Multiple choice Why do algae float in water during the day and sink at night? They require light during day for photosynthesis. They accumulate food at night and get heavy. Become buoyant in light due to attachment of oxygen bubbles. Become light due to consumption of food. Reveal answer Fill a bubble to check yourself C Correct answer Explanation Algae float in water during light and sink at night as during day it releases oxygen while photosynthesizing that makes it buoyant. However, during night it again sinks down at the bottom.