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Class 12 Chemistry Notes students can refer to the Solutions Class 12 Notes Chemistry Chapter 2 https://www.cbselabs.com/solutions-cbse-notes-class-12-chemistry/ Pdf here. They can also access the CBSE Class 12 Solutions Chapter 2 Notes while gearing up for their Board exams.

Solutions Class 12 Notes Chemistry Chapter 2

Solutions Class 12 Notes Chapter 2

1. A solution is a homogeneous mixture of two or 9.
more chemically non-reacting substances.
The components of a solution generally cannot be separated by filtration, settling or centrifuging.
2. A solution may be classified as solid, liquid or a gaseous solution.
3. Solubility is defined as the amount of solute in a saturated solution per 100g of a solvent.
4. The solubility of a gas in a liquid depends upon
(a) the nature of the gas and the nature of the liquid,
(b) the temperature of the system, and
(c) the pressure of the gas.
5. The effect of pressure on the solubility of a gas in a liquid is governed by Henry’s Law. It states that the solubility of a gas in a liquid at a given temperature in directly proportional to the partial pressure of the gas Mathematically, P = KHX where P is the partial pressure of the gas; and X is the mole fraction of the gas in the solution and KH is Henry’s Law constant.
6. The vapour pressure of a liquid is the pressure exerted by its vapour when it is in dynamic equilibrium with its liquid, in a closed container.

Class 12 Chemistry Chapter 2 Notes

7. According to Raoults Law, the vapour pressure of a solution containing a non-volatile solute is directly proportional to the mole fraction of the solvent ( X_A). The proportionality constant being the vapour pressure of the pure solvent, i.e., P× X_A or P = P° X_A.
8. A solution which obeys Raoult’s Law at all concentrations and temperatures is known as an ideal solution.
9. Characteristics of an ideal solution:
(a) ∆_sol V = 0, i.e., there is no change in volume when an ideal solution is formed.
(b) ∆_sol H= 0; i.e., heat is neither evolved nor absorbed during the formation of an ideal solution.
10. (a) The solution shows positive deviation from Raoult’s Law if its vapour pressure is higher than that predicted by Raoult’s Law.
(b) The solution shows negative deviation if its vapour pressure is lower than that predicted by Raoult’s Law.

Solutions Class 12 Chemistry Notes Chapter 2

11. Colligative properties of solutions are those properties which depend only upon the number of solute particles in the solution and not on their nature. Such properties are
(a) Relative lowering in vapour pressure,
(b) Elevation of boiling point,
(c) Depression of freezing point and
(d) Osmotic pressure.
12.

Thus, according to Raoult’s Law, the relative lowering of vapour pressure of a solution is equal to the mole fraction of the solute.
13. For a dilute solution, the elevation in boiling point is found to be proportional to the molality of the

where ∆T_b is the elevation in boiling point, ‘m’ is the molality and K_b is the Molal elevation constant

Chapter 2 Chemistry Class 12 Notes

14. The depression in freezing point (∆T_f) is proportional to the molality of the solution.

where K_f is molal depression constant (freezing point depression constant).
15. The spontaneous flow of solvent molecules from a dilute solution into a concentrated solution when the two are separated by a perfect sernipermeable membrane is called osmosis.
16. Osmotic pressure (π) is the pressure which must be applied to the solution side (more concentrated solution) to just prevent the passage of pure solvent into it through a sernipermeable membrane.
Mathematically, π = CRT= n_B/V- RT
where n is the osmotic pressure of the solution,
C is the concentration of solution
n_B is the number of moles of solute,
V is the volume of the solution in litres,
R is the gas constant, and T is the temperature on the Kelvin scale.

Chemistry Class 12 Chapter 2 Notes

17. Isotonic solutions are those solutions which have the same osmotic pressure. Also they have same molar concentration.
For isotonic solutions, π₁ = π₂ Also, C₁ = C₂
18. Van’t Hoff factor, ‘ i’ is used to express the extent of association or dissociation of solutes in solution. It is die ratio of the normal and observed molar masses of the solute, i. e.,

19. In case of association, observed molar mass being more than the normal, the factor ‘T has a value less than one. But in case of dissociation, the van’t Hoff factor is more than one because the observed molar mass has a less value.
20. In case of solutes which do not undergo any association or dissociation in a solvent, the Vant Hoff factor, ‘i’, will be equal to one because the observed and normal molar masses will be same.

