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Q. Many algae often float in the water in the day hours and sink in the night. Why this happens?
  1. Evolution and trapping of oxygen bubbles in day hours due to Photosynthesis
  2. They consume food in the day and become light
  3. In daytime, the water gets warmed and its density becomes low
Which among the above is/ are correct?
Answer: Only 1
Notes: The reason of algae float to the surface during the day & sink at night is due to photosynthesis. In Day time, the algae is producing oxygen. When enough Oxygen is produced during the day , it gets trapped in bubbles and it can lift the clumps up to the surface. In night, this oxygen is consumed and CO2 is produced. So algae sinks.
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