class xii chapter 13 – organisms and populations...

Class XII Chapter 13 – Organisms and Populations Biology

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Question 1:

How is diapause different from hibernation?

Answer

Diapause is a stage of suspended development to cope with unfavourable conditions.

Many species of Zooplankton and insects exhibit diapause to tide over adverse climatic

conditions during their development.

Hibernation or winter sleep is a resting stage where in animals escape winters (cold) by

hiding themselves in their shelters. They escape the winter season by entering a state of

inactivity by slowing their metabolism. The phenomenon of hibernation is exhibited by

bats, squirrels, and other rodents.

Question 2:

If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why

or why not?

Answer

If a marine fish is placed in a fresh water aquarium, then its chances of survival will

diminish. This is because their bodies are adapted to high salt concentrations of the

marine environment. In fresh water conditions, they are unable to regulate the water

entering their body (through osmosis). Water enters their body due to the hypotonic

environment outside. This results in the swelling up of the body, eventually leading to

the death of the marine fish.

Question 3:

Define phenotypic adaptation. Give one example.

Answer

Phenotypic adaptation involves changes in the body of an organism in response to

genetic mutation or certain environmental changes. These responsive adjustments occur

in an organism in order to cope with environmental conditions present in their natural

habitats. For example, desert plants have thick cuticles and sunken stomata on the

surface of their leaves to prevent transpiration. Similarly, elephants have long ears that

act as thermoregulators.


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Question 4:

Most living organisms cannot survive at temperature above 45°C°. How are some

microbes able to live in habitats with temperatures exceeding 100°C?

Answer

Archaebacteria (Thermophiles) are ancient forms of bacteria found in hot water springs

and deep sea hydrothermal vents. They are able to survive in high temperatures (which

far exceed 100°C) because their bodies have adapted to such environmental conditions.

These organisms contain specialized thermo-resistant enzymes, which carry out

metabolic functions that do not get destroyed at such high temperatures.

Question 5:

List the attributes that populations but not individuals possess.

Answer

A population can be defined as a group of individuals of the same species residing in a

particular geographical area at a particular time and functioning as a unit. For example,

all human beings living at a particular place at a particular time constitute the population

of humans.

The main attributes or characteristics of a population residing in a given area are:-

(a) Birth rate (Natality): It is the ratio of live births in an area to the population of an

area. It is expressed as the number of individuals added to the population with respect

to the members of the population.

(b) Death rate (Mortality): It is the ratio of deaths in an area to the population of an

area. It is expressed as the loss of individuals with respect to the members of the

population.

(c) Sex ratio: It is the number of males or females per thousand individuals.

(d) Age Distribution: It is the percentage of individuals of different ages in a given

population. At any given time, the population is composed of individuals that are present

in various age groups. The age distribution pattern is commonly represented through

age pyramids.

(e) Population density: It is defined as the number of individuals of a population

present per unit area at a given time.


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Question 6:

If a population growing exponentially double in size in 3 years, what is the intrinsic rate

of increase (r) of the population?

Answer

A population grows exponentially if sufficient amounts of food resources are available to

the individual. Its exponential growth can be calculated by the following integral form of

the exponential growth equation:

Nt = No ert

Where,

Nt= Population density after time t

NO= Population density at time zero

r = Intrinsic rate of natural increase

e = Base of natural logarithms (2.71828)

From the above equation, we can calculate the intrinsic rate of increase (r) of a

population.

Now, as per the question,

Present population density = x

Then,

Population density after two years = 2x

t = 3 years

Substituting these values in the formula, we get:

⇒ 2x = x e3r

⇒ 2 = e3r

Applying log on both sides:

⇒ log 2 = 3r log e


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Hence, the intrinsic rate of increase for the above illustrated population is 0.2311.

Question 7:

Name important defence mechanisms in plants against herbivory.

Answer

Several plants have evolved various mechanisms both morphological and chemical to

protect themselves against herbivory.

(1) Morphological defence mechanisms:

(a) Cactus leaves (Opuntia) are modified into sharp spines (thorns) to deter herbivores

from feeding on them.

(b) Sharp thorns along with leaves are present in Acacia to deter herbivores.

(c) In some plants, the margins of their leaves are spiny or have sharp edges that

prevent herbivores from feeding on them.

(2) Chemical defence mechanisms:

(a) All parts of Calotropis weeds contain toxic cardiac glycosides, which can prove to be

fatal if ingested by herbivores.

(b) Chemical substances such as nicotine, caffeine, quinine, and opium are produced in

plants as a part of self-defense.

Question 8:

An orchid plant is growing on the branch of mango tree. How do you describe this

interaction between the orchid and the mango tree?

Answer


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An orchid growing on the branch of a mango tree is an epiphyte. Epiphytes are plants

growing on other plants which however, do not derive nutrition from them. Therefore,

the relationship between a mango tree and an orchid is an example of commensalisms,

where one species gets benefited while the other remains unaffected. In the above

interaction, the orchid is benefited as it gets support while the mango tree remains

unaffected.

Question 9:

What is the ecological principle behind the biological control method of managing with

pest insects?

Answer

The basis of various biological control methods is on the concept of predation. Predation

is a biological interaction between the predator and the prey, whereby the predator

feeds on the prey. Hence, the predators regulate the population of preys in a habitat,

thereby helping in the management of pest insects.

Question 10:

Distinguish between the following:

(a) Hibernation and Aestivation

(b) Ectotherms and Endotherms

Answer

(a) Hibernation and Aestivation

Hibernation Aestivation

1. Hibernation is a state of reduced

activity in some organisms to

escape cold winter conditions.

1. Aestivation is a state of reduced

activity in some organisms to

escape desiccation due to heat in

summers.

2. Bears and squirrels inhabiting cold

regions are examples of animals

that hibernate during winters.

2. Fishes and snails are examples of

organisms aestivating during

summers.

(b) Ectotherms and Endotherms


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Ectotherms Endotherms

1. Ectotherms are cold blooded

animals. Their temperature varies

with their surroundings.

1. Endotherms are warm blooded

animals. They maintain a constant

body temperature.

2. Fishes, amphibians, and reptiles

are ectothermal animals.

2 Birds and mammals are

endothermal animals.

Question 11:

Write a short note on

(a) Adaptations of desert plants and animals

(b) Adaptations of plants to water scarcity

(c) Behavioural adaptations in animals

(d) Importance of light to plants

(e) Effect of temperature or water scarcity and the adaptations of animals.

Answer

(a) Adaptations of desert plants and animals:

(i) Adaptations of desert plants:

Plants found in deserts are well adapted to cope with harsh desert conditions such as

water scarcity and scorching heat. Plants have an extensive root system to tap

underground water. They bear thick cuticles and sunken stomata on the surface of their

leaves to reduce transpiration. In Opuntia, the leaves are entirely modified into spines

and photosynthesis is carried out by green stems. Desert plants have special pathways

to synthesize food, called CAM (C4 pathway). It enables the stomata to remain closed

during the day to reduce the loss of water through transpiration.

(ii) Adaptations of desert animals:

Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are well

adapted to their habitat. The kangaroo rat found in the deserts of Arizona never drinks

water in its life. It has the ability to concentrate its urine to conserve water. Desert

lizards and snakes bask in the sun during early morning and burrow themselves in the

sand during afternoons to escape the heat of the day. These adaptations occur in desert

animals to prevent the loss of water.


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(b) Adaptations of plants to water scarcity

Plants found in deserts are well adapted to cope with water scarcity and scorching heat

of the desert. Plants have an extensive root system to tap underground water. They bear

thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration.

In Opuntia, the leaves are modified into spines and the process of photosynthesis is

carried out by green stems. Desert plants have special pathways to synthesize food,

called CAM (C4 pathway). It enables their stomata to remain closed during the day to

reduce water loss by transpiration.

(c) Behavioural adaptations in animals

Certain organisms are affected by temperature variations. These organisms undergo

adaptations such as hibernation, aestivation, migration, etc. to escape environmental

stress to suit their natural habitat. These adaptations in the behaviour of an organism

are called behavioural adaptations. For example, ectothermal animals and certain

endotherms exhibit behavioral adaptations. Ectotherms are cold blooded animals such as

fish, amphibians, reptiles, etc. Their temperature varies with their surroundings. For

example, the desert lizard basks in the sun during early hours when the temperature is

quite low. However, as the temperature begins to rise, the lizard burrows itself inside the

sand to escape the scorching sun. Similar burrowing strategies are exhibited by other

desert animals. Certain endotherms (warm-blooded animals) such as birds and

mammals escape cold and hot weather conditions by hibernating during winters and

aestivating during summers. They hide themselves in shelters such as caves, burrows,

etc. to protect against temperature variations.

(d) Importance of light to plants

Sunlight acts as the ultimate source of energy for plants. Plants are autotrophic

organisms, which need light for carrying out the process of photosynthesis. Light also

plays an important role in generating photoperiodic responses occurring in plants. Plants

respond to changes in intensity of light during various seasons to meet their

photoperiodic requirements for flowering. Light also plays an important role in aquatic

habitats for vertical distribution of plants in the sea.

(e) Effects of temperature or water scarcity and the adaptations of animals.

Temperature is the most important ecological factor. Average temperature on the Earth

varies from one place to another. These variations in temperature affect the distribution

of animals on the Earth. Animals that can tolerate a wide range of temperature are


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called eurythermals. Those which can tolerate a narrow range of temperature are called

stenothermal animals. Animals also undergo adaptations to suit their natural habitats.

For example, animals found in colder areas have shorter ears and limbs that prevent the

loss of heat from their body. Also, animals found in Polar regions have thick layers of fat

below their skin and thick coats of fur to prevent the loss of heat.

Some organisms exhibit various behavioural changes to suit their natural habitat. These

adaptations present in the behaviour of an organism to escape environmental stresses

are called behavioural adaptations. For example, desert lizards are ectotherms. This

means that they do not have a temperature regulatory mechanism to escape

temperature variations. These lizards bask in the sun during early hours when the

temperature is quite low. As the temperature begins to increase, the lizard burrows itself

inside the sand to escape the scorching sun. Similar burrowing strategy is seen in other

desert animals.

Water scarcity is another factor that forces animals to undergo certain adaptations to

suit their natural habitat. Animals found in deserts such as desert kangaroo rats, lizards,

snakes, etc. are well adapted to stay in their habitat. The kangaroo rat found in the

deserts of Arizona never drinks water in its life. It has the ability to concentrate its urine

to conserve water. Desert lizards and snakes bask in the sun during early morning and

burrow in the sand as the temperature rises to escape the heat of the day. Such

adaptations can be seen to prevent the loss of water.

Question 12:

Define decomposition and describe the processes and products of decomposition.

Answer

Decomposition is the process that involves the breakdown of complex organic matter or

biomass from the body of dead plants and animals with the help of decomposers into

inorganic raw materials such as carbon dioxide, water, and other nutrients. The various

processes involved in decomposition are as follows:

(1) Fragmentation: It is the first step in the process of decomposition. It involves the

breakdown of detritus into smaller pieces by the action of detritivores such as

earthworms.

(2) Leaching: It is a process where the water soluble nutrients go down into the soil

layers and get locked as unavailable salts.


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(3) Catabolism: It is a process in which bacteria and fungi degrade detritus through

various enzymes into smaller pieces.

(4) Humification: The next step is humification which leads to the formation of a dark-

coloured colloidal substance called humus, which acts as reservoir of nutrients for plants.

