How does plankton make their food?

Answer 1

Phytoplankton make their food by photosynthesis.

Zooplankton are tiny animals and are consumers.

Answer 2

"Plankton" is a name that designates living organisms that share a particular way of living: they float near the surface of the water, and cannot move on their own (in some cases) or can only move by themselves on a very small scale (especially migrating up and down in the water column), and are mostly carried and moved about by water currents.

Compare this word with "nekton"= the living organisms in water that propel themselves by swimming, etc.

For example, adult fish are part of nekton, but many begin life as tiny semitransparent larvae that float as part of plankton.

So "plankton" is not a particular species. 'Phytoplankton' is another collective noun for a subgroup of these= the passively floating plants, which includes bacteria and algae. They make food by photosynthesis, like other plants.

'Zooplancton' is the collective noun for the floating animals. Some of these are herbivores, and eat phytoplancton. Others are carnivorous, and yet others are detritivorous (they eat small particles of organic material).

Here's an interesting article:
http://www.whaledolphintrust.co.uk/whales_dolphins/plankton.asp

Answer 3

Some plankton are actually tiny "plants" - they contain green chloroplasts and can make their own sugars from sunlight just like traditional plants.

Others actually prey on other plankton - they are predatory. There are both active forms, which "hunt", and passive forms, which filter for food and eat whatever they get.