NCERT Exemplar for Class 12 Biology Chapter-13 (Book Solutions)

Exercise

Multiple-Choice Questions

1. Autecology is the: 

A. Relation of heterogeneous populations to their environment

B. Relation of an individual to its environment 

C. Relation of a community to its environment

D. Relation of a biome to its environment 

Ans: The relation of an individual to its environment is called auto ecology. It is the ecological study of a particular species in the environment. So B is the correct answer.

Correct Option: B

2. Ecotone is:

A. A polluted area 

B. The bottom of a lake 

C. A zone of transition between two communities

D. A zone of developing community

Ans: An ecotone is a region where two biological communities meet. It means that it forms an area of transition between two communities. 

Correct Option: C

3. Biosphere is:

A. The component in the ecosystem 

B. Composed of the plants present in the soil

C. Life in the outer space 

D. Composed of all living organisms present on earth which interact with the physical environment.

Ans: The living world has many ecosystems. Two main factors of the ecosystem are biotic that are living ones and abiotic that are nonliving ones. And all these factors interact with each other.  The living world is divided into different parts that are:

(I)Lithosphere

(II)Hydrosphere

(III)Atmosphere

Correct Option: D

4. An ecological niche is: 

A. The surface area of the ocean

B. An ecologically adapted zone

C. The physical position and functional role of a species within the community

D. Formed of all plants and animals living at the bottom of a lake 

Ans: A niche is a place. It includes how an individual survives, how it can feed itself, obtains shelter, and its overall behavior. So it is the physical position and functional role of a species within a community.

Correct Option: C

5. According to Allen’s Rule, the mammals from colder climates have:

A. shorter ears and longer limbs

B. longer ears and shorter limbs 

C. longer ears and longer limbs

D. shorter ears and shorter limbs

Ans: According to Allen's Rule, the limbs, ears, and other parts of animals in cold areas are shorter than those in warmer ones. Their sizes help them to keep them warm and adapt to the environment.

Correct Option: D

6. Salt concentration (Salinity) of the sea measured in parts per thousand is:  

A. 10 – 15 

B. 30 – 70 

C. 0 – 5 

D. 30 – 35 

Ans: The salt concentration in the sea is 3.5 percent which means it is about 30-35 ppm. So it means that there is 35 gms of salt for every 1 liter of seawater.

Correct Option: D

7. Formation of tropical forests needs mean annual temperature and mean annual precipitation as:

A. 18 – 25°C and 150 – 400 cm 

B. 5 – 15°C and 50 – 100 cm

C. 30 – 50°C and 100 – 150 cm

D. 5 – 15°C and 100 – 200 cm

Ans: As we move from the equator to the poles, the temperature range goes on decreasing and rainfall varies from place to place. At the poles, there Ishardly any rain but snowfall is seen regularly. For the tropical forest to grow a temperature range of 18-25 degrees is required. Rainfall of around 150-400 cm is also required for the same.

Correct Option: A

8. Which of the following forest plants controls the light conditions on the ground?

A. Lianas and climbers

B. Shrubs

C. Tall trees

D. Herbs

Ans: Tall trees form a crown over their surfaces. They are made up of many branches called a canopy. They are very dense and hence capture the sunlight falling on the ground.

Correct Option: C

9. What will happen to a well-growing herbaceous plant in the forest if it is transplanted outside the forest in a park? 

A. It will grow normally

B. It will grow well because it is planted in the same locality

C. It may not survive because of changes in its microclimate 

D. It grows very well because the plant gets more sunlight

Ans: It may not survive because of changes in its microclimate like soil type, microorganisms present in the zone surrounding its roots and the tree canopies that create certain microenvironmental conditions along with other plants growing in the vicinity.

Correct Option: C

10. If a population of 50 Paramoecium present in a pool increases to 150 after an hour, what would be the growth rate of the population?

A. 50 per hour

B. 200 per hour 

C. 5 per hour 

D. 100 per hour 

Ans: Population of paramecium at time t1 = 50

Population of paramecium at time t2 = 1 hour = 150

Growth rate of population = 150 - 50 per hour 100 per hour.

Correct Option: D

11. What would be the percent growth or birth rate per individual per hour for the same population mentioned in the previous question (Question 10)? 