(5) Mineralization: The humus is further degraded by the action of microbes, which

finally leads to the release of inorganic nutrients into the soil. This process of releasing

inorganic nutrients from the humus is known as mineralization.

Decomposition produces a dark coloured, nutrient-rich substance called humus. Humus

finally degrades and releases inorganic raw materials such as CO2, water, and other

nutrient in the soil.

Question 13:

Give an example for:

(a) An endothermic animal

(b) An ectothermic animal

(c) An organism of benthic zone

Answer

(a) Endothermic animal: Birds such as crows, sparrows, pigeons, cranes, etc. and

mammals such as bears, cows, rats, rabbits, etc. are endothermic animals.

(b) Ectothermic animal: Fishes such as sharks, amphibians such as frogs, and reptiles

such as tortoise, snakes, and lizards are ectothermic animals.

(c) Organism of benthic zone: Decomposing bacteria is an example of an organism

found in the benthic zone of a water body.

Question 14:

Define population and community.

Answer

Population:

A population can be defined as a group of individuals of the same species residing in a



of humans.

Community:


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A community is defined as a group of individuals of different species, living within a

certain geographical area. Such individuals can be similar or dissimilar, but cannot

reproduce with the members of other species.

Question 15:

Define the following terms and give one example for each:

(a) Commensalism

(b) Parasitism

(c) Camouflage

(d) Mutualism

(e) Interspecific competition

Answer

(a) Commensalism:Commensalism is an interaction between two species in which one

species gets benefited while the other remains unaffected. An orchid growing on the

branches of a mango tree and barnacles attached to the body of whales are examples of

commensalisms.

(b) Parasitism: It is an interaction between two species in which one species (usually

smaller) gets positively affected, while the other species (usually larger) is negatively

affected. An example of this is liver fluke. Liver fluke is a parasite that lives inside the

liver of the host body and derives nutrition from it. Hence, the parasite is benefited as it

derives nutrition from the host, while the host is negatively affected as the parasite

reduces the host fitness, making its body weak.

(c) Camouflage:It is a strategy adapted by prey species to escape their predators.

Organisms are cryptically coloured so that they can easily mingle in their surroundings

and escape their predators. Many species of frogs and insects camouflage in their

surroundings and escape their predators.

(d) Mutualism: It is an interaction between two species in which both species involved

are benefited. For example, lichens show a mutual symbiotic relationship between fungi

and blue green algae, where both are equally benefited from each other.

(e) Interspecific competition: It is an interaction between individuals of different species

where both species get negatively affected. For example, the competition between

flamingoes and resident fishes in South American lakes for common food resources i.e.,

zooplankton.


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Question 16:

With the help of suitable diagram describe the logistic population growth curve.

Answer

The logistic population growth curve is commonly observed in yeast cells that are grown

under laboratory conditions. It includes five phases: the lag phase, positive acceleration

phase, exponential phase, negative acceleration phase, and stationary phase.

(a) Lag phase: Initially, the population of the yeast cell is very small. This is because of

the limited resource present in the habitat.

(b) Positive acceleration phase: During this phase, the yeast cell adapts to the new

environment and starts increasing its population. However, at the beginning of this

phase, the growth of the cell is very limited.

(c) Exponential phase: During this phase, the population of the yeast cell increases

suddenly due to rapid growth. The population grows exponentially due to the availability

of sufficient food resources, constant environment, and the absence of any interspecific

competition. As a result, the curve rises steeply upwards.

(d) Negative acceleration phase: During this phase, the environmental resistance

increases and the growth rate of the population decreases. This occurs due to an

increased competition among the yeast cells for food and shelter.

(e) Stationary phase: During this phase, the population becomes stable. The number of

cells produced in a population equals the number of cells that die. Also, the population of

the species is said to have reached nature’s carrying-capacity in its habitat.

A Verhulst−pearl logistic curve is also known as an S-shaped growth curve.


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Question 17:

Select the statement which explains best parasitism.

(a) One organism is benefited.

(b) Both the organisms are benefited.

(c) One organism is benefited, other is not affected.

(d) One organism is benefited, other is affected.

Answer

(d) One organism is benefited, other is affected.

Parasitism is an interaction between two species in which one species (parasite) derives

benefit while the other species (host) is harmed. For example, ticks and lice (parasites)

present on the human body represent this interaction where in the parasites receive

benefit (as they derive nourishment by feeding on the blood of humans). On the other

hand, these parasites reduce host fitness and cause harm to the human body.

Question 18:

List any three important characteristics of a population and explain

Answer

A population can be defined as a group of individuals of the same species, residing in a



of humans.

Three important characteristics of a population are:

(a) Birth rate (Natality): It is the ratio of live births in an area to the population of an

area. It is expressed as the number of individuals added to the population with respect

to the members of the population.

(b) Death rate (Mortality): It is the ratio of deaths in an area to the population of an

area. It is expressed as the loss of individuals with respect to the members of the

population.

(c) Age Distribution: It is the percentage of individuals of different ages in a given

population. At any given time, a population is composed of individuals that are present

in various age groups. The age distribution pattern is commonly represented through

age pyramids.


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Class XII Chapter 14 – Ecosystem Biology

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Question 1:

Fill in the blanks.

(a) Plants are called as_________ because they fix carbon dioxide.

(b) In an ecosystem dominated by trees, the pyramid (of numbers) is _________ type.

(c) In aquatic ecosystems, the limiting factor for the productivity is _________.

(d) Common detritivores in our ecosystem are_________.

(e) The major reservoir of carbon on earth is_________.

Answer

(a) Plants are called as because they fix carbon dioxide.

(b) In an ecosystem dominated by trees, the pyramid (of numbers) is of

type.

(c) In aquatic ecosystems, the limiting factor for productivity is .

(d) Common detritivores in our ecosystem are .

(e) A major reservoir of carbon on Earth is .

Question 2:

Which one of the following has the largest population in a food chain?

(a) Producers

(b) Primary consumers

(c) Secondary consumers

(d) Decomposers

Answer

(d) Decomposers

Decomposers include micro-organisms such as bacteria and fungi. They form the largest

population in a food chain and obtain nutrients by breaking down the remains of dead

plants and animals.

Question 3:

The second trophic level in a lake is-

(a) Phytoplankton


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(b) Zooplankton

(c) Benthos

(d) Fishes

Answer

(b) Zooplankton

Zooplankton are primary consumers in aquatic food chains that feed upon

phytoplankton. Therefore, they are present at the second trophic level in a lake.

Question 4:

Secondary producers are

(a) Herbivores

(b) Producers

(c) Carnivores

(d) None of the above

Answer

(d) None of the above

Plants are the only producers. Thus, they are called primary producers. There are no

other producers in a food chain.

Question 5:

What is the percentage of photosynthetically active radiation (PAR), in the incident solar

radiation.

(a) 100%

(b) 50 %

(c) 1-5%

(d) 2-10%

Answer

(b) 50%

Out of total incident solar radiation, about fifty percent of it forms photosynthetically

active radiation or PAR.

Question 6:

Distinguish between


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(a) Grazing food chain and detritus food chain

(b) Production and decomposition

(c) Upright and inverted pyramid

(d) Food chain and Food web

(e) Litter and detritus

(f) Primary and secondary productivity

Answer

(a) Grazing food chain and detritus food chain

Grazing food chain Detritus food chain

1. In this food chain, energy is

derived from the Sun.

1. In this food chain, energy comes

from organic matter (or detritus)

generated in trophic levels of the

grazing food chain.

2. It begins with producers,

present at the first trophic level.

The plant biomass is then eaten

by herbivores, which in turn are

consumed by a variety of

carnivores.

2. It begins with detritus such as dead

bodies of animals or fallen leaves,

which are then eaten by decomposers

or detritivores. These detritivores are

in turn consumed by their predators.

3. This food chain is usually large. 3. It is usually smaller as compared to

the grazing food chain.

(b) Production and decomposition

Production Decomposition

1. It is the rate of

producing organic

matter (food) by

producers.

2. It is the process of breaking down of complex

organic matter or biomass from the body of

dead plants and animals with the help of

decomposers into organic raw material such as

CO2, H2O, and other nutrients.


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2. It depends on the

photosynthetic

capacity of the

producers.

2. It occurs with the help of decomposers.

3 Sunlight is required

by plants for primary

production.

3. Sunlight is not required for decomposition by

decomposers

(c) Upright and inverted pyramid

Upright pyramid Inverted pyramid

1. The pyramid of energy is always

upright.

1. The pyramid of biomass and the

pyramid of numbers can be

inverted.

2. In the upright pyramid, the number

and biomass of organisms in the

producer level of an ecosystem is

the highest, which keeps on

decreasing at each trophic level in a

food chain.

2. In an inverted pyramid, the

number and biomass of

organisms in the producer level

of an ecosystem is the lowest,

which keeps on increasing at

each tropic level.

(d) Food chain and Food web

Food chain Food web

1. It is a single linear sequence of

organisms.

1. It contains a number of

interconnected food chains.

2. Members present at higher trophic

levels feed on single types of

organisms.

2. One organism has alternate

food sources.

(e) Litter and detritus


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Litter Detritus

1. Litter contains all kinds of wastes

generated above the ground.

1. Detritus is composed of the

remains of dead plants and

animals.

2. Litter contains both biodegradable

and non-biodegradable matter.

2. Detritus contains only

biodegradable matter.

(f) Primary and secondary productivity

Primary productivity Secondary productivity

1. It is defined as the amount of

organic matter produced by

producers per unit area over a

period of time.

1. It is defined as the rate of

production of organic matter by

consumers over a period of time.

Question 7:

Describe the components of an ecosystem.

Answer

An ecosystem is defined as an interacting unit that includes both the biological

community as well as the non-living components of an area. The living and the non-

living components of an ecosystem interact amongst themselves and function as a unit,

which gets evident during the processes of nutrient cycling, energy flow, decomposition,

and productivity. There are many ecosystems such as ponds, forests, grasslands, etc.

The two components of an ecosystem are:

(a) Biotic component: It is the living component of an ecosystem that includes biotic

factors such as producers, consumers, decomposers, etc. Producers include plants and

algae. They contain chlorophyll pigment, which helps them carry out the process of

photosynthesis in the presence of light. Thus, they are also called converters or

transducers. Consumers or heterotrophs are organisms that are directly (primary

consumers) or indirectly (secondary and tertiary consumers) dependent on producers for

their food.


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Decomposers include micro-organisms such as bacteria and fungi. They form the largest

population in a food chain and obtain nutrients by breaking down the remains of dead

plants and animals.

(b) Abiotic component: They are the non-living component of an ecosystem such as

light, temperature, water, soil, air, inorganic nutrients, etc.

Question 8:

Define ecological pyramids and describe with examples, pyramids of number and

biomass.

Answer

An ecological pyramid is a graphical representation of various ecological parameters such

as the number of individuals present at each trophic level, the amount of energy, or the

biomass present at each trophic level. Ecological pyramids represent producers at the

base, while the apex represents the top level consumers present in the ecosystem. There

are three types of pyramids:

(a) Pyramid of numbers

(b) Pyramid of energy

(c) Pyramid of biomass

Pyramid of numbers:It is a graphical representation of the number of individuals

present at each trophic level in a food chain of an ecosystem. The pyramid of numbers

can be upright or inverted depending on the number of producers. For example, in a

grassland ecosystem, the pyramid of numbers is upright. In this type of a food chain, the

number of producers (plants) is followed by the number of herbivores (mice), which in

turn is followed by the number of secondary consumers (snakes) and tertiary carnivores

(eagles). Hence, the number of individuals at the producer level will be the maximum,

while the number of individuals present at top carnivores will be least.


