Ecosystem Class 12 Biology Important Questions

Please refer to Ecosystem Class 12 Biology Important Questions with solutions provided below. These questions and answers have been provided for Class 12 Biology based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 12 Biology for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 12.

Class 12 Biology Important Questions Ecosystem

Question. In an Ecological pyramid the base represents the
(a) Primary consumer
(b) Secondary consumer
(c) Producer
(d) Top consumer

Question. Pyramid of energy is always
(a) Inverted
(b) Upright
(c) May be inverted or upright
(d) Straight

Question. The pyramid of number in food chain having big trees—>insects—>small birds —> large birds will be
(a) Inverted
(b) Upright
(c) May be inverted or upright
(d) Straight

Question. Final community that is in equilibrium with the environment is called
(a) Pioneer community
(b) Climax community
(c) Intermediate commmunity
(d) None of these

Question. The entire sequence of community that successively change in a given area are called
(a) Pioneer community
(b) Sere
(c) Climax community
(d) None of these

Question. Type of succession that starts on the bare rock is
(a) Primary succession
(b) Secondary succession
(c) Tertiary succession
(d) None of these

Question. Which of the following is the example of an area where primary succession occurs?
(a) Cooled lava
(b) Cut forests
(c) Abandoned farmland
(d) All of these

Question. Succession of plant in a dry area is called
(a) Hydrarch succession
(b) Xerarch succession
(c) Mesarch succession
(d) None of these

Question. The species that invade a bare area is called
(a) Pioneer species
(b) Producers
(c) Climax species
(d) None of these

Question. After a Pioneer species invade the bare Rock during primary succession, species that invades is
(a) Gymnosperm
(b) Algae
(c) Bryophyte
(d) None of these

Question. Which of the following is incorrect?
(a) Both hydrarch and xerarch succession lead to medium water condition
(b) The climax community remains stable as long as the environment remains unchanged
(c) Since soil is already there, secondary succession is much faster
(d) Climax reaches very late in secondary succession

Question. The amount of nutrients such as carbon, nitrogen, phosphorus, calcium etc present in the soil at any given time is referred as
(a) Climax
(b) Succession
(c) Mesic state
(d) Standing state

Question. Which of the following is a type of nutrient cycle?
(a) Gaseous nutrient cycle
(b) Sedimentary nutrient cycle
(c) Water nutrient cycle
(d) Both 1 and 2

Question. The following does not come under gaseous nutrient cycle
(a) Nitrogen
(b) Phosphorus
(c) Carbon
(d) None of these

Question. Maximum part of composition of living organism is
(a) Carbon
(b) Phosphorus
(c) Nitrogen
(d) Water

Very Short Answer Questions

Question. All the primary productivity is not available to a herbivore. Give one reason.
Ans. All the primary productivity is not available to a herbivore because a considerable amount is utilised by the plant by respiration.

Question. Name an omnivore which occurs in both grazing food chain and the decomposer food chain.
Ans. Sparrow/crow

Question. Climax stage is achieved quickly in secondary succession as compared to primary succession. Why? 
Ans. The rate of succession is much faster in secondary succession as the substratum (soil) is already present as compared to primary succession where the process starts from a bare area (rock).

Question. Outline salient features of carbon cycling in an ecosystem.
Ans. Carbon Cycle –
• Carbon constitutes 49 per cent of dry weight of an organism.
• 71 per cent of the carbon is found dissolved in oceans which is responsible for its regulation in atmosphere.
• The carbon cycle occurs through atmosphere, oceans and through living and dead organisms.

Question. Standing crop and biomass are related to each other, how?
Ans. The standing crop is measured as the mass of living organisms or the number of plants in a unit area. The biomass of a species is expressed in terms of fresh or dry weight.

Question. Write the equation that helps in deriving the net primary productivity of an ecosystem.
Ans. GPP – R = NPP

Question. Why is the pyramid of biomass inverted in a pond ecosystem?
Ans. The pyramid of biomass is inverted in a pond ecosystem because the biomass of fish (top consumer) is far larger than the producers (phytoplanktons).

Question. Write a difference between net primary productivity and gross productivity.
Ans. Gross productivity (GPP) is the rate of production of organic matter during photosynthesis.
Net primary productivity (NPP) is the available biomass for the consumption by heterotrophs.
GPP − R = NPP

Short Answer Questions

Question. What is primary productivity? Give brief description of factors that affect primary productivity.
Ans. Primary productivity is the rate of synthesis of biomass by producers, per unit time, per unit area through the process of photosynthesis.
For factors affecting primary productivity, refer to Basic Concepts Point 6.

