What Is the Equation for Photosynthesis?
Learn the word and balanced symbol equations for photosynthesis, what each substance means, and the common mistakes to avoid in AQA GCSE Biology.
The word equation for photosynthesis is:
carbon dioxide+water→lightglucose+oxygen\text{carbon dioxide} + \text{water} \xrightarrow{\text{light}} \text{glucose} + \text{oxygen}carbon dioxide+waterlightglucose+oxygenThe balanced symbol equation is:
6CO2+6H2O→lightC6H12O6+6O26\mathrm{CO_2} + 6\mathrm{H_2O} \xrightarrow{\text{light}} \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2}6CO2+6H2OlightC6H12O6+6O2What does the equation mean?
During photosynthesis, plants use carbon dioxide and water to produce glucose and oxygen.
- Carbon dioxide enters a leaf through small pores called stomata.
- Water is absorbed from the soil by root hair cells and transported to the leaves through the xylem.
- Light energy is absorbed by chlorophyll inside chloroplasts.
- Glucose is produced and can be used by the plant for respiration or converted into other substances.
- Oxygen is released as a product.
Photosynthesis is an endothermic reaction. This means that energy is transferred from the environment to the chloroplasts by light.
Understanding the balanced equation
The large numbers in front of the formulae are needed to balance the atoms. For example, the left side contains six carbon atoms because there are six molecules of carbon dioxide, 6CO26\mathrm{CO_2}6CO2. The glucose molecule on the right also contains six carbon atoms, C6H12O6\mathrm{C_6H_{12}O_6}C6H12O6.
You should recognise these chemical formulae:
- carbon dioxide: CO2\mathrm{CO_2}CO2
- water: H2O\mathrm{H_2O}H2O
- glucose: C6H12O6\mathrm{C_6H_{12}O_6}C6H12O6
- oxygen: O2\mathrm{O_2}O2
Quick balance check
Count each type of atom on both sides. Each side has 666 carbon atoms, 121212 hydrogen atoms and 181818 oxygen atoms. On the left, oxygen comes from carbon dioxide and water; on the right, it is in glucose and oxygen. Matching totals show the equation is balanced. Never alter the small numbers within a chemical formula when balancing. Change only the large coefficients in front.
Common exam mistake
Do not write light as a reactant added to the left-hand side. Light provides the energy for photosynthesis, so it is normally written above the arrow. Also, do not confuse photosynthesis with aerobic respiration: the substances are arranged in the opposite direction.
Scope assumed: AQA GCSE Biology 8461 separate science, Higher tier. This equation is also part of Foundation-tier content and is not marked biology only.
