Ecosystems | Class 12 Botany| Previous Years Questions and Answers (2018 to 2020)


2020 SAY

1.   Choose the correct answer: (1)

The pioneer species in xerarch succession is:

(a)    Phytoplankton                         (b)  Lichen

(c)    Zooplankton                            (d)  Bryophyte

ü Answer:

(b) Lichen

2.   Observe the figure given below and identify the type of age pyramid for human population: (1)

ü Answer:

Expanding/ Broad based age pyramid.

3.   Decomposition has five important steps. (3)

(a)    Write that five steps.

(b)   Give an example of a detritivore.

ü Answer:

(a) 1. Fragmentation, 2. Leaching, 3. Catabolism, 4. Humifaction, 5. Mineralization.

(b) Earthworm.

2020 MARCH

1.   Which one of the following has the largest population in a food chain? (1)

a.      Producers                   b.   Primary consumers

c.      Secondary consumers d.   Tertiary consumers

ü Answer:

(a) Producers

2.   What is the difference between hydrarch succession and xerarch succession? (2)

ü Answer:

Hydrarch succession: It is the succession in water body that leads to change from hydric to mesic condition.

Xerarch succession: It is the succession in dry areas that leads to change from xeric to mesic condition.

3.   Given below is a data showing number of individuals and dry weight of different trophic levels in a grassland ecosystem. Construct,

a.      Pyramid of number.

b.     Pyramid of biomass. (2)

Trophic level

Number of individuals

Dry weight (Kg m-2)

Primary producer



Primary consumer



Secondary consumer



Tertiary consumer



ü Answer:

(a) Pyramid of number:

(b) Pyramid of biomass:

2019 SAY June

1.   Decomposition takes place through different steps. The first step is fragmentation. Write the other four steps. (2)

ü Answer:

Leaching, Catabolism, Humification, Mineralization.

2.   Observe the flowchart showing the stages of a kind of succession. Identify and write the kind of succession. Fill in the blanks a, b, c. (2)

ü Answer:

Hydrarch (Water succession).

(a) Submerged plant stage.

(b) Reed-swamp stage.

(c) Marsh-meadow stage.

3.   Observe the figure given below: (2)

Name the nutrient cycle and fill in the blank (a), (b).

ü Answer:

Name of the cycle: Phosphorous cycle.

(a) Producers (Plants)

(b) Detritus

2019 MARCH

1.   (a) Identify the type of ecological pyramid given below. (2)

(b) Pyramid of energy is always upright. Why?

ü Answer:

(a) Pyramid of biomass.

(b) Energy flows from a trophic level to next higher trophic level, only 10% of energy of a trophic level will be transferred to next higher trophic level.

2.   Detritivores play a major role in decomposition. (2)

a.      What are detritivores?

b.     Write an example for a detritivore.

ü Answer:

(a) Detritivores are the organisms that breaks detritus to smaller particles.

(b) Earthworm, termites etc.

2018 SAY June

1.   In a forest ecosystem, different plant species are occupied in different vertical levels. Name such vertical arrangement. (1)

ü Answer:


2.   Humification leads to accumulation of a dark coloured amorphous substance. Identity the substance and its peculiarities. (2)

ü Answer:

The substance is Humus.


It is highly resistant to microbial action and decomposition.

Serves as a reservoir of nutrients.

Release inorganic nutrients.

3.   Hydrach succession take place in wetter areas and the successional series progress from 'hydric' to 'mesic' condition. List out the stages in correct sequence. (3)

ü Answer:

Phytoplankton (pioneers) → rooted-submerged plants → rooted-floating angiosperms → free-floating plants → reed-swamp → marsh-meadow → scrub → forest (climax community).

2018 MARCH

1.   The products of ecosystem processes are named as ecosystem services. list out any four such services. (2)

ü Answer:

Ÿ Purify air and water.

Ÿ Reduce global warming, droughts and floods.

Ÿ Maintain biodiversity.

Ÿ Pollinate crops.

Ÿ Provide aesthetic, cultural and spiritual values etc.

2.   Pyramid of energy is never been inverted. Why? (2)

ü Answer:

When energy flows from a trophic level to the next higher trophic level, some energy is always lost as heat at each step.

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