Question. Differentiate between a detritivore and a decomposer giving an example of each.
Ans. Table 14.10: Differences between detritivore and decomposer (Table 513)

Question. Define ecological pyramids and describe with examples, pyramids of number and biomass.
Ans. Ecological Pyramid
QU The relationship between producers and consumers at different trophic levels in an ecosystem can be graphically represented in the form of a pyramid called ecological pyramid.
QU Structure: The base always represents the producers or the first trophic level and the apex represents top level consumer or the last trophic level.

Question. Sometimes due to biotic/abiotic factor the climax remain in a particular seral stage (preclimax)without reaching the climax. Do you agree with this statement. If yes, give a suitable example. 
Ans. It is true that any change in the abiotic/biotic factor will arrest a particular seral stage leading to a pre-climax condition before the climax stage is achieved. This can happen in cases of forest fires, landslide, change in soil characteristics, increase in herbivore population leading to over-grazing.

Question. Construct a grazing food chain and detritus food chain using the following, with 5 links each:
Earthworm, bird, snake, vulture, grass, grasshopper, frog, decaying plant matter.
Ans. Grazing food chain:
Grass → Grasshopper → Frog → Snake → Vulture
OR
Grass → Grasshopper → Bird → Snake → Vulture

Detritus food chain:
Decaying plant matter Earthworm Bird Snake Vulture

Question. Explain with the help of two examples, how the pyramid of number and the pyramid ofbio mass can look inverted.
Ans. The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton and the number of big fishes eating the small fishes is also greater than the small ones. Also in pyramid of number, the number of insects feeding on a big tree is far greater than the number of trees. Now the number of small birds depending on the insects and the number of larger birds eating the smaller ones also increases in the order.

Question. Write important features of a sedimentary cycle in an ecosystem.
Ans. Sedimentary cycle is circulation of non-gaseous biogeochemical nutrients between abiotic and biotic components of ecosystem with reservoir pool being lithosphere or sediments of earth. 
Important features of a sedimentary cycle in an ecosystem are:
(i) Input: Weathering of rocks, industrial processing and mining adds the nutrient to the cycling pool.
(ii) Internal cycling: Nutrients contained in the cycling pool are picked up by producers and the process is called uptake. Organic matter with nutrients is then passed to the next trophic levels.
Wastes and dead remains of organisms give rise to detritus which undergoes decomposition.
(iii) Output: It is the loss of nutrients from cycling pool. It occurs through soil erosion, run-off water, etc.

Long Answer Questions

Question. (a) What is meant by ecological succession? Explain how it occurs.
(b) What properties distinguish a pioneer community from a climax community?
Ans. (a) Ecological Succession
• The sequential, gradual and predictable changes in the species composition in an area are called succession or ecological succession.
• It mainly focuses on changes in vegetation that in turn affect types of animals.
• The entire sequence of communities that successively changes in a given area are called sere(s).
• The individual transitional communities are termed as seral stages or seral communities.
• The community that is in near equilibrium with the environment is called a climax community.
(b) Table 14.12: Differences between pioneer community and climax community 

S.No.	Pioneer community	Climax community
(i)	The species which invade a bare area or land to initiate succession is called pioneer community.	The last or final stage in a succession constitute the climax community.
(ii)	The pioneer species have high reproductive rate.	The climax species have low reproductive rate.
(iii)	The pioneer species have short life span.	The climax species have long life span.
(iv)	They are replaceable.	They are stable and not replaced.

Question. Differentiate between primary and secondary succession. Provide one example of each.
Ans. Table 14.11: Differences between primary and secondary succession

S.No.	Primary Succession	Secondary Succession
(i)	It begins with areas where no living organisms ever existed.	It begins in areas where natural biotic communities have been destroyed.
(ii)	Establishment of a biotic community is very slow.	Establishment of a biotic community is faster.
(iii)	Example: Newly cooled-lava/barerocks/newly created ponds or reservoir.	Example: Abandoned farm lands/burnt or cut forests/lands that have been flooded.

Question. Carbon cycle in nature is a biogeochemical event. Explain.
OR
Explain the carbon cycle with the help of a simplified model. 
Ans. Carbon is returned to atmosphere as CO2 by animals and plants through respiration and the activities of decomposers.
• Some amount of fixed carbon is lost as sediments and removed from circulation.
• Burning of wood, forest fire, volcanic activity and combustion of organic matter and fossil fuels are some additional sources for releasing CO2 in the atmosphere.
• Human activities like deforestation and vehicular burning of fossil fuels have caused an increase in the amount of CO2 in atmosphere.