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On the other hand, in a parasitic food chain, the pyramid of numbers is inverted. In this

type of a food chain, a single tree (producer) provides food to several fruit eating birds,

which in turn support several insect species.

Pyramid of biomass

A pyramid of biomass is a graphical representation of the total amount of living matter

present at each trophic level of an ecosystem. It can be upright or inverted. It is upright

in grasslands and forest ecosystems as the amount of biomass present at the producer

level is higher than at the top carnivore level. The pyramid of biomass is inverted in a

pond ecosystem as the biomass of fishes far exceeds the biomass of zooplankton (upon

which they feed).


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Question 9:

What is primary productivity? Give brief description of factors that affect primary

productivity.

Answer

It is defined as the amount of organic matter or biomass produced by producers per unit

area over a period of time.

Primary productivity of an ecosystem depends on the variety of environmental factors

such as light, temperature, water, precipitation, etc. It also depends on the availability of

nutrients and the availability of plants to carry out photosynthesis.

Question 10:

Define decomposition and describe the processes and products of decomposition.

Answer

Decomposition is the process that involves the breakdown of complex organic matter or

biomass from the body of dead plants and animals with the help of decomposers into

inorganic raw materials such as carbon dioxide, water, and other nutrients. The various

processes involved in decomposition are as follows:

(1) Fragmentation: It is the first step in the process of decomposition. It involves the

breakdown of detritus into smaller pieces by the action of detritivores such as

earthworms.

(2) Leaching: It is a process where the water soluble nutrients go down into the soil

layers and get locked as unavailable salts.

(3) Catabolism: It is a process in which bacteria and fungi degrade detritus through

various enzymes into smaller pieces.

(4) Humification: The next step is humification which leads to the formation of a dark-

coloured colloidal substance called humus, which acts as reservoir of nutrients for plants.

(5) Mineralization: The humus is further degraded by the action of microbes, which

finally leads to the release of inorganic nutrients into the soil. This process of releasing

inorganic nutrients from the humus is known as mineralization.

Decomposition produces a dark coloured, nutrient-rich substance called humus. Humus

finally degrades and releases inorganic raw materials such as CO2, water, and other

nutrient in the soil.


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Question 11:

Give an account of energy flow in an ecosystem.

Answer

Energy enters an ecosystem from the Sun. Solar radiations pass through the atmosphere

and are absorbed by the Earth’s surface. These radiations help plants in carrying out the

process of photosynthesis. Also, they help maintain the Earth’s temperature for the

survival of living organisms. Some solar radiations are reflected by the Earth’s surface.

Only 2-10 percent of solar energy is captured by green plants (producers) during

photosynthesis to be converted into food. The rate at which the biomass is produced by

plants during photosynthesis is termed as ‘gross primary productivity’. When these

green plants are consumed by herbivores, only 10% of the stored energy from producers

is transferred to herbivores. The remaining 90 % of this energy is used by plants for

various processes such as respiration, growth, and reproduction. Similarly, only 10% of

the energy of herbivores is transferred to carnivores. This is known as ten percent law of

energy flow.

Question 12:

Write important features of a sedimentary cycle in an ecosystem.

Answer

Sedimentary cycles have their reservoirs in the Earth’s crust or rocks. Nutrient elements

are found in the sediments of the Earth. Elements such as sulphur, phosphorus,

potassium, and calcium have sedimentary cycles.


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Sedimentary cycles are very slow. They take a long time to complete their circulation

and are considered as less perfect cycles. This is because during recycling, nutrient

elements may get locked in the reservoir pool, thereby taking a very long time to come

out and continue circulation. Thus, it usually goes out of circulation for a long time.

Question 13:

Outline salient features of carbon cycling in an ecosystem

Answer

The carbon cycle is an important gaseous cycle which has its reservoir pool in the

atmosphere. All living organisms contain carbon as a major body constituent. Carbon is a

fundamental element found in all living forms. All biomolecules such as carbohydrates,

lipids, and proteins required for life processes are made of carbon. Carbon is

incorporated into living forms through a fundamental process called ‘photosynthesis’.

Photosynthesis uses sunlight and atmospheric carbon dioxide to produce a carbon

compound called ‘glucose’. This glucose molecule is utilized by other living organisms.

Thus, atmospheric carbon is incorporated in living forms. Now, it is necessary to recycle

this absorbed carbon dioxide back into the atmosphere to complete the cycle. There are

various processes by which carbon is recycled back into the atmosphere in the form of

carbon dioxide gas. The process of respiration breaks down glucose molecules to

produce carbon dioxide gas. The process of decomposition also releases carbon dioxide

from dead bodies of plants and animals into the atmosphere. Combustion of fuels,

industrialization, deforestation, volcanic eruptions, and forest fires act as other major

sources of carbon dioxide.


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Class XII Chapter 15 – Biodiversity and Conservation Biology

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Question 1:

Name the three important components of biodiversity.

Answer

Biodiversity is the variety of living forms present in various ecosystems. It includes

variability among life forms from all sources including land, air, and water. Three

important components of biodiversity are:

(a) Genetic diversity

(b) Species diversity

(c) Ecosystem diversity

Question 2:

How do ecologists estimate the total number of species present in the world?

Answer

The diversity of living organisms present on the Earth is very vast. According to an

estimate by researchers, it is about seven millions.

The total number of species present in the world is calculated by ecologists by statistical

comparison between a species richness of a well studied group of insects of temperate

and tropical regions. Then, these ratios are extrapolated with other groups of plants and

animals to calculate the total species richness present on the Earth.

Question 3:

Give three hypotheses for explaining why tropics show greatest levels of species

richness.

Answer

There are three different hypotheses proposed by scientists for explaining species

richness in the tropics.

(1) Tropical latitudes receive more solar energy than temperate regions, which leads to

high productivity and high species diversity.

(2) Tropical regions have less seasonal variations and have a more or less constant

environment. This promotes the niche specialization and thus, high species richness.

(3) Temperate regions were subjected to glaciations during the ice age, while tropical

regions remained undisturbed which led to an increase in the species diversity in this

region.


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Question 4:

What is the significance of the slope of regression in a species − area relationship?

Answer

The slope of regression (z) has a great significance in order to find a species-area

relationship. It has been found that in smaller areas (where the species-area relationship

is analyzed), the value of slopes of regression is similar regardless of the taxonomic

group or the region. However, when a similar analysis is done in larger areas, then the

slope of regression is much steeper.

Question 5:

What are the major causes of species losses in a geographical region?

Answer

Biodiversity is the variety of living forms present in various ecosystems. It includes

variability among life forms from all sources including land, air, and water. Biodiversity

around the world is declining at a very fast pace. The following are the major causes for

the loss of biodiversity around the world.

(i) Habitat loss and fragmentation: Habitats of various organisms are altered or

destroyed by uncontrolled and unsustainable human activities such as deforestation,

slash and burn agriculture, mining, and urbanization. This results in the breaking up of

the habitat into small pieces, which effects the movement of migratory animals and also,

decreases the genetic exchange between populations leading to a declination of species.

(ii) Over-exploitation: Due to over-hunting and over-exploitation of various plants and

animals by humans, many species have become endangered or extinct (such as the tiger

and the passenger pigeon).

(iii) Alien species Invasions: Accidental or intentional introduction of non-native

species into a habitat has also led to the declination or extinction of indigenous species.

For example, the Nile perch introduced in Lake Victoria in Kenya led to the extinction of

more than two hundred species of native fish in the lake.

(iv) Co−extinction: In a native habitat, one species is connected to the other in an

intricate network. The extinction of one species causes the extinction of other species,

which is associated with it in an obligatory way. For example, the extinction of the host

will cause the extinction of its parasites.


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Question 6:

How is biodiversity important for ecosystem functioning?

Answer

An ecosystem with high species diversity is much more stable than an ecosystem with

low species diversity. Also, high biodiversity makes the ecosystem more stable in

productivity and more resistant towards disturbances such as alien species invasions and

floods.

If an ecosystem is rich in biodiversity, then the ecological balance would not get

affected. As we all know, various trophic levels are connected through food chains. If any

one organism or all organisms of any one trophic level is killed, then it will disrupt the

entire food chain. For example, in a food chain, if all plants are killed, then all deer’s will

die due to the lack of food. If all deer’s are dead, soon the tigers will also die. Therefore,

it can be concluded that if an ecosystem is rich in species, then there will be other food

alternatives at each trophic level which would not allow any organism to die due to the

absence of their food resource.

Hence, biodiversity plays an important role in maintaining the health and ecological

balance of an ecosystem.

Question 7:

What are sacred groves? What is their role in conservation?

Answer

Sacred groves are tracts of forest which are regenerated around places of worship.

Sacred groves are found in Rajasthan, Western Ghats of Karnataka,and Maharashtra,

Meghalaya, and Madhya Pradesh. Sacred groves help in the protection of many rare,

threatened, and endemic species of plants and animals found in an area. The process of

deforestation is strictly prohibited in this region by tribals. Hence, the sacred grove

biodiversity is a rich area.

Question 8:

Among the ecosystem services are control of floods and soil erosion.

How is this achieved by the biotic components of the ecosystem?

Answer


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The biotic components of an ecosystem include the living organisms such as plants and

animals. Plants play a very important role in controlling floods and soil erosion. The roots

of plants hold the soil particles together, thereby preventing the top layer of the soil to

get eroded by wind or running water. The roots also make the soil porous, thereby

allowing ground water infiltration and preventing floods. Hence, plants are able to

prevent soil erosion and natural calamities such as floods and droughts. They also

increase the fertility of soil and biodiversity.

Question 8:

What measures, as an individual, you would take to reduce environmental pollution?

Answer

The following initiatives can be taken to prevent environmental pollution:

Measures for preventing Air pollution:

(i) Planting more trees

(ii) Use of clean and renewable energy sources such as CNG and bio-fuels

(iii) Reducing the use of fossil fuels

(iv) Use of catalytic converters in automobiles

Measures for preventing water pollution:-

(i) Optimizing the use of water

(ii) Using kitchen waste water in gardening and other household purposes

Measures for controlling Noise pollution:-

(i) Avoid burning crackers on Diwali

(i) Plantation of more trees

Measures for decreasing solid waste generation:-

(i) Segregation of waste

(ii) Recycling and reuse of plastic and paper

(iii) Composting of biodegradable kitchen waste

(iv) Reducing the use of plastics

Question 10:

Can you think of a situation where we deliberately want to make a species extinct? How

would you justify it?

Answer


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Yes, there are various kinds of parasites and disease-causing microbes that we

deliberately want to eradicate from the Earth. Since these micro-organisms are harmful

to human beings, scientists are working hard to fight against them. Scientists have been

able to eliminate small pox virus from the world through the use of vaccinations. This

shows that humans deliberately want to make these species extinct. Several other

eradication programmes such as polio and Hepatitis B vaccinations are aimed to

eliminate these disease-causing microbes.

Class XII Chapter 16 – Environmental Issues Biology

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Question 1:

What are the various constituents of domestic sewage? Discuss the effects of sewage

discharge on a river.

