Question

Algae and other submerged plants float in water during day time and sink at night, because

• A. They become light due to food material accumulation.
  
• B. They lose weight at night.
• C. They become bouyant due to accumulation of $O_2$ as a result of photosynthesis.
• D. None of the above.

Answer 1

Answer: (C)

They become bouyant due to accumulation of $O_2$ as a result of photosynthesis.

Algae and other green plants carry out oxygenic photosynthesis during day time. In this process, oxygen is released as a byproduct, which makes the plant body buoyant allowing them to float on the surface.