Solutions Notes Class 12 Chapter 2

21. Inclusion of van’t Hoff factor, ‘F, modifies the equations for colligative properties as follows:

HSSLive Chemistry

Class 12 Chemistry Notes students can refer to the The Solid State Class 12 Notes Chemistry Chapter 1 https://www.cbselabs.com/solid-state-cbse-notes-class-12-chemistry/ Pdf here. They can also access the CBSE Class 12 The Solid State Chapter 1 Notes while gearing up for their Board exams.

The Solid State Class 12 Notes Chemistry Chapter 1

Solid State Class 12 Notes Chapter 1

1. Solids are substances which have fixed shape
and volume. 1’hey are characterised by rigidity, incompressibility, slow diffusion and mechanical strength. They are classified as:
(a) Crystalline solids
(b) Amorphous solids .
2. The crystalline solids are further classified as:
(a) Metallic solids
(b) Ionic solids
(c) Covalent solids
(d) Molecular solids
3. A regular three dimensional arrangement of points in space is called a space lattice or crystal lattice. There are only 14 three-dimensional lattices known as Bravais lattices. The basic difference between the 14 Bravais lattices are the angles between the faces and the relative proportion of the sides.
4. A unit cell is the smallest unit of the crystal which when repeated again and again gives the crystal of the given substance.

Class 12 Chemistry Chapter 1 Notes

5. There are three types of unit cells based on the cube. These are:
(a) Primitive or simple cube which has one constituent at each comer.
(b) Body-centred cube in which one constituent at the centre of the cube as well as one at each comer.
(c) Face-centred cube in which there is one constituent at the centre of each face as well as one at each comer.
6. A pure metal in the solid crystalline state is composed of atoms that are identical in shape and size. The identical spheres can be packed in a number of ways.
7. The number of nearest neighbours of an atom, ion or a molecule is called its coordination number.
8. In the hcp and ccp structures, about 74 percent of the available space is occupied by the spheres. In bcc arrangement, about 68 percent of the available space is filled up. In simple cubic structures, about 52.4 percent of the available space is occupied by the spheres.
9. The density of the unit cell, d = \(\frac{ZM}{a^3N_A}\)

Solid State Notes Chapter 1 Class 12

10. Any departure from perfectly ordered arrangement of atoms or ions in crystals is called imperfection or defects. These are of two types:
(a) Point defects (b) Line defects
11. Schottky defects occurs when a pair of ions of opposite charge, i.e., cations and anions are missing from the ideal lattice. The presence of a large number of schottky defects lowers the density of a crystal, e.g., AgBr.
12. The atoms or ions which occupy the normally vacant interstitial sites in a crystal are known as interstitials. It results in increase in density of crystal.
13. Frenkel defects is a combination of schottky defects and interstitials. It occurs when an ion leaves its position in the lattice and occupies an interstitial site leaving a gap in the crystal.
14. Non-stoichiometric defects are a large number of inorganic solids in which the ratio of the number of atoms of one kind to the number of atoms of the other kind does not correspond to the ideal whole number ratio. Such compounds are called non-stoichiometric compounds.
15. When there is an excess of metal ions in non- stoichiometric compounds, the crystal lattice has vacant anion sites. These sites are occupied by electrons. Hie anion sites occupied by electrons are called F-centres.
16. Based on their electrical conductivity, solids are classified as:
(a) Conductors
(b) Insulators
(c) Semi conductors

Chemistry Class 12 Chapter 1 Notes

17. Pure substances that show conducting behaviour like that of silicon and germanium are called intrinsic semiconductors.
18. When solid substances are placed in a magnetic field, they do not show the same behaviour. Depending on their response to magnetic field, the substances are classified as:
(a) Diamagnetic substances:
(i) These substances are weakly repelled by a magnetic field.
(ii) The electrons are paired.
(b) Paramagnetic substances:
(i) These substances are weakly attracted by the magnetic field.
(ii) These substances have permanent magnetic dipoles due to die presence of atoms, molecules or ions containing unpaired electrons.

Solid State Notes Class 12 Chapter 1

19. Substances having unpaired electrons are classified as:

students can refer to the Environmental Issues – CBSE Notes for Class 12 Biology https://www.cbselabs.com/environmental-issues-cbse-notes-class-12-biology/ Pdf here. They can also access the CBSE Class 12 Environmental Issues Notes while gearing up for their Board exams.

