NCERT Solutions for Class 12 Science Biology Chapter 14 - Ecosystem

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NCERT Solutions for Class 12 Science Biology Chapter 14 Ecosystem are provided here with simple step-by-step explanations. These solutions for Ecosystem are extremely popular among Class 12 Science students for Biology Ecosystem Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 12 Science Biology Chapter 14 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 12 Science Biology are prepared by experts and are 100% accurate.

Page No 98:

Question 1:

Decomposers like fungi and bacteria are:

i. autotrophs

ii. heterotrophs

iii. saprotrophs

iv. chemo-autotrophs.

Choose the correct answer:

(a) i and iii
(b) i and iv

(d) i and ii

Answer:

Decomposers like fungi and bacteria are heterotrophs and saprotrophs.
Hence, the correct answer is option (c).

Page No 98:

Question 2:

The process of mineralisation by micro organisms helps in the release of:

a. inorganic nutrients from humus

b. both organic and inorganic nutrients from detritus

c. organic nutrients from humus

d. inorganic nutrients from detritus and formation of humus.

Answer:

The humus is degraded by some microbes and the release of inorganic nutrients occurs through the process known as mineralisation.
Hence, the correct answer is option (a).

Page No 98:

Question 3:

Productivity is the rate of production of biomass expressed in terms of:

i. (kcal m^–3) yr^–1

ii. g^–2 yr^–1

iii. g^–1 yr^–1

iv. (kcal m^–2) yr^–1

(a) ii,
(b) iii,
(c) ii and iv,
(d) i andiii

Answer:

The rate of biomass production is called productivity. It is expressed in terms of gm^–2 yr ^–1 or (kcal m^–2 ) yr ^–1 to compare the productivity of different ecosystems.
Hence, the correct answer is option (c).

Page No 98:

Question 4:

An inverted pyramid of biomass can be found in which ecosystem?

a. Forest

b. Marine

c. Grass land

d. Tundra

Answer:

The pyramid of biomass in sea is generally inverted because the biomass of fish far exceeds that of phytoplankton.
Hence, the correct answer is option (b).

Page No 99:

Question 5:

Which of the following is not a producer?

a. Spirogyra

b. Agaricus

c. Volvox

d. Nostoc

Answer:

Agaricus (mushroom) is a fungus and it is not a producer. Spirogyra, Volvox and Nostoc are producers
Hence, the correct answer is option (b).

Page No 99:

Question 6:

Which of the following ecosystems is most productive in terms of net primary production?

a. Deserts

b. Tropical rain forests

c. Oceans

d. Estuaries

Answer:

In terms of net primary production, tropical rain forests ecosystems are the most productive.
Hence, the correct answer is (b).

Page No 99:

Question 7:

Pyramid of numbers is:

a. Always upright

b. Always inverted

c. Ether upright or inverted

d. Neither upright nor inverted.

Answer:

In a parasitic food chain, the pyramid of number is inverted while in grassland or forest ecosystem, it is upright.
Hence, the correct answer is option (c).

Page No 99:

Question 8:

Approximately how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis?

a. Less than 1%

b. 2-10%

c. 30%

d. 50%

Answer:

Plants capture only 2-10 per cent of the PAR (photosynthetically active radiation) and this small amount of energy sustains the entire living world.
Hence, the correct answer is option (b).

Page No 99:

Question 9:

Among the following, where do you think the process of decomposition would be the fastest?

a. Tropical rain forest

b. Antarctic

c. Dry arid region

d. Alpine region

Answer:

The process of decomposition would be the fastest in tropical rainforests due to warm and moist environment.
Hence, the correct answer is option (a).

Page No 99:

Question 10:

How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?

a. 1%

b. 10%

c. 40%

d. 90%

Answer:

10% of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores.
Hence, the correct answer is option (b).

Page No 100:

Question 11:

During the process of ecological succession the changes that take place in communities are:

a. Orderly and sequential

b. Random

c. Very quick

d. Not influenced by the physical environment.

Answer:

An important characteristic of all communities is that their composition and structure constantly change in response to the changing environmental conditions. This change is orderly and sequential, parallel with the changes in the physical environment.
Hence, the correct answer is option (a).

Page No 100:

Question 12:

Climax community is in a state of:

a. non-equilibrium

b. equilibrium

c. disorder

d. constant change.

Answer:

The climax community is in a state of equilibrium with the environment.
Hence, the correct answer is option (b).

