Building food from air
How Do Plants Eat Light?
Plants use light energy to join air and water into sugar. That is where food starts.
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Step 1 of 5
Plants do not eat soil.
A tree's mass comes overwhelmingly from air, not ground. Soil supplies water and a few minerals; the carbon is pulled out of the atmosphere.
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Step 2 of 5
Leaves take carbon dioxide from the air.
Tiny pores on the underside of each leaf let air in. Carbon dioxide is the raw material — the actual substance a plant is built from.
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Step 3 of 5
Roots pull water up.
Water travels from the roots up through the trunk to every leaf. In a tall tree it climbs over a hundred metres with no pump at all.
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Step 4 of 5
Chlorophyll captures the light energy.
Green is the one colour a leaf throws away. That is the colour you get to see. The green pigment absorbs red and blue light and uses that energy to break water apart, which is the hard step of the whole process.
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Step 5 of 5
Sugar is the product; oxygen is the waste.
Carbon and water are assembled into sugar, and the leftover oxygen is released. Every breath you take is a plant's discarded by-product.
Almost every food chain on Earth starts here. Nearly all the energy in your dinner was sunlight caught by a leaf.
The short version
A tree is built mostly out of air: the carbon comes from carbon dioxide, not soil, and water climbs a hundred metres with no pump. Green is the one colour a leaf discards, and the oxygen you breathe is its leftover.
Try it yourself
Put a leafy sprig in water in the sun. Bubbles collect on the leaves — that is oxygen being made in front of you.