Environmental Issues – CBSE Notes for Class 12 Biology

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Environmental Issues Class 12 Notes

Pollution, Solid and Radioactive Wastes:
1. Pollution is an undesirable change’in the physical, chemical and biological characteristics of air, water, land and soil.
(i) Pollutants are agents that cause undesirable change in the environment.
(ii) The Government of India has passed the Environment Protection Act, 1986 to protect and improve the quality of our environment (air, water and soil).
2. Air pollution occurs due to undesirable change in the physical, chemical and biological characteristics of air that exerts harmful effects on human beings.
(i) Causes of Air Pollution
(a) Smoke stacks from thermal power plants, forest fires, volcanic eruptions, etc.
(b) Garbage decomposition also releases unwanted gases in the air.
(c) Excessive use of fossil fuels by automobiles and industries release particulate and air pollutants.
(d) Use of leaded petrol.
(ii) Types of Air Pollutants

(iii) Harmful Effects of Air Pollution on Health
(a) Carbon monoxide (CO) causes giddiness, headache, cardiovascular malfunction, asphyxia, etc.
(b) Hydrogen sulphide (H₂S) causes nausea, eye and throat irritation.
(c) Sulphur dioxide (SO₂) causes respiratory tract diseases like asthma, bronchitis, cancer, emphysema, etc.
(d) Fine particulates released by industries cause breathing and respiratory problems, inflammation and damage to the lungs.
(e) In plants reduced growth and yield and premature death occurs.
(iv) Control Methods of Air Pollution
There are several methods used for controlling air pollution in India.
These are:
(a) Electrostatic Precipitator (ESP) is an electrical device to remove particulate matter present in the exhaust of thermal power plant.

• About 99% of particulate matter can be removed by ESP.
• It has electrode wires and a stage of collecting plates.
• Electrode wires are provided with an electric current of several thousand volts, which produces a corona that releases electrons.
Discharged corona Negatively charged wire
• These electrons get attach to the dust Electrostatic precipitatorn particles and give them negative charge within a small fraction of a second.
• Collecting plates are grounded that attract the charged dust particles.
• The velocity of air between the plates must be low enough to allow the dust to fall.
(b) Scrubber is used to remove harmful gases like sulphur dioxide from industrial exhaust.

The exhaust is passed through a spray of water or lime.
• Water dissolves the gases and lime reacts with sulphur dioxide to form a precipitate of calcium sulphate and sulphide.
* Drawbacks Recently, the dangers of particulate matter that are very small and cannot be removed by these precipitators has been found. According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) if inhaled can cause breathing and respiratory problems, irritation, damage to lungs and premature deaths.
(c) Catalytic convertors are fitted into automobiles for
reducing emission of poisonous gases like NO₂ and CO.
• They are made of expensive metals like platinum, palladium and rhodium as catalysts.
• When exhaust passes through the catalytic convertor, nitric oxide splits into nitrogen and oxygen; carbon monoxide is oxidised into carbon dioxide and unburnt hydrocarbons get burnt completely into CO₂ and H₂O.
• Unleaded petrol should be used in motor vehicles fitted with catalytic convertor as leaded petrol inactivates the catalyst.
(i) A Case Study— Control of Air Pollution in Delhi
(a) Delhi leads the country in high levels of air pollution due to large numbers of vehicles. In 1990s, Delhi ranked fourth among the 41 most polluted cities of the world.
(b) As per directives of Supreme Court, all buses of Delhi were converted to run on Compressed Natural Gas (CNG) by the end of 2002.
(c) Benefits of CNG over diesel/petrol
* Burns most efficiently and leaves no unburnt remains.
– Cheaper than diesel/petrol.
* Cannot be siphoned off by thieves and adulterated like petrol or diesel.
(d) Other ways to reduce vehicular pollution
* Phasing out of old vehicles.
* Use of unleaded petrol.
* Use of low-sulphur petrol and diesel.
* Application of stringent pollution-level norms for vehicles.
* Use of catalytic convertors in vehicles.
(vi) Auto Fuel Policy of Government of India
(a) Euro II norms stipulate that sulphur be controlled at 350 parts per million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42% of the concerned fuel.
(b) According to it, all automobiles have to meet the Euro III emission specification in eleven Indian cities by 1 April, 2005.
(c) The same eleven cities have to meet the Euro IV norms by 1 April, 2010.
(d) The rest of the country will have Euro III emission norm compliant automobiles and fuels by 2010.
(e) By all these efforts, a substantial fall in CO₂ and SO₂ level has been found in Delhi between 1997 and 2005.