Question. Fill in the missing stages in the given primary hydrarch succession.
Phytoplankton → (a) → (b) → (c) → Submerged free-floating → (d) → Forest plant stage
What is common between hydrarch and xerarch succession?
Ans. (a) Reed-swamp stage
(b) Submerged plant stage
(c) Marsh-meadow stage
(d) Scrub stage
Both the hydrarch and xerarch lead to mesic conditions of forest.

Question. Describe the advantages for keeping the ecosystems healthy. 
Ans. By keeping the ecosystem healthy we can take advantage of the ecosystem services which are the products of ecosystems.
Following are the economic and environmental goods that we obtain from the ecosystem. They 
(i) Purify air and water
(ii) Mitigate drought and floods
(iii) Cycle nutrients
(iv) Generate fertile soil
(v) Provide wildlife habitat
(vi) Maintain biodiversity
(vii) Pollinate crops
(viii) Provide storage site for carbon
(ix) Provide aesthetic, cultural and spiritual value
(x) Provide stable food chain
(xi) Provide economically useful forest products
(xii) Provide sustainable biological legacy to future generations.

Question. State the function of a reservoir in a nutrient cycle. Explain the simplified model of carbon cycle in nature. 
Ans. The function of a reservoir is to meet the deficit of nutrient which occurs due to imbalance in the rate of influx and efflux.
For Carbon Cycle,

Question. Why is the length of a food chain in an ecosystem generally limited to 3–4 trophic levels? Explain with an example.
Ans. The amount of energy flow decreases with successive trophic levels as only 10% of energy is transferred from one trophic level to the next successive level. The energy is lost in the form of respiration and other vital activities to maintain life. If more trophic levels are present, the residual energy will be limited and decreased to such an extent that it cannot further support any trophic level by the flow of energy. So, the food chain is generally limited to 3–4 trophic levels only.
For, e.g., 

Question. 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.
Ans. (a) Reduction in primary productivity. No biomass available for consumption by higher trophic levels/heterotrophs and hence heterotrophs also die of starvation.
(b) Increase in primary productivity and biomass of producers. Carnivore population will subsequently dwindle due to food shortage.
(c) Increase in number of herbivores which leads to over-grazing by herbivores, finally resulting in desertification.

Question. Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Litter and detritus
(d) Upright and inverted pyramid
(e) Food chain and food web
(f) Primary and secondary productivity
Ans. (a) Grazing food chain and detritus food chain:

S.No.	Grazing food chain (GFC)	Detritus food chain (DFC)
(i)	It starts with green plants called producers as first trophic level.	It begins with dead organic matter and decomposers called saprophytes as first trophic level. Decomposers secrete digestive enzymes that breakdown dead and waste into simple, inorganic materials which are absorbed by them.
(ii)	A much less fraction of energy flows through this type of food chain.	A much large fraction of energy flows through this type of food chain.
(iii)	Energy for food chain comes from sun.	Energy for the food chain comes from organic remain or detritus.

(b) Production and decomposition

S.No.	Production	Decomposition
(i)	It is the process of formation of fresh biomass from inorganic matter by producers (plants) using sunlight.	It is the process of degradation of waste biomass into its constituents by decomposers.
(ii)	It traps energy.	It releases energy.
(iii)	It needs sunlight.	It does not require sunlight.
(iv)	It is an anabolic process.	It is a catabolic process.

(c) Litter and detritus

S.No.	Litter	Detritus
(i)	It is made of dried fallen plant matter.	It is freshly deposited organic matter, i.e., remains of plants and animals.
(ii)	It is found above the ground.	It is found both above and below the ground.

(d) Upright and inverted pyramid

S.No.	Upright pyramid	Inverted pyramid
(i)	The base bar comprises of producers in large number.	The base bar comprises producers in smallest number.
(ii)	The number of consumers decrease and become least in top consumer level.	The number of consumers increase and become largest in top consumer level.
(iii)	Pyramid of energy is always upright.	Pyramid of number and biomass may be inverted.

(e) Food chain and food web

S.No.	Food chain	Food web
(i)	The transfer of energy from producers to top consumers through a series of organisms is called food chain.	A number of food chains are inter-connected with each other, forming a web-like pattern is called food web.
(ii)	One organism holds only one position.	One organism can hold more than one position.
(iii)	The flow of energy can be easily calculated.	The flow of energy is very difficult to calculate.
(iv)	It is always straight and proceed in a progressive straight line.	Instead of straight line it is a series of branching lines.

(f) Primary and secondary productivity

S.No.	Primary productivity	Secondary productivity
(i)	It is the rate at which organic matter is built up by producers.	It is the rate at which organic matter is built up by consumers.
(ii)	It is the result of synthesis of fresh organic matter from inorganic materials.	It is the result of synthesis of organic matter from plant organic matter.