Question

how are photosynthesis and cellular respiration opposite in terms of carbon dioxide

Answer 1

Photosynthesis is the process by which plants take in (use) Carbon-dioxide and water to make food (starch).
Photosynthesis:

`CO_(2) + H_(2) 0 +sunlight ----> C_(6)H_(12)O_(6)+O_(2)`

Cellular respiration is the process in which cells use oxygen to break down starch into energy molecules and give out Carbon-dioxide.
Cellular respiration:

`C_(6)H_(12)O_(6)+O_(2)----->CO_(2) + H_(2) 0 +energy`

So, in Photosynthesis, carbon-dioxide is taken in (used) and in cellular respiration, carbon-dioxide is thrown out (waste product)

Answer 2

Things that use Photosynthesis use carbon dioxide and release oxygen (like plants)
Things that use cellular respiration use oxygen and release carbon dioxide (like humans)