Environmental Issues Class 12 Notes Pdf 

3. Noise pollution is undesirable high level of sound. In India, the Air (Prevention and Control of Pollution) Act came into force in 1881, but was amended in 1987 to includes noise as art air pollutant.
Noise measurement Sound is expressed in decibels (dB). A sound of over 115 dB is very harmful for ears. Prolonged exposure to noise level above 80 dB leads to perma nent hearing loss.
(i) Causes are
(a) Use of loudspeakers and music systems. (b) Jet planes and rockets take-off.
(c) Industrial, factory noises, etc.
(ii) Harmful effects are sleeplessness, stress, increased heartbeat, breathing problems, damage to ear drums and impaired hearing ability.
(iii) Control Methods
(a) By applying sound-absorbent materials or by muffling noise in industrial units.
(b) Delimitation of horn-free zones around hospitals and schools.
(c) Strict laws for permissible sound levels of crackers and loudspeakers should be followed.
(d) Loudspeakers should be played up to a fixed time only.

Environmental Issues Notes Class 12

4. Water pollution is any undesirable change in the physical, chemical or biological properties of water that may affect the human beings and aquatic species.
(ii) The Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974 to safeguard our water resources.
(ii) Sources of Water Pollution
(a) Domestic sewage includes everything that comes from residential area to common public sewage system. A mere 0.1% impurities make domestic sewage unfit for human use.
Composition of domestic sewage
* Suspended solids, e.g. sand, silt and clay.
* Colloidal material, e.g. faecal matter, bacteria, cloth and paper fibres.
* Dissolved materials, e.g. nutrients (nitrate, ammonia, phosphate, sodium and calcium).
* It mainly contains biodegradable organic wastes, which are readily decomposed with the help of decomposers.
(b) Industrial wastes are released by petroleum, paper manufacturing, metal • It contains heavy metals like mercury and many organic compounds.
(iii) Effects of Water Pollution

(a) Biological magnification can be defined as the increase in concentration of toxicants at successive trophic levels.
• Mercury and DDT are well known for biological magnification.
• Toxic materials cannot be metabolised or excreted. Therefore, they get accumulated in an organism and pass on to higher trophic levels.
• DDT accumulates in birds and disturbs calcium metabolism, which results in thinning of egg shell. This results in decline of bird population.
(b) Eutrophication can be defined as the natural ageing of a lake by nutrient enrichment of its water.
Process of Eutrophication
• Water in young lake is cold and clear to support life.
• Gradually with time, it gets enriched with nutrients as nitrogen and phosphorus by streams draining in it.
• Due to this, aquatic life (plants and animals) flourish in lake.
• Organic remains deposit at the bottom of the lake and with time, water becomes warmer.
Eventually, floating plants develop in the lake, finally converting it into land. This accelerated ageing of lakes due to sewage, agricultural and industrial wastes is called cultural or accelerated eutrophication.
(c) Biochemical Oxygen Demand (BOD) is the amount of oxygen required for microbial breakdown of biodegradable organic matter. It is higher in polluted water and lesser in clean water.

(d) Algal bloom is excessive growth of planktonic (free-floating) algae in aquatic bodies.
• In domestic sewage, nutrients like nitrogen and phosphorus favours the growth of algal bloom.
• It causes fish mortality and deterioration of water quality.
Example, Excessive growth of water hyacinth (Eichhornia crassipes). It is the most problematic aquatic weed, also called Terror of Bengal.
It grows abundantly in eutrophic water bodies and imbalances water ecosystem.
(vi) A Case Study— Integrated Wastewater Management
(a) Wastewater including sewage can be treated in an integrated manner by utilising a mix of artificial and natural processes.
• One such example is town of Areata situated along Northern coast of California. An integrated wastewater treatment process was developed with the help of biologists from Humboldt State University in this town.
• The cleaning occurs in two steps:
— The conventional sedimention, filtrating and chlorine treatment is carried out.
The treated water still contain lots of heavy metals and other toxic pollutants.
– In second step, algae, fungi and bacteria are grown in marsh land through which water flowed. These life forms neutralise, absorb and assimilate the pollutants and purify the water naturally.
The marshes also constitute a sanctuary, with a high level of biodiversity.
(b) Ecosan toilets have been developed in areas of Kerala and Sri Lanka for ecological sanitation. The advantages of ecological sanitation are:
• A practical, hygienic and efficient method of disposal.
• Cost effective approach.
• Human excreta can be recycled into natural fertiliser to reduce need of chemical fertiliser.

