity: The rate of biomass production.

→ Phenology: Study of periodic phenomena of plant and animal life like breeding, migration in relation to seasonal changes.

→ Rain gauge: Instrument for measuring rainfall.

→ Root detritus: Detritus formed by dead, underground roots of plants.

→ Photosynthetic active radiation (PAR): Visible light which carries about 50% of the energy of total incident solar radiation and iš available to producers for absorption.

→ Standing biomass: The biomass present in an ecosystem at a given time.

→ Standing crop: Amount of living material in a component population of a specific trophic level at a given time.

→ Stratification: Vertical distribution of different species occupying different levels.

→ Species composition: Identification and enumeration of plant and animal species of an ecosystem.

By going through these CBSE Class 12 Biology Notes Chapter 13 Organisms and Populations, students can recall all the concepts quickly.

Organisms and Populations Notes Class 12 Biology Chapter 13

→ Ecology is the study of the relationship of living organisms with the abiotic and biotic components of their environment.

→ Ecology is concerned with four levels of biological organization. These include – organisms, populations, communities, and biomes.

→ Regionals and local variations within each biome lead to the formation of a wide variety of habitats.

→ Temperature, light, water, and soil are the most important physical factors of the environment to which the organisms are adapted in various ways.

→ The physicochemical components alone do not characterize the habitat of an organism completely; the habitat includes biotic components also – pathogens, parasites predators, and competitors of the organism with whom it interacts constantly.

→ In the face of changing external environment, maintenance of a constant internal environment (homeostasis) by the organisms, contributes to optical performance, but only some organisms (regulations) are capable of homeostasis.

→ Some species have evolved adaptations to avoid unfavorable conditions in space (migration) or in time (aestivation, hibernation, and diapause).

→ A population is a group of individuals of a given species sharing or competing for similar resources in a defined geographical area.

→ In a population, the proportion of different age groups of males and females is often presented graphically as an age pyramid. The shape of the pyramid indicates whether a population is stationary, growing, or declining.

→ On a population, the ecological effects of any factors are generally reflected in its size, which may be empressed in different ways depending on the species.

→ The size of a population keeps changing in time, depending on various factors, including food availability, predation pressure, and reduce weather. The changes in population density give us some idea of what is happening to the population – whether it is flourishing or declining.

→ Natality refers to the number of births during a given period in the population that are added to the initial density.

→ Mortality is the number of deaths in the population during a given period.

→ Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.

→ Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

→ Populations grow through births and immigration and decline through deaths and emigration. Growth in both cases is ultimately limited by the carrying capacity of the environment. The intrinsic rate of natural increase (r) is a measure of the inherent potential of a population to grow.

→ Populations of different species, in nature, in a habitat do not live in isolation but interact in many ways. These interactions between two species are classified as competition, predation parasitism, commensalism, and mutualism.

→ One of the most important processes is predation. Through this process, trophic energy transfer is facilitated and some predators help in controlling the prey populations.

→ In competition, the superior competition eliminates the inferior one. However many closely related species have evolved various mechanisms which facilitate their co-existence.

→ Ecology: A study of the relationship of living organisms with abiotic and biotic components of their environment.

→ Population: A group of individuals of a given species sharing or competing for similar resources in a defined geographical area.

→ Abiotic: Non-living components such as temperature. light. water and soil.

→ Biotic: Living components such as plants, animals, human beings, and micro-organisms.

→ Age pyramids: The age distribution of males and females in a combined diagram.

→ Population density: Refers to population size.

→ Natality: Refers to the number of births during a given period in the population that are added to the initial density.

→ Mortality: Refêrs to the number of deaths in the population during a given period.

→ Immigration: Refers to a number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.

→ Emigration: Refers to a number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

→ Migration: Moving organisms temporarily from the stressful habitat to a more hospitable area and return when the stressful period is over.

→ Hibernation: Refers to winter sleep undertaken by animals to save themselves from extreme cold conditions.

→ Diapause: A stage of suspended development.

→ Mutualism: interspecific interaction in which both the species benefit.

→ Competition: Interspecific interaction in which both the species lose.

→ Parasitism: Interspecific interaction in which one species benefits and the interaction is detrimental to the other species.

→ Commensalism: The interaction where one species is benefitted and the other is neither benefitted nor harmed.

→ Amensalism: The interaction in which one species is harmed whereas the otheî is unaffected.

By going through these CBSE Class 12 Biology Notes Chapter 12 Biotechnology and its Applications, students can recall all the concepts quickly.

Biotechnology and its Applications Notes Class 12 Biology Chapter 12

→ Biotechnology is the interaction between technology and biology. It is as old as human civilization. It may be defined as ‘The controlled use of biological agents, such as micro-organisms or cellular components, for beneficial use’. It deals with the industrial-scale production of biopharmaceuticals using genetically modified organisms.

→ The main objectives of biotechnology are:

1. providing the best catalyst (improved organism) like a pure enzyme or some micro¬organism,
2. Creating optimum conditions for the catalyst to perform,
3. Downstream processing techniques for the purification of the organic compound.

→ Food production can be increased in three ways,

1. Agrochemical based agriculture,
2. Organic agriculture,
3. Genetically engineered crop-based agriculture.

Crop yields are increased by using improved crop varieties and agrochemicals maximise the yield.

→ Genetically Modified Organisms (GMO) are plants, bacteria, fungi and animals whose genes are altered for human or animal consumption using the latest molecular biology techniques. The genetic modifications have made crops more tolerant to abiotic stresses like cold, drought, salt, heat etc.; reduced reliance on chemical pesticides by making pest-resistant crops, helped to reduce post-harvest losses, increased efficiency of mineral usage by plants, enhanced nutritional value of food, for example, vitamin A-rich rice.

The enhancement of desired traits has traditionally been undertaken through breeding, but conventional plant breeding methods can be very time consuming and are often not very accurate. Genetic engineering can create plants with the exact desired traits very rapidly and with great accuracy.

For example, geneticists can isolate a gene responsible for drought-tolerant and insert it into a different plant. The new genetically modified plant will gain drought tolerance. The characteristic of a genetically modified organism depends on the nature of genes transferred and the nature of the host plant as well as some regulatory environmental factors.

→ Recombinant DNA technology or genetic engineering is the latest technique that transfers one or more genes (DNA fragments) from one plant to another. The plant in which a foreign gene is introduced is called a transgenic plant. Two techniques are used to introduce foreign genetic material into the plant cell genome. One is through a vector and the other is direct introduction of DNA.

→ Several transgenic plants have been developed, one example is Bt cotton. Bt is a toxin produced by the bacterium Bacillus Thuringiensis. B toxin gene is cloned from bacterium and expressed in plants to provide resistance from insect without using insecticides. Thus by the application of biotechnology pest-resistant plants are developed. Some other examples are Bt com, Bt rice, Bt tomato, potato and soybean.

→ Bacillus Thuringiensis produces proteins that kill some insects like lepidopterans, e.g. tobacco budworm and armyworm, coleopterans like beetles, dipterans, e.g. flies and mosquitoes. B.Thuringiensis is a soil bacterium that forms some protein crystals which contain a toxic insecticidal protein that is present as inactive protoxin, when an insect ingests it, the inactive toxin is converted to the active toxin by the alkaline pH of the gut. The activated toxin bind to the surface of midgut epithelial cells and creates pores which cause swelling and lysis and ultimately death of the insect.

→ The toxin produced by B.thuringiensis is called Cry protein. The gene encoding Cry protein is called the Cry gene. There are several kinds of Cry proteins that are toxic to different groups of insects for example genes Cry-I AC and Cry-II Ab control the cotton bollworms, Cry-I Ab controls corn borer, Cry III Ab controls Colorado potato beetle and Cry-III Bb controls com rootworm.

→ Biotechnologists isolated the toxin-producing genes arid introduced into other crop plants with the help of Agrobacterium Ti-plasmid. These transgenic plants are resistant to insects and pests. Their prime advantage is the production of labour free insect protection of plants and also restrict the use of pesticides which helps in making soil and groundwater pollution-free.

Cotton boll (a) destroyed by bollworms and (b) a fully mature cotton boll (to be redrawn)

→ Another strategy is used to control nematode infestation of tobacco plant roots. Two normal nematode genes were introduced into the tobacco plant by the Agrobacterium vector. The tobacco plant makes a double-stranded RNA (dsRNA) with these genes. The dsRNA binds to mRNA and interfere with nematode RNA. This neutralises the nematode and it dies. The transgenic tobacco plant is protected from the parasite.

→ Modem biotechnology is contributing a lot to the field of medicine, for disease diagnosis and disease therapy. For example, insulin used to cure diabetes was earlier extracted from slaughtered cows and pigs, which may develop allergies. It was quite tiresome and difficult and the yield was very low.

Now by using recombinant DNA technology insulin can be produced by the fermentation of appropriate recombinant E.Coli clones. This method can produce large quantities of pure insulin in a short time and a small space. On 5th July 1983, an American firm Eli Lilly launched the first genetically engineered human insulin, which was named Humulin.

→ Insulin consists of 51 amino acids arranged in two short polypeptide chains viz. Chain A (21 amino acids) and Chain B (30 amino acids). Chain-A and Chain-B are linked together by (S-S) disulphide bridges.
proinsulin

Maturation of pro-insulin into insulin after removal of C-peptide (to be simplified)

In mammals, insulin is produced as a prohormone which contains an extra stretch of C-peptide. This C-peptide is removed during the processing and maturation of prohormone and produces functional and fully mature insulin.
In recombinant techniques, the genes corresponding to both chains A and B are introduced in plasmids of E.Coli, which produces insulin chains. Chain-A and Chain-B are produced separately, extracted and joined together by disulphide bonds. This produces human insulin.