Answer

Domestic sewage is the waste originating from the kitchen, toilet, laundry, and other

sources. It contains impurities such as suspended solid (sand, salt, clay), colloidal

material (fecal matter, bacteria, plastic and cloth fiber), dissolved materials (nitrate,

phosphate, calcium, sodium, ammonia), and disease-causing microbes. When organic

wastes from the sewage enter the water bodies, it serves as a food source for micro-

organisms such as algae and bacteria. As a result, the population of these micro-

organisms in the water body increases. Here, they utilize most of the dissolved oxygen

for their metabolism. This results in an increase in the levels of Biological oxygen

demand (BOD) in river water and results in the death of aquatic organisms. Also, the

nutrients in the water lead to the growth of planktonic algal, causing algal bloom. This

causes deterioration of water quality and fish mortality.

Question 2:

List all the wastes that you generate, at home, school or during your Trips to other

places, could you very easily reduce? Which would be Difficult or rather impossible to

reduce?

Answer

Wastes generated at home include plastic bags, paper napkin, toiletries, kitchen

wastes (such as peelings of vegetables and fruits, tea leaves), domestic sewage, glass,

etc.

Wastes generated at schools include waste paper, plastics, vegetable and fruit peels,

food wrappings, sewage etc.

Wastes generated at trips or picnics include plastic, paper, vegetable and fruit peels,

disposable cups, plates, spoons etc.

Yes, wastes can be easily reduced by the judicious use of the above materials. Wastage

of paper can be minimized by writing on both sides of the paper and by using recycled

paper. Plastic and glass waste can also be reduced by recycling and re-using. Also,

substituting plastics bags with biodegradable jute bags can reduce wastes generated at


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home, school, or during trips. Domestic sewage can be reduced by optimizing the use of

water while bathing, cooking, and other household activities.

Non- biodegradable wastes such as plastic, metal, broken glass, etc are difficult to

decompose because micro-organisms do not have the ability to decompose them.

Question 3:

Discuss the causes and effects of global warming. What measures need to be taken to

control global warming?

Answer

Global warming is defined as an increase in the average temperature of the Earth’s

surface.

Causes of global warming: Global warming occurs as a result of the increased

concentration of greenhouse gases in the atmosphere. Greenhouse gases include carbon

dioxide, methane, and water vapour. These gases trap solar radiations released back by

the Earth. This helps in keeping our planet warm and thus, helps in human survival.

However, an increase in the amount of greenhouse gases can lead to an excessive

increase in the Earth’s temperature, leading to global warming. Global warming is a

result of industrialization, burning of fossil fuels, and deforestation.

Effects of global warming: Global warming is defined as an increase in the average

temperature of the Earth’s surface. It has been observed that in the past three decades,

the average temperature of the Earth has increased by 0.6ºC. As a result, the natural

water cycle has been disturbed resulting in changes in the pattern of rainfall. It also

changes the amount of rain water. Also, it results in the melting of Polar ice caps and

mountain glaciers, which has caused a rise in the sea level, leading to the inundation of

coastal regions.

Control measures for preventing global warming:

(i) Reducing the use of fossil fuels

(ii) Use of bio-fuels

(iii) Improving energy efficiency

(iv) Use of renewable source of energy such as CNG etc.

(v) Reforestation.

(vii) Recycling of materials


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Question 4:

Match the items given in column A and B:

Column A Column B

(a) Catalytic converter (i) Particulate matter

(b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides

(c) Earmuffs (iii) High noise level

(d) Landfills (iv) Solid wastes

Answer

Column A Column B

(a) Catalytic converter (ii) Carbon monoxide and nitrogen oxides

(b) Electrostatic precipitator (i) Particulate matter

(c) Earmuffs (iii) High noise level

(d) Landfills (iv) Solid wastes

Question 5:

Write critical notes on the following:

(a) Eutrophication

(b) Biological magnification

(c) Groundwater depletion and ways for its replenishment

Answer

(a) Eutrophication:- It is the natural ageing process of a lake caused due to nutrient

enrichment. It is brought down by the runoff of nutrients such as animal wastes,

fertilizers, and sewage from land which leads to an increased fertility of the lake. As a

result, it causes a tremendous increase in the primary productivity of the ecosystem.

This leads to an increased growth of algae, resulting into algal blooms. Later, the


Page 4 of 9



decomposition of these algae depletes the supply of oxygen, leading to the death of

other aquatic animal life.

(b) Biological magnification: - To protect the crops from the several diseases and

pests, a large number of pesticides are used. These pesticides reach the soil and are

absorbed by plants with water and minerals from the soil. Due to rain, these chemicals

can also enter water sources and into the body of aquatic plants and animals. As a

result, chemicals enter the food chain. Since these chemicals cannot be decomposed,

they keep on accumulating at each trophic level. The maximum concentration is

accumulated at the top carnivore’s level. This increase in the concentration of pollutants

or harmful chemicals with an increase in the trophic level is called biological

magnification. For example, high DDT concentrations were found in a pond. The

producers (phytoplankton) were found to have 0.04 ppm concentration of DDT. Since

many types of phytoplankton were eaten by zooplankton (consumers), the concentration

of DDT in the bodies of zooplankton was found to be 0.23 ppm. Small fish that feed on

zooplankton accumulate more DDT in their body. Thus, large fish (top carnivore) that

feed on several small fish have the highest concentration of DDT.

(c) Ground water depletion and ways for its replenishment: - The level of ground

water has decreased in the recent years. The source of water supply is rapidly

diminishing each year because of an increase in the population and water pollution. To

meet the demand of water, water is withdrawn from water bodies such as ponds, rivers

etc. As a result, the source of ground water is depleting. This is because the amount of

groundwater being drawn for human use is more than the amount replaced by rainfall.

Lack of vegetation cover also results in very small amounts of water seeping through the

ground. An increase in water pollution is another factor that has reduced the availability

of ground water.

Measures for replenishing ground water:-


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(i) Preventing over-exploitation of ground water

(ii) Optimizing water use and reducing water demand

(iii) Rain water harvesting

(iv) Preventing deforestation and plantation of more trees

Question 6:

Why ozone hole forms over Antarctica? How will enhanced ultraviolet Radiations affect

us?

Answer

The ozone hole is more prominent over the region of Antarctica. It is formed due to an

increased concentration of chlorine in the atmosphere.

Chlorine is mainly released from chlorofluorocarbons (CFC’s) widely used as refrigerants.

The CFC’s magnate from the troposphere to the stratosphere, where they release

chlorine atoms by the action of UV rays on them. The release of Chlorine atoms causes

the conversion of ozone into molecular oxygen. One atom of chlorine can destroy around

10,000 molecules of ozone and causes ozone depletion.

The formation of the ozone hole will result in an increased concentration of UV - B

radiations on the Earth’s surface. UV −B damages DNA and activates the process of skin

ageing. It also causes skin darkening and skin cancer. High levels of UV −B cause

corneal cataract in human beings.

Question 7:

Discuss the role of women and communities in protection and conservation of forests.

Answer

Women and communities have played a major role in environmental conservation

movements.

(i) Case study of the bishnoi community: TheBishnoi community in Rajasthan strictly

believes in the concept of living peacefully with nature. In 1731, the king of Jodhpur

ordered his ministers to arrange wood for the construction of his new palace. For this

purpose, the minister and the workers went to bishnoi village. There, a Bishnoi woman

called Amrita Devi along with her daughter and hundreds of other Bishnois showed the

courage to step forward and stop them from cutting trees. They embraced the trees and


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lost their lives at the hands of soldiers of the king. This resistance by the people of the

village forced the king to give up the idea of cutting trees.

(ii) Chipko movement: The Chipko movement was started in 1974 in the Garhwal

region of the Himalayas. In this movement, the women from the village stopped the

contractors from cutting forest trees by embracing them.

Question 8:

What measures, as an individual, you would take to reduce environmental pollution?

Answer

The following initiatives can be taken to prevent environmental pollution:

Measures for preventing Air pollution:

(i) Planting more trees

(ii) Use of clean and renewable energy sources such as CNG and bio-fuels

(iii) Reducing the use of fossil fuels

(iv) Use of catalytic converters in automobiles

Measures for preventing water pollution:-

(i) Optimizing the use of water

(ii) Using kitchen waste water in gardening and other household purposes

Measures for controlling Noise pollution:-

(i) Avoid burning crackers on Diwali

(i) Plantation of more trees

Measures for decreasing solid waste generation:-

(i) Segregation of waste

(ii) Recycling and reuse of plastic and paper

(iii) Composting of biodegradable kitchen waste

(iv) Reducing the use of plastics

Question 9:

Discuss briefly the following:

(a) Radioactive wastes

(b) Defunct ships and e-wastes

(c) Municipal solid wastes

Answer


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(a) Radioactive wastes: - Radioactive wastes are generated during the process of

generating nuclear energy from radioactive materials. Nuclear waste is rich in radioactive

materials that generate large quantities of ionizing radiations such as gamma rays.

These rays cause mutation in organisms, which often results in skin cancer. At high

dosage, these rays can be lethal.

Safe disposal of radioactive wastes is a big challenge. It is recommended that nuclear

wastes should be stored after pre-treatment in suitable shielded containers, which

should then be buried in rocks.

(b) Defunct ships and e-wastes: - Defunct ships are dead ships that are no longer in

use. Such ships are broken down for scrap metal in countries such as India and Pakistan.

These ships are a source of various toxicants such as asbestos, lead, mercury etc. Thus,

they contribute to solid wastes that are hazardous to health.

E-wastes or electronic wastes generally include electronic goods such as computers etc.

Such wastes are rich in metals such as copper, iron, silicon, gold etc. These metals are

highly toxic and pose serious health hazards. People of developing countries are involved

in the recycling process of these metals and therefore, get exposed to toxic substances

present in these wastes.

(c) Municipal solid wastes: - Municipal solid wastes are generated from schools,

offices, homes, and stores. It is generally rich in glass, metal, paper waste, food, rubber,

leather, and textiles. The open dumps of municipal wastes serve as a breeding ground

for flies, mosquitoes, and other disease-causing microbes. Hence, it is necessary to

dispose municipal solid waste properly to prevent the spreading of diseases. Sanitary

landfills and incineration are the methods for the safe disposal of solid wastes.

Question 10:

What initiatives were taken for reducing vehicular air pollution in Delhi?

Has air quality improved in Delhi?

Answer

Delhi has been categorized as the fourth most polluted city of the world in a list of 41

cities. Burning of fossil fuels has added to the pollution of air in Delhi.

Various steps have been taken to improve the quality of air in Delhi.


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(a) Introduction of CNG (Compressed Natural Gas):By the orderof the supreme court of

India, CNG-powered vehicles were introduced at the end of year 2006 to reduce the

levels of pollution in Delhi. CNG is a clean fuel that produces very little unburnt particles.

(b) Phasing out of old vehicles

(c) Use of unleaded petrol

(d) Use of low-sulphur petrol and diesel

(e) Use of catalytic converters

(f) Application of stringent pollution-level norms for vehicles

(g) Implementation of Bharat stage I, which is equivalent to euro II norms in vehicles of

major Indian cities.

The introduction of CNG-powered vehicles has improved Delhi’s air quality, which has

lead to a substantial fall in the level of CO2 and SO2. However, the problem of suspended

particulate matter (SPM) and respiratory suspended particulate matter (RSPM) still

persists.