Class 12 Biology Chapter 16 Notes

5. Solid wastes refer to everything that goes out in trash. The various types are:
(i) Municipal solid wastes contain wastes from homes, offices, schools, hospitals, etc., that are collected and disposed by the municipality, which generally consists of paper, leather, textile, rubber and glass, metals and plastic, etc.
(ii) Industrial wastes contain wastes like scraps, fly ash, etc., generated by industries.
(Hi) Hospital wastes contain disinfectants and other harmful chemicals generated by
hospitals.
(iv) Electronic wastes (e-wastes) are the damaged electronic goods and irreparable computers.
(a) Methods of Solid Waste Disposal
There are various methods of solid waste disposal. Some of them are:
• Open burning involves burning of municipal waste in open dumps but the unburnt piled waste serves as breeding ground for rats and flies.
• Sanitary landfills are areas where wastes are dumped in a depression or trench after compaction and covered with dirt. The problem is seepage of chemicals from these landfills can pollute underground water resources.
• Rag-pickers and kabadiwallas collect and separate out wastes into reusable or recyclable categories.
• Natural breakdown involves dumping biodegradable materials into deep pits for natural degradation.
• Incineration is a method of hospital waste disposal.
• E-Wastes
– E-wastes are buried in landfills or in ~inerated.
– About half of the e-wastes generated in the developed world are exported to developing countries, mainly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during recycling process.
– Developed countries have specifically built facilities for recycling of e-wastes.
– Recycling is only solution available for treating e-waste but caution should be taken to carry out process environment friendly.
(b) A Case Study — Remedy for Plastic Waste
• A plastic sack manufacturer, Ahmad Khan from Bengaluru realised that plastic waste was a real problem.
His company developed a fine powder, called polyblend of recycled modified plastic.
• This mixture is mixed with the bitumen and used to lay roads.
• It enhanced the bitumen’s water repellant properties and helped to increase road life by a factor of three.
• Using this technique, by the year 2002, more than 40 kms of road in Bengaluru has already been laid.

Environmental Issues Class 12 Ncert Notes

6. Soil pollution is any undesirable change in soil profile affecting its productivity.
(i) Green revolution led to manifold increase in crop production by the use of inorganic fertilisers and pesticides.
(ii) Pesticides, herbicides, fungicides, etc., are being increasingly used afterwards which resulted in so’l pollution.
(iii) Causes of Soil Pollution
(a) Chemical seepage from industries.
(b) Excessive use of inorganic fertilisers, pesticides, etc.
(iv) Harmful Effects of Soil Pollution
(a) Non-target organisms are killed in the soil.
(b) Soil becomes unfertile.
(c) Pesticides can result in biomagnification.
(vi) Control Methods
(a) Strict ways should be adopted by the industries and other sources for waste disposal.
(b) Use of organic farming It is a cyclical, zero-waste method, where waste products from one process are cycled in as nutrients for other processes, allowing maximum utilisation of resources and increasing the efficiency of production.
(ini) A Case Study— Organic Fanning
(a) Ramesh Chandra Dagar, a farmer in Sonipat (Haryana) included bee-keeping, dairy management, water harvesting, composting and agriculture in a chain of processes.
(b) This chain supports each other and allow an extremely economical and sustainable venture.
(c) Chemical fertilisers are not required as cattle excreta is used as manure.
(d) Crop waste is used for making compost, which is used as natural fertiliser or to generate natural gas, which is used for satisfying energy needs of farm.
(e) To spread information and help the practice of integrated organic farming. Dagar has created the Haryana Kisan Welfare club, with current membership of
5000 farmers.
7. Radioactive wastes include nuclear waste, which is given off as radiation.
(i) Nuclear energy was initially considered as a non-polluting way for generating electricity initially.
(ii) Later, two serious inherent problems were realised. The first is accidental leakages as occurred in the Three Mile Island and Chernobyl, which proved that radioactive wastes are most potent pollutants. The second is safe disposal of radioactive wastes.
(iii) Harmful Effects
(a) Radiations causes mutation at a very high rate.
(b) At high doses, nuclear radiations are lethal.
(c) At low doses, these cause disorders and diseases like cancer.
(iv) Disposal method of radioactive wastes involve pretreatment and storage in shielded containers and then burying at about 500m deep below the earth’s surface. However, this method of disposal is getting opposition from public.

