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UPSC Prelims 2012 · Environment · Species Watch
What would happen if phytoplankton of an ocean is completely destroyed for some reason? Select the correct answer using the codes given below:
- The ocean as a carbon sink would be adversely affected.
- The food chains in the ocean would be adversely affected.
- The density of ocean water would drastically decrease.
- (a) 1 and 2 only
- (b) 2 only
- (c) 3 only
- (d) 1, 2 and 3
Show the answer and explanation
Answer: (a) 1 and 2 only
The carbon sink and the food chains both collapse; density is set by salt and temperature.
Statement by statement
1. ✓ YES Phytoplankton take up CO₂ by photosynthesis and send carbon to the deep sea (the biological pump).
2. ✓ YES They are the base of almost every marine food chain.
3. ✗ NO Seawater density depends on temperature and salinity — tiny plankton don’t change it.
The idea
Phytoplankton do two jobs for the planet. They are the “grass of the sea”, the food on which everything else in the ocean finally depends. And by taking up carbon dioxide and sinking when they die, they carry carbon into the deep ocean.
Phytoplankton → Zooplankton and krill → Small fish → Big fish, seabirds, whales
Also know
The density of sea water depends on its temperature and its salt content, not on the microscopic life in it.
🔒 Phytoplankton: base of ocean food chains + biological carbon pump + ~50% of Earth’s oxygen.