Question 31:
Which of the following is true about the “10% law” of energy transfer in an ecosystem?
(A) 10% of energy is lost as heat at each trophic level.
(B) Only 10% of the energy from one trophic level is passed on to the next.
(C) 10% of energy is transferred from the producer level to the consumer level.
(D) 10% of the total energy is available to decomposers.
Answer: (B) Only 10% of the energy from one trophic level is passed on to the next.
Explanation:
The 10% law states that only about 10% of the energy at one trophic level is transferred to the next trophic level. The remaining 90% is lost in various forms, primarily as heat through metabolic processes.
Question 32:
What is the primary factor that limits the length of food chains in ecosystems?
(A) Amount of water available
(B) Size of organisms at each trophic level
(C) Loss of energy between trophic levels
(D) Rate of photosynthesis
Answer: (C) Loss of energy between trophic levels
Explanation:
The loss of energy between trophic levels limits the length of food chains. Because only about 10% of energy is transferred from one trophic level to the next, the amount of energy available decreases at each successive level, restricting the number of trophic levels an ecosystem can support.
Question 33:
Which term refers to the interaction where one species benefits and the other is unaffected?
(A) Parasitism
(B) Mutualism
(C) Commensalism
(D) Competition
Answer: (C) Commensalism
Explanation:
Commensalism is a relationship between two species in which one benefits, while the other is neither helped nor harmed. Examples include barnacles on whales or birds nesting in trees.
Question 34:
Which of the following organisms is involved in ammonification during the nitrogen cycle?
(A) Nitrifying bacteria
(B) Denitrifying bacteria
(C) Fungi
(D) Phytoplankton
Answer: (C) Fungi
Explanation:
Ammonification is the process by which organic nitrogen in dead organisms and waste products is converted into ammonia (NH₃) by decomposers like fungi and bacteria. Nitrifying bacteria are involved in nitrification, and denitrifying bacteria in denitrification.
Question 35:
In a grassland ecosystem, which trophic level would a snake occupy if it feeds on a frog that feeds on insects?
(A) Primary consumer
(B) Secondary consumer
(C) Tertiary consumer
(D) Quaternary consumer
Answer: (C) Tertiary consumer
Explanation:
The snake would be a tertiary consumer in this food chain. The grass (producer) is consumed by the insects (primary consumer), which are eaten by the frog (secondary consumer). The snake, feeding on the frog, is a tertiary consumer.
Question 36:
Which of the following factors does not limit the primary productivity of an ecosystem?
(A) Availability of nutrients
(B) Solar energy
(C) Availability of carbon dioxide
(D) Biomass of secondary consumers
Answer: (D) Biomass of secondary consumers
Explanation:
The primary productivity of an ecosystem is limited by factors such as nutrient availability, sunlight, and carbon dioxide for photosynthesis. The biomass of secondary consumers does not directly affect primary productivity, as it refers to consumers rather than producers.
Question 37:
What is the approximate efficiency of energy transfer from producers to primary consumers?
(A) 1%
(B) 5%
(C) 10%
(D) 20%
Answer: (C) 10%
Explanation:
According to the 10% law, about 10% of the energy captured by producers (plants) is transferred to primary consumers (herbivores). The rest is lost as heat or used in metabolic processes.
Question 38:
Which of the following is an example of an ecosystem service?
(A) A beehive producing honey
(B) A plant undergoing photosynthesis
(C) Nutrient cycling in a forest
(D) A deer eating grass
Answer: (C) Nutrient cycling in a forest
Explanation:
Ecosystem services are benefits that humans obtain from ecosystems. Nutrient cycling is an essential ecosystem service that helps maintain soil fertility, supports plant growth, and sustains life. Photosynthesis is a process within the ecosystem, but nutrient cycling broadly benefits ecosystem sustainability.
Question 39:
Which biogeochemical cycle is responsible for weathering of rocks as an important component?
(A) Water cycle
(B) Phosphorus cycle
(C) Carbon cycle
(D) Nitrogen cycle
Answer: (B) Phosphorus cycle
Explanation:
The phosphorus cycle involves the weathering of rocks, which releases phosphate ions into the soil. Unlike the nitrogen and carbon cycles, the phosphorus cycle lacks a significant atmospheric component and is driven by the slow release of phosphorus from rocks.
Question 40:
Which of the following contributes most to the “greenhouse effect”?
(A) Nitrogen
(B) Carbon dioxide
(C) Oxygen
(D) Ozone
Answer: (B) Carbon dioxide
Explanation:
Carbon dioxide (CO₂) is a major greenhouse gas that traps heat in the Earth’s atmosphere, contributing to the greenhouse effect and global warming. Although other gases like methane and nitrous oxide are also involved, CO₂ is the primary contributor.
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