When a plant carries out photosynthesis, is that its biochemical reaction to carbon?

Question

I have to explain how various organisms' biochemical reactions contribute to the recycling of carbon in an ecosystem,

Answer 1

It's not a biochemical reaction to carbon, per se.  I would say it is a biochemical reaction involving carbon.

The process of photosynthesis takes carbon dioxide and converts the carbon into food for the plant.  (It also does other things, of course, but they're not relevant to carbon.)  The plant uses that carbon and grows...eventually dying...thus returning the carbon to the ecosystem through decay.

Hope that helps!