What would happen if phytoplankton of an ocean is completely destroyed for some reason?

Answer: (a) 1 and 2 only

Statements 1 and 2 are correct, so the answer is (a). Phytoplankton are the ocean's main producers and the main route by which carbon dioxide moves from the air into the sea. Losing them would damage both the carbon sink and the food chains. Ocean water density depends chiefly on temperature and salinity, not on phytoplankton.

• ✓ 1. Phytoplankton take in carbon dioxide during photosynthesis, and some of that carbon sinks to the deep ocean. They are responsible for most of the transfer of CO2 from the atmosphere to the ocean. Without them, the ocean's role as a carbon sink would weaken.
• ✓ 2. Phytoplankton are producers in aquatic ecosystems and form the base of ocean food chains. They feed zooplankton, which in turn feed small fish and larger animals. If phytoplankton were destroyed, every higher trophic level would be affected.
• ✗ 3. The density of sea water is closely linked to its temperature and salinity, which chiefly determine it. Phytoplankton do not control these factors, so their loss would not cause a drastic fall in density.

Remember · Phytoplankton are the ocean's primary producers and a key part of its carbon pump. Sea-water density is set chiefly by temperature and salinity, not by living organisms.

📘 Read it in NCERT: Class 12 Biology, Ch 12 (practise this chapter) · Class 11 Fundamentals of Physical Geography, Ch 12 (practise this chapter)

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