Why might photosynthesis and respiration be considered complementary processes?

Question

Why might photosynthesis and respiration be considered complementary processes?

Answer 1

Both use nitrogen and oxygen.Both used to sustain life.

Answer 2

Photosynthesis uses carbon dioxide and leaves oxygen as a by product.  Respiration uses oxygen and leaves carbon dioxide as a by product.

Answer 3

The overall equations for the two processes are identical if you only switch the direction of the arrow.

Photosynthesis:

6 carbon dioxide + 6 water + energy = 6 oxygen + glucose

Respiration:

6 oxygen + glucose = 6 carbon dioxide + 6 water + energy