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students can refer to the Biodiversity and Conservation – CBSE Notes for Class 12 Biology https://www.cbselabs.com/biodiversity-conservation-cbse-notes-class-12-biology/ Pdf here. They can also access the CBSE Class 12 Biodiversity and Conservation Notes while gearing up for their Board exams.

Biodiversity and Conservation – CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

Biodiversity And Conservation Class 12 Notes

Biodiversity:
1. Biodiversity can be defined as the occurrence of different types of genes, gene pools, species, habitats and ecosystem in a given region.
(i) The term biodiversity was given by a socio biologist Edward Wilson to describe the combined diversity at all the levels of biological organisation.
(ii) There are more than 20,000 species of ants, 3,00,000 species of beetles, 28,000 species of fishes and nearly 20,000 species of orchids.
(iii) Biodiversity can be divided into following three levels:
(a) Genetic diversity is the diversity at the genetic level.
• It enables a population to adapt to its environment.
• India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.
Example, Genetic variation in the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces.
(b) Species diversity is diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
(c) Ecological diversity is the diversity at ecosystem level. For example, India with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries and alpine meadows has a greater ecosystem diversity.

Biodiversity And Conservation Class 12

2. Global species diversity means total species present on the earth.
(i) According to IUCN (2004) the total number of plant and animal species is slightly more than 1.5 million.
(ii) For many taxonomic groups, species inventories are more complete in temperate than in tropical countries.
(iii) A more conservative and scientifically sound estimate by Robert May, places the global species diversity at about 7 million.
(iv) More than 70% of all the species recorded are animals, while plants comprise no more than 22% of the total.
(v) Among animals, insects are most species rich-taxonomic group, making about 70% of the total. It means, out of every 10 animals, 7 are insects on the earth.
3. Biodiversity in India
(i) Although India has only 2.4% of the world’s land area, its share of the global species diversity is 8.1%. This makes India one of the 12 megadiversity countries of the world.
(ii) About 45,000 species of plants and twice as many of animals have been recorded from India.

(iii) According to May’s global estimates, only 22% of the total species have been recorded so far. If this proportion.is applied to India’s diversity figures, there may be probably more than 1,00,000 plant species and more than 3,00,000 animal species yet to be discovered and described.

Biodiversity And Its Conservation Notes Class 12

4. Patterns of biodiversity indicate that the biodiversity is not uniform throughout the world because it is affected by:
(i) Latitudinal gradients demonstrates the decrease in species diversity as we move away from the equator towards the poles.
(a) Tropics (latitudinal range of 23.5°N to 23.5°S) harbour more species than temperate or polar areas.
(b) Example, Colombia located near the equator has around 1,400 species of birds, while New York at 41°N has 105 species and greenland at 71°N has only 56 species.
(c) Studies indicate that the tropical areas have more biodiversity.
For example,
• India with much of its land area in the tropical latitudes, has more than 1,200 species of birds.
• A tropical forest in equator has up to 10 times as many species of vascular plants as a forest of equal area in a temperate region like the midwest of USA.
• Tropical Amazonian rainforest in South America has the greatest biodiversity on earth. It homes 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles and of more than 1,25,000 invertebrates.
• Scientists estimate that in these rainforests, there might be at least 2 million insect species waiting to be discovered and named.
(d) Reasons for Greater Biodiversity in Tropics
• Speciation is generally a function of time. The temperate regions were subjected to frequent glaciation in the past, but the tropics have remained undisturbed and hence, had evolved more species diversity.
• Tropical environments, unlike temperates are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
• More solar energy is available in tropics, which contributes to higher productivity, this in turn might contribute indirectly to greater diversity.
(ii) Species-Area Relationships
(a) Alexander Von Humboldt, a German naturalist and geographer observed that within a region, species richness increased with increasing explored area, but up to a limit.
(b) In fact, the relation between species richness and area for a wide variety of taxa (like angiosperm plants, birds, bats and freshwater fishes) turn out to be rectangular hyperbola.

(c) On a logarithmic scale, the relationship is a straight line as given in the following equation
log S = log C + Z log A where, S = Species richness, A=Area
C = Y-intercept, Z = Slope of the line (regression coefficient)
(d) The value of Z lies in the range of 0.1-0.2 regardless of taxonomic group or the region.
(e) If we analyse the species-area relationship among very large areas like the entire continents, the slope of the line will be much steeper, i.e. Z values in the range of 0.6-1.2. For example, for fruit eating birds and mammals in the tropical forests of different continents, the slope is found to be 1.15.