→ Gene therapy is a collection of methods that allows the correction of a gene defect present in an embryo or a child. It involves the delivery of a normal gene into the individual to take over the function of the defective gene. A genetic disorder caused by a single defective gene can be corrected by replacing this with a normal gene. Some genetic diseases like severe combined immunodeficiency (SCID) can be cured using gene therapy.

The SCID patients have adenosine deaminase (ADA) deficiency, this enzyme is crucial for the immune system to function. The patient lacks functional T-lymphocytes and fails to fight the infecting pathogens. Children with ADA deficiency are cured by bone marrow transplantation or by enzyme replacement therapy, where ADA is given by injection. By using gene therapy techniques, lymphocytes are taken from the patient’s bone marrow and the normal gene for ADA is introduced into the lymphocytes using retrovirus. These cells are reintroduced in the patient’s immune system.

→ Polymerase Chain Reaction (PCR) helps a lot in the early diagnosis of a disease, prenatal disorders and even the presence of the HIV virus. It is a powerful technique to find many genetic disorders, suspected cancer patients, and disease before the arrival of the symptoms. Genetic cloning helps in developing sensitive diagnostic techniques like ELISA and to identify a normal mutant gene.

→ Transgenic animals have their DNA manipulated to contain and express an extra or foreign gene. These are produced for various reasons like to study the process of gene regulation, how gene help in the development of diseases like cancer, Alzheimer etc., to produce useful biological products for humans, for testing medicines and vaccines before using them for humans, for testing the toxicity of any new drug in less time.

→ Intellectual Property Right (IPRs) are the rights to make, use and sell a new product or technology for 20 years. A patent is an official document to give all rights to make, use or sell an invention and prevent others from copying it.

→ Biopatents are government protection for biological agents and their products. It can be granted for genetically modified microbes, newly established cell times, genetically modified plants and animals, gene sequences, protein sequences, biotechnological procedures, production processes, new products and production applications.

→ Biopiracy is the use of bio-resources and genetic resources indigenous to a country by some organisations without proper authorisation or compensatory payment. Bio-piracy is widespread in Asia, Africa and Latin America which have the most diverse ecosystems in the world and produce abundant bio-resources.

→ Genetically modified crops and organisms have found higher acceptance in industry and agriculture but these deprive farmers to use their year’s harvest as seed for next year or share it with someone else. The plant variety protection and Farmer’s Right Act grants plant breeders, right on a new variety of seeds. The Farmer’s Rights Act has granted farmers to save, use, sow, and exchange, share or sell their farm product.

→ Antibiotics: An antibiotic is an organic compound produced by a microorganism that inhibits the growth of the other-micro organism.

→ Antisense nucleic acid: This is single-stranded molecules of DNA or RAN which base pairs with mRNA of virus and block their translation.

→ Bt cotton: It is a variety of cotton which contains the Bt toxin from Bacillus thuringienSis that kills certain insects.

→ Biopiracy: Biopiracy is the theft of biological and genetic resources without proper authorisation or compensation from the concerned countries.

→ Biopatent: Biopatents are patents given to biological agents and their products, exclusive right for their manufacturing, using and selling fr a specific period.

→ DNA vaccines: DNA vaccines use one or more isolated genes of a pathogen. incorporate into plasmids and inject them into the muscle or delivered into the human body.

→ Enzymes: Enzymes are bio-catalysis which catalyse biological reactions without undergoing any change. They are proteinaceOuS in nature.

→ Humulin: Humulin is a commercial name given to human insulin.

→ Monoclonal antibodies: Monoclonal antibodies are derived from a single parent and are specific for antigens.

→ Probe: A probe is a piece of single-stranded DNA that is tagged with a radioactive molecule.

→ Recombinant proteins: These are proteins produced by transgenes. These are used to treat diseases and as vaccines.

→ Stem cells: The cells of a young embryo are called stern cells. These are pluripotent i.e.: they can transform into any of 220 cell types of the human body.

→ Steroids: Steroids are complex crystallisable lipids of high molecular weight which possess a tetracyclic hydrocarbon core and along side chain, e.g. cholesterol.

→ Transgenic organisms: These are organisms that have had their DNA manipulated to contain and express an extra (foreign) gene.

→ Terminator seeds: The seeds produced by genetic engineering develop into fertile parents but produce non-germinable seeds.

→ Vaccines: Vaccine ¡sa liquid containing dead or attenuated pathogen or its antigen which provides temporary or permanent immunity to a disease.

→ Vitamins: Vitamins are accessory food factors that are required in small quantities for various metabolic processes of the body.

By going through these CBSE Class 12 Biology Notes Chapter 11 Biotechnology: Principles and Processes, students can recall all the concepts quickly.

Biotechnology: Principles and Processes Notes Class 12 Biology Chapter 11

→ The European Federation of Biotechnology (FEB) has defined biotechnology as ‘The integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services. Biotechnology is a science which deals with techniques of using live organisms or enzymes from organisms to produce products and processes useful for man.

All microbes mediated processes, genetically modified organisms, test-tube babies, in vitro fertilization, synthesising a gene, developing a DNA vaccine all processes are a part of biotechnology.

→ Genetic engineering is the science that deals with the synthesis of artificial genes, repair of genes, combining genes from two organisms (recombinant DNA) and manipulation of artificial genes for the improvement of living organisms.

To grow the desired microbe in large quantities for the production of antibiotics, vaccines or enzymes etc., it is very important to maintain microbial-contamination free sterile conditions.

→ For genetically modifying an organism three things are necessary which are:

1. modification of DNA,
2. the introduction of modified DNA into the host,
3. maintenance of introduced DNA in the host and transfer of this DNA in the next progeny.

→ In 1972, Stanley Cohen and Herbert Boyer constructed the first recombinant DNA molecule. They isolated an antibiotic resistance gene and linked it with a native plasmid of Salmonella typhimurium.

→ Plasmids are autonomously replicating circular extrachromosomal DNA. Plasmids are the most widely used cloning vectors. These are double-stranded, circular DNA molecules that can self replicate. A suitable plasmid vector has three properties like low molecular weight, ability to confer readily with selected phenotype traits on host cells and single sites for a large number of restriction endonucleases.

The plasmids carry genes for sexuality, antibiotic resistance etc., but not any vital genes. The cell can survive without them. They can replicate independently of the main genome and being small, can easily come out or get into a cell.

→ Recombinant DNA techniques include DNA at specific sites by using enzymes restriction endonucleases and joining the fragments by enzyme ligases.

It includes the following steps:

1. DNA fragments coding for proteins of interest is synthesized chemically or isolated from an organism.
2. These DNA fragments are inserted in a restriction endonuclease cleavage site of the vector that does not inactive any gene required for vector’s maintenance.
3. The recombinant DNA molecules are now introduced into a host to replicate.
4. Recipient host cells that have acquired the recombinant DNA, are selected. Selection pressure is applied to enrich bacteria with a selectable marker.
5. Desired clones are then characterised to ensure that they maintain true copies of the DNA segment that was originally cloned.

Sequential steps in the formation of recombinant DNA

→ The tools for genetic engineering or recombinant DNA technology are restriction enzymes, polymerase enzymes, biases, vectors and the host organism. After cutting a suitable gene with a restriction enzyme, it is associated with an origin of replication, only then it can multiply itself after insertion into the host genome.

→ Restriction enzymes are also called molecular scissors. In 1968, H.O. Smith, K.W. Wilcoxand T.J. Kelley isolated and characterised the first restriction endonuclease. Hind II from Haemophilus Influenzae bacteria. They found that Hind II always cut DNA at a specific sequence known as recognition sequence. With the help of restriction enzymes, it is possible to cut a DNA sequence. Restriction enzymes belong to class nucleases. These may be of two types-endonucleases and exonucleases.

The action of DNA cleaving enzymes

→ Restriction exonucleases, cut the DNA from the ends and restriction endonucleases cut at a specific position within the DNA, e.g. Restriction endonuclease ECORI will cut DNA only if sequence:
5′ — GAATTC — 3′
3′ — CTTAAG — 5′
is present. It cuts the DNA between bases G and A only when sequence GAATTC is present in the DNA (shown in the figure above)

→ The restriction enzyme will act on both the strands and produce a break. If the vector and the source DNA are cleaved using the same restriction enzyme they will have the same kind of sticky ends which can be joined by DNA ligases to produce a recombinant vector.

→ When restriction enzymes make a cut in the DNA strand, it will leave single-stranded portions at the ends. These are overhanging, called sticky ends. Sticky ends can form hydrogen bonds with their complementary cut counterparts by DNA ligases.

→ Palindromes are DNA sequences with base pairs that read the same on the two strands when the orientation of reading is kept the same. For example:
5′ — GAATTC — 3′
3′ — CTTAAG — 5′
In both the strands if read from 5? direction it will be the same. These are the sites for restriction enzymes.

→ After cutting the DNA with restriction enzymes, the fragments of DNA are separated by gel electrophoresis. DNA molecules being negatively charged move towards an anode under an electric field. The matrix used is a natural polymer, agarose. It acts as a sieve and DNA fragments separate according to their size.

