Free Man and His Environment MCQs with Answers

141. Competition for light, nutrients and space is most severe between

• A. closely related organisms growing in different niches
• B. closely related organisms growing in the same area/niche
• C. distantly related organisms growing in the same habitat
• D. distantly related organisms growing in different niches.

Explanation: Competition is the rivalry for obtaining the same resource. Competition is of two types, intraspecific and interspecific. Intraspecific competition is the competition amongst members of the same species for a common resource. It may be for food, space, and mate. So if the density of elephant population in an area increases, it will lead to intraspecific competition. This will lead to the establishment of territories in elephants which will result in pushing out of the extra numbers, securing shelter, mate and food for the rest.

142. The primary producers of the deep­-sea hydrothermal vent ecosystem are

• A. green algae
• B. chemosynthetic bacteria
• C. blue­green algae
• D. coral reefs.

Explanation: Hydrothermal vents are cracks in the ocean floor that emit jets of hot water loaded with minerals and chemosynthetic bacteria. These bacteria are autotrophs that oxidise hydrogen sulphide in vent water to obtain energy which is used to produce organic material. These chemosynthetic bacteria are the primary producers and form the base of vent food webs. All vent animals ultimately depend on bacteria for food.

143. Which of the following would appear as the pioneer organisms on bare rocks?

• A. Mosses
• B. Green algae
• C. Lichens
• D. Liverworts

Explanation: The bare rocky habitat is extremely hostile to living beings. There is no water, as the substratum does not absorb rain water. There is no nutrient holding mechanism. Plants cannot grow on these rocks. The first inhabitants or pioneers of such a habitat are usually lichens as they are resistant to desiccation and extreme temperatures.

144. Which one of the following is a characteristic feature of cropland ecosystem?

• A. Absence of weeds
• B. Ecological succession
• C. Absence of soil organisms
• D. Least genetic diversity

Explanation: Cropland ecosystem is an artificial or man­ made terrestrial ecosystem which is created and maintained by human beings for their maximum benefits. Therefore, they will have least genetic diversity.

145. The term ecosystem was coined by

• A. E. Haeckel
• B. E.Warming
• C. E.P. Odum
• D. A. G. Tansley.

Explanation: The term ecosystem was coined by A.G. Tansley in 1935.

146. Most animals that live in deep oceanic waters are

• A. tertiary consumers
• B. detritivores
• C. primary consumers
• D. secondary consumers.

Explanation: Benthos is the community of organisms which live on, in, or near the sea bed, also known as the benthic zone. As no light is available at this zone of sea, the energy source for deep benthic ecosystems is often organic matter from higher up in the water column which drifts down to the depths. This dead and decaying matter sustains the benthic organisms, and therefore, most organisms in benthic zone i.e., in deep oceanic waters, are scavengers or detritivores.

147. During ecological succession:

• A. The numbers and types of animals remain constant
• B. The changes lead to a community that is in near equilibrium with the environment and is called pioneer community
• C. The gradual and predictable change in species composition occurs in a given area
• D. The establishment of a new biotic community is very fast in its primary phase

Explanation: Biotic or ecological succession is the natural development of a series of biotic communities at the same site, one after the other till a climax community develops which does not change further because it is in perfect harmony with the environment of the area. The change is orderly and sequential. There is a parallel change in the physical environment. During an ecological succession, the number and types of animals go on increasing with time. The community that is in near equilibrium with the environment is called the climax community. The establishment of a new biotic community is slow in its primary phase but gradually becomes fast in its secondary phase.

148. Which of the following options has both correct combinations?

• A. (a)
• B. (b)
• C. (c)
• D. (d)

Explanation: Biogeochemical cycles are of two types: gaseous and sedimentary. In gaseous nutrient cycles, the materials involved in circulation between biotic and abiotic components of the biosphere are gases or vapours and the reservoir pool is the atmosphere or hydrosphere, e.g., carbon, hydrogen, oxygen, nitrogen, water. In sedimentary nutrient cycles, materials involved in circulation between the biotic and abiotic components of biosphere are non­ gaseous and the reservoir pool is the lithosphere, e.g., phosphorus, calcium, magnesium. Sulphur has both sedimentary and gaseous nutrient cycles.

149. The mass of living material at a trophic level at a particular time is called

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

150. Secondary succession takes place on/in a

• A. newly created pond
• B. newly cooled lava
• C. bare rock
• D. degraded forest.

Explanation: Secondary succession (subsere) is the biotic succession that occurs in an area that becomes secondarily bare due to the destruction of a community previously present there. Secondary succession starts from previously built up substrata with already existing living matter. The action of any external force, such as a sudden change in climatic factors, biotic intervention, fire, etc., had resulted in the destruction of a previous community. Thus, the area became devoid of living matter but its substratum is built up. It has organic matter, so is biologically fertile and thus the successions are comparatively more rapid.