Biodiversity And Conservation Notes Class 12

5. Importance of Species Diversity to the Ecosystem
(i) According to ecologists, communities with more species tend to be more stable than those with less species.
(ii) Attributes of a stable community are
(a) It should not show too much variation in productivity from year to year.
(b) It must be either resistant or resilient to occasional disturbances (natural or man made).
(c) It must be resistant to invasions by alien species.
(iii) David Tilman’s longterm experiments on ecosystem found that plots with more species showed less year-to-year variation in total biomass. He also showed that increased diversity contributed to higher productivity.
(iv) It is not clear how species richness contributes to the well-being of an ecosystem. But, it is enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the survival of the human race on this planet.
(v) Paul Ehrlich through his rivet popper hypothesis tried to explain the importance of biodiversity for the survival of species.
(a) The hypothesis assumes the ecosystem to be an airplane and the species to be the rivets joining all parts together.
(b) If every passenger pops a rivet to take home (resulting in species extinction), it may not affect the flight safety initially (proper ecosystem functioning) but with time as more and more rivets are removed, the plane becomes dangerously weak.
(c) Loss of rivet on the wings (key species that drives major ecosystem functions) is a more serious threat to flight safety than loss of a few rivets on the seats or windows of the plane.

Biodiversity Class 12

6. Loss of biodiversity is caused by the over population, urbanisation and industrialisation.
(i) The colonisation of tropical Pacific Islands by humans have led to the extinction of more than 2,000 species of native birds.
(ii) The IUCN Red list (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
(iii) Some latest examples of recent extinctions are dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s sea cow (Russia) and three sub-species (Bali, Javan and Caspian) of tiger.
(iv) The last twenty years alone have witnessed the disappearance of 27 species.
(v) Presently, 12% of bird species, 23% of all mammal species, 32% of all amphibian species and 31% of all gymnosperm species in the world face the threat of extinction.
(vi) Careful analysis of records shows that amphibians appear to be more vulnerable to extinction.
(vii) The grim scenario of extinctions is the fact that more than 15,500 species world wide are facing the threat of extinction.

Notes Of Biodiversity And Conservation Class 12

Results of Loss of Biodiversity in a Region
(a) Decline in plant production.
(b) Lowered resistance to environmental perturbations, such as drought.
(c) Increased variability in certain ecosystem processes such as plant productivity, water use, pest and disease cycles.
Causes of Biodiversity Losses
These are mainly four as given below. They are also named as The Evil Quartet.
(i) Habitat Loss and Fragmentation
(a) The main cause of extinction of species is the destruction of their habitat
(b) Examples,
• Tropical rainforests once covering more than 14% of the land surface, now cover only 6% of land area.
• Amazon rainforest (called lungs of the planet) is being cut and cleared for the cultivation of soybeans and for conversion to grasslands for raising beef cattle.
(c) When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to their population decline.
(d) The degradation of many habitats by pollution also threatens the survival of many species, many have extincted in last 500 years.
(ii) Over-exploitation of natural resources by humans results in degradation and extinction of the resources. For example, Steller’s sea cow, passenger pigeon and many marine fishes have extincted in last 500 years.
(iii) Alien (exotic) Species Invasions
When alien (exotic) species are introduced unintentionally or deliberately, some become invasive and cause harmful impact resulting in extinction of the indigenous species. Examples,
(a) Nile perch a large predator fish when introduced in Lake Victoria (East Africa) caused the extinction of an ecologically unique species of cichlid fish in the lake.
(b) Invasive weed species like Parthenium (carrot grass), Lantana and Eichhornia (water hyacinth) caused environmental damage and pose threat to native species.
(c) The recent example is of the African cat fish (Clarias gariepinus) introduced for aquaculture purpose, is posing a threat to the indigenous cat fishes of Indian rivers.
(iv) Co-extinctions When a species become extinct, the plant and animal species associated with it in an obligatory manner, also become extinct. For example, if the host species becomes extinct, all those parasites exclusively found on it will also become extinct. In plant pollinator mutualism, extinction of one results in the extinction of the other.

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students can refer to the Ecosystem – CBSE Notes for Class 12 Biology https://www.cbselabs.com/ecosystem-cbse-notes-class-12-biology/ Pdf here. They can also access the CBSE Class 12 Ecosystem Notes while gearing up for their Board exams.

