NEET Biology Ecosystem Important Questions Set 01

These Class 12 NEET Biology important questions on Ecosystem give 44 questions with step-by-step answers, arranged as very short, short and long answer types, as asked in school and board examinations. They help NEET aspirants revise the definitions, structures, differences and key terms of the chapter.

Very Short Answer Type Questions

Question 1. Pyramid of biomass can be inverted, erect or spindle-shaped. State true or false.
Answer: True.

Question 2. The standing crop can be measured in terms of fresh weight or dry weight. State true or false.
Answer: True.

Question 3. The major conduit of energy flow in a terrestrial ecosystem is through __________.
Answer: Detritus Food Chain (DFC).

Question 4. __________ being colloidal in nature, serves as a reservoir of nutrients.
Answer: Humus.

Question 5. Name the process involved in breaking down of complex organic matter into CO₂, water and nutrient.
Answer: Decomposition.

Question 6. Mention the name of process where predictable and gradual change occurs and pre-existing community makes habitat more suitable for upcoming communities.
Answer: Ecological succession.

Question 7. What percentage of total global carbon is found dissolved in ocean?
Answer: 71%.

Question 8. Which category of ecological pyramid can never be of more than one type?
Answer: Pyramid of energy.

Question 9. Give one example each for terrestrial and aquatic artificial ecosystem.
Answer: Terrestrial–Crop fields Aquatic–Aquarium.

Question 10. Identify the possible reservoir for the gaseous type of cycle.
Answer: Atmosphere and Hydrosphere e.g., Carbon, hydrogen and oxygen cycle.

Short Answer Type Questions

Question 11. Distinguish between standing crop and standing state.

Answer:

Standing crop Standing state

It is amount of biomass present at each It is amount of inorganic matter present in trophic level at a particular time. the soil at anygiven time.

Question 12. (i) Construct pyramid of number using following group of organisms.
Tree, Insects, Birds, Grasses, Ectoparasites.
(ii) How many different kind of pyramids of number are possible?
Birds Ectoparasites Birds Birds
Answer: (i) Insects Insects Tree Grasses Tree
(a) (b) (c)
(ii) Three different types of pyramid of number are possible :
(a) Erect (b) Spindle-shaped (c) Inverted

Question 13. Explain why pyramid of biomass is generally inverted in sea.
Answer: Pyramid of biomass depend upon biotic potential and longevity of organisms at different trophic level. If we consider total biomass of producers (phytoplanktons) w.r.t. consumers it will always give erect pyramid for a given time span.

Question 14. Mention different limitations of ecological pyramids.
Answer: Limitations of ecological pyramids are:
(i) Does not take into account the same species belonging to two or more trophic levels.
(ii) Does not accommodate food web.
(iii) Saprophytes are not given any place.

Question 15. Differentiate between primary and secondary succession.
Answer: Primary succession Secondary succession
1. It starts from previously unoccupied 1. It startsfrom recently denuded area. barren region.
2. Climax stage is reached very late. 2. Climate stage is reached early.

Question 16. How many different kind of nutrient cycle exist? Mention their reservoir pool.
Answer: Two broad categories of nutrient cycle exist viz; Gaseous cycle and Sedimentary cycle. Reservoir pool for gaseous cycle is atmosphere or hydrosphere and earth crust for sedimentary cycle.

Question 17. Define Ecosystem. What is global ecosystem?
Answer: Ecosystem is functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. Biosphere is called global ecosystem.

Question 18. What is stratification? Which ecosystem shows maximum stratification?
Answer: Stratification is vertical distribution of different species occupying different levels. For example, different strata occupied by trees, shrubs and herbs in a forest ecosystem. Tropical rain forest shows as many as five layers (strata).

Question 19. What represent available biomass for the consumption to heterotrophs? Define secondary productivity.
Answer: Net primary productivity (NPP) represent the maximum available biomass for the consumption to heterotrophs. Secondary productivity is the rate of formation of new organic matter by consumers.

Question 20. Give annual net primary productivity of the whole biosphere. What is the productivity of oceans?
Answer: Annual net primary productivity of the whole biosphere is approximately 170 billion tons. Productivity of oceans is only 55 billion tons.

Question 21. Enumerate structural features of Ecosystem.
Answer: Structures of an ecosystem are:
(i) Species composition
(ii) Stratification
(iii) Trophic structure
(iv) Standing crop
(v) Standing state

Question 22. Why do we call earthworms as farmer's friend?
Answer: Earthworms are referred to as farmer's friend because they help in the breakdown of complex organic matter as well as in loosening of the soil.

Question 23. What constitutes detritus?
Answer: Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute detritus.

