Plants swap gases by day and by night
Plants breathe too. Day and night, plants take in oxygen and release carbon dioxide in respiration, just like animals do, to release energy from their food. In daylight they also do photosynthesis, taking in carbon dioxide and giving out oxygen. In bright light, photosynthesis makes more oxygen than respiration uses, so the plant gives out oxygen overall. At night there is no light, so photosynthesis stops, but respiration goes on. Do not say that plants breathe only at night. To see photosynthesis, place a few fresh leaves of a water plant in a jar of water in the sun with an adult: small bubbles of oxygen may form on the leaves. A clear plastic bag over a plant with gas detector tubes can measure the changes, but this is done by teachers.
| Photosynthesis | Respiration | |
|---|---|---|
| Needs light? | yes | no, day and night |
| Gas taken in | carbon dioxide | oxygen |
| Gas given out | oxygen | carbon dioxide |
| Time | Plant gas exchange (overall) |
|---|---|
| bright day | gives out oxygen |
| night | gives out carbon dioxide |
Bubbles look. With a grown-up, place fresh leaves in a clear jar of water in a sunny place. Look after an hour and again later. Draw what you see. A result may not appear on a cloudy day, and that is fine to record.