Page No 100:

Question 13:

Among the following bio-geo-chemical cycles which one does not have losses due to respiration?

a. Phosphorus

b. Nitrogen

c. Sulphur

d. All of the above

Answer:

In phosphorus, nitrogen and sulphur cycles does not have losses due to respiration.
Hence, the correct answer is option (d).

Page No 100:

Question 14:

The sequence of communities of primary succession in water is:

a. phytoplankton, sedges, free-floating hydrophytes, rooted hydrophytes, grasses and trees.

b. phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses and trees.

c. free-floating hydrophytes, sedges, phytoplankton, rooted hydrophytes, grasses and trees.

d. phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees.

Answer:

In primary succession in water, the pioneers are the small phytoplanktons, which are replaced with time by rooted-submerged plants, rooted-floating angiosperms followed by free-floating plants, then reed swamp, marsh-meadow, scrub and finally the trees.
Hence, the correct answer is option (d).

Page No 100:

Question 15:

The reservoir for the gaseous type of bio-geo chemical cycle exists in

a. stratosphere

b. atmosphere

c. ionosphere

d. lithosphere

Answer:

The reservoir for the gaseous type of bio-geo chemical cycle exists in the atmosphere.
Hence, the correct answer is option (b).

Page No 100:

Question 16:

If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be.

a. scavenger

b. tertiary producer

c. tertiary consumer

d. secondary consumer

Answer:

The trophic level of the last species would be the tertiary consumer.
tHence, the correct answer is option (c).

Page No 101:

Question 17:

Which of the following type of ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below 100mm

(a) Grassland

(b) Shrubby forest

(d) Mangrove

Answer:

An area where evaporation exceeds precipitation, and mean annual rainfall is below 100mm is a desert ecosystem.
Hence, the correct answer is option (c).

Page No 101:

Question 18:

The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called:

a. Pelagic zone

b. Benthic zone

c. Lentic one

d. Littoral zone

Answer:

The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called littoral zone.
Hence, the correct answer is option (d).

Page No 101:

Question 19:

Edaphic factor refers to:

a. Water

b. Soil

c. Relative humidity

d. Altitude

Answer:

Edaphic factor refers to the structure and composition of soil.
Hence, the correct answer is option (b).

Page No 101:

Question 20:

Which of the following is an ecosystem service provided by a natural ecosystem?

a. Cycling of nutrients

b. Prevention of soil erosion

c. Pollutant absorption and reduction of the threat of global warming

d. All of the above

Answer:

The products of ecosystem processes are named as ecosystem services, for example, healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, prevention of soil erosion, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values.

Hence, the correct answer is option (d).

Page No 101:

Question 1:

Name an organism found as secondary carnivore in an aquatic ecosystem.

Answer:

Catfish are secondary catfish in an aquatic ecosystem.

Page No 101:

Question 2:

What does the base tier of the ecological pyramid represent?

Answer:

Producers represent the base tier of the ecological pyramid.

Page No 101:

Question 3:

Under what conditions would a particular stage in the process of succession revert back to an earlier stage?

Answer:

In case of any natural calamity such as a volcano, earthquake etc. or any human interference (fire, deforestation) the process of succession reverts to an earlier stage.

Page No 101:

Question 4:

Arrange the following as observed in vertical stratification of a forest: Grass, Shrubby plants, Teak, Amaranths.

Answer:

In vertical stratification of a forest, the arrangement will be- Grass, Amaranths, Shrubby plants, Teak

Page No 101:

Question 5:

Name an omnivore which occurs in both grazing food chain and the decomposer food chain.

Answer:

Crow can be found in both grazing food chain and the decomposer food chain.

Page No 102:

Question 6:

Justify the pitcher plant as a producer.

Answer:

Because pitcher plants have the green pigment chlorophyll, they are photosynthetic and capable of producing food on their own. This justifies them as a producer.

Page No 102:

Question 7:

Name any two organisms which can occupy more than one trophic level in an ecosystem.

Answer:

Sparrow and humans can occupy more than one trophic level in an ecosystem.

Page No 102:

Question 8:

In the North East region of India, during the process of jhum cultivation, forests are cleared by burning and left for regrowth after a year of cultivation. How would you explain the regrowth of forest in ecological term?

Answer:

This can be termed as secondary succession.

Page No 102:

Question 9:

Climax stage is achieved quickly in secondary succession as compared to primary succession. Why?

