Organisms And Populations Class 12th Biology CBSE Solution

Class 12^th Biology CBSE Solution

Exercises

1. How is diapause different from hibernation?
2. If a marine fish is placed in a fresh water aquarium, will the fish be able to survive?…
3. Define phenotypic adaptation. Give one example.
4. Most living organisms cannot survive at temperature above 450C. How are some microbes able…
5. List the attributes that populations but not individuals possess.…
6. If a population growing exponentially double in size in 3 years, what is the intrinsic…
7. Name important defence mechanisms in plants against herbivory.
8. An orchid plant is growing on the branch of mango tree. How do you describe this…
9. What is the ecological principle behind the biological control method of managing with…
10. Hibernation and Aestivation Distinguish between the following:
11. Ectotherms and Endotherms Distinguish between the following:
12. Adaptations of desert plants and animals Write a short note on
13. Adaptations of plants to water scarcity Write a short note on
14. Behavioural adaptations in animals Write a short note on
15. Importance of light to plants Write a short note on
16. Effect of temperature or water scarcity and the adaptations of animals. Write a short note…
17. List the various abiotic environmental factors.
18. An endothermic animal Give an example for:
19. An ectothermic animal Give an example for:
20. An organism of benthic zone Give an example for:
21. Define population and community.
22. Commensalism Define the following terms and give one example for each:…
23. Parasitism Define the following terms and give one example for each:…
24. Camouflage Define the following terms and give one example for each:…
25. Mutualism Define the following terms and give one example for each:…
26. Interspecific competition Define the following terms and give one example for each:…
27. With the help of suitable diagram describe the logistic population growth curve.…
28. Select the statement which explains best parasitism. A. One organism is benefited. B. Both…
29. List any three important characteristics of a population and explain.…

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Exercises

Question 1.

How is diapause different from hibernation?

Answer:

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, it will be difficult for it to survive. For aquatic organism the quality of water (chemical composition, pH, salt concentration) is an important factor for it’s survival. Many freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems. The bodies of the marine fish are adapted to survive in high salt concentrations. In fresh water conditions, due to the presence of high water condition outside their body they are unable to regulate the water entering inside their body. This results in the swelling up of the body and eventually leading to the death of the marine fish.

Question 3.

Define phenotypic adaptation. Give one example.

Answer:

Any change that occurs in the body of an organisms in response to changing environmental conditions is termed as Phenotypic adaptation. It includes non-genetic changes in individuals such as physiological modification, acclimatization or behavioural changes to escape or adapt to the environmental conditions.

Examples:

i. Kangaroo rat: Internal fat oxidation occurs to produce water as by product, which helps it to survive in desert conditions.

ii. Desert plants: Thick cuticle, stomata in deep to minimize transpiration

iii. Cold climate Mammals: short ears and limbs to minimize heat loss.

iv. People at high altitude: increased R.B.C production and increased breathing rate.

v. Desert lizards: bask in sun when cold and move to shade when hot.

Question 4.

Most living organisms cannot survive at temperature above 450C. How are some microbes able to live in habitats with temperatures exceeding 1000C?

Answer:

For survival of an organism temperature plays an important role. In most animals, the metabolic reactions occur in a narrow range of temperature such organisms are called stenothermal. The enzymes in such organisms get denatured, if they are placed in temperature above it’s normal range. Some microbes can survive temperature exceeding 100° C, because they have adapted to such high temperature due to the presence of thermos-resistant enzymes (these enzymes do not get destroyed or denatured at high temperature).

Question 5.

List the attributes that populations but not individuals possess.

Answer:

A population has certain attributes that an individual organism does not. An individual may have births and deaths, but a population has birth rates and death rates. Each population has a certain pattern of distribution, variation in number, natality, mortality, dispersal, biotic potential, growth forms and sex ratio. All these attributes are not possessed by individuals. Further, a population has a gene pool shared by its member.

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:

When resources are unlimited, populations exhibit exponential growth, resulting in a J-shaped curve. Its exponential growth can be calculated by the following equation:

Where,
N_t = Population density after time t
N_o = 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:

Applying log on both sides:
⇒ log 2 = 3r log e

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:

For plants, herbivores are the predators. Nearly 25 per cent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants). Plants cannot escape from predator like animals. So, plants have developed a variety of morphological and chemical defence to escape herbivores animals. The various methods adapted by plants are enlisted below:

1. Morphological defence mechanism:

A. Sharp thorns present in plants such as Acacia and Cactus is the most common morphological means of defence.

B. In some plants, the margins of their leaves are spiny or have sharp edges that prevent herbivores from feeding on them.

