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Plants make their food from light, water and carbon dioxide. Can we see it happening?
Photosynthesis lab · Last updated: 16 October 2026
Plants make their food from light, water and carbon dioxide. Can we see it happening? In this 3D lab, you watch a plant take in what it needs and give out oxygen, and see what speeds the process up. It explains where nearly all our food and the oxygen we breathe come from.
What you'll discover
- Plants use light energy to turn carbon dioxide and water into sugar, releasing oxygen.
- The green pigment chlorophyll, inside chloroplasts, captures the light.
- Brighter light and more carbon dioxide speed photosynthesis up, until something else becomes the limit.
The science in plain words
Photosynthesis is how green plants, algae and some bacteria make their own food. In the leaves, chloroplasts contain the green pigment chlorophyll, which absorbs mainly red and blue light. The plant uses this captured energy to combine carbon dioxide from the air with water from the soil, making glucose, a sugar. Oxygen is released as a by-product. In words: carbon dioxide plus water, with light and chlorophyll, gives glucose plus oxygen.
You can see the evidence. Water plants such as Hydrilla give off tiny bubbles of oxygen in bright light, and the bubbles slow down in dim light. Leaves store some of the sugar as starch, which turns blue-black with iodine solution, while a leaf kept in the dark for a couple of days shows little or none.
The rate of photosynthesis depends on light intensity, carbon dioxide level and temperature. Increasing any one of them speeds the process up only until another factor runs short; that factor is then the limiting one. Carbon dioxide enters through tiny pores called stomata, mostly on the underside of leaves, and water travels up from the roots. Almost every food chain on Earth begins with photosynthesis, and it supplies nearly all the oxygen in the air.
Where it fits
Common questions
What do plants need for photosynthesis?
Plants need light, carbon dioxide, water and chlorophyll. Light supplies the energy, carbon dioxide comes from the air through pores in the leaves, and water comes up from the roots. Suitable warmth also helps, because the reactions are controlled by enzymes.
Why are leaves green?
Leaves contain chlorophyll, which absorbs red and blue light well but reflects much of the green light. That reflected green light is what reaches our eyes. In autumn, some trees break down their chlorophyll, revealing yellow and orange pigments that were there all along.
Do plants breathe?
Plants respire all the time, day and night, taking in oxygen and giving out carbon dioxide, just as animals do. In daylight, photosynthesis usually runs faster than respiration, so overall a plant gives out more oxygen than it uses. They exchange gases through stomata rather than lungs.
Related labs
- Cellular Respiration: Living things get energy from food. Does it make a difference whether they have oxygen?
- Ecosystem Balance: Can plants and animals live for weeks in a sealed jar? Where does their oxygen come from?
- Carbon Cycle: When we burn fuel, where does the carbon go? And how much of it stays in the air?
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Try it yourself
The Photosynthesis lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.