Important Questions for CBSE Class 12 Biology Chapter 14 - Ecosystem

CBSE Class 12 Biology Chapter-14 Important Questions – Free PDF Download

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CBSE Class 12 Biology Important Questions
Chapter 14 – Ecosystem

1 Mark Questions

Chapter 14
Ecosystem

1 Marks Questions
1. Decomposition is faster if deteritus is rich in nitrogen and water soluble substance like sugars. When is the decomposition process slower?
Ans.Its slower if detritus is rich in lignin and chitin.

2. If we count the number of insects on a tree and number of small birds depending on those insects as also the number of larger birds eating the smaller, what kind of pyramid of number would we get?
Ans.Inverted Pyramid of Number .

3. Differentiate between Sere and Seral communities.
Ans.Sere :Entire sequence of communities that successively change in a given area.Serial community :Individual transitional community .

4. Who are generally the pioneer species in a Xerarch succession and in a Hyararch succession?
Ans.Pioneer species in Hydrarch succession are usually the small phytoplanktons and that in Xerarch succession are usually lichens.

5. Which metabolic process causes a reduction in the Gross Primary Productivity?
Ans.Respiration.

6. What percentage of photosyntheticallyactive radiation is captured by plants?
Ans.2 – 10%

7. Name the pioners of primary succession in water.
Ans.Phytoplanktons

8.Name any two man – made ecosystem?
Ans.Aquarium & Garden.

9.Define stratification?
Ans.Stratification in an ecosystem refers to the vertical distribution of different species occupying different levels.

10.Name the ecological pyramid that is always upright?
Ans.Pyramid of energy.

11.Name the trophic level occupied by secondary consumers & tertiary consumers?
Ans.Third trophic level & fourth trophic level respectively

12.Define standing crop?
Ans.The amount of living matter or biomass present at every tropic level is known as standing crop.

13.Name the ecological pyramid that is inverted in tree ecosystem?
Ans.Pyramid of Number.

14.What are the products of decomposition?
Ans. CO₂, H₂O & nutrients.

15.What is 10% law?
Ans.At each trophic level, 90% energy is degraded into heat & only 10% is transferred to next trophic level this rule is called 10% law.

16.Mention one similarity between hydrach&Xerach secession?
Ans.Both hydrach&xerach leads to establishment of similar mesic conditions.

17.What is the approximate value of net primary productivity of biosphere?
Ans.170 billion tons.

18.Name two climatic factors that regulate decomposition?
Ans.Chemical composition of detritus & climatic factors.

19.What is sere?
Ans.The entire sequence of communities that successively change in a given area resulting in climax community is called sere.

20.Name the primary consumers in aquatic ecosystem?
Ans.Zoo planktons.

21.Name the pioneer species in the primary succession on rock?
Ans.Lichens.

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2 Mark Questions

Chapter 14
Ecosystem

2 Marks Questions
1. What is the shape of pyramid of biomass in sea? Why?
Ans. Inverted, because biomass of fishes far exceeds that of phytoplankton.

2. Give an example of an ecological pyramid which is always upright. Justify your Answer.
Ans.Pyramid of energy is always upright and can never be inverted, because when energy flows from a trophic level to the next trophic level some energy is always lost as heat at each step.

3. Differentiate between primary succession and secondary succession. Which one occurs faster?
Ans. Primary Succession :Aprocess that starts where no living organisms are there. Secondary succession :Aprocess that starts in areas which have lost all the living organisms that existed there.

4. Gaseous nutrient cycle and sedimentary nutrient cycles have their reservoir . Name them. Why is a reservoir necessary?
Ans.Reservoir for Gaseous nutrient cycle : Atmosphere; for sedimentary nutrient cycle : Earth’s crust. Reservoir is needed to meet with the deficit which occurs due to imbalance in the rate of influx and efflux.

5. Fill up the missing links depicted as A, B, C and D in the given model of primary succession.

Ans. A = Submerged plant stage B = Reed Swamp Stage
C = Scrub stage D = Forest stage

6. In the model of phosphorus cycle given below , what does A, B, C and D refer to?

Ans. A = Detritus B = Decomposition
C = Weathering D = Producers.

7. Differentiate between Hydrarch and a Xerarch succession.
Ans.HydrarchSuccession :Starts in water proceeds from hydric (aquatic) to mesic (neither dry nor wet) situations. Xerarchsuccession :Starts on barren rock Proceeds from Xeric (dry) conditons.

8. What is the effect on decomposition rate if :–
a) Detritus is rich in lignin and chitin
b) Detritus is rich is nitrogen and sugars
Ans. a) Decomposition rate is slower
b) Decomposition rate is faster.

