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Do you know that living organisms and their surroundings together create a network of biotic and abiotic factors? The NCERT Exemplar Class 12 Biology Solutions Chapter 14 Ecosystem comes with different kinds of questions like MCQs, very short, short and long answer types with proper solutions. These NCERT exemplar solutions support students in learning the chapter step by step and help to clear their concepts easily.
The topics included in the NCERT Exemplar Solutions for Class 12 Biology explain ecosystem structure, energy movement, and features of land and water ecosystems. It also talks about ecological pyramids, cycles of nutrients like carbon and nitrogen, and how human actions such as pollution and deforestation disturb nature. By practising these questions again and again, students can hold on to important facts and small points better and also sharpen their problem-solving skills. Going through these resources regularly gives confidence and makes the Ecosystem chapter prepared well for the exam with help of the NCERT Exemplar Solutions for Class 12.
Different types of questions, like MCQs, short and long answers, help students understand the topics better and do well in exams.
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 (c) ii and iii, (d) i and ii
Answer:
Decomposers like fungi and bacteria cannot make their own food, so they depend on organic matter from dead plants and animals, making them heterotrophs. Since they feed by breaking down and absorbing nutrients from decaying matter, they are also saprotrophs. Therefore, they belong to both these categories but not autotrophs or chemo-autotrophs.
Hence, the correct answer is option (c), (ii) heterotrophs and (iii) saprotrophs.
Question:2
The process of mineralization by microorganisms 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:
Mineralization is the process where microorganisms convert organic matter in humus into inorganic nutrients, such as nitrates, phosphates, and other mineral salts. These minerals are then available to plants for reuse in the ecosystem. It does not release organic nutrients, but rather makes inorganic forms available for plant uptake.
Hence, the correct answer is option (a), inorganic nutrients from humus.
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 and iii
Answer:
Productivity measures the biomass generated per unit area or volume per year. It is usually expressed in units like grams per square meter per year (g m⁻² yr⁻¹) or kilocalories per square meter per year (kcal m⁻² yr⁻¹). The other options are incorrect units or wrongly presented.
Hence, the correct answer is option (c), (ii) g m⁻² yr⁻¹ and (iv) kcal m⁻² yr⁻¹.
Question:4
An inverted pyramid of biomass can be found in which ecosystem?
a. Forest
b. Marine
c. Grassland
d. Tundra
Answer:
In the marine ecosystem, phytoplankton are microscopic producers with very little biomass, but they support larger consumers like fish with much greater biomass. This makes the pyramid of biomass inverted, unlike a forest where producers have the most biomass.
Hence, the correct answer is option (b), marine.
Spirogyra, Nostoc, and Volvox are photosynthetic autotrophic organisms (producers). Agaricus, however, is a mushroom (fungus) that feeds on decaying matter, making it a saprotroph, not a producer. Hence, it does not contribute to producing energy from sunlight.
Hence, the correct answer is option (b), Agaricus.
Question:6
Which of the following ecosystems is most productive in terms of net primary production?
a. Deserts
b. Tropical rainforests
c. Oceans
d. Estuaries
Answer:
Tropical rainforests have ideal warm, wet conditions and dense plant life, which results in very high net primary productivity (NPP). Deserts, estuaries, and oceans have lower rates in comparison. Rainforests capture a huge amount of solar energy through their dense canopy.
Hence, the correct answer is option (b), tropical rainforests.
Question:7
The pyramid of numbers is:
a. Always upright
b. Always inverted
c. Either upright or inverted
. Neither upright nor inverted.
Answer:
The pyramid of numbers may be upright if there are many producers and fewer consumers, or inverted when a single large producer supports many small consumers (like a big tree supporting insects). So its shape depends on the ecosystem structure.
Hence, the correct answer is option (c), either upright or inverted.
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 can only convert about 2–10% of the total solar energy falling on their leaves into chemical energy through photosynthesis. The rest is reflected, lost as heat, or not absorbed. So their energy capture efficiency is low but crucial for ecosystems.
Hence, the correct answer is option (b), 2–10%.
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
. Alpine region
Answer:
Tropical rainforests have warm temperatures, high moisture, and rich organic matter, which creates perfect conditions for rapid decomposition. Cold or dry regions slow down microbial activity, making decomposition there much slower.
