Free Man and His Environment MCQs with Answers

181. Plant decomposers are

• A. Monera and Fungi
• B. Fungi and Plants
• C. Protista and Animalia
• D. Animalia and Monera.

Explanation: Microorganisms (bacteria and fungi) are decomposers of the ecosystem. They feed upon dead decaying living organisms (both plant and animal) and break them into simpler compounds. These are released free in the atmosphere and are utilized by producers for the synthesis of their food materials. They mainly belong to monera and fungi.

182. What is the reason for the highest biomass being present in the aquatic ecosystem?

• A. Nano plankton, blue-green algae, and green algae
• B. Sea grass and slime moulds
• C. Benthoic and brown algae
• D. Diatoms

Explanation: The benthic region includes all the seafloor from the wave-­washed shore-­line to the greatest depths. Depending upon the penetration of light it is subdivided into two main zones: the lighted or littoral zone and the deep sea system. Due to an abundance of light, water, oxygen, carbon dioxide, and less salinity of water, the tidal zone is characterized by an exorbitant growth of plants. The dense growth of vegetation, on the other hand, provides shelter and food for animals. A wide variety of algae, a few types of grass, and animals of every phylum of the animal kingdom are represented in this region.

183. Energy transfer from one trophic level to other, in a food chain, is

• A. 10%
• B. 20%
• C. 1%
• D. 2%.

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.

184. In a terrestrial ecosystem such as a forest, which trophic level posseses the maximum amount of energy?

• A. T 3
• B. T 4
• C. T 1
• D. T 2

Explanation: In a terrestrial ecosystem, maximum energy is in trophic level I because the organisms that trap solar energy are primary producers and they have maximum energy. Only 10% of energy is transferred from one trophic level to the next trophic level.

185. Which of the following ecosystem has the highest gross primary productivity?

• A. Mangroves
• B. Rainforest
• C. Grassland
• D. Coral reef

Explanation: Gross primary productivity is the total rate of photosynthesis, including the organic matter used up in respiration during the measurement period. Tropical evergreen/rainforests occur over equatorial/subequatorial regions with abundant warmth and rainfall (200-350 cm/yr) almost throughout the year. The forests are impenetrable (= jungle) with maximum diversity, e.g., 200 types of trees in one hectare, 70-80% of all insects, and 80-85% of all birds. Productivity is maximum here; it equates to 12000 kcal/m 2 /yr.

186. Which of the following act as "nature's scavengers"?

• A. Insects
• B. Microorganisms
• C. Man
• D. Animals

Explanation: Microorganisms (bacteria and mold) are decomposers of the ecosystem. They feed upon dead decaying organisms (both plants and animals) and break them into simpler compounds. These are released free in the atmosphere and are utilized by producers for the synthesis of their food materials. They are called nature's scavengers as they are consumers of dead matter.

187. The 10% energy transfer law of food chain was given by

• A. Lindemann
• B. Tansley
• C. Stanley
• D. Weismann.

Explanation: Herbivores are eaten by primary carnivores. Only 10% of the herbivore's productivity is utilized for raising the 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 the energy present in primary carnivores. It is called the 10% law which was proposed by Lindemann. Accordingly, if a plant traps 20 J of energy, mice will have 2 J, snakes will have 0.2 J, and hence, peacocks will have 0.02 J of energy.

188. If we completely remove the decomposers from an ecosystem, its functioning will be adversely affected, because

• A. Mineral movement will be blocked
• B. The rate of decomposition will be very high
• C. Energy flow will be blocked
• D. Herbivores will not receive solar energy.

Explanation: Decomposers are saprotrophs which decompose the organic remains by secreting extracellular digestive enzymes. They are also known as mineralisers as they release minerals trapped in organic remains. So in the absence of microorganisms the flow of minerals will stop.

189. Which of the following pairs is a sedimentary type of biogeochemical cycle?

• A. Phosphorus and nitrogen
• B. Phosphorus and sulphur
• C. Oxygen and nitrogen
• D. Phosphorus and carbon dioxide

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

190. Which of the following is the most stable ecosystem?

• A. Mountain
• B. Ocean
• C. Forest
• D. Desert

Explanation: Of all the ecosystems, the ocean is the largest and most stable ecosystem. Aquatic life is protected from vigorous climates and weather such as extreme climatic conditions, problems of water supply, food, fire and artificial forces such as industrialization, farming and grazing.