Question 11:

Discuss briefly the following:

(a) Greenhouse gases

(b) Catalytic converter

(c) Ultraviolet B

Answer

(a) Greenhouse gases: - Thegreenhouse effect refers to an overall increase in the

average temperature of the Earth due to the presence of greenhouse gases. Greenhouse

gases mainly consist of carbon dioxide, methane, and water vapour. When solar

radiations reach the Earth, some of these radiations are absorbed. These absorbed

radiations are released back into the atmosphere. These radiations are trapped by the

greenhouse gases present in the atmosphere.. This helps in keeping our planet warm

and thus, helps in human survival. However, an increase in the amount of greenhouse

gases can lead to an excessive increase in the Earth’s temperature, thereby causing

global warming.

(b) Catalytic converter: - Catalytic converters are devices fitted in automobiles to

reduce vehicular pollution. These devices contain expensive metals such as platinum,

palladium, and rhodium that act as catalysts. As the vehicular discharge passes through


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the catalytic converter, the unburnt hydrocarbons present in it get converted into carbon

dioxide and water. Carbon monoxide and nitric oxide released by catalytic converters are

converted into carbon dioxide and nitrogen gas (respectively).

(c) Ultraviolet-B: - Ultraviolet-B is an electromagnetic radiation which has a shorter

wavelength than visible light. It is a harmful radiation that comes from sunlight and

penetrates through the ozone hole onto the Earth’s surface. It induces many health

hazards in humans. UV −B damages DNA and activates the process of skin ageing. It

also causes skin darkening and skin cancer. High levels of UV −B cause corneal cataract

in human beings.

CHAPTER 13

ORGANISMS AND POPULATIONS

POINTS TO REMEMBER

Adaptation : Any attributes of the organism (morphological, physiological, behavioural) that enables the organism to survive and reproduce in its habitat.

Aestivation : Strategy to escape in time during summers (summer sleep). E.g., Snails and some fishes.

Allen.s Rule : Mammals from colder climates generally have shorter ears and limbs to minimise heat loss.

Carrying Capacity : Maximum number of individuals of a population which can be provided with all the necessary resources for their healthy living.

Commensalism : One organism is benefitted while the other is neither harmed nor benefitted except to a negligible extent.

Competition : Rivalry between two organisms for obtaining the same resources.

Ectoparasite : Parasites which live on the surface of their host.

Emigration : Number of individuals of the population who have left the habitat and gone elsewhere during a given time period.

Exponential Growth Curve : Shows that if food and space for a population are unlimited and each species has the ability to grow, then the population grows in exponential or geometric ratio.

Hibernation : Strategy to escape in time during winters (winter sleep). E.g., Polar bears.

Homeostasis : Maintaining constancy of internal environment despite varying external environmental conditions.

Immigration : Number of individuals of the same species that have come into the habitat from elsewhere during a given time period.

XII - BIOLOGY120

Ecology : A branch of science that studies the reciprocal relationships between organism and their physical environment. Ecology is basically concerned with four levels of biological organisation. organisms, populations, communities and biomes.

Organisms : Organisms form the basic unit of study in ecology. Organisms with similar features and the potential interbreed among themselves and produce fertile offspring, constitute a species.

Populations : Population is a group of individuals of the same species, inhabiting in a given area. Interspecific competition for basic needs operate among the individuals of a population.

Biological Community : Biological community is constituted by an assemblage of the populations of all different species that live in an area and interact with each other. A biotic community has a distinct species composition and structure.

Biomes : Biome is a very large unit, constituting of a major vegetation type and associate fauna found in a specified zone. Annual variations in the intensity, duration of temperature and precipitation account for the formation of major biomes like desert, rain forest and tundra.

Major Biomass of India : Tropical rain forest, deciduous forest, desert, sea coast. Regional and local variations within each biome lead to the formation of a wide variety of habitats.

Environment : Environment is a sum total of all biotic and abiotic factors that surround and potentially influence an organism. Temperature, water, light and soil are the major abiotic factors. Response to Abiotic Factors :

(i) Regulators : Some organisms are able to maintain homeostasis by physiological (Some times behavioural) means which ensures body temperature, constant osmotic concentration. All birds and mammals, a very few lower vertebrates and invertebrates are regulators (Thermoregulation and osmoregulation). For example, human beings maintain their body temperature by sweating in summer and shivering during winter season. Plants do not have such mechanisms to maintain internal temperatures.

(ii) Conformers : Majority of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. In aquatic animals the osmotic concentration of the body fluids change with that of the ambient water and osmotic concentration. Some species have evolved the ability to regulate, but only over a limited range of environmental conditions, beyond which they simply conform.

XII - BIOLOGY121

A diagrammatic representation of organismic response is shown below.

(iii) Partial regulators : Hair on the body . Hair on body acts as heat insulator. Surface area and volume ratio . In smaller organisms the surface area is large as compared to the volume. But in large animal this ratio is small. So, the larger animals effectively controls the body temp erature.

(iv) Migration : The organisms can move away temporarily from the stressful habitat to a more hospitable area and return when stressful period is over.

(v) Suspend : The organisms may avoid the stress by escaping in time. Bears go into hibernation winter, some snails and fish go into aestivation in summer.

Age Pyraminds of Populations : A population at any given time is composed of individuals of different ages. If the age distribution is plotted for the population, the resulting structure is called an age pyramid. The shape of the pyramids reflects the growth status of the populations (a) Whether it is growing (expanding) (b) Stable or (c) Declining. A pyramids for human population (males and females) are represented below.

Conformers Regulators

Partial Regulators

External LevelIn

tern

al L

eve

rl

Post reproductive

Reproductive

Pre-reproductive

Expanding(Most common)

Which is not possible

Stable(It is an ideal condition)

Declining(In adverse condition)

XII - BIOLOGY122

dN )— rN (K — N=td —— K

dN — rN=td

Time (t)

Po

pu

latio

n d

en

sity

Population Growth : If .N. is the population density at time .t., then its density at time t + 1 is :

Nt+1 = Nt + [(B + I)—(D + E)]

Where B = The number of births

I = The number of immigrants

D = The number of deaths

E = The number of Emigrants.

N = Population Density


t = Time period

K = Carrying capacity (The maximum population size that an environment can sustain)

Population Interactions :

Predation : Interaction between species involving killing and consumption of prey is called predation. The species which eats the other is called the predator and the one consumed is termed the prey. The predator keeps check on prey population. The reduction in predator population may lead to increase in prey population.

Competition.In this fitness of one species is significantly lower in presence of another species

Competitive release : A species whose distribution is restricted to a small geographical area because of a competitively superior species, is found to expand its distributional range when the competing species is experimentally removed.

XII - BIOLOGY123

Competitive Exclusion Principle - Two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated.

Resource partitioning . If two species compete for the same reasource, they could avoid competition by choosing different times for feeding.

Commensalism : This is the interactio in which one species benefits and the other is neither harmed nor benefited under normal conditions.

Parasitism : Parasitism is a kind of relationship between two species in which one derives its food from the other (host). Parasitism also involves shelter, in addition to food obtained by a parasite. Parasites may be ectoparasites or endoparasites.

Mutualism : In mutualism both the interacting species are benefited mutually. It is also known as symbiosis.

Co-evolution . 1) Fig species and wasp. Female wasp uses the fruit as an qviposition (egg-laying) and also uses the developing seeds within the fruits for nourishing its larvae. Wasp pollinates the fig inflorescence while searching for egg laying site, in return big offers developing seeds as food for developing larvae. 2) Mediternanean orchid Ophrys and bee.

Amensalism : Interaction between two different species, in which one species is harmed and the other is neither benefited nor harmed.

Examples of Parasitism :

(i) Cuscuta growing in shoe flower plant

(ii) Head louse and humans

(iii) Ascaris, Taenia, Plasmodium causing diseases in humans

Examples of Brood parasitism :

(i) Koel laying its eggs in crow's nest.

Examples of Commensalism :

(i) Clown fish living among tentacles of sea anemone

(ii) Pilot fish (Remora) accompanies sharks

(iii) Orchid growing on mango tree

(iv) Sea anemone on the shell of hermit crab

(v) Barnacles on back of whales

(vi) Egret and grazing cattle

XII - BIOLOGY124

Examples of Mutualism

(i) Mycorrhiza living in roots of higher plants

(ii) Rhizobium in root nodules of legumes

(iii) Algae and fungi in lichens

(iv) Orchid Ophrys and bee for pollination (employs sexual deceit)

Example of Amensalism

(i) Penicillium whose toxin kills many bacteria is neither benefitted nor harmed

Examples of Predation

(i) Biological control methods to control pests

(ii) Carnivorous animals like tiger eating deers, snake eating frog

(iii) Insectivorous plants like Nepenthes, Drosera, Utricularia

Growth Models : The two growth models are :

(i) Exponential growth model :

rtExponential Growth Equation is N = N e t O

Where

Nt = Population density after time t

N0 = Population density at time zero

r = intrinsic rate of natural increase

e = the base of natural logarithms (2.71828)

(ii) Logistic growth model :

Verhulst-Pearl Logistic Growth is described by the following equations :

dN/dt = rN (K—N / N)

Where N = Population density at time t


K = Carrying capacity

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(i) Exponential growth ('J' shape curve is obtained).

* When responses are not limiting the growth.

* Any species growth exponentially under unlimited resources conditions can reach enormous population densities in a short time.

* Growth is not so realistic.

(ii) Logistic Growth (Sigmoid curve is obtained)

* When responses are limiting the Growth.

* Resources for growth for most animal populations are finite and become limiting.

* The logistic growth model is a more realistic one.

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QUESTIONS

VSA (1 MARK)

1. Which are the factor responsible for the wide variety of habitat formed within each biome?

2. Fresh water animals are unable to survive for long in sea water. Give reason.

3. With which population growth model is the Verhulst Pearl equation associated?

4. Define diapause. Which organisms exhibit it?

5. Calculate the death rate if 6 individuals in a laboratory population of 60 fruit flies died during a particular week.

6. In biological control method, one living organism is used against another to check its uncontrolled growth. Which kind of population interaction is involved in this?

7. An organism has to overcome stressful condition for a limited period of time. Which strategies can it adopt to do so?

8. Write what do phytophagous insects feed on?

SA-II (2 MARKS)

9. What are the four levels of biological organisation with which ecology basically deals?

10. Differentiate between stenohaline and euryhaline organisms.

11. List four features which enable the Xeric plants to survive in the desert conditions.

12. Mention the attributes which a population has but not an individual organism.

13. Differentiate between stenothermal and eurythermal organisms.

14. What are the four ways through which the living organisms respond to abiotic factors?

15. Why do clown fish and sea anemone pair up? What is this relationship called?

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SA-I (3 MARKS)

16. How does the shape of age pyramid reflect the growth status of a population?

17. Darwin showed that even a slow growing animal like elephant could reach enormous number in absence of checks. With the help of your understanding of growth models, explain when is this possible? Why is this notion unrealistic?

18. How will you measure population density in following cases?

(i) fish in a lake

(ii) tiger census in a national park

(iii) single huge banyan tree with large canopy.

19. Species facing competition might evolve mechanism that promotes coexistence rather than exclusion. Justify this statement in light of Gause.s competitive exclusion principle, citing suitable examples.