2. Chemical defence mechanism:

A. Chemical substances such as nicotine, caffeine, quinine, and opium are produced in plants as a part of self-defence.

B. Calotropins weeds contain toxic cardiac glycosides, which can be fatal if ingested by herbivores.

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:

The interaction presents between the orchid and the mango tree is an example of commensalism as one species is benefited and other remains unaffected. An orchid plant that is growing on the branch of a mango tree is considered as an epiphyte. So, Epiphytes are the plants which grows on other plants but do not derive nutrition from them. In the given case the orchid is considered as an epiphyte as it gets support and the mango tree remains unaffected.

figure showing epiphytic relationship between orchid and mango tree

Question 9.

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

Answer:

The principle behind using of various biological control methods is the use of predator to control the growth of pest. Predation can be termed as a biological interaction between the two species in which one organism feed on other. The organism that feed on other is termed as predator and the other one is termed as prey. The predators help in regulating the population of preys in a given habitat and helps in the management of pest insects thus preventing the crop from getting damaged.

This ecological principle is used in integrated pest management where instead of chemical pesticides, the population of the insect in a farm is controlled by its ecological enemy. This will also not let the insect species to increase to a level where it can damage the crop or decrease to a level where it may disturb the ecological balance.

Question 10.

Distinguish between the following:

Hibernation and Aestivation

Answer:

Question 11.

Distinguish between the following:

Ectotherms and Endotherms

Answer:

Question 12.

Write a short note on

Adaptations of desert plants and animals

Answer:

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 absorb 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 synthesize food through C4 pathway. It enables the stomata to remain closed during the day to reduce the loss of water through transpiration.

Adaptations of desert animals: the common animals that are found in deserts are desert kangaroo rats, insects, reptiles such as lizards and snakes, etc. The integument of Insects and reptiles that are found in desert is impervious tp prevent any loss of water. They excrete nitrogen in the form of uric acid. Rodents stay in burrows during the day to avoid evaporation and water loss and conserve water by excreting highly concentrated urine and by not using water for temperature regulation. 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.

Question 13.

Write a short note on

Adaptations of plants to water scarcity

Answer:

the plant shows following adaptations to water scarcity:

1. Succulents such as cacti (Opuntia) and Euphorbia possess thick cuticles which prevents water loss, by cuticular transpiration.

2. In succulents, the stem is flattened, and the function of leaf is performed by stem. In Opuntia, leaves are reduced to spines.

3. 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.

4. Absence of broad leaves and abundance of spines further protect desert plants from being eaten by animal consumers.

5. The roots in perennial xerophytes are very deep to absorb ground water.

Question 14.

Write a short note on

Behavioural adaptations in animals

Answer:

Adaptations help organisms survive in their ecological niche or habitat; adaptations can be anatomical, behavioural or physiological. The adaptations in the behaviour of an organism are termed as behavioural adaptations. It includes hibernation, aestivation, migration, etc. which enable the organisms to escape environmental stress.

For example, Ectotherms are cold blooded animals and they cannot regulate their own body temperature e.g. fish, amphibians, reptiles, etc. To maintain their body temperature, they have shown various behavioural changes such as, the desert lizard basks in the sun during early hours when the temperature is low. As the temperature rises, the lizard escapes the scorching sun by burrows itself inside the sand. Certain endotherms (warm-blooded animals) such as birds and mammals also show behavioural adaptation. They escape cold hibernating during winters and hot weather conditions by aestivating during summers.

Question 15.

Write a short note on

Importance of light to plants

Answer:

Sunlight is considered as the ultimate source of energy. Plants are termed as autotrophic organisms as they require light for carrying out the photosynthesis process. The amount of light and intensity of light effect plant distribution, flowering and fruiting. Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering. The amount of light in aquatic habitats is responsible for the vertical distribution of plants in oceans.

Question 16.

Write a short note on

Effect of temperature or water scarcity and the adaptations of animals.

Answer:

Temperature is the most ecologically relevant environmental factor. The average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops. It ranges from sub-zero levels in polar areas and high altitudes to more than 50°C in tropical deserts in summer. These variations in temperature affect the distribution of animals on the Earth. Some animals can tolerate a wide range of temperature, such animals are termed as eurythermal animals. While others which can tolerate a narrow range of temperature are termed stenothermal animals.

Animals also shows various 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. This rule is known as allen’s rule. Animals found in Polar regions or cold conditions have thick layers of fat below their skin and thick coats of fur to prevent the loss of heat. These all adaptations help the organism to survive in the adverse conditions of their habitat.