A. 100

B. 200 

C. 50

D. 150 

Ans: Initial number of paramecium = 50

Number of paramecium after 1 hour = 150

Birth rate = (number of new paramecium/initial number of paramecium)* 100

Birth rate = (100/50)*100 = 200 percent.

Correct Option: B

12. A population has more young individuals compared to older individuals. What would be the status of the population after some years? 

A. It will decline 

B. It will stabilize

C. It will increase 

D. It will first decline and then stabilize 

Ans: If in a population, more young individuals are present than the older one then this population will increase after some years. This is because the number of individuals in the reproductive stage is high and the high number of individuals will also enter the reproductive age in the coming years.

Correct Option: C

13. What parameters are used for tiger census in our country’s national parks and sanctuaries?

A. Pugmarks only

B. Pugmarks and fecal pellets

C. Fecal pellets only

D. Actual headcounts 

Ans: The Tiger census is carried out to determine the number of tigers in our country. This is based on their pug marks and fecal pellets of the tigers. This allows them to count their numbers and judge their species.

Correct Option: B

14. Which of the following would necessarily decrease the density of a population in a given habitat?

A. Natality > mortality

B. Immigration > emigration

C. Mortality and emigration

D. Natality and immigration 

Ans: The population density in a given habitat is influenced by four factors:

1. Natality: Number of births in a given time in a population

2. Mortality: Number of deaths in a population during a given period

3. Immigration: Number of individuals coming from other habitats in a given time. 

4. Emigration: Number of individuals existing from a given population in a given period. 

Mortality and emigration, therefore decrease the population density while natality and immigration will increase it.

Correct Option: C

15. A protozoan reproduces by binary fission. What will be the number of protozoans in its population after six generations? 

A. 128

B. 24 

C. 64

D. 32

Ans: By binary fission, each protozoan will divide into two. In this way, after six generations their number will be 64.

First-generation: 1----2

Second generation: 2---4

Third generation: 4---8

Fourth generation: 8----16

Fifth generation: 16----32

Six generation: 32----64

Correct Option: C

16. In 2005, for each of the 14 million people present in a country, 0.028 were born and 0.008 died during the year. Using the exponential equation, the number of people present in 2015 is predicted as:

A. 25 million 

B. 17 million

C. 20 million

D. 18 million 

Ans: Exponential equation gives population growth rate as:dN = rN

Here, r = Rate of natural increase, N = Size of original population 

dN/dt = Increase in population size per unit time (1 year in this case) 

r is the difference between birth and death rate.

r = 0.028 - 0.008 = 0.02 

{dN}/{dt}= 0.02 x 14 million = 0.28 million 

over 10 years (2005 - 2015), this number will become = 2.8 million 

Expected population in 2015 = (14+2.8) million 

= 17 million (approx),

So, the correct answer is '17 millions'.

Correct Option: B

17. Amensalism is an association between two species where: 

A. one species is harmed and the other is benefitted

B. one species is harmed and the other is unaffected 

C. one species is benefitted and the other is unaffected

D. both the species are harmed

Ans: When one species is harmed and the other is benefitted, it is called parasitism. Mutualism is the case when both species is benefitted. Commensalism is the condition in which one species is benefitted and other is unaffected. 

Correct Option: B

18. Lichens are an association of: 

A. bacteria and fungus

B. alga and bacterium 

C. fungus and alga 

D. fungus and virus 

Ans: Lichen is an association between fungus and alga.  The role of the fungal part is providing body structure and absorption of minerals and water. The role of the algal part is to perform photosynthesis and make food.

Correct Option: C

19. Which of the following is a partial root parasite? 

A. Sandalwood 

B. Mistletoe

C. Orobanche

D. Ganoderma

Ans: Sandalwood is a partial root parasite that synthesis its food but it is dependent on the host's root for water and inorganic nutrients.

Correct Option: A

20. Which one of the following organisms reproduces sexually only once in its lifetime?

A. Banana

B. Mango 

C. Tomato

D. Eucalyptus

Ans: Bananas are a perennial plant. It reproduces sexually once in its lifetime. Hence, it flowers only once in a lifetime. After reproducing sexually once, reproduction in the banana plant is done by parthenocarpy.