Question 24. What is the sere? Give examples of areas where primary succession occurs.
Answer: Sere represents entire sequence of communities that successively occupy a given region. Examples of primary succession are:
(i) Newly cooled lava
(ii) Bare rock
(iii) Newly created pond or reservoir

Question 25. How much carbon is fixed annually through photosynthesis? Which human activities have significantly influenced the carbon cycle?
Answer: 4 × 10¹³ kg of carbon is fixed in the biosphere annually through photosynthesis. Human activities that have significantly influenced carbon cycle include
(i) Rapid deforestation
(ii) Burning of fossil fuel

Question 26. Define mineralisation. What are important climatic factors that regulate decomposition?
Answer: Mineralisation is a process in which final decomposition of organic matter is achieved and release of minerals takes place. Warm temperature, humid environment and aerobic condition promotes decomposition.

Question 27. Group of Organisms
Man, Phytoplanktons, Lion, Birds, Fishes, Wolf, Zooplankton, Grasshopper, Cow, Grass, Trees.
Arrange the above given group of organisms into different trophic levels/ecological groups.
Answer: Primary producers (First trophic level) – Grass, Trees, Phytoplanktons. Primary consumers (Second trophic level) – Grasshopper, Zooplankton, Cow. Secondary consumers (Third trophic level) – Birds, Fishes, Wolf. Tertiary consumers (Fourth trophic level) – Man, Lion.

Question 28. What is meant by PAR? What percentage of PAR sustain the entire living world?
Answer: PAR means photosynthetically active radiation i.e., 400–700 nm. Plants capture only 2–10% of PAR which sustains the entire living world.

Question 29. Why do we find variation in standing state in different ecosystems and on seasonal basis?
Answer: Earth crust is the source of inorganic matter which constitutes standing state of a region. Composition of earth strata differs in terms of kind and quantity of these minerals. Also temperature and moisture affect mineralisation process that bring about fluctuation in standing state.

Question 30.

SUN

Identify A, B, NA, NU in the above drawn energy flow. Do you think cyclic flow of energy takes place?

Answer:

A – Decomposers B – 30% Respiration loss (R) NA – Not Assimilated NU – Not Utilized Energy does not show cyclic flow but it flows unidirectionally.

Long Answer Type Questions

Question 31. Define humus and describe the processes and products of decomposition.
Answer: Humus is dark-coloured amorphous substance that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Decomposition is largely an oxygen-requiring process where complex organic matter gets broken down into inorganic substances like CO₂, H₂O and minerals. It involves processes like:
(i) Fragmentation : Breakdown of detritus into small particles.
(ii) Leaching : Water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
(iii) Catabolism : Enzymatic degradation of detritus into simpler inorganic substances by bacteria and fungi. All the above processes occur simultaneously on the detritus.

Question 32. Discuss energy flow in ecosystem.
Answer: (i) Sun in the only source of energy for all ecosystems on earth, deep sea hydrothermal ecosystem being the only exception. Plants capture only 2–10% of the PAR which sustains the entire living world.
(ii) Unidirectional flow of energy from the sun to producers and then to consumers is achieved.
(iii) All organisms are dependent for their food on producers, either directly or indirectly. The food chain or food web is formed which mark interdependency of different organisms.
(iv) No energy that is trapped into an organism remains in it forever. Death of an organism is the beginning of the detritus food chain.
(v) In an aquatic ecosystem GFC is the major conduit for energy flow whereas in a terrestrial ecosystem DFC is the major conduit.
(vi) We find only 10% of the energy is transferred to each trophic level from the lower trophic level.

Question 33. Give a simplified model of phosphorous cycle. What are different biological components where phosphorous is present?

Answer:

Phosphorous Cycle Consumers Producers

Litter fall Detritus Decomposition Uptake Soil solution Weathering Run off Rock minerals Phosphorous is a major constituent of biological membranes, nucleic acids, ATP, NADPH etc. Large quantity of phosphorous is also present in bones, shells and teeth.

Question 34. (i) Segregate following ecosystem services as narrowly utilitarian and broadly utilitarian.
Purification of Air and Water, Mitigation of droughts and floods, Pollination, Medicine, Resin, Gums, Dyes
(ii) What is the price tag given to nature's life-support services?
(iii) Maximum price tag is estimated for which ecosystem service by Robert Costanza.

Answer:

(ii) Fundamental ecosystem services are given an average price tag of 33 trillion US dollars a year.
(iii) Soil formation – 50%

Question 35. (i) Identify different communities for hydrarch succession.
(ii) What do you mean by climax community?

Answer:

Submerged Phytoplanktons free–floating swamp plants plants stage Marsh Scrub Forest meadow stage stage
(ii) Climax community represents last community in biotic succession which is relatively stable and in harmony with environment of that area.

Question 36. (i) Give four examples each for terrestrial and aquatic ecosystem.
(ii) "Ecosystem is an open system". Justify this statement.
Answer: (i) Terrestrial ecosystem : e.g.,: (i) Crop land, (ii) Grass land, (iii) Forest, (iv) Desert.
(ii) Aquatic ecosystem : e.g.,: (i) Estuary, (ii) Pond, (iii) River, (iv) Aquarium. Ecosystem are open both for energy as well as matter. For example, A crocodile can feed on deer thus biomass of deer, both energy as well as matter become part of food chain. Earth is largest ecosystem is open for energy but close for material exchange.