LA (5 MARKS)

20. What is altitude sickness? What its causes and symptoms? How does human body try to overcome altitude sickness?

21. Orchid flower, Ophrys co-evolves to maintain resembelance of its petal to female bee. Explain how and why does it do so?

ANSWERS

VSA (1 MARK)

1. Regional and local variations

2. Due to osmotic problems.

3. Logistic Growth.

4. A stage of suspended development, zooplanktons.

5. 6/60 =0.1 individuals per fruitfly per week.

6. Predation.

7. (i) Migration

(ii) Suspension of active life by hibernation/aestivation/spore formation.

8. Plant sap and other parts of plant.

128

SA-II (2 MARK)

9. Organisms, population, communities and biomes.

10. Euryhaline : Organisms tolerant in wide range of salinities.

Stenohaline : Organisms tolerant to narrow range of salinities.

11. (i) thick cuticle

(ii) Stomata in deep pits

(iii) Stomata closed during day time

(iv) leaves reduced to spines (CAM photosynthetic pathway).

12. Birth rate, Death rate, Sex ratio, age groups.

13. Eurythermal : Organisms that can tolerate and thrive in wide range of temperatures

Stenothermal : Organisms restricted to a narrow range of temperature.

14. (i) Regulate (ii) Conform (iii) migrate (iv) Suspend

15. Clown fish lives in tentacles of sea Anemone and gets protection from predators.

Interaction . commeasalisn.

SA-I (3 MARKS)

16. Shape of pyramids reflects growth statusof the population (a) growing (b) Stable (c) declining.

Refer page 227, Fig. 13.4, NCERT book, Biology - XII

17. Possible if the growth model is Exponential, i.e., having unlimited resources. Its an unrealistic situation because resources are limited. Hence, it follows logistic growth model.

18. (a) fish caught per trap.

(b) number per unit area

(c) percentage cover in biomass.

19. State Gause.s competitive exclusion principle. Mechanisms is resource partitioning. E.g., experiment of Mac Arthur on Warblers (Refer page 325, NCERT book, Biology - XII).

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LA (5 MARKS)

20. Breathlessness at high attitudes.

Cause : Low atmospheric pressure at high altitudes due to which body does not get enough oxygen.

Symptoms : Nausea, fatigue and heart palpitations. Body adapts by :

(a) increasing red blood cell production

(b) decreasing binding affinity of haemoglobin

(c) by increasing breathing rate.

21. lemploys .Sexual deceit.

l one petal bears uncanny resemblance to female of the bee.

lMale bee is attracted to what it perceives as a female 'pseudocopulates,' during which pollen dusted on male bee¡¦s body.

l Male bee transfers pollen to another flower when the same bee pseudocopulates with another flower.

l Ophrys does so because pollination success will be reduced unless it co-evolves with female bee.

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CHAPTER 14

ECOSYSTEM

POINTS TO REMEMBER

Ecosystem : Relationship between living organisms and their abiotic surroundings.

Stratification : Vertical distribution of different species occupying different levels in an ecosystem.

Primary Production : Amount of biomas or organic matter produced per unit area over a time period by plants during photosynthesis.

Gross Primary Productivity : Rate of production of organic matter during photosynthesis.

Net Primary Productivity NPP = GPP - R : Gross primary productivity minus the respiration losses.

Secondary Productivity : Rate of formation of new organic matter by consumers.

Detritus : Dead leaves, twigs, animal remains etc. constitute detritus. Detrivore : Organisms who break down detritus into smaller particles. e.g., earthworm.

Ecological succession : The successive and orderly replacement of one community by the other community in an area, over a period of time.

Ecological Pyramids : The sequential graphic representation of an ecological parameter (number/ biomass/energy) depicting different trophic levels in a food chain.

Climax community : The stable and final biotic community that develops at the end of ecological succession and is in perfect harmony with its physical environment.

Pioneer species : The species that invade a bare area at the onset of ecological succession.

Process of Decomposition : The decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients. This process is called decomposition. Steps of decomposition are :

(i) Fragmentation : Break down of detritus into smaller particles by detritivores (earthworm).

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(ii) Leaching : Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

(iii) Catabolism : Bacterial and fungal enzymes degrade detritus into simple inorganic substances.

(iv) Humification : Accumulation of a dark coloured amorphous substances called humus.

(v) Mineralisation : The humus is further degraded by some microbes and release of inorganic nutrients occur.

Factors affecting decoposition: Decomposition is controlled by:-

a) Chemical composition of detritus - The decomposition will slower if detritus is rich in lignin and chitin and will faster if detritus is rich in nitrogen and water soluble substance (sugar).

d) Climatic factor.In warm and moist environment , the process of decomposition is inhibited at low temperature and anaerobiosis.

Energy Flow : Energy flow is the key function in the ecosystem. The plants (producers) capture only 2 — 10 percent of the photosynthetically active radiation (PAR). Unidirection flow of energy is taken place from the sun to producers and then to consumers. About 10% energy flows from one trophic level to another.Grazing Food Chain (GFC) : It begins with producers.

Detritus Food Chain : (DFC) It begins with dead organic matter. It is made up of decomposers (Fungi, Bacteria). They meet their energy and nutrient requirements by degrading detritus. These are also known as saprotrophs.Ecological Pyramids(i) Pyramid of Numbers : (Grass land Ecosystem)

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Lion(Secondaryconsumer)

Grass(Producer

deer (Primary Consumer)

TC

SC

PC

PP

132

(ii) Pyramid of Energy : (Always upright in all Ecosystems)

(iii) Pyramid of Biomass :

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TC

SC

PC

PP

(In Terestrial Ecosystem)

PC

PP

TC

SC

PC

PP

(In Terrestrial Ecosystem)

(In Aquatic Ecosystem)

133

HR

PR

OD

UC

ER

S

EB

IVO

RE

S

SC

PC

PP

CARNIVORES

1

Inverted Pyramid of Biomass in aquatic Ecosytem

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Tc

sc

pp

pc

TERTIARY CONSUMERS

SECONDARYCONSUMERS

PRIMARYCONSUMERS

pare

sent

Top carnivorous

TC

SC

PC

PP

Pyramid of Number

2

Pyramid of ENERGY

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Ecological Succession : The gradual and fairly predictable change in the species composition of a given area is called ecological succession. The species that invade a bare area is called pioneer species. The final community is an ecological succeesion that is in near equilibrium with the environment is called climax communitySecondary Succession begins in the area where natural biotic communities have been destroyed (burned or cut forests, land that have been devastated by flood).Succession on a Bare Rock (Xerarch)

Secondary Ecological Succession

Primary Ecological Succession

Thousand of Years

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Phytoplankton Stage Submerged Plant Stage Submerged Free (Pioneer Community) Floating Plant Stage

Forest Scrub Stage Marsh-Meadow Reed Swamp(Climax Community) stage stage

Bare rock Lichen moss stage Annual herb stage Perennial (Pioneer Species) herb stage

Forest Scrub Stage (Climax Community)

Succession in Aquatic environment (Hydrach)

1- Secession in aquatic environment (Hydrach)

2- Secession on a bare rock (xerach)

137

Nutrient Cycling - Movement of nutrient elements through the various components of an ecosystem also called Biogeochemical cycles.

Carbon cycle - occurs through atmosphere, ocean, and though living and dead organisms. Considerable amount of carbon returns to atmosphere as CO through respiratory activities, decomposers also contribute to 2

Carbon di-oxide pool, burning of wood, forest fire and combustion of organic matter, fossil fuels, volcanic activity also release CO in 2

atmosphere.

Phosphorous cycle - Sedimentary cycle Rocks contain phosphorous in the form of phosphates

Carbon Cycle Phosphorous Cycle

1. Amount of atmospheric 1. Amount of atmosphericinputs more in amount inputs less in amounts

2. Degree of exchanges between 2. Degree of exchange high between organism and

environment organism and environment negligible.

XII - BIOLOGY

Nutrient cycle Gaseous — Reservoir in atmosphereSedimentary — Reservoir eg. earth's crusl

Consumeres

Detritus Litter fall

Decomposition

Soil Solution

Weathering Run Off

Rock mineral

Produceres

Uptake

138

QUESTIONS

VSA (1 MARK)

1. Decomposition is faster if deteritus is rich in nitrogen and water soluble substance like sugars. When is the decomposition process slower?

2. If we count the number of insects on a tree and number of small birds depending on those insects as also the number of larger birds eating the smaller, what kind of pyramid of number would we get?

3. Differentiate between Sere and Seral communities.

4. Who are generally the pioneer species in a Xerarch succession and in a Hyararch succession?

5. Which metabolic process causes a reduction in the Gross Primary Productivity?

6. What percentage of photosynthetically active radiation is captured by plants?

7. Name the pioners of primary succession in water.

SA-II (2 MARKS)

8. What is the shape of pyramid of biomass in sea? Why?

9. Give an example of an ecological pyramid which is always upright. Justify your answer.

10. Differentiate between primary succession and secondary succession. Which one occurs faster?

11. Gaseous nutrient cycle and sedimentary nutrient cycles have their reservoir. Name them. Why is a reservoir necessary?

12. Fill up the missing links depicted as A, B, C and D in the given model of primary succession.

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A

CD

Submerged free floating stagePhytoplankton

Marsh Meadow Stage B

139

13. In the model of phosphorus cycle given below, what does A, B, C and D refer to?

14. Differentiate between Hydrarch and a Xerarch succession.

15. What is the effect on decomposition rate if :.

a) Detritus is rich in lignin and chitin

b) Detritus is rich is nitrogen and sugars

16. What are the limitations of ecological pyramids?

17. Name any four ecosystem services. Who gave the price tags on nature.s life support services? Which is the most important ecosystem service provider?

18. Study the table given below and fill the blanks from .A. to .F..

S.No Component of Position of the Organism present in the Ecosystem trophic level the Food chain.

1. E Fourth trophic level F

2. Secondary D Bird, fish, wolf.consumer

3. B Second trophic level C

4. Primary producer A Phytoplankton,grass, tree.

19. In the pyramid of biomass drawn below, name the two crops (i) one which is supported (ii) one which supports in which ecosystem is such a phyramid found

XII - BIOLOGY

Consumeres

ALitter fall

B

Soil Solution

C Run Off

Rock mineral

D

Uptake

PC

PP

140

LA (5 MARKS)

20. Detrivores like earthworm are involved in the process of decomposition of dead plants and animals. Describe the different steps involved in the process of decomposition.

ANSWERS

VSA (1 MARK)

1. Its slower if detritus is rich in lignin and chitin.

2. Inverted Pyramid of Number.

3. Sere : Entire sequence of communities that successively change in a given area.

Seral community : Individual transitional community.

4. Pioneer species in Hydrarch succession are usually the small phytoplanktons and that in Xerarch succession are usually lichens.

5. Respiration.

6. 2 — 10%

7. Phytoplanktons

SA-II (2 MARKS)

8. Inverted, because biomass of fishes far exceeds that of phytoplankton.

9. Pyramid of energy is always upright and can never be inverted, because when energy flows from a trophic level to the next trophic level some energy is always lost as heat at each step.

10. Primary Succession : A process that starts where no living organisms are there.

Secondary succession : A process that starts in areas which have lost all the living organisms that existed there.

11. Reservoir for Gaseous nutrient cycle : Atmosphere; for sedimentary nutrient cycle : Earth.s crust. Reservoir is needed to meet with the deficit which occurs due to imbalance in the rate of influx and efflux.