9. What are the limitations of ecological pyramids?
Ans. (i) Does not take into account same species belonging to two or more trophic levels.
(ii) Assumes simple food chain, does not accomodate food web.
(iii) Saprophytes have not been given any place in ecological pyramids.

10. Name any four ecosystem services. Who gave the price tags on nature’s life support services? Which is the most important ecosystem service provider?
Ans.

• Forest (ecosystem) purify water and air
• Mitigate Droughts and floods
• Nutrient cycling
• Generate fertile soil
• Provide habitat for wildlife
• Pollinate flower
• Maintain Biodiversity
• Provide aesthetic, cultural & spiritual values
• Robert Constanza gave price tags to ecosystem services.
• Most important ecosystem services provider : Soil formation.

11. Study the table given below and fill the blanks from ‘A’ to ‘F’.

Ans.A = First trophic level
B = Primary consumer
C = Zooplankton, Cow, Grass hopper
D = Third trophic level
E = Tertiary consumer
F = Man, Lion

12. In the pyramid of biomass drawn below , name the two crops (i) one which is supported (ii) one which supports in which ecosystem is such a phyramid found?

Ans. (i) Supported trophic level is founded by zooplanktons
(ii) Supporting trophic level is formed by phytoplanktons ecosystem It is found in aquatic ecosystem.

13.Why is secondary sucession faster than primary sucession?
Ans.Secondary succession refers to community development on sites previously occupied by welldeveloped communities where the environment is both organic & inorganic. Since these bare areaspossesses suitable soil for proper growth so, secondary successes is more rapid them primarysuccession.

14.Distinguish between upright & inverted pyramids?
Ans.In upright pyramid the number of producers or its biome is maximum in an ecosystem & it decreases progressively at each trophic level. Whereas in inverted pyramid at producer level is minimum & is increasing progressively at each trophic level in a food chain.

15.Explain with an example, why is the length of a food chain in an ecosystem generally limited to 3-4 tropic level?
Ans.In a food chain at each trophic level about 90% of energy is degraded into heat & only 10% energy is transferred to next tropic level thus of trophic levels in the food chain the amount energy to be transferred to next trophic level will be approximately negligible thus a food chain is generally limited to 3-4 trophic levels.

16.What is meant by ecological succession? Describe the different stages in which succession occurs?
Ans.Ecological succession is a community – controlled phenomenon in which the structure &composition of community changes in an orderly & sequential manner, leading ultimately toestablishment climax community.
STAGES OF SUCESSION :-
i) Invasion :- Invasion is the arrival of propagating organ e.g. seed spores bulbils etc on a bare areaof primary or secondary succession. Those for which conditions are favorable germinate is newarea& some of them grow into mature plants. These new arrivals from outside are called pioneer.
ii) Establishment :- The process by which migrants adjust themselves in new areas after migrationis called ecesis. It consists of three essential processes – germination, growth & reproduction.
iii) Aggregation :- The coming together of individuals of various species in an area are calledaggregation.
iv) Competition :- The species which have similar requirements of nutrition are known ascompetitive species eg. those with different requirement are complimentary species.
v)Reaction :- It is the change brought about by colonizers in the habitat. The influence of vegetation on the site is called reaction till a stable community develops in that area.

17.What is meant by ecological pyramid? With the help of one example each, show that pyramid of number can be both upright as well as inverted.
Ans.The graphic representation of the trophic structure of a food chain is known as ecologicalpyramid. The ecological pyramid of number represents the numerical representation betweendifferent trophic both upright or inverted.
In upright pyramid of numbers, the more abundant species form the first trophic level & forms thebase of pyramid & less abundant species remains near the top e.g. Grass land ecosystem.
Green plants →→ Rabbit →→fox→→Lion

In inverted pyramid of number, the most abundant species occurs at the top while the less abundantspecies forms the base eg. Tree ecosystem
Tree →→Birds →→Parasite

18.Describe the components of an ecosystem?
Ans.Ecosystem is a functional unit of nature consisting of biotic & abiotic factors where the livingorganisms interact among themselves & with physical environment. Ecosystem consists of twocomponents:-
i) ABIOTIC COMPONENTS :- e.g.
a) Inorganic substances phosphorus, sulphur, carbon, nitrogen hydrogen tec.
b) Organic substances e.g. carbohydrates, proteins, lipids.
c) Climatic regime e.g. light, humidity, rainfall, temperature.
ii) BIOTIC COMPONENTS:
a) Producers :- The organisms which produce food for themselves & for all living organism frominorganic raw material with the solar radiation are called producers.
b) Consumers :- Those living heterotrophic members of ecosystem which consume the foodsynthesized lay producers. They are broadly classified as.
i) Primary consumers:- They are directly dependent on producers called herbivores e.g. rat, deer,cow, goat,.
ii)Secondary consumers:- The organism that use primary consumers as their food are calledcarnivores e.g. fox cats, lions.
iii)Tertiary consumers:- These are top carnivores which prey upon other carnivores, & herbivores
e.g. crow, man.
c)Decomposers :- Organism that break up the dead bodies of plants animals & the related wasteproducts are called decomposers e.g. bacteria, Fungi etc.

