Q1. Which of the following is a marine flowering plant (angiosperm)?
- Seagrass
- Dinoflagellate
- Diatom
- Seaweed
Correct Option: 1. Seagrass
Explanation: Seagrasses are angiosperms (flowering plants) adapted to saltwater. They have true roots, stems, leaves, and flowers, unlike seaweeds which are algae. Seagrasses grow in shallow coastal waters and support high marine biodiversity.
Q2. Which gas is produced during seaweed decomposition and is considered toxic?
- Methane
- Carbon dioxide
- Hydrogen sulfide
- Nitrous oxide
Correct Option: 3. Hydrogen sulfide
Explanation: Decomposing seaweed releases hydrogen sulfide (H₂S), a toxic and foul-smelling gas. Inhaling high concentrations can lead to serious health issues including respiratory problems, vomiting, or even death. It’s especially dangerous when seaweed accumulates on beaches and decomposes.
Q3. Why are seagrass beds important for marine biodiversity?
- They release toxic chemicals to deter predators
- They increase salinity of the coastal water
- They trap carbon dioxide from the air
- They provide habitat, shelter, and food
Correct Option: 4. They provide habitat, shelter, and food
Explanation: Seagrass meadows are nurseries and feeding grounds for many marine species including fish, invertebrates, and birds. They stabilize sediments, reduce wave energy, and improve water clarity, all of which help in maintaining marine biodiversity.
Q4. Which of the following is a major threat to both seagrass and seaweed ecosystems?
- Ocean tides
- Eutrophication and siltation
- Tectonic movement
- Low pH of rainwater
Correct Option: 2. Eutrophication and siltation
Explanation:
• Eutrophication causes excessive algal growth which blocks sunlight.
• Siltation increases turbidity and buries plants.
Both reduce light penetration and damage the photosynthetic ability of seagrass and seaweeds, leading to habitat degradation.
Q5. How do phytoplankton contribute to climate regulation on Earth?
- They absorb methane from the ocean
- They reflect sunlight back into space
- They fix atmospheric nitrogen
- They absorb carbon dioxide during photosynthesis
Correct Option: 4. They absorb carbon dioxide during photosynthesis
Explanation: Phytoplankton perform photosynthesis, absorbing CO₂ from the atmosphere and producing oxygen. They act as part of the biological carbon pump, transferring carbon to deeper ocean layers. This helps regulate global temperatures by lowering greenhouse gas levels.