Answer:

Secondary succession begins in areas where natural biotic communities have been destroyed such as in abandoned farm lands, burned or cut forests, lands that have been flooded. Since some soil or sediment is present, succession is faster than primary succession. So, the climax stage is achieved quickly in secondary succession as compared to primary succession.

Page No 102:

Question 10:

Among bryophytes, lichens and fern which one is a pioneer species in a xeric succession?

Answer:

Lichens act as a pioneer species in a xeric succession.

Page No 102:

Question 11:

What is the ultimate source of energy for the ecosystems?

Answer:

Sun (solar energy) is the ultimate source of energy for the ecosystems.

Page No 102:

Question 12:

Is the common edible mushroom an autotroph or a heterotroph?

Answer:

The common edible mushroom is an autotroph since it belongs to the kingdom fungi.

Page No 102:

Question 13:

Why are oceans least productive?

Answer:

Due to limited solar light and less amount of nutrients, oceans are least productive.

Page No 102:

Question 14:

Why is the rate of assimilation of energy at the herbivore level called secondary productivity?

Answer:

The rate of assimilation of energy at the herbivore level is called secondary productivity because the biomass available to the consumer for consumption is a result of the primary productivity from plants.

Page No 102:

Question 15:

Why are nutrient cycles in nature called biogeochemical cyles?

Answer:

Because the nutrient cycle involves both living (bio) and non-living components (rocks, air, water), they are called the biogeochemical cycle.

Page No 102:

Question 16:

Give any two examples of xerarch succession.

Answer:

Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions. The examples of xerarch succession are -

Lithosere - Ecological succession on a bare rock.
Psammosere - Ecological succession on sand.

Page No 102:

Question 17:

Define self sustainability.

Answer:

The ability of an ecosystem to maintain itself without any external support is known as self-sustainability.

Page No 102:

Question 18:

Given below is a figure of an ecosystem. Answer the following questions.

i. What type of ecosystem is shown in the figure.

ii. Name any plant that is characteristic of such ecosystem.

Answer:

i. Desert ecosystem
ii. Cactus, Opuntia

Page No 102:

Question 19:

What is common to earthworm, mushroom, soil mites and dung beetle in an ecosystem?

Answer:

All the mentioned organisms are detritivores which break down detritus into smaller particles.

Page No 103:

Question 1:

Organisms at a higher trophic level have less energy available. Comment.

Answer:

According to the 10 percent law, only 10 percent of the energy is transferred to each trophic level from the lower trophic level. Due to this, energy loss occurs as we move to the higher trophic levels.

Page No 103:

Question 2:

The number of trophic levels in an ecosystem are limited. Comment.

Answer:

After a certain number of trophic levels, the energy becomes zero because only 10% of the energy is transmitted from one level to another. As a result, the succession of trophic levels comes to an end, and the total number of trophic levels in an ecosystem is therefore limited.

Page No 103:

Question 3:

Is an aquarium a complete ecosystem?

Answer:

Yes, an aquarium is a complete ecosystem because it has all the biotic (bacteria, plants, small aquatic organisms) and abiotic components (water, light, temperature, oxygen in the water) of an ecosystem.

Page No 103:

Question 4:

What could be the reason for the faster rate of decomposition in the tropics?

Answer:

The soil in the tropics is rich in nutrients and includes organic matter that helps in quick decomposition. Also, the hot and humid climate provides an ideal situation for the microbes to speed up the process of decomposition.

Page No 103:

Question 5:

Human activities interfere with carbon cycle. List any two such activities.

Answer:

Burning of fossil fuels and active deforestation are major human activities that interfere with the carbon cycle.

Page No 103:

Question 6:

Flow of energy through various trophic levels in an ecosystem is unidirectional and non-cyclic. Explain.

Answer:

The flow of energy through various trophic levels in an ecosystem is unidirectional and non-cyclic because energy is passed on through successive trophic levels in the food chain. The movement of energy is only in one direction from lower to higher trophic level and it does not reverse back to the previous energy level.

Page No 103:

Question 7:

Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs and animals as heterotrophs, what are microbes referred to as? How do the microbes fulfil their energy requirements?

Answer:

Since microbes receive their energy requirements from the organic matter obtained by dead and decaying animals and plants., they can be referred to as heterotrophs and saprotrophs.

