Free Man and His Environment MCQs with Answers

191. The primary succession refers to the development of communities on a

• A. Forest that is clearing after a devastating fire
• B. Newly­-exposed habitat with no record of earlier vegetation
• C. Freshly cleared crop field
• D. Pond freshly filled with water after a dry phase.

Explanation: When succession begins on an area that has not been previously being occupied by a community, for e.g., a newly exposed rock area, sand dunes, new islands, deltas, shore or recent lava flow, it is known as primary succession. The first group of organisms (plants or animals) which becomes established in such an area is termed the pioneer community.

192. The dominant second trophic level, in a lake ecosystem, is

• A. Phytoplankton
• B. Zooplankton
• C. Benthos
• D. Plankton.

Explanation: A trophic level is a step or division of a food chain that is characterized by the method of obtaining its food. The two fundamental trophic levels are producers and consumers. Producers belong to the first trophic level. In a lake, the producers are mainly some rooted or floating plants and phytoplanktons.

193. A pyramid of numbers deals with the number of

• A. Species in an area
• B. Individuals in a community
• C. Individuals in a trophic­ level
• D. Subspecies in a community.

Explanation: The pyramid of numbers is an ecological pyramid that employs the number of individuals per unit area at various trophic levels sequence-wise with producers at the base and various consumers at successively higher levels. The pyramid of numbers assumes different shapes in different ecosystems. The pyramid of numbers in a pond ecosystem is also upright. In a forest ecosystem, the pyramid of numbers is intermediate. Here, the number of primary consumers is more than producers as well as top consumers. In the parasitic food chain, the pyramid of numbers is inverted.

194. Pyramid of numbers in a pond ecosystem is

• A. Irregular
• B. Inverted
• C. Upright
• D. Spindle shaped.

Explanation: The pyramid of numbers is an ecological pyramid that employs the number of individuals per unit area at various trophic levels sequence-wise with producers at the base and various consumers at successively higher levels. The pyramid of numbers assumes different shapes in different ecosystems. The pyramid of numbers in a pond ecosystem is also upright. In a forest ecosystem, the pyramid of numbers is intermediate. Here, the number of primary consumers is more than producers as well as top consumers. In the parasitic food chain, the pyramid of numbers is inverted.

195. The food chain in which microorganisms breakdown the food formed by primary producers is a

• A. Parasitic food chain
• B. Detritus food chain
• C. Consumer food chain
• D. Predator food chain.

Explanation: The dead organic matter of plants or animals is called detritus. While a part of it remains on the soil surface as litter, the other part enters the soil. Many animals such as protozoans, nematodes, insects, etc., depend on detritus and hence they are called detritivores. Even human beings are detritivores when they eat cooked food. From detritus, the chain proceeds to detritivores, then to carnivores, and finally to top carnivores.

196. Select the correct food chain.

• A. Grass -- Chameleon -- Insect -- Bird
• B. Grass -- Fox -- Rabbit -- Bird
• C. Phytoplankton -- Zooplankton -- Fish
• D. Fallen leaves -- Bacteria -- Insect larvae

Explanation: The process of transfer of energy from producers through a series of organisms, i.e., from primary consumers to secondary consumers and from secondary consumers to tertiary consumers by the process of eating and being eaten constitutes a food chain. The correct food chain is: Phytoplankton - Zooplankton - Fish

197. Pyramid of numbers in a grassland/tree ecosystem is

• A. Always inverted
• B. Always upright
• C. Both (a) and (b)
• D. Spindle-­shaped.

Explanation: Pyramid of numbers in a grassland/tree ecosystem is always upright. It shows the number of individual organisms at each level. In a grassland, the producers, which are mainly grasses, are always maximum in number. This number then shows a decrease towards the apex, primary consumers are lesser in number than the grasses; the secondary consumers are lesser in number than the primary consumers. Finally, the top consumers are the least in number. Thus, the pyramid becomes upright.

198. Upper part of sea/aquatic ecosystem contains

• A. Plankton
• B. Nekton
• C. Plankton and Nekton
• D. Benthos

Explanation: Planktons are passively floating in upper water, nektons are actively swimming and benthos lead sedentary life upon the sea bottom. Planktons are producers and are present in large numbers.

199. What is true of an ecosystem?

• A. Primary consumers are the least dependent upon producers.
• B. Primary consumers out­number producers.
• C. Producers are more than primary consumers.
• D. Secondary consumers are the largest and most powerful.

Explanation: An ecosystem may be defined as a structural and functional unit of the biosphere comprising living organisms and their non­living environment that interact by means of food chains and chemical cycles resulting in energy flow, biotic diversity, and material cycling to form a stable, self-supporting system. The organisms in an ecosystem are classified into 3 main categories, i.e. ­producers, consumers, and decomposers. The consumers utilize materials and energy stored by the producers. Decomposers obtain their food molecules from the organic materials of dead producers and consumers. In a true ecosystem, producers are more than consumers (herbivores and carnivores).

200. In an ecosystem, which option shows one­way passage?

• A. Free energy
• B. Carbon
• C. Nitrogen
• D. Potassium

Explanation: The behavior of energy in an ecosystem can be termed as energy flow due to the unidirectional flow of energy. The flow of energy is only in one direction i.e., from solar radiation - producers -herbivores - carnivores. This energy cannot pass in the reverse direction. There is a decrease in the content and flow of energy with a rise in trophic levels.