1.Phytoplankton absorb CO₂ during photosynthesis and release oxygen.

They help store carbon in the ocean when they die.

2. Light, temperature, nutrients and water mixing.Different regions have different limits.

3. They are the base of the ocean food web, feeding zooplankton, fish, and larger animals.

4. Phytoplankton: plant-like, photosynthetic.

Zooplankton: animal-like, eat phytoplankton.

5. Warmer waters and changing currents can reduce nutrients, shifting populations.

Some species may grow, others may decline.

6. By removing CO₂ from the air, they cool the planet.

7. Can harm some species with calcium.

May lower diversity, help some types while killing others.