Correct Option: A

Very Short Answer Type Questions:

1. Species that can tolerate a narrow range of temperature are called _____.

Ans: Stenothermal are the species that can tolerate a narrow range of temperature.

Hence, the answer is Stenothermal

2. What are Eurythermal animals?

Ans: Eurythermal animals are those animals that can tolerate a large range of variations in temperature.

3. Species that can tolerate a wide range of salinity are called ____.

Ans: Euryhaline is a species that can tolerate a wide range of salinity.

Hence, the answer is Euryhaline.

4. Define stenohaline species.

Ans: Stenohaline species are those which cannot tolerate a wide range of fluctuations in the salinity.

The stenohaline word is generally used for fishes. These are the species that cannot tolerate a wide range of fluctuations in the salinity of water around them. For example, Goldfish cannot survive in high salinity.

5. What is the interaction between two species called?

Ans: Symbiosis refers to the interaction between two species that are in direct contact with each other. These species interact with each other for some purpose.

Hence, the answer is Symbiosis.

6. What is commensalism? 

Ans: It is the interaction between two species in which one species is benefitted but the other species is neither benefited nor harmed.

Commensalism is a type of symbiosis.It is an interaction between two species in which one species is benefitted but the other species are neutral which means they are neither benefited nor harmed.

7. Name the association in which one species produces a poisonous substance or a change in environmental conditions that is harmful to another species.

Ans: Ammensalism is the association of two species in which one species produces a poisonous substance or a change in environmental conditions that is harmful to another species. The species that produce poisonous substances are neither benefited nor harmed. Hence, the answer is Ammensalism.

8. What is Mycorrhiza?

Ans: Mycorrhiza is the symbiotic association between fungus and green plants (usually with its root system). The fungus grows on the roots of green plants and derives the organic molecules (sugar) from the plant for its survival. In return, the fungus provides important minerals to the plant.

9. Emergent land plants that can tolerate the salinities of the sea are called ____. 

Ans: Euryhaline are the emergent land plants that can tolerate the salinities of the sea. They are adapted to tolerate a wide range of salinities.

Hence, The answer is Euryhaline.

10. Why do high-altitude areas have brighter sunlight and lower temperatures as compared to the plains? 

Ans: High altitude areas have brighter sunlight than the plains because of particle-free air at high altitudes and low temperature due to low atmospheric pressure. 

11. What is homeostasis? 

Ans: Homeostasis is the tendency of the human body to maintain a stable equilibrium between physical, chemical, and internal body conditions that are specially maintained by physiological activities.

12. Define aestivation.

Ans: Aestivation is a type of prolonged hibernation in the summer season. Due to high temperatures in the summer season, some animals go into a state of dormancy to reduce the effects of high temperatures.

13. What is diapause and its significance? 

Ans: Diapause is a state of the body found mainly in insects. It is a time interval in which suspension of animal development takes place to tackle unfavorable conditions like drought, high temperature, etc.

14. What would be the growth rate pattern, when the resources are unlimited? 

Ans: When the resources are unlimited, the growth rate curve will be J-shaped. There will be exponential growth when unlimited resources are available.

15. What are the organisms that feed on plant sap and other plant parts called? 

Ans: The organisms that feed on plant sap and other parts of plants are called phytophagous. These organisms feed on roots, stems, branches, flowers, and fruits of the plant. Hence, The answer is Phytophagous

16. What is high altitude sickness? Write its symptoms. 

Ans: Altitude sickness is a sudden change in body condition when we go from plains to higher altitudes or mountains. It occurs due to low oxygen concentration and involves headache, nausea, etc.

17. Give a suitable example for commensalism.

Ans: Commensalism is the mutual relationship between two species in which one species is benefitted and the other is neither benefited nor harmed. For example, cattle egret and grazing cattle. When cattle graze, it causes moving insects from grass and it is easy for egrets to catch those insects.

18. Define ectoparasite and endoparasite and give suitable examples. 

Ans: Ectoparasites are the parasites that are attached to the external body surface of the host, for example, ticks, lice, and leeches whereas endoparasites are the parasites that are present inside the body of the host, for example, hookworms, roundworms, etc.

