Photosynthesis

Photosynthesis is how plants make their own food. Instead of eating, a plant takes in sunlight, water from the soil and carbon dioxide from the air, and combines them inside its leaves to produce sugar. Oxygen is released in the process — which is why plants matter so much to every animal that breathes.

Almost all the food on Earth can be traced back to photosynthesis. Even a meal with no plants in it came from animals that ate plants.

Three ingredients, and none of them is soil. Sunlight supplies the energy. Water travels up from the roots. Carbon dioxide comes in from the air through tiny holes in the leaves called stomata.

Soil matters for other reasons — it holds the water and supplies minerals — but a plant's actual food is made in the leaf, not taken from the ground.

Leaves are packed with a pigment called chlorophyll, which absorbs light energy from the sun. Chlorophyll soaks up red and blue light and reflects green light back — and that reflected green is the colour we see.

So a leaf looks green precisely because green is the part of sunlight it is not using.

Two things. The plant keeps the glucose, using it for energy and for building new leaves, roots, flowers and fruit. The oxygen it lets go.

Across ecosystems, photosynthesis continually adds oxygen to the atmosphere and stores solar energy in food. Animals and many other organisms depend on both of those outputs.