Organisms exhibit different behavioural changes to adapt to their natural habitat. The changes in the behaviour of an organism that help it to escape environmental stresses are called behavioural adaptations. For example, desert lizards are termed as ectotherms as they cannot regulate their body temperature. So, they show various behavioural changes to escape temperature variations. For example, . 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. Certain endothermic animals (warm-blooded animals) such as birds and mammals escape cold and hot weather conditions by hibernating during winters and aestivating during summers respectively.

Water is an important component and scarcity of water forces an animal to undergo various adaptation methods. Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are well adapted to stay in their habitat. The kangaroo rat stays in burrows during the day to avoid water loss through evaporation. They conserve water by excreting highly concentrated urine. Reptiles like the Texas horned lizard have thick and tough integument that doesn't let water out. Desert mammals have fewer sweat glands than their counterparts in less extreme environments. Such adaptations can be seen to prevent the loss of water.

Question 17.

List the various abiotic environmental factors.

Answer:

the various abiotic factors are as follows:

1. Temperature: the average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops. It ranges from sub-zero levels in polar areas and high altitudes to more than 50°C in tropical deserts in summer. So, it can be stated that temperature significantly affects the

(a) Latitudinal and Attitudinal distribution of organisms

(b) Enzyme kinetics and basal metabolism.

Organisms which can tolerate and thrive a wide range of temperatures and can maintain a constant body temperature are known as Eurythermal animals. These includes Mammals, birds. Organisms which can tolerate and thrive a restricted narrow range of temperature are termed as Stenothermal. It includes Polar bears, penguins.

2. Water: The productivity and distribution of plants is dependent on water. For aquatic organisms the quality (chemical composition, pH) of water becomes important.

Organisms which tolerate a wide range of salinities are termed as euryhaline e.g. Salmon. Organisms which are restricted to a narrow range of salinities are termed as Stendhalian e.g. Shark.

3. Light: Light affects significantly the production in autotrophs, photoperiodism and behavioural and physiological adaptations in organisms living in low in intensities. For example, many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering. Light also plays an important role in aquatic habitats for vertical distribution of plants in the sea.

4. Soil: Soil is an important factor affecting the distribution of organisms. Properties of soil like grain size, mineral content, percolation, pH are significant in distribution of plants and animals.

Question 18.

Give an example for:

An endothermic animal

Answer:

Animals which can regulate their body temperature are termed as endothermic animals. It includes birds such as crows, sparrows, pigeons, cranes, etc. and mammals such as bears, cows, rats, rabbits, etc. are endothermic animals.

Question 19.

Give an example for:

An ectothermic animal

Answer:

Animals which cannot regulate their body temperature are termed as ectothermic animals. It includes fishes such as sharks, amphibians such as frogs, and reptiles such as tortoise, snakes, and lizards are ectothermic animals.

Question 20.

Give an example for:

An organism of benthic zone

Answer:

It is the ecological region at the lowest level of a water body. Organisms living here are called as benthos. Light does not reach to this zone. In this zone sessile organisms such as sea anemones, sponges, hydrozoans and Decomposing bacteria are found.

Question 21.

Define population and community.

Answer:

Population:

Population is a group of individuals of the same species which resides in a particular geographical area at a particular time and functions as a unit. For example, Indian population of humans will include all human beings living in India at a particular time.

Community:

Community is a group of individuals of different species, living within a certain geographical area. For example, a forest of trees and undergrowth plants, inhabited by animals and rooted in soil containing bacteria and fungi, constitutes a biological community. Individuals in a community can be similar or dissimilar, but they cannot reproduce with the members of other species.

Question 22.

Define the following terms and give one example for each:

Commensalism

Answer:

It is a interaction between two organism, in which one species is benefited and the other is neither harmed nor benefited under normal conditions.

Examples of Commensalism

(i) Clown fish living among tentacles of sea anemone: The anemone protects the clownfish and provides a safe place to sleep and breed.

(ii) Pilot fish (Remora) accompanies sharks: pilot fish feeds on falling pieces of food when the shark is eating the prey.

(iii) Orchid growing on mango tree: the orchid is benefited as it gets support while the mango tree remains unaffected.

(iv) Sea anemone on the shell of hermit crab: sea anemone is sedentary while hermit crab is free swimming. Hermit crab resides in an empty snail shell for protection and sea anemone also uses snail shell as portable home. Anemone is benefited as it is able to find more food.

(v) Barnacles on back of whales: Barnacles are arthropods. When the whales swim into plankton-rich waters to feed the barnacles also get food. They also get protection from predators.