19. What is brood parasitism? Explain with the help of an example.

Ans: Brood parasitism is a different kind of parasitism and is commonly found in birds. In brood parasitism, the parasitic bird lays eggs in the nest of the host bird and lets the host incubate those eggs. It is found in Cuckoo birds who lay eggs in crow's nests.

Short Answer Type Questions:

1. Why are coral reefs not found in the regions from West Bengal to Andhra Pradesh but are found in Tamil Nadu and on the east coast of India? 

Ans: Coral reefs are found in those areas where salt concentration (salinity) is very high, the temperature is optimum and low siltation. Tamil Nadu and the east coast of India have appropriate conditions for coral reefs but coastal areas from West Bengal to Andhra Pradesh have high water flow and siltation which is not favorable for coral reefs.

2. If a freshwater fish is placed in an aquarium containing seawater, will the fish be able to survive? Explain giving reasons. 

Ans: No, if a freshwater fish is placed in an aquarium containing seawater it will not be able to survive because of excess salinity in its environment. Freshwater fishes are adapted to live in very low concentrations of salt but seawater is highly saline which makes it difficult to survive there.

3. Why do all the freshwater organisms have contractile vacuoles whereas the majority of marine organisms lack them? 

Ans: Contractile vacuoles are present in freshwater organisms but absent in marine organisms because they are meant to do osmoregulation function. Osmoregulation is needed in freshwater organisms because freshwater organisms are hypertonic so contractile vacuoles remove excess water from their body. There is no need for the removal of excess water from marine organisms because they are hypotonic. 

4. Define heliophytes and sciophytes. Name a plant from your locality that is either heliophyte or sciophyte. 

Ans: Heliophytes are plants that grow in the high intensity of light. They are also known as sun-loving plants. For example, Mango.

Sciophytes are plants that grow in low-intensity light and they are called shade-loving plants. For example, Thyme.

5. Why do submerged plants receive weaker illumination than exposed floating plants in a lake? 

Ans: Submerged plants receive weaker illumination than exposed floating plants in a lake because of the refraction of light. In the lake, refraction of light occurs through different layers of water due to which visible light cannot reach deep down the lake where submerged plants are present. Therefore, these plants receive weaker illumination.

6. On a seashore, the benthic animals live in sandy, muddy and rocky substrata and accordingly develop the following adaptations. 

Find the suitable substratum against each adaptation.

a. Burrowing 

Ans: Burrowing - Sandy 

b. Building cubes 

Ans: Building cubes - Muddy

c. Holdfasts/peduncle 

Ans: Holdfasts/peduncle – Rocky 

7. Categorize the following plants into hydrophytes, halophytes, mesophytes, and xerophytes. Give reasons for your answers. 

a. Salvinia

Ans: Salvinia - Hydrophyte

Salvinia is a hydrophyte because it grows over water.

b. Opuntia

Ans: Opuntia - Xerophyte

Opuntia is a xerophyte because it grows in the desert where water content is very low.

c. Rhizophora

Ans: Rhizophora - Halophyte

Rhizophora is a halophyte because it grows in highly saline areas.

d. Mangifera

Ans: Mangifera - Mesophyte

Mangifera is a mesophyte because it grows on both dry and wetlands.

8. In a pond, we see free-floating plants; rooted–submerged; rooted emergent; rooted with floating leaves. Write the type of plants against each of them. 

Ans: 

9. The density of a population in a habitat per unit area is measured in different units. Write the unit of measurement against the following: 

a. Bacteria  _______________ 

Ans: Bacteria - Volume/number

b. Banyan  _______________ 

Ans: Banyan - Biomass/area 

c. Deer  _______________ 

Ans: Deer - Number/area

d. Fish  _______________

Ans: Fish - Weight/area

10.

a. Label the three tiers 1, 2, 3 given in the above age pyramid. 

Ans: The three tiers given in the above age pyramid are:

Tier 1: Pre-reproductive population

Tier 2: Reproductive population

Tier 3: Post-reproductive population

b. What type of population growth is represented by the above age pyramid? 

Ans: The above age pyramid represents the expanding type or growing population because the pre-reproductive and reproductive population is increasing.

11. In an association of two animal species, one is a termite that feeds on wood and the other is a protozoan Trichonympha present in the gut of the termite. What type of association do they establish?

