Free Man and His Environment MCQs with Answers

151. Most animals are tree dwellers in a

• A. temperate deciduous forest
• B. tropical rainforest
• C. coniferous forest
• D. thorn woodland.

Explanation: Tropical rainforests have a very dense plant cover. They also experience a large amount of precipitation, thus the forest floor is always damp. Thus, the conditions there have led animals to get adapted to arboreal habitats. Most animals found there are tree dwellers as almost every space on the forest floor is occupied by the vegetation.

152. In an ecosystem the rate of production of organic matter during photosynthesis is termed as

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

Explanation: The amount of energy accumulation in green plants as biomass or organic matter per unit area over a time period is known as primary productivity. The rate of total capture of energy, or the rate of total production of organic material (biomass), is known as gross primary productivity.

153. If 20 J of energy is trapped at producer level, then how much energy will be available to peacock as food in the following chain? Plant -- Mice -- Snake -- Peacock

• A. 0.02 J
• B. 0.002 J
• C. 0.2 J
• D. 0.0002 J

Explanation: Herbivores are eaten by primary carnivores. Only 10% of the herbivores productivity is utilized for raising productivity of primary carnivores. The rest is consumed in ingestion, respiration, maintenance of body heat and other activities. Higher carnivores similarly are able to retain only 10% of energy present in primary carnivores. It is called 10% law which was proposed by Lindemann. Accordingly, if plant trapped 20 J of energy, mice will have 2 J, snake will have 0.2 J and hence, peacock will have 0.02 J of energy.

154. Natural reservoir of phosphorus is

• A. rock
• B. fossils
• C. sea water
• D. animal bones.

Explanation: The reservoir pool of phosphorus is in phosphate rocks while the cycling pool is soil and water for terrestrial and aquatic ecosystems respectively. Small amount of phosphate is always being added to the cycling pool through weathering of rocks. Phosphate is generally found in soil in combination with calcium, iron and aluminium. Atmosphere or gaseous cycle is absent. Phosphate circulates in the abiotic environment in lithosphere as well as hydrosphere.

155. Secondary productivity is the rate of formation of new organic matter by

• A. consumers
• B. decomposers
• C. producers
• D. parasites.

Explanation: The rate of photosynthesis of organic matter by the consumers is known as secondary productivity. It depends upon the loss while transferring energy-containing organic matter from the previous trophic level plus the consumption due to respiration and predation. Therefore, net productivity decreases with each trophic level.

156. Which one of the following processes during decomposition is correctly described?

• A. Catabolism - Last step in decomposition under fully anaerobic conditions
• B. Leaching - Water soluble inorganic nutrients rise to the top layers of soil
• C. Fragmentation - Carried out by organisms such as the earthworm
• D. Humification - Leads to the accumulation of a dark coloured substance humus which undergoes microbial action at a very fast rate.

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 catabolism. Humification and mineralisation occur during decomposition in the soil. Humification leads to the 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 the release of inorganic nutrients occur by the process known as mineralisation.

157. Which two distinct microbial processes are responsible for the release of fixed nitrogen as dinitrogen gas (N2 ) to the atmosphere?

• A. Aerobic nitrate oxidation and nitrite reduction
• B. Decomposition of organic nitrogen and conversion of dinitrogen to ammonium compounds
• C. Enteric fermentation in cattle and nitrogen fixation by Rhizobium in the root nodules of legumes
• D. Anaerobic ammonium oxidation and denitrification.

Explanation: Denitrification is a chemical process in which nitrates in the soil are reduced to molecular nitrogen (N2 ) which is released into the atmosphere. It is done by denitrifying bacteria like Pseudomonas denitrificans. Anaerobic oxidation of ammonium (NH4 ) also releases nitrogen into the atmosphere.

158. Which of the following is a primary consumer in the maize field ecosystem?

• A. Grasshopper
• B. Wolf
• C. Phytoplankton
• D. Lion.

Explanation: Primary consumers are herbivorous organisms that feed on producers. Carnivores are termed secondary, tertiary etc., consumers depending upon their position in the food chain. In a food chain on land, the grasshopper is a herbivore (primary consumer) while the wolf and lion are carnivores. Phytoplanktons are producers in aquatic food chains.

159. When man eats fish which feeds on zooplanktons which have eaten small plants, the producer in this chain is

• A. small plants
• B. fish
• C. man
• D. zooplankton.

Explanation: The transfer of food energy from producers to consumers through a series of organisms with repeated eating and being eaten is known as food chain. Green plants are always the first link of food chain because they alone are capable of synthesising organic food by using light energy by photosynthesis. The logical sequence of a food chain is :

160. Which one of the following is not a gaseous biogeochemical cycle in ecosystem?

• A. Sulphur cycle
• B. Phosphorus cycle
• C. Nitrogen cycle
• D. Carbon cycle

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