Photosynthesis vs. Cellular Respiration: What's the Difference?
Photosynthesis and cellular respiration are opposite, complementary processes in the cycle of life's energy. Photosynthesis uses sunlight to build sugar and release oxygen (storing energy), while cellular respiration breaks that sugar down using oxygen to release usable energy and carbon dioxide. One charges the battery; the other spends it.
See the difference, explained visually.
Watch a 2-minute animated lesson comparing photosynthesis and cellular respiration.
At a glance
| Photosynthesis | Cellular Respiration | |
|---|---|---|
| What it does | Stores energy as sugar (glucose) | Releases energy from sugar |
| Inputs | Sunlight, CO₂, water | Glucose, oxygen |
| Outputs | Glucose, oxygen | Energy (ATP), CO₂, water |
| Where | Chloroplasts (plants, algae) | Mitochondria (almost all cells) |
| Energy flow | Absorbs and stores energy | Liberates and uses energy |
Which should you use?
Photosynthesis
Photosynthesis happens in plants, algae, and some bacteria — the producers that capture sunlight and turn it into the chemical energy that feeds nearly every food chain.
Cellular Respiration
Cellular respiration happens in virtually all living things, including plants themselves — it's how cells actually spend stored energy to grow, move, and function.
Frequently asked questions
- Are they exact opposites?
- Almost — the inputs of one are roughly the outputs of the other, which is why they form a cycle. But they aren't a simple reverse reaction; each runs through its own distinct series of steps.
- Do plants do both?
- Yes. Plants photosynthesize to make sugar, then respire to release energy from it — they carry out cellular respiration day and night, not just photosynthesis in daylight.
- Which one makes the oxygen we breathe?
- Photosynthesis releases oxygen as a by-product. Cellular respiration consumes oxygen to release energy, producing carbon dioxide in return.