Ans: The association of termite and Trichonympha in which termite feeds on wood and Trichonympha present in the gut of the termite represents mutualism. In mutualism, both species depend on each other. The gut of termite represents proper habitat to the protozoan Trichonympha and in return, Trichonympha digest the wood on which termite feeds upon. If there is no Trichonympha in the gut of termite, it will cause the death of the termite because the wood will not get digested.

12. Lianas are vascular plants rooted in the ground and maintain the erectness of their stem by making use of other trees for support. They do not maintain direct relations with those trees. Discuss the type of association the lianas have with the trees. 

Ans: Commensalism is the interaction between two species in which one species is benefitted but the other species is neither benefited nor harmed. Here also Lianas are benefitted as they are getting support from other plants to maintain their erectness but other trees are neither benefited nor harmed in return.

13. Give the scientific names of any two microorganisms inhabiting the human intestine. 

Ans: Microorganisms inhabiting the human intestine are Lactobacillus, Escherichia coli. Both of these bacteria help to digest food in the human gut. Lactobacillus also prevents the growth of harmful bacteria in the human gut.

14. What is a tree line? 

Ans: A tree line is a line on mountains above which trees are not found. Trees cannot grow in low temperature and low moisture at higher altitudes, that's why trees are not found beyond the tree line.

15. Define 'zero population growth rate'. Draw an age pyramid for the same. 

Ans: When there is zero population growth rate, then the post-reproductive and reproductive populations are almost equal but the pre-reproductive population is less than both reproductive and post-reproductive populations. The age pyramid for such a condition will look like

16. List any four characters that are employed in the human population census. 

Ans: Census is a survey conducted for counting a population at a given time by observing all important characteristics of that population. The following characters are employed in the human population census:

1. Natality and mortality

2. Population density

3. Age group

4. Sex ratio

17. Give one example for each of the following types. 

(a) Migratory animal 

Ans: Examples of Migratory animals: Salmon fish, Siberian crane

Migratory animals are those animals that move a long distance based on the season.

(b) Camouflaged animal 

Ans: Examples of Camouflaged animals: Frog, Owl

Camouflaged animals are those who blend themselves with the environment to protect themselves from predators.

(c) Predator animal 

Ans: Examples of Predator animals: Lion, Tiger

Predator animals are those animals who kill other animals for their survival.

(d) Biological control agent 

Ans: Examples of Biological control agents: Aphidius - a parasitoid of aphids, Moth - parasitoid on prickly pear cactus.

Biological control agents are the organisms that kill pests or remove weeds or prevent diseases of plants.

(e) Phytophagous animal 

Ans: Examples of Phytophagous animals - The fruit fly, Locusta

Phytophagous animals are organisms that feed on plant sap and other parts of plants like roots, stems, branches, flowers, and fruits.

(f) Chemical defense agent 

Ans: Examples of Chemical defense agents - Geranium produces quisqualic acid, Calotropis produces cardiac glycosides.

Chemical defense agents are organisms that produce harmful chemicals to save themselves from predators.

18. Fill in the blanks:

Ans: Fill in the blanks

Predation is the species interaction in which one is benefited while the other is harmed.

Commensalism is the mutual relationship between two species in which one species is benefitted and the other is neither benefited nor harmed.

Mutualism refers to the interaction between two species that are in direct contact with each other and both of them are benefitted.

19. Observe the set of 4 figures A, B, C, and D and, answer the following questions 

i. Which one of the figures shows mutualism? 

Ans: Figure (A) shows mutualism that shows the plant-animal relationship.

ii. What kind of association is shown in D? 

Ans: Predation is shown in figure (D) where a leopard (predator) is killing deer (prey).

iii. Name the organisms and the association in C. 

Ans: Cattle and cattle egrets are the organisms and commensalism is the association in figure (C). Cattle egrets are benefitted while cattle graze but cattle do not get any benefit from this interaction.

iv. What role is the insect performing in B?

Ans: The insect in figure (B) is a phytophagous animal because it is feeding on plant sap.

Long Answer Type Questions:

1. Comment on the following figures: 1, 2, and 3.

A, B, C, D, G, P, Q, R, S are species.

Ans: Figure1: This is a single population and all individuals are of the same species that is A. Individuals can interact with them and their environment only.

