Photosynthesis

Photosynthesis is how plants and algae make their own food, glucose, using light energy. It happens in the chloroplasts, which contain the green pigment chlorophyll. Chlorophyll absorbs the light.

Stretch The balanced symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Light is not a reactant. It is the energy that drives the reaction. The reactants are carbon dioxide and water; the products are glucose and oxygen. The energy ends up in a chemical store in the glucose.

Substance	Where it comes from, or where it goes
Carbon dioxide	From the air, into the leaf through the stomata
Water	From the soil, through the root hair cells, up the stem in the xylem
Glucose	Made in the leaf. Used for respiration; stored as starch (insoluble); made into cellulose for cell walls, proteins (using nitrates) and fats and oils for seeds
Oxygen	Some is used in respiration; the rest leaves through the stomata

Mushrooms and yeast are fungi, not plants: no chlorophyll, so no photosynthesis.

The carbon cycle

Carbon keeps moving round. Photosynthesis takes carbon dioxide out of the air and builds the carbon into glucose, then into the rest of the plant. Animals get that carbon by eating plants (or animals that ate plants). Respiration by plants, animals and decomposers puts carbon dioxide back into the air, and so does burning wood and fossil fuels. Coal, oil and gas formed from the remains of living things that died millions of years ago.