Free Man and His Environment MCQs with Answers

161. Which one of the following is not a functional unit of an ecosystem?

• A. Energy flow
• B. Decomposition
• C. Productivity
• D. Stratification

Explanation: Four important functional aspects of the ecosystem are productivity, decomposition, energy flow and nutrient cycling.

162. The upright pyramid of numbers is absent in a

• A. pond
• B. forest
• C. lake
• D. grassland.

Explanation: In forests, a single tree can support a large number of birds thus a base showing producers in a pyramid of numbers will be narrower than the next slab showing primary consumers. Hence, an upright pyramid of numbers is not formed in a forest ecosystem.

163. The rate of formation of new organic matter by rabbits in a grassland is called

• A. net productivity
• B. secondary productivity
• C. net primary productivity
• D. gross primary productivity.

Explanation: The rate of photosynthesis of organic matter by consumers or the rate at which food energy is assimilated at the trophic level of consumers is called secondary productivity. In a grassland ecosystem, the rate of formation of new organic matter by rabbits is referred to as secondary productivity.

164. The second stage of hydrosere is occupied by plants like

• A. Azolla
• B. Typha
• C. Salix
• D. Vallisneria.

Explanation: Series of biotic communities that develop one after the other in a newly formed pond or lake is called hydrosere. It starts as soon as the muddy water becomes clear. The pioneer stage of hydrosere is plankton stage. Death and decomposition of planktons in the first seral stage of hydrosere produces organic matter which mixes up with clay and silt at the bottom to form soft mud which is favourable for growth of submerged hydrophytes in the next seral stage. Hence, the second stage of hydrosere is occupied by submerged hydrophytes like Vallisneria.

165. Mass of living matter at a trophic level in an area at any time is called

• A. standing crop
• B. detritus
• C. humus
• D. standing state.

Explanation: Standing crop is the total amount of living material in a specified population at a particular time, expressed as biomass (standing biomass) or its equivalent in terms of energy. The standing crop may vary at different times of the year; for example, in a population of deciduous trees between summer and winter.

166. Of the total incident solar radiation the proportion of PAR is

• A. about 70%
• B. about 60%
• C. less than 50%
• D. more than 80%.

Explanation: The source of energy in all ecosystem is solar energy. About 50% of the solar energy incident over earth is present in PAR (Photosynthetically active radiation). About 1-5% of incident solar radiation or 2 - 10% of PAR is captured by the photosynthetic organisms in the synthesis of organic matter (gross primary productivity). Roughly 20% of it is consumed in respiration so that net capture of energy (net primary productivity) is 0.8 - 4% of incident radiation or 1.6 - 8% of PAR.

167. Which one of the following statements is correct for secondary succession?

• A. It begins on a bare rock.
• B. It occurs on a deforested site.
• C. It follows primary succession.
• D. It is similar to primary succession except that it has a relatively fast pace.

Explanation: Secondary succession begins in areas where natural biotic communities have been destroyed such as in abandoned farm lands, burned or cut forests (deforested site), lands that have been flooded etc.

168. Which one of the following statements for the pyramid of energy is incorrect?

• A. Its base is broad
• B. It shows the energy content of different trophic-level organisms
• C. It is inverted in shape
• D. It is upright in shape

Explanation: Pyramid of energy is always upright, and can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.

169. Which one of the following animals may occupy more than one trophic level in the same ecosystem at the same time?

• A. Sparrow
• B. Lion
• C. Goat
• D. Frog.

Explanation: The sparrow can be herbivorous (eating seeds and fruits) or carnivorous (eating insects).

170. Both hydrarch and xerarch successions lead to

• A. Medium water conditions
• B. xeric conditions
• C. highly dry conditions
• D. excessive wet conditions.

Explanation: Hydrarch succession takes place in wetter areas and the successional series progresses from hydric to the mesic condition. Xerach succession takes place in dry areas and the series progresses from xeric to mesic condition. Hence, both hydrach and xerach succession leads to medium water conditions (mesic).