Question 37. Give the components of an ecosystem citing pond as an example.
Answer: Any ecosystem including pond is marked by four basic components.
(i) Abiotic components : Water with organic and inorganic substances.
(ii) Autotrophic components : Phytoplanktons, submerged and marginal plants etc.
(iii) Consumers : Zooplanktons, free-swimming and benthic forms etc.
(iv) Decomposers : Fungi, bacteria etc.

Question 38. (i) State the factors on which primary productivity depends upon. What is annual net primary productivity of the whole biosphere?
(ii) Define food web with diagrammatic representation.

Answer:

(i) Primary productivity depends on the photosynthetic capacity of plant species inhabitating a particular area. Alongwith this, environmental factors like temperature, amount of insolation, mineral nutrients and photosynthetic capacity also affect. Annual net primary productivity of biosphere is approximately 170 billion tons.
(ii) Interlocking pattern of organisms as per their feeding habit constitute food web. Following is the food web in a grassland ecosystem.

Question 39. (i) Explain the significance of pyramid of energy.
(ii) Which ecosystem has maximum productivity? Why?
Answer: (i) Pyramid of energy gives best picture of overall nature of the ecosystem. In contrast with the pyramids of numbers and biomass which reflect standing situation (organisms present at any moment), the pyramid of energy is a picture of the rates of passage of food mass through the food chain. It is always upright as there is always a gradual decrease in the energy content at successive higher trophic level.
(ii) Coral reefs have maximum productivity. Reason : Primary producers here are phytoplanktons with very high rate of fixation of solar energy. Turnover of algal biomass is also very high.

Question 41. (i) Explain why more energy in forest ecosystem flows through Detritus food chain (DFC)?
(ii) Draw pyramid of energy. Do you find any ecosystem can have inverted or spindle-shaped pyramid of energy?
(iii) What percentage of sunlight available to primary producer is converted to NPP?

Answer:

(i) Forest has large amount of biomass which is not fed upon by grazers and is subjected to decomposition. (ii)

TC 10 J SC 100 J PC 1000 J PP 10,000 J Pyramid of energy is always upright in all kind of ecosystem.
(iii) Only 1% of sunlight available to primary producers is converted into NPP.

41. Give an account of a gaseous cycle in nature. Gaseous cycles have atmosphere or hydrosphere as reservoir e.g., carbon cycle. Source: Carbon constituites 49% of dry weight of organisms. Oceanic reservoir regulates the amount of carbon dioxide in the atmosphere. Fossil fuel also represents a reservoir of carbon. Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. Addition: Decomposers also contribute substantially to CO₂ pool by their processing of waste materials and dead organic matter. Utilisation: 4 × 10¹³ kg of corbon is fixed in the biosphere annually. Some amount of the fixed carbon is lost to sediments and removed from circulation. Human activities significantlly influence carbon cycle. Rapid deforestation and massive burning of fossil fuel have significantly increased the rate of release of CO₂ into atmosphere.

Question 42. (i) Give the proportionate cost of various ecosystem services.
(ii) Identify the given statements as True or False.
(a) Carbon cycle has no sedimentary component.
(b) 71% of the global carbon is found in oceans.
(c) CO₂ is returned to atmosphere by respiratory activities of consumers but not of producers.
(d) Gaseous cycle like nitrogen has reservoir pool as oceans.
Answer: (i) Soil – 50% Recreation and nutrient cycle < 10% each Climate regulation – 6% Habitat for wildlife – 6%.
(ii) (a) False
(b) True
(c) False
(d) False

Question 43. Give the possible types of pyramids in given ecosystems viz., Ponds, Forest, Grasslands.

Answer:

3. Inverted pyramid of biomass 3. Upright pyramid of biomass 3. Upright pyramid of biomass
4. Spindle pyramid of biomass 4. Spindle pyramid of number

Question 44. (i) Give the trophic level for the following :
(a) Dinesh eating Dal and Chapatti
(b) Cat eating on mice which feeds on grains
(c) Lion eating on Deer
(d) Kamlesh taking curd
(ii) Find the odd one w.r.t. amount of energy present above mentioned trophic level.
Answer: (i) (a) Second
(b) Third
(c) Third
(d) Third
(ii) Dinesh belongs to second trophic level and since he feeds directly on plants this trophic level has more energy than the third trophic level.

Question 45. Give comparative account of characteristics of seral and climax communities.

Answer:

No. Characteristics Seral communities Climax communities

1. Size of individuals Small Large
2. Food chain Simple Complex
3. Nutrient conservation Low High
4. Niches Generalized Specialized
5. Species diversity Low High