Page No 103:

Question 8:

Poaching of tiger is a burning issue in today's world. What implication would this activity have on the functioning of the ecosystem of which the tigers are an integral part?

Answer:

The poaching of tigers would lead to the extinction of the animal and ultimately cause an imbalance in the natural ecosystem.
This would result in the eradication of the predator species from the environment and an increase in the population of the tiger's natural prey.

Page No 103:

Question 9:

In relation to energy transfer in ecosystem, explain the statement "10kg of deer's meat is equivalent to 1 kg of lion's flesh".

Answer:

According to the 10% law, only 10% of the energy is transferred from a lower trophic level to a higher one. So, if the lion eats 10 kg of deer meat then only 10% energy would be passed to the lion i.e., 1 kg of lion’s flesh.

Page No 103:

Question 10:

Primary productivity varies from ecosystem to ecosystem. Explain?

Answer:

ans

Page No 103:

Question 11:

Sometimes due to biotic/abiotic factor the climax remain in a particular seral stage (pre climax) without reaching climax. Do you agree with this statement. If yes give a suitable example.

Answer:

ans

Page No 103:

Question 12:

What is an incomplete ecosystem? Explain with the help of suitable example.

Answer:

ans

Page No 103:

Question 13:

What are the shortcomings of ecological pyramids in the study of ecosystem?

Answer:

ans

Page No 103:

Question 14:

How do you distinguish between humification and mineralisation?

Answer:

ans

Page No 103:

Question 15:

Fill in the trophic levels (1, 2, 3 and 4) in the boxes provided in the figure.

Answer:

ans

Page No 104:

Question 16:

The rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen, pH of the soil substratum, temperature etc. Discuss.

Answer:

ans

Page No 104:

Question 1:

A farmer harvests his crop and expresses his harvest in three different ways.

a. I have harvested 10 quintals of wheat.

b. I have harvested 10 quintals of wheat today in one acre of land.

c. I have harvested 10 quintals of wheat in one acre of land, 6 months after sowing.

Do the above statements mean one and the same thing. If your answer is yes, give reasons. And if your answer is ‘no’ explain the meaning of each expression.

Answer:

ans

Page No 104:

Question 2:

Justify the following statement in terms of ecosystem dynamics. “Nature tends to increase the gross primary productivity, while man tends to increase the net primary productivity”.

Answer:

ans

Page No 104:

Question 3:

Which of the following ecosystems will be more productive in terms of primary productivity? Justify your answer.

A young forest, a natural old forest, a shallow polluted lake, alpine meadow.

Answer:

ans

Page No 105:

Question 4:

What are the three types of ecological pyramids. What information is conveyed by each pyramid with regard to structure, function and energy in the ecosystem.

Answer:

ans

Page No 105:

Question 5:

Write a short note on pyramid of numbers and pyramid of biomass.

Answer:

ans

Page No 105:

Question 6:

Given below is a list of autotrophs and heterotrophs. With your knowledge about food chain, establish various linkages between the organisms on the principle of ‘eating and being eaten’. What is this inter-linkage established known as?

Algae, hydrilla, grasshopper, rat, squirrel, crow, maize plant, deer, rabbit, lizard, wolf, snake, peacock, phytoplankton, crustaceans, whale, tiger, lion, sparrow, duck, crane, cockroach, spider, toad, fish, leopard, elephant, goat, Nymphaea, Spirogyra.

Answer:

ans

Page No 105:

Question 7:

“The energy flow in the ecosystem follows the second law of thermodynamics.” Explain.

Answer:

ans

Page No 105:

Question 8:

What will happen to an ecosystem if:

a. All producers are removed;

b. All organisms of herbivore level are eliminated; and

c. All top carnivore population is removed

Answer:

ans

Page No 105:

Question 9:

Give two examples of artificial or man made ecosystems. List the salient features by which they differ from natural ecosystems.

Answer:

ans

Page No 105:

Question 10:

The biodiversity increases when one moves from the pioneer to the climax stage. What could be the explanation?

Answer:

ans

Page No 105:

Question 11:

What is a biogeochemical cycle. What is the role of the reservoir in a biogeochemical cycle. Give an example of a sedimentary cycle with reservoir located in earth’s crust.

Answer:

ans

Page No 105:

Question 12:

What will be the P/R ratio of a climax community and a pioneer community. What explanation could you offer for the changes seen in P/R ratio of a pioneer community and the climax community.

Answer:

ans

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