Photosynthesis

Key points

• Photosynthesis means "making with light": photo = light, synthesis = making.
• It happens mainly in the leaves. That's why leaves are called the food factories of a plant.
• Chlorophyll, the green colour in leaves, traps energy from sunlight.
• Plants take in carbon dioxide from the air through tiny holes in leaves called stomata.
• Roots absorb water from the soil, and it travels up the stem to the leaves.
• The food made is a sugar called glucose. Extra glucose is stored as starch.
• Oxygen is given out. This is the oxygen that animals and people breathe.
• Plants make their own food, so they are called autotrophs (auto = self, trophos = food).

The equation

For curious learners: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Important words

Chlorophyll

The green pigment in leaves that traps sunlight.

Stomata

Tiny pores on the surface of a leaf. Gases go in and out through them.

Autotroph

A living thing that makes its own food, like green plants.

Heterotroph

A living thing that depends on others for food, like animals and people.

Starch

The form in which plants store extra food.

Everyday examples

• A plant kept in a dark cupboard for a few days turns pale and weak, because it can't make food without light.
• Fish tanks often have water plants. They give out oxygen that the fish use.
• Potatoes, rice and wheat are full of starch that plants stored from photosynthesis.

Common mistakes

• "Plants get food from the soil." No. Plants get water and minerals from the soil, but they make their food in the leaves.
• "Plants only take in carbon dioxide." Plants also breathe (respire) all the time and take in oxygen. In daylight, photosynthesis is faster, so they give out more oxygen than they use.
• "Only leaves can do it." Any green part with chlorophyll can, such as green stems. Leaves just do most of it.

Quick check

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