19.“Energy flow in an ecosystem is always unidirectional justify the statement.
Ans.Energy flow in an ecosystem is always unidirectional meAns that energy is always trAnsferredfrom one trophic level to next trophic level & is not reverted back – e.g. energy from sun is capturedby producers which are then eaten by primary consumer & energy is trAnsferred to next tropic level.

20.Differentiate between Production & decomposition?
Ans.Production refers to the process of synthesis of organic food materials from inorganicsubstances such as CO2 H2O in the presence of sunlight whereas decomposition is a process ofbreakdown of complex substances into its constituents & it is brought about by bacteria, fungi etc.

21.Explain who pyramid of energy of an ecosystem is always uprights never inverted?

Ans. The pyramid of energy represents total amount of energy utilized by different trophic levelorganism in unit area. At each level, total energy available is relatively more than at higher trophiclevel because of loss of energy from one trophic level to other thus, pyramid of energy is always straight.

22. i) Name the compound whose cycle is depicted.
ii) In what way do vehicles add this compound to atmosphere?
iii) What adverse effect does its excess have on the environment?
iv) Cite an event which depicts this effect in modern times.
v) Suggest two ways of depleting this effect.
Ans. i) Carbon cycle
ii) By burning of fossil fuel e.g. diesel or petroleum, they introduce CO2 in the atmosphere
iii) Environmental pollution.
iv) Ozone layer depletion
v) a) By reducing use of fossil fuels
b) By planting more & more trees.

23.What do you mean by “productivity of an ecosystem? What are the types of productivity also mention the factors on which productivity of an ecosystem depends?
Ans.Productivity of an ecosystem is the rate at which solar radiations energy is fixed by vegetationof an ecosystem per unit area & per unit time. It is general expressed in terms of unit of energy (cal)produced in a unit area (m2) per unit time (year).
Productivity can be of two types:-
1) Primary Productivity:- It is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis primary productivity can further be of two types:-
a) Gross primary productivity :- It refers to the total amount of food formed lay producers.
b) Net primary productivity:- It refers to gross production minus loss lay respiration & decomposition NPP = GPP – respiration loss
2) Secondary Productivity :- The rate of storage at consumer level is secondary productivity. It isthe rate of resynthesis of organic food by consumers primary productivity depends on:-
i) a number of environmental factors
ii) availability of nutrients.
iii) photosynthetic capacity of plants.

24.What is decomposition – Describe thedifferent processes involved in decomposition?
Ans.Decomposers e.g. bacteria, fungietc. helps in breakdown of complex organic matter intoinorganic substances like CO2, water minerals & this process is called decomposition. Dead plantremains e.g. leaves, bark flowers & dead remain of animals including faecal matter constitutedetritus. The important processes involved in decomposition or :-
i) Fragmentation :-Detritivores breaks down detritus into smaller particles.
ii) Leaching :- Water soluble inorganic nutrients go down into soil horizon & get precipitated asunavailable salts lay process of leaching.
iii) Catabolism:- The enzymes of bacteria & fungi degrade detritus into simple inorganicsubstances
iv) Humification :-Humification leads to accumulation of a dark colored amorphous substancecalled humus that is highly resistant to microbial action & undergoes decomposition at extremelyslower rate.
v) Mineralisation :- The humus is further degraded by some microbes & release of inorganicnutrients occurs by the process of mineralization.

25.Why is productivity of coral reef maximum?
Ans.The productivity of coral reef is maximum because of availability of good light, enough warm water and abundant nutrients.

26.In the pyramid of biomass, drawn below, name the two crops:-
i) one which is supported & the one which supports
ii) In which ecosystem is such a pyramid found.

Ans. i) In this ecosystems bird is supported & insect supports.
ii) Such type of pyramid is found in ecosystem of pond or tree.

27.Differentiate between primary productivity & secondary productivity?
Ans.Primary productivity refers to productivity at trophic level i.e. food energy formed by way of photosynthesis using solar energy whereas secondary productivity refers to gross productivity minus losses by way of respiration & decomposition.

28.What ecological principles are derived from the study of food chains?
Ans. i) Each food chain is complete & self – containing
ii) All the food chains must always begin with photosynthesis & ends with decay
iii) Shorter food chains are more efficient because the more steps it has, greater the wastage ofenergy.
iv) The successive members of food chains are large in size but fewer in number.