Figure 2: This figure shows three populations that are A, B and C so it is a community. And they can interact with each other as well as their environment.

Figure 3: It is a biome. This figure has Three communities in which one community is in its climax and the other two are in different stages of development. All three communities have the same environment and they interact with each other as well as with their environment. 

2. An individual and a population have certain characteristics. Name these attributes with definitions.

Ans: The population has some characteristics that individuals do not have. Here are some attributes of the population:

1. Birth Rate: An individual is born but a population shows a birth rate. It is defined as the number of births per thousand population.

2. Death rate: When an individual dies the population shows a death rate and it is defined as the number of deaths per thousand population.

3. Sex Ratio: An individual is either a male or a female but a population shows a sex ratio. And it is defined as the ratio of the number of males to females.

4. Age distribution: An individual can have a certain age but a population has different age groups of individuals.  Age groups are normally categorized as pre-reproductive age groups and post-reproductive age groups.

5. Population Density: Population density is individuals per square km. 

3. The following diagrams are the age pyramids of different populations. Comment on the status of these populations.

Ans: Figure A: It is a pyramid-shaped age pyramid. In this pyramid, the pre-reproductive stage is very large when compared with the reproductive and past reproductive stages of the population. This type of age structure indicates that the population would increase rapidly.

Figure B: It is an inverted bell-shaped pyramid. In this figure, the pre-reproductive and reproductive stages are the same. This type of age structure indicates that the population is stable.

Figure C: It is an Urn-shaped pyramid. In this pyramid, the pre-reproductive and reproductive stages are less than the post-reproductive stage of this population. This type of age structure indicates that the population is declining.

4. Comment on the growth curve given below.

Ans: The growth curve in this figure shows the logistic growth of the population. As resources are limited in nature and nature cannot support the unlimited growth in population only those individuals who will survive are fit to survive. 

In the initial phase, the population shows a lag phase, that is it grows at a slow pace. The lag phase is followed by the acceleration phase during which population growth is rapid. The acceleration phase is then followed by the deceleration phase during which population growth slows down. Finally, the phase comes where population density reaches the carrying capacity. Once the population density reaches the carrying capacity, it reaches the phase of asymptomaticity. This phase is the phase when the population begins to show negative growth.

5. A population of Paramoeciumcaudatum was grown in a culture medium. After 5 days the culture medium became overcrowded with Paramoecium and had depleted nutrients. What will happen to the population and what type of growth curve will the population attain? Draw the growth curve.

Ans: The population of paramecium will show logistic growth which can be shown by a sigmoid curve. The population growth will have the following phases:

1. Lag phase

2. Acceleration phase

3. Deceleration phase

4. Asymptomatic phase

Initially, after the lag phase, the population will grow exponentially as the nutrients and space are abundant. When food resources get depleted the population density starts decreasing and ends in the asymptomatic phase then the population density reaches carrying capacity.

The growth curve that is required in the answer according to the question is given below:

6. Discuss the various types of positive interactions between species.

Ans: Following are the positive interactions between species:

Mutualism: This is a relationship between two organisms in which both the organisms are benefited. An example of mutualism is Lichen. Lichen is an association of fungi and algae. The fungal part is attached to the substratum of algae and absorbs water and minerals whereas the algal part performs -photosynthesis and provides food to the fungal part.

Commensalism: This is a relationship in which between two organisms only one is benefitted, while another one is not at harm not at any gain. Examples are Egrets sitting on the back of herbivores like a cow, buffalo, etc when they are grazing, the insects under the grass fly away haphazardly. This gives the egrets a chance to feed on insects however the cow is neither benefited nor harmed.

7. In an aquarium, two herbivorous species of fish are living together and feeding on phytoplankton. As per Gause's Principle, one of the species is to be eliminated in due course of time, but both are surviving well in the aquarium. Give possible reasons.

Ans: Competition is a rivalry between two or more organisms.  Competition between individuals of the same species is more than the individuals of different species.  But, This is true only when the resources are limited. The possible reasons for the survival of both will be: 

(i) Conditions favored the plentiful development of phytoplanktons.

(ii) There is a low number of fish of both varieties.

(iii) There are no zooplanktons and 

(iv) There is no duplication of fish.