DNA fragments can be seen after staining with ethidium bromide, an orange coloured bands when exposed to UV light. The separate strands can be cut from agarose gel and eluted by using various techniques. The selected DNA fragments, purified by gel electrophoresis are used for recombinant DNA construction.

→ Cloning vectors: The vector is an agent which is used to transfer DNA into the host cell. For example plasmid, bacteriophages. The vector is cut with the same restriction endonuclease which was used for chromosomal DNA fragments. The linearized vector and chromosomal DNA fragments are joined together by DNA ligases. Those plasmids which contain an inserted DNA fragment are called recombinant plasmids.

→ Similar to plasmids, bacteriophages can replicate within the bacterial cell independently of the control of chromosomal DNA.

Sometimes there are several copies of plasmids or a high number of bacteriophages per cell if an airy foreign DNA segment is inserted into these vectors a large number of a selected gene can be produced.

To attach a desirable gene to these vectors, the vectors are to be modified: The inserted gene must be attached with an origin of replication to start replication in the host cell, the vector needs a selectable marker so as to identify the recombinant vector. For example, a normal E.Coli cell does not carry resistance to antibiotics like tetracycline, ampicillin etc. so if the cells show resistance towards these antibiotics they are suitable recombinant vectors with suitable markers.

→ To link the desirable DNA with the vector, one or very few recognition sites for restriction enzymes is required. One recognition site will linearise the vector, several recognition sites will complicate the process. The recombinant vectors from non-recombinant vectors can be selected by a replica plating process or by using enzyme β-galactosidase activity on its colour producing substrate. The non-recombinants will produce colour due to active β-galactosidase and recombinants do not produce any colour.

→ For the purpose of clearing genes in plants and animals some vectors like disarmed (cancerous) retroviruses and modified (tumour inducing) plasmid of Agrobacterium tumefacient are used to deliver desirable genes into animals and plants cells respectively.

→ DNA is a hydrophilic molecule that cannot pass through cell membranes. The bacterial cells are made competent or forced to take up DNA. It can be done by the specific concentration of divalent ions like calcium (Ca²⁺) which increases the efficiency of DNA uptake through cell wall pores. Then the cells are incubated on ice followed by heat shock (at 42°C) and then back to ice. Other ways are microinjection i.e.; direct injection of recombinant DNA by animal cell by using a small needle. Gene gun or biolistics is used for plant cells, cells are bombarded with high-velocity micro gold or tungsten particles coated with DNA.

→ Polymerase chain reaction (PCR) is used to produce many copies of the same gene without using cells. The DNA is incubated in a test tube with DNA polymerases and a mixture of deoxy-ribonucleotides and primers. PCR can make billions of copies of DNA in few hours whereas using bacteria for the same thing will take days. It is the best way to detect an elusive infection, rapid prenatal diagnosis of genetic disorders, and even identification of criminals from tiny samples of blood, tissue or semen by amplification and identification.

→ Bioreactors provide the optimum conditions for getting the desired product by providing optimum growth conditions like temperature, pH, substrate, salts, vitamins and oxygen etc. Bioreactors can be aerobic, submerged, surface and anaerobic type. The most commonly used is the stirring type. A stirrer type bioreactor has an agitator system, an oxygen delivery system, a foam control system, a temperature control system, a pH control system, sampling pouts to withdraw small volumes of culture.

→ Genetic engineering: It is a process by which manipulation of the genetic material of an organism is done.

→ Biotechnology: It is the use of living organisms or of substances obtained from them in the industrial process.

→ Bioreactor: The fermentation tank where fermentation is carried out in the presence of micro-organisms.

→ Broad-spectrum antibiotics: These are the antibiotics that have the ability to act on several pathogenic species.

→ Hybridomas: The hybrid cells of the same clone themselves are known as hybridomas.

→ Monoclonal antibody: The same type of antibody produced by the same clone of all the hybrids.

→ Restriction enzyme: An endonuclease that recogniseS Specific nucleotide sequences in DNA and then makes a double-strand cleavage of DNA molecule.

By going through these CBSE Class 12 Biology Notes Chapter 10 Microbes in Human Welfare, students can recall all the concepts quickly.

Microbes in Human Welfare Notes Class 12 Biology Chapter 10

→ Microorganisms are present everywhere in soil, air, and water and inside plant and animal bodies. They can withstand severe climatic conditions like very high (100°C) or very low (~50°C) temperatures, high acidic (pH2) conditions, etc. These may be bacteria, viruses, fungi, cyanobacteria, bacteriophages, viroids, and prions.

→ In the middle of the nineteenth century, Louis Pasteur observed that alcoholic fermentation of sugar required the multiplication of yeast cells.

→ Fermentation is the oldest microbial process.
It is of two types:

1. Batch process and
2. Continuous process.

→ An antibiotic is an organic compound produced by a microorganism that inhibits or kills another microorganism.

→ Although there are around 7000 antibiotics, known to exist, only about 150 are marketed, 10 are produced on large scale and about 300 new antibiotics are discovered every year.

→ The most common antibiotics and their sources are – Penicillin (Penicillium Notatum), Poly mixin-B (Bacillus Polymixa), Neomycin (Streptomyces Fradiae), Erythromycin (Streptomyces Erythraens), Chloramphenicol (Streptomyces Venezuela).

→ Vitamins are essential dietary factors that are required by us in small amounts. Out of all vitamins produced during the normal metabolism of microorganisms only two viz. Vitamin Bp and Vitamin B, are manufactured biotechnologically.

→ The important organic acids produced on a commercial scale by using microorganisms are acetic acid, citric acid, lactic acid, fumaric acid, gluconic acid, itaconic acid, kojic acid, butyric acid, and gibberellic acids.

→ Many microorganisms are known to transform naturally occurring steroids. These modified steroids have much medicinal importance.

→ By using recombinant DNA technology insulin is being produced using micro-organisms, which is similar to human insulin and is called humulin.

→ Streptokinase from streptococcus bacterium acts like a clot buster. It is helpful for patients who have undergone myocardial infarction.

→ Cyclosporin: A from the fungus Trichoderma polypore is used as an immunosuppressive agent and useful in organ transplantation.

→ Statins from yeast Monascus purpose is a blood cholesterol-lowering agent.

→ The municipal wastewater is called sewage. It contains large amounts of organic matter and many pathogenic microbes. In sewage treatment plants the treatment of wastewater is done by the heterotrophic microbes present in sewage.

→ Sewage treatment takes place in two main steps:

1. primary treatment and
2. secondary treatment.

In some advanced sewage treatment plants, it also undergoes tertiary treatment.

→ Primary treatment is done to remove large objects from the sewage. Sewage is passed through 2-8 cm apart steel bars, then through the wire mesh of reducing pores. It is passed through the grit chamber and then through the settling tank where most suspended material settles down as sludge.

→ The effluent flows for secondary treatment. First, the effluent is passed into aeration tanks where it continuously agitated and allows microbial growth. The microbes consume the organic matter and decrease the biological oxygen demand (BOD) of the effluent. It then passes to the settling tank where the sediment is called activated sludge.

It is passed to anaerobic sludge digesters where the anaerobic bacteria digest it further and produce gases like methane, H₂S, and CO₂. This is called biogas and can be used as fuel. The effluent may undergo tertiary treatment or released into natural water bodies.

→ Methanogens are bacteria that grow anaerobically on cellulose-rich materials and produce a large amount of methane gas with CO₂ and H₂. It is called biogas and is used as fuel. Methanogens are found in anaerobic sludge and also in cattle rumen where they come out in dung, so dung (rich in cellulose) can be used to generate biogas.

Biogas plant

→ Biofertilizers are the microorganisms that enrich the soil with nutrients and maximize the ecological benefits and minimize environmental hazards. These include nitrogen-fixing bacteria, cyanobacteria, and fungi.

→ Manures are partially decomposed organic materials added to the soil to increase fertility of the soil.
These are of three types:

1. farm-yard manure,
2. compost, and
3. green manure.

→ The disadvantages of chemical fertilizers and pesticides can be overcome by the use of alternative harmless manures, biofertilizers, biological control methods, and biopesticides.

→ The various types of biofertilizers are:

1. Microphones bio fertilisers,
2. Free-living nitrogen-fixing bacteria like Azotobacter,
3. Symbiotic nitrogen-fixing bacteria forming an association with legumes like Rhizobium,
4. A loose association of nitrogen-fixing bacteria like Azospirillum,
5. Cyanobacterial biofertilizers and
6. Azolla-Anabaena symbiosis.

→ Mycorrhizae are the symbiotic association of fungi with the roots of higher plants. These may be ectomycorrhizae and endomycorrhizal.

→ The ectomycorrhiza is characterized by the formation of a sheath or mantle on the surface of roots. They help in the absorption of water, absorption of inorganic nutrients, and protection of plants from pathogen attack.

→ The endomycorrhiza does not form an external sheath or mantle. The fungi mycelium penetrates into the roots and lives in the intercellular spaces as well as intracellularly in the cortical cells. Some endomycorrhizal are called vesicular-arbuscular mycorrhizae (VAM). They develop vesicles and arbuscules within the cells of the root. These fungi stimulate the absorption of phosphorus, zinc, copper, sulfur, potassium, and various other elements by the roots.