12. A = Submerged plant stage B = Reed Swamp Stage

C = Scrub stage D = Forest stage

13. A = Detritus B = Decomposition

C = Weathering D = Producers.

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14. Hydrarch Succession : Starts in water proceeds from hydric (aquatic) to mesic (neither dry nor wet) situations.

Xerarch succession : Starts on barren rock Proceeds from Xeric (dry) conditons.

15. a) Decomposition rate is slower

b) Decomposition rate is faster.

16. (i) Does not take into account same species belonging to two or more trophic levels.

(ii) Assumes simple food chain, does not accomodate food web.

(iii) Saprophytes have not been given any place in ecological pyramids.

17. o Forest (ecosystem) purify water and air

o Mitigate Droughts and floods

o Nutrient cycling

oGenerate fertile soil

o Provide habitat for wildlife

o Pollinate flower

o Maintain Biodiversity

o Provide aesthetic, cultural & spiritual values

o Robert Constanza gave price tags to ecosystem services.

oMost important ecosystem services provider : Soil formation.

18. A = First trophic level

B = Primary consumer

C = Zooplankton, Cow, Grass hopper

D = Third trophic level

E = Tertiary consumer

F = Man, Lion

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19. (i) Supported trophic level is founded by zooplanktons

(ii) Supporting trophic level is formed by phytoplanktons ecosystem It is found in aquatic ecosystem.

LA (5 Marks)

20. The dead remains of plants and aminals called detritus undergo decomposition and are converted into simpler substances. The steps of this process are :

(i) Fragmentation : Breakdown of detritus into smaller pieces by detrivoures like earthworm.

(ii) Leaching : Water soluble inorganic nutrients go down into soil horizon and get precipitated as unavailable salts.

(iii) Catabolism : Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.

(iv) Humification : It leads to accumulation of dark coloured amorphous substance called humus which is highly resistant to microbial action so decomposes at slow rate and is rich in nutrients.

(v) Mineralisation : Humus is further degraded by some microbes and release of inorganic nutrients occurs.

143

CHAPTER 15

BIODIVERSITY AND CONSERVATION

POINTS TO REMEMBER

Biodiversity : Term used to describe diversity at all levels of biological organisation. Term coined by socio-biologist Edward Wilson and was also used by Walter G Rosen for the diversity of life forms. Biodiversity refers to totality of genes in species and ecosytems of a region.

Three inter-related levels of Biodiversity : Genetic diversity, Species diversity, Ecological diversity.

lGenetic diversity : Diversity in the number and types of genes, as well as chromosomes present in different species and the variations in the genes and their alleles in the same species. It helps in speciation.

l Species diversity : Varieties in the number and richness of the species of a region.

l Ecological diversity : Variety in the types of ecosystems.

IUCN : International Union for Conservation of Nature and Natural Resources. It is situated in Morges, Switzerland.

India has : more than 50,000 genetically different varieties of rice; 1000 varieties of mango;

l India has 1,42,000 known species of plants and animals (Around 45,000 species of plants and rest of animals);

l India has 8.1% of share of global biodiversity.

l India is one of 12 Mega diversity countries of the world. Latitudinal Gradients

l In general, species diversity decreases as we move away from the equator towards the poles.

l With very few exceptions, tropics (latitudinal range of 23.5°N to 23.5¢XS) harbour more species than temperate or polar areas.

l Colombia located near the equator has nearly 1,4000 species of birds while New York at 41° N has 105 species and Greenland at 71° N only 56 species

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l

l A forest in a tropical region like Equador 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 the USA.

l The largely tropical Amazonian rain forest in South America has the greatest biodiversity on earth.

Species-Area relationships

lGerman naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit.

l 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.

l On a logarithmic scale, the relationship is a straight line decribed by the equation

log S = log C + Z log A

Where S = Species richness, A = Area; Z = slope of the line (regression coefficient)

C = Y . intercept.

l Value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region.

l The species-area relationships among very large areas like the entire continents has much steeper slope of the line (Z values in the range of 0.6 to 1.2).

India has more than 1,200 species of birds.

XII - BIOLOGY

lLog- og sc

aleLog s = Log c + z Log A

Sp

eci

es r

ich

ne

ss

Area

zs=CA

145

Causes of Biodiversity Losses

1. Habitat loss and fragmentation : This is most important cause of plants and animals extinction. For example : Tropical rain forest being destroyed fast. The Amazonian rain forest is called the .lungs of the planet.. It is being cut for cultivating soyabeans.

2. Over.exploitation : Many species extinctions are due to over exploitation by humans. eg :- extinction of steller.s cow, passenger pigeon is last 500 years.

3. Alien Species Invasions : When alien species are introduced some of them turn invasive and cause decline or extinction of indigenous species. eg. :- Carrot grass (Parthenium), Lantana and water hyacinth (Eichornia) posed threat to native species.

4. Co-extinctions : When a species becomes extinct, the plant and animal species associated with it in an obligating way also become extinct. eg.:- When a host fish species becomes extinct, its assemblage of parasites also becomes extinct.

Reasons for Conservation of Biodiversity

1. Narrowly utilitarian : Humans derive countless direct economic benefit from nature food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and products of medicinal importance.

2. Broadly utilitarian : Biodiversity plays a major role in many ecosystem services that nature provides.

3. Ethical : every species has an intrinsic value, even if it may not be of any current economic value to us. We have a moral duty to care for their well-being and pass on our biological legacy in good order to future generations.

Types of Conservation Strategies

In-situ conservation : Conservation and protection of the whole ecosystem and its biodiversity at all levels in order to protect the threatened species. Endangered species protected in natural conditions.

lSacred Groves : Tracts of forest are set aside and all the trees and wildlife within are venerated and given total protection. E.g., some forest in Khasi and Jaintia hills in Meghalaya, Aravalli hills of Rajasthan.

XII - BIOLOGY146

l

diversity. E.g., Out of 34 hot spots in world, 3 occur in India. i.e., Western Ghats and Sri Lanka, Indo-Burma (North-East India) and Himalaya.

lProtected Areas : Ecological or Biogeographical areas where biological diversity with natural and cultural resources are protected. E.g., National parks, sanctuaries and Biosphere reserves.

Ex-situ conservation : Conservation and protection of selected rare plants or animals in places outside their natural homes.

l Offsite collections : Live collections of wild and domesticated species in Botanical gardens, Zoological parks etc.

lGene Banks : Institutes which maintain stock of viable seeds, live growing plants, tissue culture and frozen germplasm with the whole range of genetic variability.

Cryopreservation : Preservation of seeds, embryos etc. at — 196°C in liquid nitrogen.

National Parks : Areas reserved for wild life where they are able to obtain all the required natural resources and proper habitats. India has 89 national parks at present.

Sanctuaries : Tracts of land with or without lake where animals are protected from all types of exploitation and habitat disturbance. India has 492 sanctuaries at present.

Biosphere Reserves : Large tracts of protected land with multiple use preserving the genetic diversity of the representative ecosystem by protecting wild life, traditional life styles of the tribals and varied plant and animal genetic resources. India has 14 biosphere reserves.

Red Data Book : Record of threatened species of plants and animals maintained by IUCN. Important Wild Life Projects in India :

l Project tiger : Started in 1973 to check depletion in population of tiger. Jim Corbett National Park.

Biodiversity Hotspots : Regions of high endemism and high level of species richness.

Hot Spots : Areas with high density of biodiversity or mega

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Endemic Species : Species which are confined to a particular region and not found anywhere else.

Exotic or Alien Species : New species which enter a geographical regions.

Bio prospecting : Exploration of molecular, genetic and species level diversity for products of economic importance.

International Efforts for Biodiversity Conservation :

lWorld Conservation Union (formerly IUCN) : provides leadership, common approach and expertise in the area of conservation.

lThe Earth Summit : Historical convention on Biological diversity held in 1992 at Rio de Janerio, Brazil.

lThe World Summit on Sustainable Development : Held in 2002 in Johannesburg, South Africa to pledge to reduce biodiversity losses at global and local levels.

QUESTIONS

VSA (1 MARK)

1. Habitat loss and fragmentation has caused severe damage to a particular type of ecosystem. Name it.

2. What trend is observed in respect of species diversity when we move from equator to poles?

3. Which region is considered as the one with highest biodiversity on earth? What is the name given to such region of forests?

4. Ecologists have discovered that value of Z lies in range of 0.1 to 0.2 regardless of taxonomic group or region. When will the slope of line steeper in species area relationship?

5. Define cryopreservation. Why is it useful in conserving biodiversity?

6. What is the reason for genetic variation shown by medicinal plant Rauwolfia vomitoria?

SA-II (2Marks)

7. How many species of plants and animals have been described by IUCN in 2004? What is global species diversity according to Robert May?

8. Explain co-extinction with a suitable example.

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9. Study the pie-diagram and answer the questions which follows : What do A, B, C and D represent in these diagrams.

SA-I (3 MARKS)

10. Hot spots are the regions of exceptionally high biodiversity. But they have become regions of accidental habitat loss too. Name the three hot spots of our country. Why are they called .Hot spot.?

11. Study the diagram of the earth given below. Give the name of the pattern of biodiversity therein. Suggest any two reasons for this type of occurance.

12. What is so special about tropics that might account for their greater biological diversity?

LA (5 MARKS)13. Why is the sobriquet .The Evil Quartet. used in context of

biodiversity? Name the members of this quartet. Why do we grieve for the genes when a species is lost?

XII - BIOLOGYXII - BIOLOGY

Pole

BiodiversityIncreases

O° O°

Pole

Ferns & Allies

Angiosperms

AlgaeTaxa of Ptants

C

LichensInvertebrates

Other animal groups

A

MollusisB D

149

14. Describe at least two approaches each for ex-situ conservation nd in situ conservation as a strategy for biodiversity conservation.

ANSWERS

VSA (1 MARK)

1. Tropical Rain Forest.

2. In general, species diversity decreases as we move away from the equator towards poles.

3. Amazonian rain forests. They are also called the .Lungs of the planet..

4. Slope of line is much steeper if one analyses the species area relationship among very large areas like entire continents.

5. Preserving a material in liquid nitrogen at - 196°C. It can be done to preserve threatened species in viable and fertile condition for long period.

6. Genetic variation might be in terms of potency and concentration of the active chemical reserpine produced by plant.

SA-II (2 MARKS)

7. IUCN (2004) has described slightly more than 1.5 million species of plants and animals.

According to Robert May¡¦s estimates the global species diversity is about 7 million.

8. Coextinction refers to the disappearance of species with extinction of another species of plant or animal with which it was associated in an obligatory way. e.g., Plant-pollinator mutualism.

9. A → Crustaceans B → Insects

C → Mosses D → Fungi

SA-I (3 MARKS)

10. Western Ghats and Sri lanka; Indo-Burma; Himalaya called biodiversity hot spots as they show

(i) High level of species richness

(ii) High degree of endemism

11. Latitudinal gradients

(i) More solar energy available in tropics, more productivity.

(ii) Tropical environments are less seasonal, so more predictable.

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12. a) Speciation is a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitude have remained relatively undisturbed for million of years and thus had long evolutionary time for species diversification

b) Tropical environment are less seasonal, more constant and predictable

c) More solar energy awailable in the tropics contributing to high productivity leading to greater diversity.