29.List the factors on which pioneer species depend during secondary succession?
Ans.In secondary succession, the type of pioneer species depends on :-
i) Conditions of the soil
ii) Availability of water
iii) Environmental conditions
iv) Seeds or other propagules present.

30.The productivity of ecosystem increases from polar regions towards tropics. Why?
Ans. The productivity of ecosystem increases from polar region towards tropics because of the increasing sunlight & temperature.

31.Mention some of the ecological services provided by forests?
Ans.i) Forests purify air
ii) They mitigate droughts & floods.
iii) They help in cycling of nutrients.
iv) They provide habitat to number of wild life
v) They maintain biodiversity.

32.Differentiate between food chain & food web?
Ans.The unidirectional sequence of organisms in which energy flows in the form of food from oneorganism to another through the process of eating & being eaten is called food chain whereas thenetwork of interlinked food chains are collectively known as food web.

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3 Mark Questions

Chapter 14
Ecosystem

3 Marks Questions
1. With the help of a diagram, represent the energy flow through different trophic level.
Ans.In an ecosystem, energy flows through different trophic level by food chain. In consists of two steps:-
i) Trapping solar energy:- Primary source of energy is sun only 48% of sun’s energy reaches the surfaceof earth & only a part of it is used lay plants for photosynthesis. The chemical energy produced lay plantsis stored in plant tissues. The photosynthetic organism uses a part of this chemical energy & transfer therest to organism at next trophic level.

ii) Path & flow of energy:- The primary consumers therefore take chemical potential energy in the form offood. Most of it dissipates as heat during respiration & is lost out of ecosystem. The same process isrepeated at secondary consumers, at each trophic level 90% energy is degraded into heat& only 10% is thentransferred to next trophic level this rule of energy flow is alled ten percent law.

2. What is pyramid of biomass? Represent the pyramid of biomass in
(i) grassland ecosystem
(ii)aquatic ecosystem.
Ans.The biomass means the total weight of fry matter pyramid of biomass represents the weight of drymatter at different trophic levels of ecosystem at one time in a food chain of food web.
i) Grassland ecosystem :- In grassland ecosystem, the pyramid of biomass is upright i.e. pyramid ofbiomass shows gradual reduction in biomass at each trophic level from base to apex.
Grass →→cow→→fox →→Lion

ii) In pond aquatic ecosystem, the biomass of consumers is always greater than biomass of producers hence itoccurs as an inverted pyramid

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5 Marks Questions

Chapter 14
Ecosystem
5 Marks Questions

1.Represent schematically & describe the phosphorus cycle in an ecosystem?
Ans. The major reservoir of phosphorus is sedimentary rocks which are only available to basic cycle insmall amounts as a result of weathering. These phosphorus are weathered & later transported to thesoil by wind & water, where they exist as inorganic dissolved phosphates.
The basic phosphorus cycle begins with dissolved phosphates which are absorbed by plants for makingtheir own tissue plants are eaten by animals. Decay bacteria breakdown the tissue of dead animalsdown these product & return phosphate to soil.
The water – soluble phosphates is lost to the deep rudiments of the ocean through run-off. The major pathway of returning phosphorus to land is uplifting of marine sediments. Some amount of phosphorus is returned to absorb inorganic phosphate, when they die, most of absorbed phosphate is recycled back into ambient mater. This sort of cycling is called biological cycle or metabolic cycle.

2.Represent schematically & describe carbon cycle in ecosystem?
Ans.The source of carbon is atmosphere & water. Carbon is present in atmosphere mainly in the formof CO2CO2. It is vital to the production of carbohydrates through photosynthesis.
6CO2+ 12 H2O6CO2+ 12 H2O −→−−−−−chlorophyllh2 C6H12O6  + 6H2O + 6O2↑→chlorophyllh2 C6H12O6  + 6H2O + 6O2↑
In atmosphere, carbon is present in the form of CO2CO2 from the atmosphere it is incorporated into tissuesof green plants e.g. carbohydrates, proteins & lipids.
The CO2CO2 dissolved in sea water is utilized lay marine animals like protozoans, corals, mollusks etc fortheir life. In these animals, CO2CO2 is converted into calcium carbonate which is used for construction ofshell.
Co2+H2O→H2CO3→HCO3→CaCO3+H+Co2+H2O→H2CO3→HCO3→CaCO3+H+
After death of marine animals, CaCO3 store in shells is either deposited as sedimentary rock or dissolvedin water to release CO2CO2. A certain proportion of carbon is deposited as coal carbon from coal returns toair in the form of CO2CO2 through combustion & weathering thus, carbon from atmospheric pool moves togreen plants, then to animals & finally to bacteria fungi etc. to return it to atmosphere throughdecomposition-