→ Biopesticides are pesticides of biological origin or biological control agents which are used to control weeds and pests.
They are two main types

1. Bioherbicides and
2. Bioinsecticides.

→ Bioherbicides or biological control of weeds involve the utilization of biological agents (such as insects, fungi, bacteria, nematodes, parasitic plants, etc.) which suppress or kill the weedy plants without causing significant injuries to other plants.

→ Bioinsecticides or the control of harmful insects by biological methods include

1. The use of pathogens, parasites, and predators;
2. Sterilization strategy;
3. Use of insect hormones; and
4. Use of natural insecticides.

→ Antibiotic: An antibiotic is a substance produced by a microorganism that inhibits the growth of other microorganisms.

→ Bioreactor: The fermentation tank where fermentation is carried out in the presence of micro-organisms.

→ Broad-spectrum antibiotics: The antibiotics which have the ability to act on several pathogenic species differing from each other in structure and composition of the cell wall.

→ Biological control: introduction of living organism which destroys other harmful organisms.

→ Chemical control: Use of chemical substances such as smoke, gas, dust, and sprays to poison pests.

→ Fermentation: The anaerobic oxidation of food in the presence of micro ‘organisms which result in the production of alcohol and waste ga CO₂.

→ Fertilizer: Substance added to soil to increase the yield of crop plants.

→ Fungicide: Substances used for killing fungi.

→ Farmyard manure: The manure consisting of a mixture of cattle dung a4id crop residue.

→ Legume: The plants of the pea family i.e. Luguminosae e.g. pea plant beans etc.

→ Manure: The substances which are added to soil to increase crop yield.

By going through these CBSE Class 12 Biology Notes Chapter 9 Strategies for Enhancement in Food Production, students can recall all the concepts quickly.

Strategies for Enhancement in Food Production Notes Class 12 Biology Chapter 9

→ The agricultural practice of breeding and raising livestock is termed animal husbandry. It mainly deals with the care and breeding of commercially important livestock like cows, buffaloes, pigs, cattle, horses, sheep, camels, goats, and poultry farming, and fisheries. Bees, silk-worm, prawns, crabs, birds are also used for their products like honey, milk, and meat, etc.

→ The dairy food industry deals with the management of animals for milk production and its products for the consumption of human beings. Milk yield depends on the quality of breeds with high yielding potential and disease-resistant features.

Those processes and systems are practiced which would increase the yield and improve the quality of milk. The cattle should be well housed, given adequate water, and maintained disease-free. Feeding is done with special emphasis on the quality and quantity of fodder in a scientific manner. Cleanliness and hygiene are of paramount importance while milking, storage, and transport of milk and milk products.

→ Poultry includes all those birds which can be raised under domestication for economic purpose. Poultry farming is highly advantageous. It yields quick returns, requires less space, and easy to manage. Birds like chickens, ducks, geese, turkey, etc. are raised for their eggs and meat.

→ Poultry farm management includes the selection of disease-free and suitable breeds, proper and safe farm conditions, proper feeding and water, hygienic and healthy care.

→ To increase the yield and get desirable qualities in animals, breeding of animals is done. A group of animals that are similar in most characters such as general appearance, features, size, configuration, etc. is said to belong to a breed.

→ When breeding is done between the animals of the same breed, it is called inbreeding. When breeding is done between animals of different breeds it is called cross-breeding or out-breeding.

→ Inbreeding is done by carrying out mating between closely related individuals within the same breed for 4 to 6 generations. Superior males and females are identified and mated in pairs. The progeny is evaluated and superior males and females are selected for further mating. This is repeated for some generations, it leads to the development of pure lines. It increases homozygosity. In cattle, a superior female is one that produces more milk and a superior male is one that gives rise to superior progeny.

→ Inbreeding depression occurs because of continued, close inbreeding, which reduces fertility and productivity. This can be solved by outbreeding.

→ The breeding of unrelated animals is called outbreeding. It may be between some breeds with no ancestral link or between different breeds called cross-breeding. It may happen in different species, called interspecific hybridization.

→ Out-crossing is done within the same breed. It helps to overcome inbreeding depression and the best breeding method to increase productivity.

→ Crossbreeding allows the desirable qualities of two different breeds to combine together. The hybrids are either used commercially or allowed to inbreed so as to select a new stable breed that is superior to the existing breeds.

→ Interspecific hybridization allows the mating of male and female, of two different species. The progeny will have the combined features of both the parents, e.g. mule.

→ Controlled breeding is done with artificial insemination. The semen is collected from males and injected into the reproductive tract of females. This helps in desirable mating and ensures good quality progeny. The semen obtained from a single bull can inseminate a few thousand cows at far-off places.

→ Superovulation and embryo transplantation are new techniques employed for cattle improvement. For this, the cow is administered hormones to induce follicle maturation and superovulation. Due to which several eggs are produced per cycle. These are artificially inseminated, the fertilized eggs are surgically removed at an 8 – 32 celled stage and transferred to the surrogate mother.

→ Apiculture is the maintenance of hives of honey bees for honey production. A. dorasata, Apis, florea, A. indica species are reared for honey. It is an age-old cottage industry. Beehives can be kept in courtyards, or bee pastures of some wild shrubs, fruit orchards, and cultivated crops.

It is not labor intensive but it requires some specialized knowledge and training. Before starting apiculture practice, knowledge of the nature and habits of honey bees, selection of suitable location for keeping the beehives, catching and hiving of a group of bees, management of hives during different seasons, handling and collection of honey and beeswax, is very important.

→ Along with honey, honey bees also produce beeswax, which is used for cosmetics, polished, and various other industries. Honey is aromatic, viscid, and sweet material. Its constituents are :
(a) Levulose – 41.80%,
(b) Glucose and fructose (grape sugar) – 35.40%,
(c) Water – 15.43%,
(d) Sucrose – 5.39%,
(e) Bee wax and pollen grains – 1.68%.

Pure honey is dissolved in water, makes a thread through the depth of glass while impure honey gets dissolved in water.

→ Pisciculture is the rearing and breeding of fish. It includes catching, processing, or selling fishes, shellfish, or other aquatic animals such as prawns, crab, oysters, etc. The flesh of fish has 60 – 80% water, 13 – 20% protein, and some amount of fat. Fish is a very good source of protein and forms an excellent food as it has very little fat and more protein, has a good quantity of vitamin A and D, a rich source of iodine, and easily digested than other meals.

→ In addition to providing food, the fishing industry yields a number of by-products that are of commercial importance.
Some are:
(a) liver oil, which is extracted from fish liver. It’s a good source of vitamin A, C, D, and E,

(b) fish meal is prepared from the waste of fish oil or canning industry or whole fish. It is used as a major food for domestic animals. It is rich in proteins, calcium, and phosphorus,

(c) fish proteins are 80-90% proteins with no fats. These are used in icecreams, pharmaceuticals, paints, varnishes, textile, paper, and cosmetics. Fish protein concentrate (FPC) is also used as a diet supplement,

(d) fish flour is used in biscuits, bread, cakes sweets, and soup. It is easily digested by the infants,

(e) fish fertilizers are wastes of fish meal preparation. These are used as manures for tea, coffee, and tobacco plantation,

(f) fish rees are rich in thymine, lecithin, cholesterol, tyrosine, xanthine, hypoxanthine, and vitamin B, C, D, and E. These are valuable foods.

→ Agriculture is the science or the practice of farming or cultivation, reaping, and management of farm products. Horticulture is the branch of agriculture that deals with the art of growing vegetables, fruits, and ornamental plants.

→ Plant breeding is the purposeful manipulation of plant species in order to create desired plant types that are better suited for

→ cultivation, give better yields, and disease resistant. The main objective of plant breeding is to reproduce new superior crop varieties with respect to crop yield and quality, increased tolerance to environmental stress such as salinity, extreme temperature, and drought, resistance to pathogens like viruses, fungi, and bacteria, and increased tolerance to insect pests.

→ Plants which are both self and cross-pollinated can produce homozygous and heterozygous population and are most suitable of breeding experiments.

→ First of all collection and preservation of all different wild varieties, species, and relatives of cultivated species is done to properly use the natural available genes. The entire collection of plants or seeds with all the diverse alleles for all genes in a given crop is called germplasm collection.

→ The germplasm is evaluated to identify the plants with a desirable combination of characters. Selection is the oldest breeding method and is the basis of crop improvement.

It may be of two types:
(a) Natural selection and
(b) Artificial selection.

Natural selection is a continuous process that is operating in nature. Here the fittest survives and the remaining ones vanish away.

→ In artificial selection, various types of plants are selected from bulk by plant breeders. This is purposefully done to have a better crop from a mixed population, in a. short duration of time as compared to the natural selection process. This may be achieved by mass selection, pure line selection, and clonal selection.

→ Mass selection is based on phenotypes. The best plants from the population are selected at the time of harvesting, with desired traits. The seeds from all such plants are collected and mixed to form a bulk. This process may be repeated for some generations to get the desired improvement.

→ Pure line selection is also called single plant selection. In it, several single plants with desired traits are selected from a population. This is the best method to improve the variety in self-pollinated plants and the crop is of uniform appearance.

→ Clonal selection is used to ensure purity to race, e.g. mangoes, apples, etc., or due to lack of seed formation, e.g. banana. It is the best method for vegetatively propagated plants

→ The plants are selected by using a suitable selection method. These are then multiplied and used further for hybridization.

→ Hybridization is the crossing of two plants differing from each other genotypically in one or more traits.