LA (5 MARKS)13. The .Evil Quartet. is used as a sobriquet to refer to the cause of

loss of biodiversity :(i) Habitat loss and fragmentation : When large habitats are

broken up into smaller fragments due to various human activities, the animals requiring large territories (elephants, birds etc.) are badly affected and their populations decline.

(ii) Over-exploitation : When need of a resource becomes greed. e.g., over exploitation of passenger pigeon led to its extinction. Also marine fish is at brink of being endangered due to over exploitations.

(iii) Alien species invasion : Intentional or non-Intentional introduction of a species to a nearby area may disturb the harmony of existing species. e.g., Eichhornia after introduction posed a big threat to the native species.

(iv) Co-extinction : Extinction of one species invariably leads to extinction of another when they are associated with each other in an obligatory way. e.g., when host species is extinct, obligate parasites dependent on it also die.

(v) We grieve for the loss of genes, because the wild forms are hardy and more resistant to pathogen attack and can be beneficial in crop breeding programmes.

14. In situ conservation :(i) Identification and maximum protection of .hot spots.(ii) Legal protection to ecologically rich areas.(iii) Biosphere reserves, national parks and sanctuaries(iv) Sacred groves.Ex situ Conservation :(i) Creation of zoological parks, botanical garden, wild life

sanctuary(ii) Cryopreservation (iii) Seed bank.

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CHAPTER 16

ENVIRONMENTAL ISSUES

POINTS TO REMEMBER

Pollution : Undesirable physical/chemical/biological characteristics of air/water/ land which cause damage to the animals/plants/humans and architectural structures.

Pollutants : Agents which cause pollution. Slash and Burn Agriculture (Jhum Cultivation) : Farmers cut down trees and burn the plant remains. Ash is used as a fertiliser and the land is then used for farming or cattle grazing.

Reforestation : Process of restoring a forest that was removed at some point of time in the past.

Effluents : Something flowing over a large body of water (may be sewage or industrial effluents).

CPCB : Central Pollution Control Board

FOAM (Friends of Arcata Marsh)

JFM : Joint Forest Management.

A citizen group which is responsible for up keep and safeguarding of marcy sanctuaries.

Biochemical Oxygen Demand (BOD)

o BOD refer to the amount of oxygen that would be consumed if all the organic matter is one litre of water were oxidized by bacteria. The BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water.

oIndirectly BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, more is its polluting potential.

o In the given figure the effect of sewage on some imporant characteristic of a river is shown:

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Algal Bloom : Presence of large amounts of nutrients in water causes excessive growth of algae, called an algal bloom. Harmful effect of algal bloom are :1. Fish mortality2. Deterioration of water quality3. Toxic to animals and human beings.Biomagnificationo It refers to increase in concentration of toxic substances at

successive trophic levels.o Biomagnification of DDT in an aquatic food chain

Harmful Effect : High concentration of DDT disturbs calcium metabolism in birds, which causes thinning of egg shell and their premature breaking, causing decline in birds population.

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Water Phytoplankton Zooplankton Small Flash(0.003 ppm) (0.025 ppm) (0.04 ppm) (0.5 ppm)

Large fish(2ppm)

Fish eating birds(5 ppm)

Flash kill andDisappearance of chain water

Reappreance of clean water

Dissolved 02

Direction of How

Co

nce

ntr

atio

n

BOD

SewageChachange

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Eutrophication : It the process of nutrient enrichment of water and subsequent loss of species diversity like fishes. Excess nutrients causes algal bloom which may cover the whole surface of water body and release toxins. It causes oxygen deficiency in water that leads to the death of aquatic animals like fishes.

Global Warming : Increase in the level of greenhouse gases is mainly responsible for global warming. (Increase in mean global temperature due to trapping of infrared radiation). Carbon dioxide, Methane, CFCs, N O are themain gases that causes greenhouse 2

effect.

Harmful effects of global warming :

1. Melting of glaciers

2. Over many years, this will result in a rise in sea level that can flood the coastal plains.

Measures of Control Global Warming

1. Minimise the use of fossil fuel.

2. Improving efficiency of energy usage.

3. Reducing deforestration.

4 . Planting trees.

Ozone Depletion :

• Ozone gas is continuously formed by the action of UV-rays on molecular oxygen and also degraded into molecular oxygen in stratosphere.

• The thickness of the ozone-layer in a column of air from the ground to the top of the atmosphere is measured in tems of Dobson units (DU).

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N O2

6%

CFCs14%

CH4

20%

CO2

60%

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• Ozone layer absorbs the harmful UV-rays. These rays cause the skin cancer, damages genes, causes inflammation of cornea.

• Chlorofluro Carbons deplete the ozone layer. The part of atmosphere with lesser concentration of ozone is called ozone hole.

Steps leading to ozone depletion

• UV-rays split CFCs and release atomic chlorine (Cl)

• UV-rays also split ozone into oxygen.

• Chlorine atoms trap oxygen atoms and ozone is not formed again from oxygen. This leads to depletion of ozone in the stratosphere.

Ozone Hole : Large area of thinned ozone layer over Antartica.

Control of Vehicular Air Pollution in Delhi : All the buses of Delhi were converted to run on CNG by the end of the 2002. Other steps to reduce air pollution in Delhi include.

1. Phasing out of old vehicles.

2. Use of unleaded petrol and low sulphur petrol and diesel.

3. Use of catalytic converters in vehicles.

4. Application of Euro-IV norms for vehicles from April, 1, 2010.

Auto Fuel Policy : The Government of India has laid out a road map to cut down the vehicular air pollution in many cities of India. The goal of this policy is to reduce Sulphur to 50 ppm in petrol and diesel and reduce levels of aromatic hydrocarbons to 35% of the fuel. The Bharat Stage II will be applicable to all automobiles in all cities April, 1, 2005. The cities (like Delhi, Mumbai, Chennai, Kolkata etc.) will have to meet Euro III emission norms from April 1, 2005 and Euro IV Emission norms from April 1, 2010.

Electronoc Wastes (e-waste) : e-wastes are irreparable computer and other electronic goods.

disposal of e-waste:

1. Burried in landfills.

2. Incineration.

3. Recycling.

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QUESTIONS

VSA (1 MARK)

1. Why should the velocity of air between the plates of an electrostatic precipitator be low?

2. PM2.5 is responsible for causing greatest harm to human health. What is it? How is it harmful?

3. What is the noise level that can cause permanent impairment of hearing ability of human beings?

4. Why was the Montreal Protocol signed?

5. Jhum cultivation has been in practice from earlier days, but its considered more problematic these days. Why?

6. A radiation causes ageing of skin, skin cancer, and inflamation of cornea called snow blindness. It also damages DNA. Name the radiation.

SA-II (2 MARKS)

7. Landfills are not much a solution for getting rid of solid wastes. Why?

8. Electrostatic precipitator can remove over 99% particulate matter present in exhaust from a thermal power plant. How?

9. Why is a scrubber used? Which spray is used on exhaust gases passing through a scrubber?

10. There is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. Why? What are its adverse effects?

11. Catalytic converters use expensive metals as catalysts.

(a) Name the metals generally used.

(b) What precaution should be observed while using catalytic converter.

12. What are e-wastes? Why are they creating more problem in developing countries in comparision to developed countries?

13. Water logging and salinity are some of the problems that have come in the wake of Green revolution. How does water logging create problems of salinity?

14. What is the relationship between BOD, mcro-organisms and amount of biodegradable matter?

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SA-1 (3 MARKS)

15. Deforestation is creating a lot of problems in the environment. List the consequences of deforestation.

16. Enlist four harmful effects caused to the humans living in areas having polluted air. Suggest two measures to reduce air pollution.

17. People have been actively participating in the efforts for the conservation of forests.

(i) Name the award instituted in respect of Amrita Devi to promote such efforts.

(ii) Name the movement launched to protect the trees by hugging them.

(iii) Name the step Government of India has undertaken in 1980.s to work closely with the local communities for protecting and managing forests.

LA-(5 MARKS)

18. Pollutant released due to human activities (like effluents from industries and homes) can radically accelerate the ageing process of the water body.

(a) Explain how does this process occurs during natural ageing of lake.

(b) Give the term used for accelerated ageing of water bodies. Also give the term used for the natural ageing of lake.

19. In Arcata, the town.s people have created an integrated waste water treatment process within a natural system. A citizen group called FOAM helps in upkeep of this project.

(a) What are the main steps in waste water management done in this way?

(b) Ecosan. in Kerala and Sri Lanka is also an intiative for water conservation. How?

20. What are the contribution of Ahmed Khan in Bangalore and Ramesh Chandra Dagar in Sonipat?

ANSWERS

VAS (I MARK)

1. To allow the dust to fall.

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2. PM2.5 stands for particulate matter of size 2.5 micrometers or less in diameter. Its responsible for causing greatest harm to human health as it can be inhaled deep into lungs and cause breathing problems.

3. 150 dB or more

4. To control emission of ozone depleting substances.

5. Enough time gap is not being given for the natural process of recovery of land from the effect of cultivation.

6. Ultraviolet B rays (UV-B rays)

SA-II (2 MARKS)

7. Landfill sites are getting filled very fast due to large amount of garbage generation. Also underground water resources may get polluted due to seepage of chemicals.

8. Electrode wire at thousand volts, produce corona to release electrons, electrons attach to dust particules giving them net negative charge, charged dust particules attracted/collected by collecting plates which are grounded.

9. To remove gases like sulphur dioxide. Spray of water or lime is used.

10. Following discharge of sewage into river, micro organisms involved in biodegradation of organic matter present in sewage consume more oxygen. This cause mortality of fish and other aquatic creatures.

11. (a) Catalysts : platinum - palladium and Rhodium

(b) Motor vehicles equipped with catalytic converters should use unleaded petrol become lead inactivates the catalysts.

12. (a) Irrepairable computers and other electronic wastes.

(b) Recycling in developing countries involves manual participation thus exposing workers to toxic substances. In developed countries its mechanised so less dangerous.

13. Water logging draws salt to surface of soil. Salt deposited on land surface as a thin crust or at the roots of the plants.

14. Increase in amount of biodegradable matter leads to rapid multiplication of micro organisms to degrade it, thereby increasing BOD level of the water body.

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SA-I (3 MARKS)

15. o Enhanced CO2 concentration in atmosphere

o Loss of biodiversity

o Soil erosion

o Desertification

o Disturbed hydrological cycles.

16. reathing problems, irritation and inflammation, Damage to lungs, Premature death.

o Reduce emission from automobile exhaust

o Growing more trees.

17. (i) Amrita Devi Bishnoi Wildlife Protection Award.

(ii) Chipko movement

(iii) Joint Forest Management (JFM).

LA-I (5 MARKS)

18. (a) The phenomeon is eutrophication. More nutrients in water, aquatic life increases organic remains deposited on lake bottom, lake grows shallower and warmer, gradually transforms into land due to deposition of silt and organic debris.

(b) Cultural or Accelerated eutrophication natural ageing is Eutrophication.

19. (a) Conventional sedimentation, filtering and chlorine treatment. Absorption and assimilation of pollutants by algae fungi and bacteria.

(b) 'Ecosan' derived from ecological sanitation. Handling human excreta using dry composting toilets. Its practical, hygienic and cost effective method.

20. Refer page No. 279-280, ncert Text of Biology Class XII (the benefits of polyblend and organic farming.)

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class xii chapter 13 – organisms and populations...

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