Free Man and His Environment MCQs with Answers

171. The breakdown of detritus into smaller particles by earthworm is a process called

• A. humification
• B. fragmentation
• C. mineralisation
• D. catabolism.

Explanation: Decomposition is the process in which decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients. The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation. Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation. By the process of leaching, water­ soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts. Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism. Humification and mineralisation occur during decomposition in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.

172. The biomass available for consumption by the herbivores and the decomposers is called

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

Explanation: The total organic matter synthesised by the producers in the process of photosynthesis per unit time and area is known as gross primary productivity. Net primary productivity is equal to the rate of organic matter created by photosynthesis minus the rate of respiration and other losses. It is actually the biomass available for consumption by the herbivores and the decomposers.

173. Which of the following representations shows the pyramid of numbers in a forest ecosystem?

• A. D
• B. A
• C. B
• D. C

Explanation: The representation of the forest ecosystem in the pyramid of numbers is always upright because the higher trophic level comprising tertiary consumers is generally smaller than that of the lower trophic levels (i.e., secondary consumer, primary consumer, and primary producer). The pyramid of numbers is inverted in the case of a single tree producer which can provide nourishment to several herbivores such as birds which can further support a larger population of ectoparasites.

174. Which one of the following types of organisms occupy more than one trophic level in a pond ecosystem?

• A. Fish
• B. Zooplankton
• C. Frog
• D. Phytoplankton

Explanation: A single species may occupy more than one trophic level. In ponds, fish occupy more than one trophic level. Small fishes act as secondary consumers. They feed on primary consumers. Large fishes act as tertiary consumers. They feed on smaller fish.

175. Consider the following statements concerning food chains. A. Removal of 80% tigers from an area resulted in greatly increased growth of vegetation. B. Removal of most of the carnivores resulted in an increased population of deer. C. The length of food chains is generally limited to 3­-4 trophic levels due to energy loss. D. The length of food chains may vary from 2 to 8 trophic levels. Which two of the above statements are correct?

• A. A, D
• B. A, B
• C. B, C
• D. C, D

Explanation: Removal of 80% of tigers (i.e., tertiary consumer) from an area resulted in decreased growth of vegetation because there will be increased numbers of secondary or primary consumers that feed on a green plant. Removal of most of the carnivores resulted in an increased population of deer on which carnivores depend. The length of the food chain is generally limited to 3­-4 trophic level due to energy loss because all the food available at one level is neither eaten nor used by animals at the next level and a lot of the energy is lost in respiration to drive the organism's metabolism so less energy is left to support higher trophic level.

176. The slow rate of decomposition of fallen logs in nature is due to their

• A. The anaerobic environment around them
• B. Low cellulose content
• C. Low moisture content
• D. Poor nitrogen content.

Explanation: The microorganisms break down the complex compounds of dead protoplasm of producers and consumers absorb some of the decomposition products and release simple substances. The slow rate of decomposition of fallen logs in nature is due to their low moisture content. The cellulose is in high amounts in fallen logs. The environment around the fallen logs is aerobic. Decomposition rates are low under very wet or very dry conditions. Decomposition rates are highest in damp, moist conditions with adequate levels of oxygen. Wet soils tend to become deficient in oxygen (this is especially true in wetlands), which slows microbial growth.

177. About 71% of total global carbon is found in

• A. Oceans
• B. Forests
• C. Grasslands
• D. Agroecosystems.

Explanation: Carbon constitutes 49% of the dry weight of an organism and is next only to water. Among the total quantity of global carbon, 71% is found in oceans in dissolved form whereas only 1% is found in the atmosphere. Carbon cycling occurs through theatmosphere, ocean and living or dead organisms.

178. Which one of the following is not used for the construction of ecological pyramids?

• A. Fresh weight
• B. Dry weight
• C. Number of individuals
• D. Rate of energy flow

Explanation: Ecological pyramids represent the trophic structure and trophic function of an ecosystem. In an ecological pyramid, the first trophic level forms the base, and successive trophic levels the tiers that make up the apex. Ecological pyramids may be of three general types, i.e. pyramids of numbers, pyramids of biomass, and pyramids of energy. The pyramid of biomass indicates the decrease or the gradual reduction in biomass at each trophic level from base to apex. Fresh weight is not used in ecological pyramids.

179. An ecosystem which can be easily damaged but can recover after some time if its damaging effect stops will have

• A. Low stability and high resilience
• B. High stability and low resilience
• C. Low stability and low resilience
• D. High stability and high resilience.

Explanation: Stability can be defined as the power of a system to be in its state against unfavorable factors and resilience is the capability of regaining its original shape or position after being deformed. An ecosystem that can be damaged easily must also have high resilience.

180. A bamboo plant growing in a fir forest will occupy which trophic level?

• A. First trophic level (T1 )
• B. Second trophic level (T2 )
• C. Third trophic level (T3 )
• D. Fourth trophic level (T4 )

Explanation: The trophic structure of an ecosystem is a type of producer­-consumer arrangement in which each food level is called a trophic level and the graphical representation of the trophic structure of the ecosystem constitutes ecological pyramids. The green plants are producers and represent the first trophic level (T 1 ). So the bamboo plant is the first trophic level (T 1 ).