The purposes of doing hybridization are:
(a) to exploit and utilize the hybrid vigor and
(b) to increase and generate the genetic variations through recombination.

→ In hybridization, greater success is obtained with healthy and vigorous parents. Selfing is done to reduce heterozygosity. The selected inbreeds are used for hybridization.

→ Hybridization involves emasculation and bagging (discussed in Chapter 2) techniques, which are removal of stamens and bagging male and female flowers to prevent foreign pollen contamination. After these crossing is done by collected pollen grains from the male parent and dusting them on stigma. The same desired characters for hybridization are high protein content from one parent and disease resistance from another parent. The hybrid plant is a genetic combination of the two parents.

→ Hybridization is followed by a selection of hybrids that have desired characters. This step needs expertise and careful scientific evaluation. These plants are superior to both the parents. These are further self-pollinated for several generations to attain homozygosity and to ensure that the desired characters will not segregate in the progeny.

→ After successful experimentation, the crop is grown in the research field under ideal fertilizer application, irrigation, and crop management practices. This is followed by testing in farmer’s fields in different locations for three growing seasons. These are evaluated for their yield and quality, disease resistance qualities, etc.

→ Wheat, rice, and maize are the chief cereals of the world. These belong to the Gramineae family. Wheat flour is used for making chapatis, bread, cakes, biscuits, etc. Its straw is used as fodder and for stuffing. Sonalika and Kalyan Sona are two high-yielding and disease-resistant varieties of wheat.

→ Rice is a staple food for half of the world. It is a semi-aquatic crop. It’s used in various preparations like idli, dosa, kheer, etc. It’s straw issued for making hats. Rice flavor is used in the cosmetic industry. IR-8 and Taichung Native-1, Jaya, and Ratna are few varieties of rice.

→ Maize or corn is rich in carbohydrates, fats, and proteins. It lacks binding gluten so can’t be used for bread making. It can be boiled, roasted, or popped up.

→ Smaller grained cereals are called millets, e.g. ragi, Jowar, and Bajra.

→ Sugarcane is a hybrid obtained from crossing between Saccharum Barberi and Saccharum officinarum. It is the chief source of sugar. Baggage (leftover) is used in the fuel and paper industry. The molasses is used in alcohol anti vinegar preparation.

→ Resistance of the host plant is the ability to prevent the pathogen from causing disease. Some plants are disease resistant while some are susceptible, it is determined by the genetic constitution of the host plant. These pathogens Rhay be fungal, bacterial, or viral, e.g. brown rust of wheat (fungi), red rot of sugarcane, late blight of potato (fungi), black rot of crucifers (bacteria), tobacco mosaic, turnip mosaic (virus). Breeding helps to develop disease-resistant varieties and reduce the fungicides and bactericides treatment.

→ Breeding for disease resistance is achieved by the usual steps like screening for disease-resistant plants through germplasm, hybridization of selected parents, selection and evaluation of the hybrids, followed by testing and finally release of new varieties.

→ Due to a limited number of disease resistance genes in a species, conventional breeding has a limited scope. Other breeding methods such as induced mutations, selection among somaclonal variants, and genetic engineering have promising results in producing desirable characters. Initially, mutations are induced in plants, these are screened for disease resistance genes. Such plants are either directly multiplied or used inbreeding.

→ The mutation is a sudden, stable, and heritable change that alters the genotype of an organism. Mutations are induced artificially in plants which change base sequence in genes, creating genetic variation, this results in new traits in the progeny.

→ The application of induced mutations for crop improvement is called mutation breeding. Mutations can be induced chemically or by radiations, e.g. UV rays, X-rays, cosmic rays, gamma rays, ⁶⁰cobalt, and ¹³⁷caesium, nitrous acid, EMS, mustard gas, colchicine, etc.

→ Plant breeding experiments are used for developing pest and insect-resistant varieties. These are dependent on morphologica1, biochemical, and physiological characters of the host plant. For example, hairy leaves are associated with resistance to insect pests, solid stems of wheat are resistant to stem sawfly, sugar content in maize leads to resistance for maize stem borers. Breeding methods are the same as discussed earlier.

→ Plant breeding is also practiced for improved food quality, it is done for improving protein content and quality, oil content, and quality, for increasing vitamin content, for micronutrient and mineral content. For example, Atlas 66 wheat has high protein content, maize hybrids with more amino acids, lysine and tryptophan and rice with more iron content have been developed.

→ Single-cell proteins (SCPs) are an alternative source of proteins for animal and human nutrition.

→ Microbes like spirulina which can be grown on waste materials can serve as rice food for proteins, minerals, fats, carbohydrates, and vitamins and reduces environmental pollution too. Microbes are grown increasingly on large scale to serve as a good source of proteins.

→ Plant tissue culture is a technique of growing cells, tissues, or organs in sterilized nutrient media under controlled aseptic conditions. The plant part which is used for culture preparation is called explant. Plant cells are totipotent i.e: they can form a complete plant under suitable conditions. In specific culture medium and sterile conditions, many plant cells and tissues divide and grow to form an unorganized mass of cells called callus.

→ The nutrient medium must provide a source for carbon and inorganic salts, vitamins, amino acids, and growth regulators like cytokinins and auxins, etc.

→ Micropropagation or cloning is a novel technique devised to produce vast quantities of strong and healthy plantlets by rapid vegetative multiplication under controlled conditions. Each of these plants is genetically identical to the parent plant and is called some clones.

→ Tissue culture is useful for

1. Micropropagation,
2. Production of disease-free plants,
3. Androgenic haploids and their use in breeding,
4. Embryo rescue for successful hybridization,
5. Induction and selection of mutants,
6. Somaclonal variations,
7. Protoplast technology.

→ Culture of explant on an agar medium containing 2, 4-D results in the formation of callus. Suspension cultures are obtained by culturing pieces of callus in a liquid medium which is constantly agitated so that the larger masses are dissociated into smaller clumps and single cells.

→ The callus and suspension cultures are commonly used for achieving cell biomass production. Single cells can be isolated either from suspension culture or directly from explants by mechanical or enzymatic methods. They are cultured in liquid or semi-solid media by using filter paper raft-nurse tissue technique or by Bergmann’s plating technique. Plantlets can be regenerated from callus or suspension cultures either by shoot regeneration or by somatic embryo regeneration technique.

→ The regenerated plantlets can be transferred and established in the field. The term ‘micropropagation’ or ‘cloning’ is applied to a novel technique devised to produce vast quantities of strong and healthy plantlets by rapid vegetative multiplication under controlled conditions.

Haploid plants can be produced by another culture or by culturing microspores. These haploids can be converted to homozygous diploids by doubling their chromosomes using certain chemicals.

→ Young embryos can be cultured on artificial culture media containing specific nutrients. This technique is helpful in raising the plants from interspecific crosses as well as for ‘embryo rescue’. The multiple shootlet production techniques are useful in getting disease-free healthy plants.

→ Genetic vacations occur at all levels of the tissue culture process. They are termed somaclonal variations. These variations are useful for the improvement of crops if they are heritable and have agronomic traits.

→ Naked protoplasts of plant cells can be isolated by digesting their cell walls using certain hydrolytic enzymes. The isolated protoplasts can be cultured in a liquid or semi-solid medium. Naked protoplasts of two different plants can be allowed to fuse to form hybrids. This is called protoplast fusion and somatic hybridization.

The plant tissue culture technique is also used for the production of artificial seeds in those plants which either do not bear seeds or produce a small number of seeds.

→ Artificial seeds are used for direct field delivery of select elite genotypes, hand-pollinated hybrids, genetically engineered plants, sterile and fertile genotypes, etc.

→ Cultivation of plant cells in culture media promises great potential in large-scale production of secondary metabolites which are otherwise produced in minute amounts and their extraction from the plants is difficult and expensive.

→ Allotetraploid: AllotetraploidS are produced by the multiplication of chromosomç sets that are initially derived from two different species.

→ Apiculture: Rearing and management of beehives for obtaining honey and wax.

→ Aquaculture: Production of useful plants and animals.

→ Concentrates: They include cotton seeds, oil cakes, cereal grains, etc.

→ ElectrapOration: Genetic transformation by applying high electric potential for a few microseconds to change the porosity of protoplast to take up DNA.

→ EmasculatiOn: Removal of stamens from bisexual flowers before they burst and shed their pollen.

→ Hybrid vigor: The increased vigor often exhibited by hybrid progeny.

→ Livestock: The animals like cattle, sheep goat, camel, horse, pig, and poultry form livestock.

→ Pisciculture: The rearing of fishes for obtaining meat and oil.

→ Poultry: Rearing of fowls, ducks, turkeys for their eggs and meat.

→ Roughage: It includes straw of cereals such as wheat, rice, Jowar, and oat, etc.

→ Teratoma The partially organized tumors are called a teratoma.

By going through these CBSE Class 12 Biology Notes Chapter 8 Human Health and Disease, students can recall all the concepts quickly.

Human Health and Disease Notes Class 12 Biology Chapter 8

→ Health is a state of complete physical, mental and social well-being. It is not just the absence of diseases. Health may be defined as a state of the body when all the organs and systems are functioning properly and a perfect balance is maintained between the environment and the body.

→ The disease may be identified as any condition which impairs health or interferes with the normal functioning of the body due to one or another reason. It is any functional change from the normal state which causes discomfort or disability.

