PREVIOUS YEAR QUESTIONS
Q 1 ) In an ecosystem, why is the number of trophic levels of a food chain usually limited? CAPF 2024
- Lower trophic level has lesser energy than the higher trophic level
- Because of the loss of energy at each trophic level
- Higher trophic level individual can control the lower ones more efficiently
- Limited trophic level makes a food chain less vulnerable to parasites
Answer: B
Explanation:
- At each trophic level, about 90% of energy is lost as heat or used up in metabolism, leaving only around 10% available for the next level. This significant energy loss limits the amount of energy that can be transferred through successive trophic levels, making it unsustainable to support more than 4–5 levels in a food chain.
Q 2 ) Energy and nutrients flow from one trophic level to another in an ecosystem. Which one of the following statements correctly describes the direction of flow of energy and nutrients in an ecosystem? CDS (2023)
- Energy flow is cyclic and nutrient flow is unidirectional.
- Energy flow is unidirectional and nutrient flow is cyclic.
- Both energy and nutrient flow are unidirectional.
- Both energy and nutrient flow are cyclic.
Answer: B
Explanation
In an ecosystem, energy flows in a unidirectional manner — from producers (plants) to herbivores, then to carnivores, and is ultimately lost as heat. Energy cannot be recycled.
On the other hand, nutrients flow in a cyclic manner, as they are continuously recycled between organisms and the environment through biogeochemical cycles (e.g., carbon, nitrogen, water cycles).
Q 3 )In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle? (UPSC 2021)
- Carbon cycle
- Nitrogen cycle
- Phosphorus cycle
- Sulphur cycle
Answer: C
Explanation
- The phosphorus cycle is a sedimentary biogeochemical cycle, where phosphorus is primarily stored in rocks as phosphates. Phosphorus enters the ecosystem through weathering of phosphate rocks, which releases phosphates into the soil and water. Unlike carbon and nitrogen cycles, phosphorus does not have a significant atmospheric component and relies on geological processes for its recycling.
Q 4 ) Which one of the following organisms represents the primary consumer category in an ecosystem? NDA (2019)
- Caterpillar
- Crabapple tree
- Frog
- Sparrowhawk
Answer: A
Explanation
- In an ecosystem:
- Producers: Green plants (e.g., crabapple tree) that produce food through photosynthesis.
- Primary consumers: Herbivores that feed directly on producers (e.g., caterpillar).
- Secondary consumers: Carnivores that eat herbivores (e.g., frog).
- Tertiary consumers: Top predators that eat secondary consumers (e.g., sparrowhawk).
- The caterpillar feeds directly on plant leaves, making it a primary consumer.