Photosynthesis is the process by which plants convert sunlight, water, and carbon dioxide into food — and it is happening right now, in every green leaf visible from your window. It is one of the most consequential chemical reactions on Earth: without it, almost no free oxygen would exist in our atmosphere, and neither would we.
Trees are made of air
Most people assume a tree's mass comes mainly from the soil. The counterintuitive truth is that the bulk of a tree's solid weight — the wood, bark, branches, and leaves — is carbon. That carbon comes not from the ground but from CO₂ in the atmosphere, captured leaf by leaf over decades through photosynthesis.
Here is how it works. Leaves draw CO₂ in through microscopic pores called stomata (up to 300 per square millimetre on the underside of a leaf). Roots pull water up through the stem. Inside leaf cells, structures called chloroplasts — filled with the green pigment chlorophyll — capture energy from sunlight and use it to bond CO₂ and water molecules together into glucose. The oxygen produced in this reaction is a by-product: the plant does not need it and releases it into the air.
The glucose is then used to build every part of the plant: roots, stems, wood, fruit. The next time your child looks at a large, ancient birch tree, tell them: "Most of that tree is air that got caught by leaves." It is completely true — and children rarely forget it.
Why this matters in a child's education
The Norwegian national curriculum (LK20) emphasises understanding the connections between living things and their environment, not merely memorising facts. Photosynthesis is an ideal entry point because it links sunlight, atmosphere, plants, animals, and humans in one unbroken cycle. A child who genuinely understands photosynthesis also understands why forests matter for the climate, why food is stored solar energy, and why the oxygen in every breath was recently inside a plant.
Research on science education consistently finds that direct observation beats reading alone for building lasting understanding. Fortunately, photosynthesis is one of the few biological processes children can actually watch happen.
Watch it happen: the oxygen bubble experiment
Place an aquatic plant — Elodea works best, and is sold in most pet shops — in a clear glass of water. Set the glass in direct sunlight. Wait 30–60 minutes. Watch the leaves closely: small transparent bubbles will begin to collect on the leaf surface and rise to the top. Those bubbles are pure oxygen, produced by the plant as it photosynthesises in real time.
Move the glass into a dark room and observe. The bubbles stop forming almost immediately. Bring it back into sunlight: they start again. The on/off simplicity of this makes the connection between light and photosynthesis instantly visible to children as young as six.
Extension question: Cover half the plant with dark paper and leave the other half in sunlight. Does oxygen production split evenly between the two sides? Why or why not? Let the child predict first, then observe.
Three questions worth wondering about
- Plants take in CO₂ during the day and release oxygen — we do the opposite. What does that suggest about the relationship between plants and animals?
- Some marine animals carry chloroplasts inside their own cells and can photosynthesise. What kind of animal might do that?
- If you could design a plant three times more efficient at capturing sunlight, what would it look like?
Photosynthesis is not something that happens in textbooks. It is happening now, in the garden, in the park, in the leaf your child picked up on the way home. Every child is made of good atoms — and so is every tree, every blade of grass, every spring flower unfolding this week. Explore free content at goodatoms.com and see what your child discovers the next time they look at a tree.