→ Any factor or substance which causes disease by its excess or deficiency or absence is called a disease agent.

→ The disease agents may be biological (e.g. virus, bacteria, fungi, protozoans, helminths, and anthropods) they are called pathogens; or Nutrient agents, e.g. food components viz. proteins, fats, carbohydrates, minerals, vitamins, and water; or chemical agents, may be exogenous or endogenous ones. Exogenous agents enter the body from outside e.g.-pollutants such as fumes, dust, metals, gases, etc., or allergens such as pollen and spores.

Endogenous chemical agents are formed inside the body, e.g. hormones, enzymes, uric acid, etc.; or Physical agents such as humidity, pressure, radiation, heat, cold, electricity, and sound; or mechanical agents such as chronic friction or other mechanical forces which cause a sprain, fracture or dislocation, etc; err genetic agents which cause genetic disorders or underdeveloped organs.

→ Diseases are broadly classified into two types as

1. Congenital disease and
2. Acquired diseases.

→ Congenital disease is anatomical or physiological abnormalities that are present at the time of birth. These may be single gene mutation, e.g. phenylketonuria, albinism, sickle-cell anemia, color blindness, hemophilia, etc., or chromosomal aberrations e.g. Down’s syndrome, Klinefelter’s syndrome, or Turner’s syndrome. These are further transmitted to the children.

→ Harelip and cleft palate are some environment-related congenital diseases that are not transferred to children.

→ Acquired diseases: These develop after birth. They may be communicable or non-communicable diseases.
Classification:

→ Acquired diseases are further of two types – Communicable and non-communicable. Communicable diseases are infectious which are caused by pathogens. Non-communicable diseases are non-infectious ones that remain confined to the diseased person only.
These are of four types:

1. Organic diseases occur due to the malfunctioning of important organs such as heart diseases, epilepsy.
2. Deficiency diseases are produced by a deficiency of minerals, nutrients, vitamins, and hormones such as beriberi, diabetes, goiter, etc.
3. Allergies are caused when the body becomes hypersensitive to some foreign substance e.g. Hay fever,
4. Cancer is caused by the uncontrolled growth of certain tissues in the body.

→ Communicable diseases are classified into seven types:

1. Viral diseases e.g. smallpox, chickenpox, polio, common cold, etc.
2. Rickettsial diseases are caused by obligate intracellular parasitic organisms known as rickettsias, e.g. typhus fever, Q fever, Rocky Mountain spotted fever, etc.
3. Bacterial diseases e.g. diphtheria, tetanus, food poisoning, etc.
4. Spirochaetal diseases are caused by long, spiral, corkscrew-shaped bacteria called spirochaetes e.g. syphilis,
5. Protozoan diseases are caused by protists, e.g. amoebic dysentery, malaria, kala-azar, sleeping sickness, etc.
6. Fungal diseases are caused by non-green heterotrophic organisms, fungi e.g. ringworm and athlete’s foot,
7. Helminth diseases are caused by flatworms and ringworms e.g. liver rot, taeniasis, etc.

→ Typhoid is caused by gram-negative bacteria, Salmonella those commonly found in the human intestine. It is a communicable disease, spread through the intestinal discharge of typhoid carriers. Its incubation period is 1 – 3 weeks.

Its symptoms include headache, typical typhoid fever which increases in the afternoon and enhances every day, in a second week its high and decreases during the third and fourth week, lesions of the intestinal mucosa, hemorrhage, ulcer of the intestine, red rashes on chest and upper abdomen. It is confirmed by S.typhi bacterium detection in stools or blood and also by the Widal test.

As typhoid spreads through contaminated food and water, precautions should be taken for screening of water and food sources, proper sanitation of human feces.
Its therapy includes

1. Thyphoral is an oral vaccine,
2. TAB – this vaccine provides immunity for 3 years,
3. Chloramphenicol, ampicillin, and chloromycetin are effective drugs against typhoid bacterium.

→ Pneumonia is a lung infection caused by bacteria like Streptococcus pneumonia and Haemophilus influenza or mycoplasma or viruses. This is an airborne disease spread through cysts present in the patient’s sputum. Its incubation period is 1 – 3 days. Pneumonia is characterized by lymph collection and mucus in the bronchioles and alveoli, thus decreasing the respiratory efficiency of the lungs. It includes fever, chills, cough, and headache. In severe cases, the fingernails and lips may turn grey to bluish.

The bacteria present in the body secretion of the patient are released out as aerosols or droplets which are inhaled by healthy person and cause infection. It also spread by glasses and utensils sharing with the patient so the best precaution is the isolation of the infected person. It is treated, with penicillin, flucloxacillin, etc. antibiotics.

→ The common cold is caused by a large number of viruses that belong to a group ‘rhinoviruses. It is the most infectious human disease. These viruses infect the nose and respiratory passage but not the lungs of the patient. Its symptoms are nasal congestion, discharge, sore throat, cough, headache, tiredness, etc. It lasts for 3 to 7 days. The infection spreads through droplets from sneezes or cough, through contaminated objects like books, cups, doorknobs, computer keyboard pens, mice, etc.

Salmonella typhosa

Diplococcus pneumoniae

→ Amoebic dysentery or Enteritis or Amoebiasis is caused, by an intestinal endoparasitic protozoan, Entamoeba histolytic which inhabits the large intestine. It may also spread to the lower part of the small intestine, liver, lungs, and brain. E. histolytic occurs in two forms (diagonal) minute form, its an absorptive stage and undergoes encystment and magma form, its large-sized, destroys epithelial cells and holozoic stage. Its main sources of infection are drinking water and food, contaminated by the fecal matter of infected person. Houseflies act as carriers and transfer the parasite from feces to food products.

Stool detection of the patient shows the presence of E. histolytic. The symptoms include constipation, abdominal pain, and cramps, stools with excess mucous, and blot clots. The protozoan secretes leading to ulcers.

Its precautions include

1. proper sanitary conditions,
2. coverage of tables to prevent contamination by vectors,
3. proper washing of fruits and vegetables before eating. Its treatment is done by antibiotics like Terramycin, erythromycin, aureomycin, and metronidazole.

→ Malaria is a vector-borne disease which is caused by the protozoan parasite Plasmodium. It is caused by toxic pigment hemozoin from RBC’s Hb. This is produced when RBC are destroyed by developing stages of the Plasmodium. Plasmodium is digenetic (two hosts) and triphasic. The primary host is the female Anopheles mosquito and the secondary host is human beings.

Three phases include asexual schizogony (in liver and RBCs of man), sexual cosmogony (starts in RBCs and completes in mosquito’s stomach), asexual sporogony (stomach of mosquito). Malaria is of several types which are caused by different species of Plasmodium. Malaria caused by Plasmodium falciparum is most dangerous, it is called malignant malaria and it can be fatal.

Plasmodium enters the human body through the Anopheles mosquito. The parasite multiplies within the RBCs and ruptures the cells. Symptoms include headache, chill, shivering, nausea, muscular pain, recurring fever every 3rd or 4th day, increase in pulse and respiration rate, sweating, and anemia.

Its symptoms are divided into three stages:

1. cold state,
2. hot stage and
3. sweating stage.

The mosquitoes acquire the parasite from infected persons and transmit it to healthy individuals.

Its precautions include

1. wire gauzing of doors and windows etc.,
2. using mosquito nets,
3. use of mosquito- repellents.
4. spraying insecticides like D.D.T. and B.H.C.,
5. do not allow any stagnant water. Its treatment is done by quinine, chloroquine, palustrine, Daraprim, etc., anti-malarial drugs.

→ Filariasis is caused by the filarial worm, Wuchereria ban crafti and Wuchereria malayi. The worm is digenetic, its primary host is man, and the secondary or vector host is mosquitoes Aedes and Culex. It causes slowly chronic inflammation of organs for many years.

They are found in lymph vessels and lymph nodes and due to infection the lymphatic vessels of lower limbs become enlarged due to blockage and chronic inflammation. The disease is called elephantiasis or filariasis. Genital organs are also affected. This causes enormous swelling of legs, scrotal sacs, breasts, etc.

The pathogens are transmitted through the bite of female mosquito vectors. Its precautions are the same as for malaria. Its treatment includes Hetrazan and diethylcarbamazine.

→ Ascariasis is caused by intestinal endoparasite of man, Ascaris lumbricoid known as roundworm. It is a monogenetic helminth that spreads through water, vegetables, fruits that are contaminated with the eggs of the parasite. Its symptoms include abdominal pain, indigestion, weakness, anemia, nausea, vomiting, diarrhea, internal bleeding, muscular pain, fever, etc.

Heavy infection may cause pneumonia, hepatitis, blockage of the intestine, convulsions, etc. Flies and cockroaches serve as vectors for spreading the diseases. It is diagnosed by doing stool test, Dermol test or Scratch test, its precautions are same as for Amoebic dysentery. Its treatment is done by Hexyl-resorcinol crystals, a mixture of oil of chenopodium and tetrachloroethylene.

→ Ringworms are a common infectious disease caused by fungi Microsporum, Trichophyton, Candida, and Epidermophyton. Their symptoms include dry and scaly lesions on skin, nails, and scalp. These are accompanied by intense itching.

Moisture and warmth help in fungal growth. It’s most likely to grow in skin folds like the groin and between the toes. These generally spread from soil or sharing towels, clothes, or comb with an infected person. These are treated with antifungal ointments.