8. While living in and on the host species, the animal parasite has evolved certain adaptations. Describe these adaptations with examples.

Ans: Parasites have evolved special adaptations. Some of them are given below with examples:

(i) Loss of unnecessary sense organs as in lice, mites, and fleas they do not have wings.

(ii) Presence of adhesive organs or suckers to cling on to the host. This is seen in tapeworm and leech.

(iii) Loss of digestive system that is seen in tapeworm.

(iv) The high reproductive capacity that is seen in roundworms produces large progeny.

9. Do you agree that regional and local variations exist within each biome? Substantiate your answer with a suitable example.

Ans: Yes, regional and local variations exist within each biome. Biome is a climatically and geographically continuous area with similar climatic conditions. However regional and local variations exist within each biome. To understand this let us take one example:

Coniferous forest is a type of biome. It has many trees that bear cones with seeds inside. But regional variations occur in coniferous forests. The coniferous forest of North America is dominated by black spruce. Whereas the coniferous forest of northeast Europe is dominated by Norway spruce. This is an example of regional variation in a biome.

10. Which element is responsible for causing soil salinity? At what concentration does the soil become saline

Ans: Soil salinity is called the presence of salt content in the soil. And this is caused by improper irrigation. The process of increasing salt content is termed salinization. Cause of salinity are as follows:

Improper irrigation method from a salt-laden water table, when the salt concentration in soil is increased then it gets accumulated due to evaporation. Human activities like fertilizing crops are also responsible for the salinity of the soil. As fertilizer contains potassium, which forms a naturally occurring salt-sylvite. The salinity of soil degrades soil and vegetation. Normally, the pH value of soil comprises between 2.2-9.7, while above which the soil is degrading by salt content.

11. Does light factor affect the distribution of organisms? Write a brief note giving suitable examples of either plants or animals.

Ans: Yes, light factors affect the distribution of organisms. As we know green plants need light for photosynthesis and hence the distribution of green plants is highly dependent on the amount of light available in a particular place. This is the reason that tropics have dense plant cover but poles have a small amount of plant cover. Plants also need sunlight at the flowering stage. This phenomenon is also called photoperiodism. Based on this photoperiodism plants are based on short-day plants, long-day plants, and day-neutral plants. 

Animals too are dependent on sunlight and show certain behavior patterns based on diurnal and seasonal variations in light. The nocturnal animals remain active during the night only, for example, owls. 

12. Give one example for each of the following: 

(i) Eurythermal plant species _______________ 

Ans: Eurythermal plant species Gracilaria.

Eurythermal plants are plants having tolerance to a wide range of temperatures.

(ii) A hot water spring organism _______________

Ans: A hot water spring organism Alycyclobacillus.

A hot spring is a spring that is produced by the emergence of geothermally heated groundwater that rises from the earth's crust.

(iii) An organism seen in deep ocean trenches _______________

Ans: An organism seen in deep ocean trenches Giant tube worms

Deep ocean trenches are long narrow steep-sided depressions in the ocean bottom.

(iv) An organism seen in compost pit _______________ 

Ans: An organism is seen in compost pit Earthworms

Compost pit is burying kitchen soft yard waste, such as chopped leaves.

(v) A parasitic angiosperm _______________ 

Ans: A parasitic angiosperm Mistletoe

Parasitic angiosperms are usually considered holoparasites and hemiparasites and they feed on insects.

(vi) A stenothermal plant species _______________

Ans: A stenothermal plant species Pine

Stenothermal; plants are plants that have a very narrow or low tolerance to high temperatures.

(vii) Soil organism _______________

Ans: Soil organism Earthworm

Organisms that live in the soil.

(viii) A benthic animal _______________

Ans: A benthic animal Sponge

Benthic animals are the organisms that live at the lowest level of a body such as a lake or ocean.

(ix) Antifreeze compound seen in antarctic fish _______________ 

Ans: Antifreeze compound is seen in antarctic fish Antifreeze glycoprotein.

Antifreeze proteins are biological antifreeze materials originally found in polar fish.

(x) An organism which can conform ______________

Ans: An organism that can conform to Mangifera. Conforms meaning those organisms that regulate, maintain life system parameters at a constant level possibly wide ambient environmental variations.

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