How plants turn carbon dioxide and water into glucose and oxygen using light, why that is endothermic, and what happens to the glucose.
What you will learn
- Write the word equation and pick out the balanced symbol equation
- Explain why photosynthesis is endothermic
- Describe five uses of the glucose a plant makes
Light in, glucose out
Plants make their own food.
In the chloroplasts of leaf cells, light energy is used to turn two simple substances into glucose, with oxygen given off as a by-product.
carbon dioxide + water → glucose + oxygen
6CO2 + 6H2O → C6H12O6 + 6O2
Learn the word equation (all boards). Learn the formulae too: AQA asks you to recognise CO2, H2O, O2 and C6H12O6, and the balanced version is worth knowing for every board. Light is written over the arrow: it is not a reactant.
- Count carbon: 6 × 1 = 6 on the left; 6 in one glucose on the right
- Count hydrogen: 6 × 2 = 12 on the left; 12 in glucose on the right
- Count oxygen: 6 × 2 + 6 × 1 = 18 on the left; 6 + 6 × 2 = 18 on the right
- Balanced: the numbers are in the ratio 6 : 6 : 1 : 6
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- Light in, glucose out
- An endothermic reaction
- What the glucose is for
- Try it: Start with the words
10 practice questions, marked as you go; about 20 minutes in all.
Key terms
Endothermic, Chlorophyll, Respiration, Starch, Cellulose, Amino acids
In this unit: Bioenergetics: photosynthesis and respiration
Photosynthesis and its rate, limiting factors and the pondweed practical, aerobic and anaerobic respiration, exercise and metabolism.