Q1. Which factor does not directly affect the transparency of water in aquatic ecosystems?
- Phytoplankton
- Clay and silt
- Salinity
- Suspended particles
Correct Option: 3. Salinity
Explanation: Salinity affects water chemistry but not transparency directly. Transparency is mainly affected by phytoplankton, silt, and suspended particles that block sunlight.
Q2. What is the difference between oligotrophic and eutrophic lakes?
- Eutrophic lakes are deeper
- Oligotrophic lakes have high nutrient content
- Eutrophic lakes have more plant and animal species
- Oligotrophic lakes have better water quality
Correct Option: 4. Oligotrophic lakes have better water quality
Explanation: Oligotrophic lakes are nutrient-poor, with clearer water and better quality for domestic and industrial use, while eutrophic lakes are nutrient-rich, supporting excessive plant growth and poor water quality.
Q3. Cultural eutrophication is mainly caused by:
- Volcanic activity
- Rainwater runoff
- Agricultural runoff and sewage
- Natural lake aging
Correct Option: 3. Agricultural runoff and sewage
Explanation: Cultural eutrophication is human-induced and results from the inflow of nitrates and phosphates from fertilizers, sewage, etc., causing accelerated lake ageing and algal blooms.
Q4. What happens during an algal bloom in a eutrophic lake?
- Increased oxygen and fish population
- Enhanced transparency
- Reduced sunlight penetration and oxygen depletion
- Increased nekton population
Correct Option: 3. Reduced sunlight penetration and oxygen depletion
Explanation: An algal bloom blocks sunlight, reducing photosynthesis and leading to oxygen depletion as decomposers break down dead algae, killing aquatic life.
Q5. Which of the following is the correct match for benthos?
- Floating algae
- Surface insects
- Organisms attached to submerged plants
- Organisms living at the bottom of water bodies
Correct Option: 4. Organisms living at the bottom of water bodies
Explanation: Benthos includes organisms such as worms, crustaceans, and certain algae that live on or in the bottom of aquatic environments.