→ Vaccination is a common method of preventing the infection of microorganisms like bacteria and viruses. Infectious diseases like polio, diphtheria, pneumonia, and tetanus are controlled to great extent by vaccination. Smallpox is completely eradicated by vaccines and immunization programs. Various antibiotics are also very effective against infectious diseases.

→ Disease resistance or immunity is the ability of an organism to resist disease. Immunology is the branch of science which deals with immunity. The immune system forms the third line of defense. The immune system can differentiate between self (body cells) and non-self (foreign microbes).

→ Any foreign substance entering the body stimulates an immune response it is called an antigen. The protective chemicals (proteins) produced by the body in response to antigens are called antibodies.

→ Immunity is of two main types:

1. Innate immunity and
2. Acquired immunity.

1. Innate immunity or inborn or natural immunity is non-specific and present at the time of birth. It is inherited from the mother through the placenta. It provides four different types of barriers to the foreign agents as (a) physical barriers: Skin is the foremost barrier that prevents the entry of microorganisms, similarly, the mucus coating of the epithelial layer lining the respiratory, gastrointestinal, and urogenital tracts also defend the entry of microorganisms,

2. Physiological barriers such as gastric acids, saliva in the mouth, tears, all prevent microbial growth.

3. Cellular barriers, some leukocytes (WBC) like polymorphonuclear leukocytes (PMNL-neutrophils) and monocytes and some lymphocytes (e.g. natural killer) from blood and macrophages from tissue can phagocytose and destroy the invading microbes,

4. Cytokine barriers, virus-infected cells produce anti-viral proteinous molecules called interferons, which protect the unattacked cells from viral attack.

→ Acquired or adaptive immunity is not present from birth but is acquired or developed by the organisms in response to a disease. It is pathogen-specific and is characterized by memory. When the body encounters any antigen (pathogen) the lymphocytes produce antibodies which are termed as a primary response, it’s of less intensity.

Lymphocytes also provide immunity against further attack, a subsequent encounter with the same pathogen produces a highly intensified secondary or anamnestic response. The acquired immunity may be temporary (influenza) or permanent (measles, mumps, polio, smallpox, etc.) for life long.

→ Acquired immunity is of two types:

1. Active or natural immunity is developed by antibodies from the individual’s body,
2. Passive or artificial immunity: In it, readymade antibodies are obtained from human or animal serum, who had recovered from the same infection and injected into the patient. It is known as inoculation
   e.g. tetanus treatment, snake bite, etc.

→ The primary and secondary immune responses are carried out with lymphocytes. Lymphocytes are a kind of agranulocytes of leucocytes (WBC) of blood. Lymphocytes are of two types: B-lymphocytes and T-lymphocytes. Both types of lymphocytes are formed from the stem cells called haemocytoblasts in the bone marrow and undergo further processing.

Showing formation of lymphocytes

→ B-lymphocytes produce antibodies when stimulated by an antigen. After stimulation one B-lymphocyte synthesize RNA, divide rapidly and differentiate into the RER-rich histologically distinctive plasma cells. A group of plasma cells is called a clone. They produce antibodies at a rate of about 2000 molecules per second. These antibodies circulate in the lymph to fight antigens. They form the humoral immune system or Antibody-Mediated Immune System (AMIS).

→ An antibody molecule is made up of four peptide chains, two small peptide chains called light chains, and two long heavy chains. An antibody may be designated as H₂L. There are five classes of antibodies (immunoglobulins) namely IgM, IgG, IgA, IgD, and IgE. IgG is not abundant in man whereas IgM and IgG cause the lysis of foreign cells.

→ The second type of acquired immune response is Cell-Mediated Immune System (CMIS). It is mediated by T-lymphocytes. T-cells do not secrete antibodies but help B-cells to produce them. T-lymphocytes attack directly the pathogenic microorganisms entering the body or grafts such as transplanted kidney or skin grafts. It also protects the body from its own cells which have become cancerous.

→ Vaccination or immunization is based on the property of memory of the immune system. A preparation of antigenic proteins of pathogen or weakened or inactive pathogen is given. The body produces antibodies against these antigens and neutralizes the pathogenic agent during actual infection. The vaccines also produce memory B and T cells which recognize the pathogen or subsequent exposure and counteract with massive production of antibodies. Vaccines are also produced by recombinant DN A technology where bacteria or yeast produce antigenic polypeptides of pathogens, e.g. hepatitis B vaccine.

→ Allergies are an exaggerated immune response to certain antigens called allergens e.g. dust mites, pollens, animal dung, fur, venom, etc. Allergy symptoms are inflammation of mucous membranes, sneezing, watery eyes, running nose, irritation of upper respiratory tract, rashes, itching, etc. In allergic people, the body develops a primary immune response on encounter with the allergen. B-cells produce antibody IgE. On the next exposure, the body produces a secondary immune response called allergy.

→ The allergens combine with antibody-bound mast cells and basophils. This complexing ruptures the mast cells and basophils, releasing histamine from vesicles called granules. The process of the release of histamine is termed degranulation. The histamine acts as an allergy mediator. It increases the permeability of capillaries constricts smooth muscles in many parts such as those around the bronchioles, causing breathing problems; and stimulates mucous glands. It also widens the small arteries but not the veins.

Thus, the affected area (where histamine has been released receives more blood than it returns. As a result of this, fluid accumulates in the tissue which swells up. This causes allergy.

Showing allergic reaction and release of histamines by rupturing of mast cells

→ The immune system sometimes rejects certain tissues of the body as non-self. Due to genetic and other unknown reasons the body attacks self-cells. This is called autoimmunity. The body tissues act as autoantigens and autoantibodies, e.g. Hashimoto’s thyroiditis, systemic lupus erythematosus, rheumatoid arthritis.

→ The immune system plays a role in allergic reactions, autoimmune diseases, and organ transplantation. The immune system consists of lymphoid organs, tissues, cells, and soluble molecules like antibodies. Lymphoid organs help in the origin or maturation and proliferation of lymphocytes.

The primary lymphoid organs are bone marrow and thymus, here immature lymphocytes differentiate into antigen-specific lymphocytes. After maturation lymphocytes migrate to secondary lymphoid organs which are the spleen, lymph nodes, tonsils, appendix, and Peyer’s patches of the small intestine. Here the lymphocytes interact with antigens and then proliferate to become effector cells.

→ Bone marrow provides a suitable environment for the development and maturation of B-lymphocytes. Bone marrow is the main lymphatic organ where all blood cells, as well as lymphocytes, are produced.

→ The thymus is a lymphatic organ, located near the heart beneath the chest bone. It is prominent in children but keeps on reducing with age, by puberty it becomes very small in size. Development and maturation of T-lymphocytes take place in the thymus. It educates the fetal lymphocytes to distinguish between self and non-self.

→ The spleen is the largest component of the lymphatic system. It is bean-shaped, vascular, dark red in color, located in the abdomen below the diaphragm. It consists of red pulp and white pulp. It helps in the destruction of worn-out RBCs, as a reservoir of RBCs, production of antibodies, disposal of foreign elements.

→ Lymph nodes are present at intervals in the course of lymphatic vessels. They contain lymphocytes, plasma cells, and macrophages. They trap the microorganisms and antigens and stimulating the immune response.

→ Lymphatic tissue present in the lining of respiratory, digestive, and urogenital tracts is known as mucosal-associated lymphoid tissue (MALT). Lymphatic tissue present in the gut is called get-associated lymphoid tissue (GALT).

AIDS is an acquired immunodeficiency disease. A detailed account of the retrovirus and the disease has been discussed in detail in previous chapters. Its control and prevention were also discussed.

The figure shows the aids virus.

Diagram of AIDS virus

Cancer is a malignant growth or tissue enlargement due to unlimited and uncontrolled mitotic division of some cells known as cancerous cells.

Showing development stages of cancer due to smoking in lung epithelium

Cancerous cells grow rapidly and form a mass of cells called tumors. Tumors are of two types: Benign or non-malignant tumors these remain confined to one place and cause little damage, cancerous or malignant tumors – these are a mass of proliferating cells known as neoplastic cells. They grew rapidly, damage the nearby normal tissue. Cancerous cells divide actively and compete for nutrients with the normal tissue. These cells reach another place through blood and form new tumors. This is called metastasis.

→ Cancer is neither contagious nor hereditary. Factors that cause cancer are called carcinogenic agents. These may be ionizing radiations, e.g. x-rays and gamma rays or non-ionizing rays like U.V rays, chemical carcinogens like beetle and tobacco, aniline dyes, heavy smoking, viral oncogenes, and cellular oncogenes. Cellular oncogenes (c-onc) or protooncogenes are present in normal cells which get activated under certain conditions and become oncogenes.

→ Detection of cancer is done by biopsy and histopathological studies of tissues, blood, and bone marrow for increased cell count (leukemia). X-rays, CT scans, and MRIs are used to detect cancer of internal organs. Mammography is done to detect breast cancer. Pap test is done for cancer detection in the cervix and other genital parts. Monoclonal antibodies against the cancer-specific antigen are coupled to the suitable radioisotope, these antibodies are used further for cancer detection.

→ Cancer is treated with surgery, radiation therapy and immunotherapy, and chemotherapy. Biological response modifiers such as γ – interferons are used to activate the immune response to destroy the tumor.