Hence, the correct answer is option (a), tropical rainforest.
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:
About 10% of the net primary productivity of a terrestrial ecosystem is consumed and digested by herbivores. The remaining 90% is used by decomposers or stays in the system as dead matter. This follows the “ten percent law” of energy transfer.
Hence, the correct answer is option (b), 10%.
Get the very short answers of all the questions here:
Question:1
Name an organism found as a secondary carnivore in an aquatic ecosystem.
Answer:
SharkQuestion:3
Answer:
Under natural or human-induced disturbances, a particular stage in the process of succession would revert to an earlier stage.Question:4
Answer:
Teak → Amaranths → Shrubby plants →GrassQuestion:6
Justify the pitcher plant as a producer.
Answer:
Pitcher plant contains chlorophyll and carries out photosynthesis. It feeds on insects only to obtain nitrogen from them. Hence, a pitcher plant is a producer.Question:7
Name any two organisms that can occupy more than one trophic level in an ecosystem.
Answer:
Sparrow: It is a primary consumer when it feeds on grains, but becomes a secondary consumer when it feeds on worms and insects.Question:8
Answer:
In this case, the regrowth of forests is an example of ecological succession. After clearing of forests, the conditions become xerarch which proceeds to mesarch condition after the growth of forests.Question:9
The climax stage is achieved quickly in secondary succession as compared to primary succession. Why?
Answer:
Soil becomes available after primary succession. It provides an ideal condition for the growth of bigger plants. Secondary succession can be obtained quickly compared to primaryQuestion:10
Among bryophytes, lichens and fern which one is a pioneer species in a xeric succession?
Answer:
Lichens are considered as a pioneer species in a xeric succession.Question:11
What is the ultimate source of energy for the ecosystems?
Answer:
The sun is the ultimate source of energy for the ecosystems.Question:12
Is the common edible mushroom an autotroph or a heterotroph?
Answer:
The common edible mushroom is a Heterotroph.Question:13
Why are oceans least productive?
Answer:
Availability of solar radiation is least in oceans, especially in deep oceans. Due to this, oceans are the least productive.Question:14
Why is the rate of assimilation of energy at the herbivore level called secondary productivity?
Answer:
Secondary productivity is the rate of formation of new organic matter by consumers. The consumers get raw materials for this purpose from producers, which is made possible through assimilation. Due to this, the rate of assimilation of energy at the herbivore level is called secondary productivity.Question:15
Why are nutrient cycles in nature called biogeochemical cycles?
Answer:
Nutrients are cycled through biotic components as well as through abiotic components. The term 'bio' shows biotic components, while 'geo' shows abiotic components. Hence, the nutrient cycles in nature are called biogeochemical cycles.Question:16
Give any two examples of xerarch succession.
Answer:
Lichen → Bryophytes → Pteridophytes → Gymnosperms and AngiospermsQuestion:17
Answer:
A sustainable system without relying on any external input is called a self-sustainable system. This ability of the system is referred to as self-sustainability. Natural ecosystems are self-sustainable.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 an ecosystem.
Answer:
(a) Desert ecosystemQuestion:19
What is common to the earthworm, mushroom, soil mites and dung beetle in an ecosystem?
Answer:
All of them are part of the detritus food chain.Get all the short answers to the questions here:
Question:1
Organisms at a higher trophic level have less energy available. Comment.
Answer:
As per the law of 10%, just 10% of the total energy consumed by an organism at a particular trophic level is available for the organism at the next trophic level. Therefore, a producer converts whatever energy into biomass; just 10% of it is available for the primary consumer. Similarly, just 10% of the energy consumed by the primary consumer is available for the secondary consumer. Due to this, organisms at a higher trophic level have less energy available.Question:2
The number of trophic levels in an ecosystem is limited. Comment
Answer:
In any ecosystem, the number of trophic levels can go up to a maximum of five, and in that case, the food chain will look like the following:Question:3
Is an aquarium a complete ecosystem?
Answer:
The aquarium is a man-made ecosystem, and it has its own limitations. The confined space of an aquarium cannot have an endless supply of inorganic materials for producers. For supporting even a small number of consumers, there is a need for a large number of producers, which is not possible in a small space provided in an aquarium.Question:4
What could be the reason for the faster rate of decomposition in the tropics?