Ecosystem – CBSE Notes for Class 12 Biology

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Ecosystem Class 12 Notes

Ecosystem—Structure and Function,- Productivity and Decomposition:
1. An ecosystem is a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. The word ‘Ecosystem’ was coined by Sir AG Tansley (1935).
2. The size of an ecosystem varies greatly from a small pond to a large forest or a sea.
3. Ecosystem can be grouped into two main categories:
(i) Terrestrial ecosystem Forest, grassland, desert, etc.
(ii) Aquatic ecosystem Pond, lake, river, wetland, estuary, etc.
4. Crop fields and an aquarium are considered as man-made ecosystems.
5. Structure and Function of Ecosystem
(i) Each ecosystem consists of biotic (autotrophs, herbivores and carnivores) and abiotic components and their interactions with each other results in a physical structure, that is characteristic for each type of ecosystem.
(ii) Identification and enumeration of plant and animal species of an ecosystem gives its specific composition.
(iiii) Vertical distribution of different species occupying different levels is called stratification. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.
(iv) Major functional components of an ecosystem are:
(a) Productivity (b) Decomposition
(c) Energy flow (d) Nutrient cycling
(v) Let us understand these components in a pond ecosystem:
(a) A pond is a shallow water body in which all the above mentioned basic structural and functional components are present.
(b) Abiotic components are water with all the dissolved inorganic and organic materials and soil deposited at the bottom.
(c) Autotrophic components are phytoplanktons, some algae and the floating, submerged and marginal plants found at the edges.
(d) Consumers are zooplanktons, which are free swimming and bottom dwellers.
(e) Decomposers are the fungi, bacteria and flagellates found abundantly in the bottom.
(f) Functioning of pond ecosystem occurs in following steps:
* Autotrophs convert inorganic material into organic material with the help of solar energy.
* Heterotrophs consume autotrophs.
* Decomposers decompose dead organic materials and mineralise it to release them back for reuse by the autotrophs.
* The above events are repeated again and again.
Unidirectional movement of energy occur towards the higher trophic levels and lost in the form of heat to the environment.

Ecosystem Class 12

6. Productivity is the rate of biomass production. It is expressed in g^-2 yr^-1 or (kcal m^-2) yr^-1.
(i) The amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis is called primary production.
(ii) The primary productivity can be divided into:
(a) Gross Primary Productivity (GPP) of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration.
(b) Net Primary Productivity (NPP) is gross primary productivity minus respiratory losses (R).
NPP = GPP – R
NPP is the available biomass for the consumption to heterotrophs, i.e. herbivores and decomposers.
(iii) Secondary productivity is defined as the rate of formation of new organic matter by . consumers.
(iv) Primary productivity of an ecosystem depends on:
(a) Plant species inhabiting a particular area.
(b) Availability of nutrients.
(c) Photosynthetic capacity of plants.
(d) Variety of environmental factors.
(v) Annual net primary productivity of the whole biosphere is about 170 billion tons (dry weight) of organic matter. Of this, despite of occupying about 70% of the surface of earth, the productivity of the oceans are only 55 billion tons.

Ecosystem Notes Class 12

7. Decomposition is the process in which decomposers breakdown complex organic matter into inorganic substances like carbon dioxide, water and nutrients.
(i) The raw materials called detritus are dead plant remains such as leaves, barks, flowers and dead remains of animals, including faecal matter.
(ii) Process of decomposition occurs in the following steps:
(a) Fragmentation is the breakdown of detritus into smaller particles by detritivores, e.g. earthworm.
(b) Leaching is the process by which water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
(c) Catabolism is the process of degradation of detritus into simple inorganic substances by bacterial and fungal enzymes.
(d) Humification is the process of accumulation of a dark coloured amorphous substance called humus. It is highly resistant to microbial action, undergoes decomposition at an extremely slow rate and serves as a reservoir of nutrients.
(e) Mineralisation is the process by which humus is further degraded by some microbes to release inorganic substances.

Class 12 Biology Chapter 14 Notes

Leaves partially consumed by decomposers such as fungi and bacteria.
They begin to lose form and become litter.
Diagrammatic representation of decomposition cycle in a terrestrial ecosystem
(iii) Decomposition rate depends on
(a) Oxygen availability
(b) Chemical composition of detritus
(c) Climatic factors
(d) Temperature and soil moisture
(iv) Decomposition rate is slower, if detritus is rich in lignin and chitin. It is quicker, if detritus is rich in nitrogen and water soluble substances like sugars.
(v) Warm and moist environment speeds up decomposition, whereas low temperature and anaerobiosis inhibits decomposition and causes the formation of organic materials.

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