→ Drugs are normally used for the treatment of diseases. An addictive drug modifies the biological, psychological, or social behavior of an individual by stimulating, depressing, or distorting mind and body functions. This habit of taking drugs beyond voluntary control is called an Addition. Commonly abused drugs include opioids, cannabinoids, and coca alkaloids.

TABLE: SHOWING MAJOR GROUPS OF PSYCHOTROPIC DRUGS WITH EXAMPLES AND EFFECTS

Type of Drug	Examples	Effects
I. Sedatives and tranquillisers (depressant)	Benzodiazephines {eg.. Valium) Barbiturates	Depress brain activity and produce feelings of calmness relaxation, drowsiness, and deep sleep (high doses).
II. Opiate narcotics	Opium Morphine. Heroin Pethidine. Methadone	Suppresses brain function, relieves intense pain.
III. Stimulants Caffeine (very mild).	Cocaine. Amphetamines	Stimulates the nervous systems makes a person more wakeful, increases alertness and activity, produces excitement.
IV. Hallucinogens	LSD. Mescal in. psilocybin. Bhang. Ganja. Charas. Marijuana	Alters thought feelings and perceptions cause illusions.

Opioids bind to opioid receptors in the central nervous system and gastrointestinal tract. These suppress brain activity and relieve pain. These are called pain killers e.g. opium and its derivatives.

(a) Somniferum (Opium poppy) plant (b) Chemical structure of Morphine

Heroin or smack is diacetylmorphine. It is a white, odorless, bitter crystalline compound. It is formed by the acetylation of morphine, which is extracted from poppy latex. It is a depressant and slows down body functions.

→ The products of the Hemp plant Cannabis Sativa are Bhang, Ganja, Charas, Hashish, and Marijuana. These are less harmful but may lead to opiates addiction. Their active compound is delta-9- tetrahydrocannabinol or THC.

(a) Leaf of Cannabis Sativa
(b) Skeletal structure of cannabinoid molecule

Cocaine or coke is an alkaloid from Erythroxylum coca. It has a potent stimulating effect on the central nervous system, produces a sense of euphoria and increased energy.

→ Datura spp. and Atropabeliadona also have hallucinogenic properties. Cannabinoids are misused by some sportspersons.

→ Other abused drugs are barbiturates, amphetamines, benzodiazepines, and lysergic acid diethyl amides (LSD).

→ The adolescence period is very vulnerable to the mental and psychological development of an individual. Curiosity, adventure and excitement, and experimentation motivate youngsters towards drug and alcohol misuse.

TABLE: SHOWING EFFECTS OF ALCOHOL AND DRUGS

Combination	Effect
Alcohol + barbiturates	Dramatically increased depressant effect
Alcohol + antihistamines	Marked drowsiness
Alcohol + Valium	The rapid increase in the sedative effect
Alcohol + Marijuana or Hashish	Decreased coordination, increased reaction time, impaired judgment
Alcohol + Aspirin	Increased risk of damage to the gastric mucosa

→ Smoking paves the way to hard drugs. Tobacco is derived from Nicotiana tabacum and N, Rustica leaves. Its main constituent is the toxin alkaloid Nicotine. It stimulates the release of adrenaline and nor-adrenaline which cause high blood pressure and increased heartbeat. It is associated with lung cancer, bronchitis, emphysema, coronary heart disease, urinary bladder cancer, throat cancer, gastric ulcer, and oral cavity cancer.

→ Alcohol is obtained from the fermentation of cereals or grains by yeast Saccharomyces cerevisiae and further distillation. It has depressant effects on the central nervous system.

→ The symptoms of addiction include undue excitement, irritable and violent nature, exhausted and drowsy appearance, loss of interest in studies, poor concentration and memory, reduced appetite, vigor, and weight.

→ Parents should keep a watch on their children and seek medical and professional help if needed.

→ Allografting: A graft taken from another person. e.g. skin.

→ Antibody: The proteinous molecules produced to counter the specific antigen.

→ Antigen: A foreign agent which stimulates the immune system to produce antibodies.

→ ARC: AIDS-related complex.

→ Autoimmunity: An immune disorder when the immune system of a person rejects its own body cells.

→ Addiction: Dependency on certain drugs.

→ Anesthetic: Chemical which causes the loss of sensation, e.g. opiates.

→ Benign tumor: Cäncer type which remains localized in the organ affected.

→ Communicable disease: The disease which can be transmitted from an infected person to a healthy person.

→ Cancer: Disease characterized by uncontrolled growth and division leading to tumor formation.

→ Carcinogens: Cancer-causing agents e.g. radiations.

→ Carcinomas: Cancers located in the epithelial tissues. e.g. breast cancer.

→ Congenital diseases: Inborn diseases caused by gene or chromosomal mutations, e.g. hemophilia.

→ Cirrhosis: A liver disease caused by the storage of fats.

→ Co-poisoning: CO of tobacco smoke binds lib of RBCs and decreases their Oxygen carrying capacity.

→ Depressant: Chemical which lowers the activity of CNS, e.g. alcohol.

→ Disease: A condition impairing health.

→ Epidemiology: Mode of transmission of disease.

→ Epidemic: A disease that attacks a large number of people at the same time and in the same region e.g. cholera.

→ Endemic: A disease restricted to a certain region, e.g. sleeping sickness.

→ Gastritis: Inflammation of gastric mucosa.

→ hallucinogens: Chemicals which change thoughts, feelings, and perceptions of a person e.g. LSD.

→ Health: A state of complete physical, mental and social norms.

→ Hypertension: High blood pressure.

→ Immunodeficiency: An immune disorder characterized by a deficiency of B-cells and T-cells in the body.

→ Immunoglobulin: Antibodies (γ-globulins) produced against the antigen.

→ Immunity: Resistance of body towards diseases.

→ Immunosuppression: Immune disorder in which the immune system rejects transplanted organs.

→ Infection: Entry and multiplication of living pathogenic microorganisms in some part of the host’s body.

→ Infestation: Presence of a large number of parasitic organisms on the surface of the host’s body or clothing.

→ Incubation period: Period between infection and appearance of the first symptom of a disease.

→ Leukemia: Blood cancer, increased WBC count of the blood.

→ Metastasis: Spread of cancer.

→ Lymphocytes: Type of WBCs which produce antibodies.

→ Lysozyme: A bacterial protein.

→ Neoplasm: A tumor formed by uncontrolled growth of the tissue in cancer.

→ Neuritis: Inflammation of nervous tissue of the brain.

→ Oncogenes: Cancer-causing genes.

→ Prophylaxis: Prevention of occurrence of a disease.

→ Psychotropic drug: mood-altering drug.

→ Pyrexia: Increase in temperature.

→ Pathogen: An organism causing disease.

→ Pyrogen: A fever-causing substance.

→ Serology: Study f antigen-antibody interactions.

→ Sedative: A chemical that decreases functional efficiency and has a calming effect, e.g. alcohol.

→ Therapy: Mode of treatment of a disease.

→ Tranquilizer: A drug having a calming effect without inducing sleep e.g. valium.

→ Vaccine: An inoculation with dead or weakened or virulent germs, which stimulates the formation of antibodies of the host’s body.

→ Vector: Organism which spreads the disease.

By going through these CBSE Class 12 Biology Notes Chapter 7 Evolution, students can recall all the concepts quickly.

Evolution Notes Class 12 Biology Chapter 7

→ The study of the history of life forms on earth is called Evolutionary Biology.

→ The origin of life on earth can be understood only against the background of the origin of the universe especially earth.

→ The universe is vast. The earth is almost a speck. The universe is about 20 billion years old. The universe comprises huge clusters of galaxies.

→ The Big Bang theory explains to us the origin of the universe. It states that a singular huge explosion laid the foundation of the universe.

→ Most scientists believe that the formation of biomolecules preceded the appearance of the first cellular forms of life.

→ Conventional religious literature tells us that the theory of creation has connotations.

• One, that all living organisms that we see today, were created as such.
• Two, the diversity was always the same since creation and will be the same in the future also.
• Three, that the earth is about 4000 years old.

→ Charles Darwin concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago.

→ According to Darwin, fitness refers ultimately and only to reproduce fitness. Thus, those who are a better fit in an environment, leave more progeny than others. There therefore will survive more and hence are selected by nature. He called it natural selection and implied it as a mechanism of evolution.

→ Comparative anatomy and morphology show similarities and differences between organisms of today and those that existed millions of years ago. Such similarities can be interpreted to understand common ancestors were shared or not.

→ The diversity of life forms on earth has been changing over millions of years.

→ It is believed that variations in a population either due to meiotic recombination during gametogenesis or germ live mutations result in variable fitness in learning fertile progeny.

→ Branching descent and natural selection are the two key concepts o.f the Darwinian Theory of Evolution.

→ Hardy-Weinberg Principle states that allele frequencies in a population are stable and constant from generation to generation. The gene pool remains a constant.

→ Homology is accounted for by the idea of branching descent; study of comparative anatomy, fossils comparative, biochemistry provide evidence for evolution.

→ The story of the evolution of modern man among the stories of the evolution of individual species is most interesting. It appears to parallel the evolution of the human brain and language.

→ Evolutionary Biology: Study of history of life forms on earth.

→ Big Bang Theory: Theory that explains the origin of the universe.

→ Fossils: Remains of hard parts of life forms found in rocks.

→ Divergent evolution: In animals, the same structure developed in different directions due to adaptations to different needs.

→ Homology: It indicates common ancestry.

→ Adaptive Radiation: The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography.