2nd PUC Biology Question Bank Chapter 14 Ecosystem

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Karnataka 2nd PUC Biology Question Bank Chapter 14 Ecosystem

2nd PUC Biology Ecosystem NCERT Text Book Questions and Answers

Question 1.
Fill in the blanks.

  1. Plants are called as _________ because they fix carbon dioxide.
  2. In an ecosystem dominated by trees, the pyramid (of numbers) is _________ types.
  3. In aquatic ecosystems, the limiting factor for productivity is __________
  4. Common detritivores in our ecosystem are _____________
  5. The major reservoir of carbon on earth is _______________


  1. Producers
  2. Spindle
  3. light
  4. Earthworms ants and mites
  5. Oceanic.

Question 2.
Which one of the following has the largest population in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers
(d) Decomposers
(d) Decomposers can have a maximum number but not included in the food chain.
So (a) Producers is the answer.

KSEEB Solutions

Question 3.
The second trophic level in a lake is-
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes
(b) Zooplankton

Question 4.
Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above
(a) Herbivores

Question 5.
What is the percentage of photosynthetically active radiation (PAR), in the incident solar radiation?
(a) 100%
(b) 50 %
(c) 1-5% .
(d) 2-10%
(b) 50%.

Question 6.
Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Upright and inverted pyramid
(d) Food chain and Food web
(e) Litter and detritus
(f) Primary and secondary productivity
(a) Grazing food chain and detritus food chain

Grazing food chain Detritus food chain
1. Also known as Predator-prey food chain. 1. Also known as Saprotrophs food chain.
2. It is a common food chain where producers are eaten by herbivores, herbivores by carnivores, and the latter by higher-order carnivores.
Eg: Grass→ grasshopper → frog →Snake → Vulture.
2. It proceeds from dead bodies and organic remains. Eg: Decaying plant matter → earthworm-) bird →Snake → Vulture.
3. It binds the inorganic nutrients into organic matter. 3. It releases the inorganic nutrients bound up in the organic matter.
4. It adds organic matter to detritus food chain 4. Provides inorganic nutrients to grazing food chain.

(b) Production and decomposition

Production Decomposition
1. It is the pheno­menon of synthesis of fresh biomass.
2. It locks up inor­ganic nutrients into the biomass.
3. It traps energy.
1. It is the pheno­menon of degra­dation of waste organic matter.
2. It releases inor­ganic nutrients from the organic matter into the environment.
3. It releases energy.

(c) Upright and inverted pyramid

Upright pyramid Inverted pyramid
It is the ecological pyramid where the producers form a broad base and the consumers keep decreasing (in energy number or biomass) It is the ecological pyramid, where the producers form a narrow base while the consumers keep increasing (in number of biomass)

(d) Food chain and Food web

Food chain Food web
1. Food chain refers to the transfer of energy from the producers through a series of organisms.
2. It is less realistic in nature
1. A number of interconnected food chains constitute a food web.
2. It is more realistic in nature.

(e) Litter and detritus

Litter Detritus
1. Freshly fallen parts of plants dead parts of plants, and animals and faecal matter of animals that haven’t strapped to decompose, constitute litter. 1. Freshly fallen and dead parts of plants and animals and faecal matter that have started to decompose constitute detritus.

(f) Primary and secondary productivity

Primary productivity Secondary productivity
1. It is the rate at which matter is built up by producers.
2. It is due to photosynthesis
3. There is a net gain of the energy in the biosphere
1. It is the rate at which matter is built up by consumers.
2. It is due to herbivores and predation.
3. There is no such activity

Question 7.
Describe the components of an ecosystem.
The components of an ecosystem can be divided into two categories: biotic and abiotic.
(i) Biotic components:
(i) Producers – Green plants which can synthesize their own food.
(ii) Consumers – They do not synthesize their food. They may be
-Primary consumer/herbivores – consuming plants as food.
-Secondary and tertiary consumers or carnivores – They feed on either herbivores or carnivores.
(iii) Decomposers – These organisms breakdown the dead bodies or waste products of plants and animals into simpler inorganic compounds.
(2) Abiotic components:
(i) Climatic components
•Atmospheric gases
•Atmospheric humidity
(ii) Soil factors
•Organic materials
•Soil, water
•Soil air
(iii) Topographic factors
•Direction and steepness slope

KSEEB Solutions

Question 8.
Define ecological pyramids and describe with examples, pyramids of number and biomass.
Ecological pyramids They are the graphical representations of the various ecological parameters at the successive trophic levels of food chains with producers at the base top carnivores at the apex and intermediate levels .in between. Quantity at each level is indicated by the length of the bar in the graph. The pyramids are therefore also called bar diagrams.

Pyramids of number:
It is a graphical representation of the numerical strength of various populations in different trophic levels per unit area of an ecosystem with producers forming base intermediate levels forming intermediate tiers and apex formed by top carnivores length of the bar at each trophic level is proportional to the number of individuals at this level.
2nd PUC Biology Question Bank Chapter 14 Ecosystem 1

Pyramid of biomass
Biomass is the amount of living matter measured in terms of fresh or dry weight. Dry weight is preferred as it avoids seasonal variations in the moisture content of biomass.

The pyramid of biomass is the graphical representation of the amount of biomass per unit area sequence-wise in rising trophic levels with producers at the base and top carnivores at the apex. Length of the bar indicates the comparative amount of biomass at that trophic level. Biomass is maximum in producers. Only 10% to 20% biomass is passed from producer level to herbivore level.
2nd PUC Biology Question Bank Chapter 14 Ecosystem 2

Question 9.
What is primary productivity? Give a brief description of factors that affect primary productivity.
Primary productivity is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (g/m2/yr) or energy (kcal/m2/yr). It is of two types: gross primary productivity and net primary productivity. The Gross primary productivity of an ecosystem is the rate of production for organic matter during photosynthesis. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP).

Factors affecting primary productivity are as follows:

  • Solar radiation: Maximum light is available in the tropics. Poles receive minimum light. Due to this, photosynthesis is maximum and net primary productivity (NPP) is highest (> 20 t ha-1 year-1) in tropics against (8 t ha-1 year-1) in temperate forests.
  • Temperature: Temperate forests have lesser productivity (about 8 t ha-1 year-1) than tropical rain forests (20 t ha-1 year-1) due to the cold climate.
  • Moisture: Rain and humidity increase the productivity of the ecosystem.
  • Nutrients: Nutrients are essential for the producer’s growth. Desert soils are deficient in nutrients and therefore, are less productive.
  • Photosynthetic efficiency of producers: C4 plants are more productive than C3 plants.

KSEEB Solutions

Question 10.
Define decomposition and describe the processes and products of decomposition.
Decomposition is the process of breaking down a substance into its constituent parts. It is a complex, enzymatic process that involves step-wise degradation of detritus. It involves three steps- fragmentation of detritus, leaching, and catabolism involving humification and mineralization. Humification results in the formation of humus in the soil. Mineralization results in the release of inorganic substances (CO2, H2O) and nutrients in the soil.

Question 11.
Give an account of energy flow in an ecosystem.
Energy flow:- The passage of energy through various trophic levels of an ecosystem is called energy flow. Their is no circulation of energy. Instead unidirectional flow of energy occurs in the ecosystem.

(1) Capture of energy:- Under favorable conditions, 1-5% solar radiation is captured by producers and used for photosynthesis. It is gross primary productivity some 20% this is used by producers in their own activities. The net primary productivity is available to herbivores. 8-4% of incident radiations.

(2) Transfer to herbivores:- Herbivores get a part of net primary productivity. The remaining is changed into detritus which is a source of energy for decomposers. Herbivores waste a lot of food energy during ingestion about 30% food energy is used up by herbivores for their life activities and liberated as heated. The remaining is used in building biomass of herbivores. It is about 10% of the productivity of producers. The transfer of about 10% of biomass energy from one tropic level to the next tropic level is called 10% law (ten percent law).

(3) Transfer to Primary carnivores:- Host of the herbivores are eaten by primary carnivores. Lots of energy wastage occurs during the predation. About 60% of assimilated food energy is used up by primary carnivores for their external activities. The rest amount of the energy is transferred to Secondary carnivores.

(4) Transfer of energy to higher-level carnivores:- 10% of biomass energy available at the level of primary carnivore becomes incorporated into biomass of secondary carnivores. If there is a still higher level carnivore, it uses 10% of biomass energy present at the level of secondary carnivores. As energy available at higher carnivore level becomes small, an ecosystem doesn’t have more than 3-5 trophic levels. eg….
2nd PUC Biology Question Bank Chapter 14 Ecosystem 3

Question 12.
Write important features of a sedimentary cycle in an ecosystem.
In the sedimentary cycle materials involved in circulation between biotic and abiotic components of the biosphere are non-gaseous and the lithosphere is the reservoir pool, e.g., phosphorus, calcium, and magnesium. Sulphur has both sedimentary and gaseous phases. Sedimentary cycles are slow and less perfect as compared to gaseous cycles.

KSEEB Solutions

Question 13.
Outline salient features of carbon cycling in an ecosystem.
Carbon is the most abundant element as it occurs in every organic substance. It forms 49% of the dry weight of organic matter. Carbon occurs as free carbon dioxide in the atmosphere and dissolved as CO2 in the hydrosphere. Carbon dioxide is being added to the cycling pool of the atmosphere and hydrosphere through two processes, biological and non-biological.
2nd PUC Biology Question Bank Chapter 14 Ecosystem 4
Biological- All living organisms produce carbon dioxide through respiration Carbon trapped in organic matter is released as CO2 during its decomposition.
Non-Biological – Combustion or burning of biomass and fossil fuels produce carbon dioxides.
2nd PUC Biology Question Bank Chapter 14 Ecosystem 5

2nd PUC Biology Ecosystem Additional Questions and Answers

2nd PUC Biology Ecosystem One Mark Question

Question 1.
Define ecosystem.
An ecosystem is a functional unit of nature, where living organisms (biotic) interact among themselves and also with the abiotic factors or their physical environment.

Question 2.
By observing the relationship between the first pair, write the missing word.
a. Plants : producers :: Animals : ……………..
b. Food chain : food web :: Ecosystem : ……………………
a. consumers
b. biosphere

Question 3.
What is the net primary productivity of an ecosystem? (CBSE Delhi 2005)
It is the rate of energy stored or biomass accumulated by the producers. It depends upon the rate of photosynthesis as well as respiration.

Question 4.
What PAR?
The part of incident solar radiation that can be absorbed and used by plants autotrophs for photosynthesis, is called photosynthetically active radiation (PAR).

Question 5.
Explain consumers of ecosystems.

  1. Producers: All the green plants.
  2. Consumers: Depends on others for food.
    • Primary consumer: Depends on plants called herbivores.
    • Secondary consumers: Depends on herbivores for food.
    • Tertiary consumers: Depends on secondary consumers.
  3. Decomposers: They decomposed dead organic matter.

Question 6.
What does the detritus food chain begin with?
Detritus food chain begins with dead organic matters.

Question 7.
Why type of nutrition is shown by decomposers?
Saprophytic nutrition.

Question 8.
What term is given to the inter-connected food chain?

KSEEB Solutions

Question 9.
What do mean by “Ten percent law”?
Ten percent law states that only 10% of the energy is transferred from one trophic level to the next trophic level through food chain.

Question 10.
Identify the type of ecological pyramids shown here?
2nd PUC Biology Question Bank Chapter 14 Ecosystem 7

  • Pyramid of number in a tiee ecosystem.
  • Pyramid of biomass in an aquatic ecosystem.

Question 11.
What do you mean by ecological succession?
It is the phenomenon of gradual and fourly predictable changes in the species composition of a given area leading ultimately to the establishment of a climax community.

Question 12.
Define the term “Sere1
The entire sequence of communities that successively change and lead to the establishment of a climax community is called a sere.

Question 13.
Define the term ‘climax community”?
The community that is in near equilibrium with the environment, and does not undergo much change and occupied a large area is called climax community.

Question 14.
What do you mean by ‘Pioneer species’?
The species that invades a bare area and starts establishing a community is called pioneer species.

Question 15.
Name the pioneer species
(1) On a bare rock
(2) In a water body (CBSE foreign 2008)

  1. Lichen
  2. Phytoplankton.

Question 16.
What is the structure and composition of a community expected to remain unchanged?
Un disturbed climax community

Question 17.
In the pyramid of biomass given below, name 2 types of crops
(i) One which is supported and
(ii) One which supports. In which ecosystem such type of pyramids found.
2nd PUC Biology Question Bank Chapter 14 Ecosystem 8
(i) primary producer (phytoplankton)
(ii) primary consumer (zooplankton)
In aquatic ecosystem such type of pyramid found.

Question 18.
Give an example of an inverted ecological pyramid, what kind of pyramid of energy would it have?
Inverted ecological Pyramid Pyramid of numbers based on a large tree as a producer supporting a number of herbivorous birds each having a number of parasites.
2nd PUC Biology Question Bank Chapter 14 Ecosystem 9

2nd PUC Biology Ecosystem Two Marks Questions

Question 1.
In the following table the ecological units are mentioned in the first column vertically and their attributes are mentioned horizontally. Match the ecological unit and its attribute and put a tick mark in the blanks with the table
2nd PUC Biology Question Bank Chapter 14 Ecosystem 10
2nd PUC Biology Question Bank Chapter 14 Ecosystem 11

Question 2.
Match column A with any two of column B
2nd PUC Biology Question Bank Chapter 14 Ecosystem 12
2nd PUC Biology Question Bank Chapter 14 Ecosystem 13

Question 3.
Differentiate between primary succession and secondary succession. (CBSE 2006)

Primary succession Secondary succession
(1) It occurs in biologically sterile areas. (1) Occurs in an area which is biologically quite fertile
(2) Humus/organic matter is absent in the early stages (2) Present from the very beginning.
(3) It begins on a soilless area. (3) Occurs on an area having sufficient soil.
(4) It takes a long time ie. 1000 years and more. (4) It takes place in lesser time 50-200 years.

Question 4.
Differentiate between standing crop and standing state (CBSE 2008)

Standing crop Standing state
(1) It is the amount of living matter or biomass of biotic components of an ecosystem. (1) It is the amount of inorganic nutrients present in an ecosystem.
(2) It is present all over the ecosystem. (2) It occurs in the growth medium of producers.
(3) It indicates the productivity of the ecosystem. (3) It determines the productivity of the ecosystem.

Question 5.
Mention four functional aspects of in ecosystem.
The four functional aspects of an ecosystem are

  • Productivity
  • Decomposition
  • Energy flow
  • Nutrient cycling.

Question 6.
Define Productivity? How is it expressed?
Productivity refers to the rate of biomass production.
It is expressed as g-2 yr-2 or (Keal m-2) yr-1

Question 7.
Differentiate between gross primary productivity and net primary productivity.

Gross Primary Productivity (GPP) Net Primary Productivity (NPP)
It is the rate of produ­ction of biomass/organic matter by producers during photosynthesis It refers to the biomass or organic matter available at the producer level to the primary consumers i.e. GPP (Respiration losses)

Question 8.
Write the factors which determine primary productivity.
Primary productivity depends on

  • The photosynthetic capacity of the plant species.
  • Availability of nutrients
  • Amount of sunlight available
  • Water availability and temperature.

Question 9.
What would happen to the successive trophic levels in the pyramid of energy, if the rate of reproduction of phytoplankton was slowed down? The suggestion in phytoplankton reproduction. (CBSE Delhi 2006)
As phytoplanktons are the producers in the ecosystem, the amount of energy available for transfers will decrease. Organisms at successive trophic levels will also decrease. ‘
The two factors responsible for the reduction in the phytoplankton population are

  • Low nutrients and
  • Less availability of oxygen.

KSEEB Solutions

Question 10.
Distinguish between standing crop and standing state.

  • Standing crop: Each trophic level has a certain mass of living material at a particular time. This is called a standing crop.
  • Standing state: The amount of nutrients such as carbon, nitrogen, phosphorus, calcium, etc. present in the soil at any given time is called a standing state.

Question 11.
Differentiate between Hydrarch succession and Xerarch succession

Hydrarch succession Xerarch succession
1. The ecological succession that starts in water bodies and proceeds to mesic condition is called hydrarch succession
2. Phytoplantation from the pioneer community.
1. The ecological succession, that starts With bare rocks xeric conditions and proceeds to mesic condition is called  Xerarch succession.
2. Lichens form the pioneer community.

Question 12.
The climax community of every succession is not isolated with one or two species of organisms.’ Justify.
The climax community of every succession is the forest. It is a stable community. The community organization becomes more complex in the climax community. A large number of plant and animal species occur in a forest.

Question 13.
Differentiate between the carbon cycle and phosphorus cycle

Carbon cycle Phosphorus Cycle
1. The reservoir of the carbon cycle in the atmosphere as carbon dioxide and also the lithosphere, as fossil fuel.
2. There is the respiratory release of CO2
1. The reservoir of the phosphorus cycle is the phosphate-containing rocks of the lithosphere.
2. There is no respiratory release of phosphorus.

Question 14.
Differentiate between production and decomposition

Production Decomposition
1. It is the process of the formation of biomass or organic matter from a simpler inorganic substance
2. It occurs at the level of producers and consumers.
1. It is the process of the breakdown of larger organic molecules into simple molecules and ultimately into inorganic substances.
2. It occurs at the level of decomposers.

Question 15.
When is the structure and composition of a community expected to remain unchanged?
The climax community remains stable as long as the environment remains unchanged. With time the xerophytic habitat gets converted into a mesophytic.

Question 16.
Differentiate between the Gaseous and sedimentary cycle.

Gaseous cycle Sedimentary Cycle
1. The reservoir of the gaseous cycle lies in the atmosphere
2. Exchange occurs in the form of gases between the living and nonliving comp­onents of the ecosystem.
1. The reservoir of the sedimentary cycle lies in the lithosphere.
2. Exchange occurs mainly in the form of dissolved nutrients between the non-living and the living components.

Question 17.
In the terrestrial ecosystem, the detritus food chain (DFC) and the grazing good chain (GFC) become interlinked. Justify the above statement. What term is given to such interconnection? (HOTS)

  • Certain organisms of the GFC are predators to certain animals of DFC. As a result, the food chains become interconnected.
    eg. earthworms which are detrivores are eaten by small birds (DFC) which become prey to vultures/kites or even cats of the GFC.
  • Organisms like cockroaches and cows, which are omnivores play an important role in the interconnections of the food chain constitute a food web.

2nd PUC Biology Ecosystem Three Marks Questions

Question 1.
Describe the factors that control decomposition?
Decomposition is controlled by
(i) Chemical composition of detritus

  • Decomposition is faster when detritus is rich in nitrogen and water-soluble substances like sugars.
  • Decomposition is slow when detritus is rich in lignin and chitin.

(ii) Temperature and soil moisture, through their effects on the activities of microbes.

  • Warm and moist environment favour decomposition.
  • Low temperature and absence/reduced moisture levels inhibit decomposition.

(iii) Oxygen

  • Decomposition is an oxygen-consuming process
  • Anaerobic condition inhibits decomposition.

Question 2.
Represent schematically the decomposition cycle in a terrestrial ecosystem
2nd PUC Biology Question Bank Chapter 14 Ecosystem 14

Question 3.
What is humus? Mention its properties.
Humus is a dark coloured, amorphous substance produced by the process of humification during the decomposition of detritus.
Properties of humus:

  • It is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
  • Being colloidal in nature, it serves as a reservoir of nutrients.
  • It improves the water holding capacity of the soil.
  • Further decomposition of it provides inorganic nutrients to the plants.

Question 4.
A given species may occupy more than one trophic level in the same ecosystem at the same time. Explain with an example (2008)
A snake eating a mouse in a field/lawn occupies the third trophic level in the food chain.
Plants → Mice → Snake
When the snake eats a frog in the same field, it occupies the 4th trophic level in a food chain it is because the frog feeds on some of the insects which depend on the plants.
Plants → Insects → Frog → Snake
Thus in the same ecosystem, one animal (snake) occupies more than one trophic level at the same time as it cannot satisfy its food need from one trophic level.

2nd PUC Biology Ecosystem Five Marks Question

Question 1.
(a) Mention 2 human activities that affect the carbon cycle
(b) What are the different ways in which CO2 is added to the atmosphere?
(c) How does the chemical nature of detritus determine the rate of decomposition.
(a) The major human activities that influence the carbon cycle are

  • Burning of fossil fuels.
  • Deforestation

(b) CO2 is added to the atmosphere in the following ways:

  • Burning of fossil fuels
  • Volcanic activity
  • Forest fire
  • Respiratory activities


  • If the detritus is rich in lignin and chitin the decomposition is slow.
  • If the detritus rich in nitrogen and water-soluble substances like sugars, decomposition is faster.

Question 2.
Explain the different steps in the process of decomposition.

  • Fragmentation:- It is the process of breaking the detritus into smaller particles by detrivores like earthworms.
  • Leaching:- It is the process in which water-soluble inorganic substances rundown into soil horizon and get precipitated as salts.
  • Catabolism:- The enzymatic conversion of the detritus into simple organic compounds and then into inorganic compounds is called catabolism. The enzymes are secreted by the decomposers like bacteria and fungi.
  • Humification:- Humification during decomposition leads to the accumulation of a dark coloured amorphous substance called, humus.
  • Mineralization:- It is the process in which the humus is degraded by certain microorganisms and the inorganic nutrients are released.

KSEEB Solutions

Question 3.
Describe the pond as an ecosystem.

  • A pond is a fairly self-sustainable unit that shows even complex interactions of an aquatic ecosystem.
  • It is a shallow water body in which all the major/basic components of an ecosystem are well exhibited.

The abiotic components include

  • Water with all the dissolved inorganic and organic substances.
  • The rich soil deposits at the bottom.
  • The solar input.
  • The cycle of day length and temperature
  • Other elematic factors.

The biotic components include.

  • The producers or autotrophic components include phytoplankton, some algae, floating, submerged, and marginal plants.
  • The consumers represented by zooplanktons free-swimming animals, bottom-dwelling animals, etc.

Question 4.
Show schematically the energy flow through different trophic levels of an ecosystem.
2nd PUC Biology Question Bank Chapter 14 Ecosystem 15

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