Answer:
Decomposition is largely an oxygen-requiring process. Moreover, ambient temperature and moisture are also required for this. If detritus is rich in nitrogen and water-soluble substances, then decomposition is faster. All these conditions are available in the tropical climate. Hence, there is a faster rate of decomposition in the tropics.Question:5
Human activities interfere with the carbon cycle. List any two such activities.
Answer:
Following are the two activities, which interfere with the carbon cycle:Question:6
Answer:
About 90% of the energy consumed by an organism at a particular trophic level is dissipated in the form of heat energy. This leaves just 10% for the organism at the next trophic level. By the time, it reaches the topmost trophic level; the available energy is an extremely small portion of the energy, which was originally converted by the producer. Due to this, energy flow is unidirectional through various trophic levels and is non-cyclic.Question:7
Answer:
Productivity, decomposition, energy flow and nutrient cycling are integral features of any ecosystem. Plants and animals play important roles in productivity. Some microbes play a role in productivity as some of the microbes are autotrophs, e.g. some algae and some chemosynthetic bacteria. Most of the microbes are heterotrophs. Parasitic microbes get nutrition from the host on which they depend. Many microbes are saprotrophs. They get nutrition from detritus, i.e. they are an important part of the detritus food chain.Question:8
Answer:
Tigers are at the top of the food pyramid in the forest ecosystem and are tertiary consumers. A tertiary consumer helps in checking the uncontrolled population growth of secondary and primary consumers. If all tigers are killed, then no animal will be left to control the population of herbivores. This will result in quick exhaustion of producers. Finally, in the absence of producers, the herbivores will die because of starvation. This will destroy the whole ecosystem.Question:9
Answer:
We know that just 10% of the energy consumed at a trophic level is available for the next trophic level. Here 10 kg of deer's meat means 10kg of biomass at the level of primary consumer. Out of this, the deer for its own needs utilizes 90%. Rest 10%, i.e. just 1 kg, is available for the lion. Hence, it is correct to say that 10 kg of deer's meat is equivalent to 1 kg of lion's flesh.Question:10
Primary productivity varies from ecosystem to ecosystem. Explain?
Answer:
Primary productivity is the biomass produced per unit area over some time by photosynthesis. In simple terms, we can say that it is the amount of biomass produced by green plants in a particular ecosystem. Plant population varies from one ecosystem to another. The number of plants is higher in tropical rainforests compared to deserts. Therefore, primary productivity would be much higher in tropical rainforests than in deserts. This shows that primary productivity varies from one ecosystem to another ecosystem.Question:11
Answer:
This entire sequence of communities that successively change in a given area is called sere (s). All the biotic and abiotic factors play a crucial role in this transition process and thus enable a community to reach the climax. If biotic and abiotic factors are not supportive enough for the climax, then the community may remain in a particular seral stage without reaching the climax. The presence of sparse vegetation at Tabletop Mountain can be one example of a community in the seral stage. The community at the tabletop mountain may be in a stage in which only ferns and mosses may be present. In due course of time, it would pave the way for higher plants.Question:12
What is an incomplete ecosystem? Explain with the help of a suitable example.
Answer:
An ecosystem, which is devoid of certain biotic or abiotic factors, is called an incomplete ecosystem. An incomplete ecosystem cannot be a self-sustaining ecosystem. The aquarium is a good example of an incomplete ecosystem. The aquarium may be having producers and consumers, but it does not have decomposers. Lack of decomposers necessitates frequent cleaning of the aquarium.Question:13
What are the shortcomings of ecological pyramids in the study of the ecosystem?
Answer:
The following are the shortcomings of ecological pyramids:Question:14
How do you distinguish between humification and mineralization?
Answer:
Both humification and mineralization are important aspects of the detritus food chain. Humification leads to the formation of a dark-coloured amorphous substance called humus, while decomposition leads to the formation of inorganic compounds from organic matter.Question:15
Fill in the trophic levels (1, 2, 3 and 4) in the boxes provided in the figure.
Answer:
1: ProducerThe detailed answers to all long-answer questions in here:
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 the same thing? If your answer is yes, give reasons. And if your answer is no, explain the meaning of each expression.