(vi) Egret and grazing cattle: egrets are small white birds follow herds of livestock to eat the grasshoppers that are stirred up by the cattle’s hoofs.

Question 23.

Define the following terms and give one example for each:

Parasitism

Answer:

Parasitism is a kind of relationship between two species in which one species which is termed as parasite, derives its food from the other species which is termed as host. Parasitism also involves shelter, in addition to food obtained by a parasite. Parasites may be ectoparasites or endoparasites. Ectoparasites live on the surface of their host while endoparasites live inside the body of the host.

Examples of Parasitism

(i) Cuscuta growing on shoe flower plant: Cucuta grows on the stem of shoe and derive nutrition from the plant.

(ii) Head lice is an ectoparasite and suck human blood

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

(iv) Koel laying its eggs in crow’s nest is an example of Brood parasitism. Birds lay egg in the nest of its host and host incubate it.

Question 24.

Define the following terms and give one example for each:

Camouflage

Answer:

It is a type strategy that is adapted by the 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.

Question 25.

Define the following terms and give one example for each:

Mutualism

Answer:

It is a type of interaction between two organisms where both the interacting species are benefited mutually. It is also known as symbiosis.

Examples of Mutualism

(i) Mycorrhiza living in roots of higher plants: in this interaction the root provides food and shelter to the fungus and the fungus help in absorption of minerals, water uptake and also provide protection against pathogenic fungi.

(ii) Rhizobium in root nodules of legumes: plant root provide food and shelter to the bacteria and the bacteria help is fixing of nitrogen and absorption of nitrogen

(iii) Algae and fungi in lichens: the fungus provide water, mineral and shelter to the algae. Algae manufacture food not only for itself but also for the fungi.

(iv) Orchid Orphreys and bee for pollination: orchid is pollinated by the plant and in return they get rewards in the form of nectar.

Question 26.

Define the following terms and give one example for each:

Interspecific competition

Answer:

It is a type of interaction between individuals of different species where both species are harmed. For example, in some shallow South American lakes visiting flamingos and resident fishes compete for their common food, the zooplankton in the lake. The feeding efficiency of one species is reduced due to the interfering and inhibitory presence of the other species, even if resources (food and space) are abundant. Therefore, competition is best defined as a process in which the fitness of one species is significantly lower in the presence of another species

Question 27.

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

Answer:

No population of any species in nature has its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. Eventually, the ‘fittest’ individual will survive and reproduce.

A population growing in a habitat with limited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote when the population density reaches the carrying capacity.

Since resources for growth for most animal populations are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one.

A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth and is described by the following equation:

Where N = Population density at time t r = Intrinsic rate of natural increase K = Carrying capacity

Lag phase: Initially, the population is very small because of the presence limited resource in the habitat.

Positive acceleration phase: During this phase, the organism starts adapting to its new environment and the population starts increasing. However, at the beginning of this phase, the is still limited.

Exponential phase: During this phase, the population organisms grows exponentially due to the availability of sufficient food resources, constant environment, and the absence of any interspecific competition. So, the population grows rapidly, the curve rises steeply upwards.

Negative acceleration phase: During this phase, due to increase in the environmental resistance, the growth rate of the population decreases. Increased competition among the organisms for their food and shelter is the factor responsible for the decline in the growth.

Stationary phase: During this phase, the population becomes stable. The population of the species has reached its nature’s carrying-capacity in its habitat and cannot increase any further.

Question 28.

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 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. Ectoparasites live on the surface of their host while endoparasites

live inside the body of the host.

Examples of Parasitism

(i) Cucuta growing on shoe flower plant

(ii) Head lice and humans

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

Question 29.

List any three important characteristics of a population and explain.

Answer:

A population is 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 tigers living in a biosphere reserve at a particular time constitute the population of tigers.

The three important characteristics of a population are:

(i) Birth rate or Natality Rate: It is expressed as the number of births per thousand individuals of a population per year.

If in a pond there are 20 lotus plants last year and through reproduction 8 new plants are added, taking the current population to 28, we calculate the birth rate as 8/20 = 0.4 offspring per lotus per year.

(ii) Death rate or Mortality rate: It is expressed as the number of deaths per thousand individuals of a populations during a given period.

If 4 individuals in a laboratory population of 40 fruit flies died during a specified time interval, say a week, the death rate in the population during that period is 4/40 = 0.1 individuals per fruit fly per week.

(iv) Sex ratio: It is expressed as the number of females per 1000 males of a population in given time.