Answer:
No, they do not mean the same thing.Question:2
Answer:
Gross Primary Productivity (GPP) is the rate of production of organic matter in an ecosystem. We get Net Primary Productivity (NPP) on removing respiratory losses (R) from GPP. Nature contributes various factors (biotic and abiotic) to improve the GPP. In other words, nature tends to increase GPP.Question:3
Answer:
A young forest will have a lower tree density and thus, lower primary productivity. A shallow, polluted lake may also have a lower density of flora due to toxicity from pollution. An Alpine meadow is full of grass and thus, a lower tree density.Question:4
Answer:
The following are the three types of ecological pyramids: -Question:5
Write a short note on the pyramid of numbers and the pyramid of biomass.
Answer:
Pyramid of Numbers: It is arranged from the lower trophic levels at the bottom to higher trophic levels above and shows the number of individuals at each level. Mostly, these pyramids have a wider base (higher producer population)Question:6
Given below is a list of autotrophs and heterotrophs. With your knowledge about the 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:
This linkage that has been established herewith is known as a food web. It pertains to the interlocking between two or more types of the food chain at several trophic levels.Question:7
"The energy flow in the ecosystem follows the second law of thermodynamics." Explain.
Answer:
The entropy of an isolated system never decreases, and such a system will proceed towards thermodynamic equilibrium. A system in thermodynamic equilibrium will have maximum entropy. An ecosystem requires a constant supply of energy for the synthesis of molecules. Energy always flows unidirectionally in an ecosystem. This is because a reverse flow of energy will make the system unstable (non-equilibrium state). Producers get energy from the sun and become the suppliers of energy to the higher trophic levels. Energy always flows from a lower trophic level to a higher one.Question:8
What will happen to an ecosystem if:
a. All producers are removed.
b. All organisms at the herbivore level are eliminated; and
c. All top carnivore population is removed
Answer:
(a) If all producers are removed from the ecosystem, primary consumers will die due to a lack of food. In turn, the secondary and tertiary consumers will also become extinct as they will also lose their source of nutrients. Essentially, the ecosystem will end.Question:9
Answer:
Natural EcosystemQuestion:10
Answer:
A rich diversity of flora which can support a larger and diverse consumer set will lead to greater biodiversity of a community.Question:11
Answer:
P/R ratio of a community is the ratio of gross production and community respiration. This can be one, less than one or more than one.NCERT Exemplar Class 12 Solutions Subject Wise
Also, Read NCERT Solution subject-wise
Given below are the most important topics and subtopics of this chapter:
Also, check the NCERT Books and the NCERT Syllabus here
An important question is provided below, which can guide students for doing exam preparation in the right direction.
Question: In which ecosystem is the autotroph-fixed energy likely to reach the primary carnivore level in the shortest time?
A. Temperate deciduous forest
B. Grasslands
C. Ocean
D. Tropical rainforest
Answer: The correct answer is option(4).
Explanation:
Tropical rainforests are known for their high productivity and biodiversity. They have a dense and complex structure with a wide variety of plant and animal species. This high productivity means that autotrophs, such as trees, plants, and other photosynthetic organisms, produce a significant amount of organic matter and fixed energy through photosynthesis.
Must Read NCERT Notes subject-wise
Below are the links of all the chapters for easy access:
Some of the most basic and important topics to study from chapter 14, ecosystem are structures and function of ecosystem, the concept of productivity, decomposition, energy flow, relationship between different organisms at varied tropical levels of the food chain, system of ecological succession and different services provided by the ecosystem.
Yes, the chapter is important from the view of Board exams and helps students to learn better with the help of proper guidance and solutions provided.
The ecosystem has been defined as the functional unit of nature that is an organization of biotic and abiotic components interacting with one another.
The 10% law of energy transfer in an ecosystem explains that only roughly 10% of the energy at one trophic level is transferred to the next, and the rest of the 90% is lost as heat, utilized in metabolic processes, or not consumed. This indicates that energy is reduced at each subsequent trophic level. Consequently, fewer organisms are able to be sustained at higher trophic levels. The law exemplifies the inefficiency in energy transfer via food chains.
According to the NCERT Exemplar, decomposers are responsible for recycling nutrients in an ecosystem. Decomposers decompose dead and decaying organic matter, including plant and animal tissues, into simpler compounds like nitrogen and carbon. This process makes necessary nutrients available for producers by returning them to the soil. Decomposers ensure ecosystem balance through continuous energy and nutrient flow.
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