Plants use the energy from the sun to convert carbon dioxide and water into organic materials such as glucose, a carbohydrate, for the plant's growth.
Chemical Equation for Photosynthesis
6CO₂ + 6H₂O --> C₆H₆O + 6O₂
Carbon Dioxide Water Glucose Oxygen
Photosynthesis takes place at the leaves in the chloroplasts of plant cells, which contains the pigment chlorophyll to absorb light energy. Only a small percentage of the sun's light energy is used because:
- 60% is the wrong wavelength.
- 5% passes through the leaf.
- 33% is wasted
Uses of glucose
Once the plant has created the glucose it is used in numerous ways:
- In the production of fats and oils
- A raw material in growth and repair
- A source of energy, stored as sucrose
- A long term source of energy, stored as starch in leaves, seed, roots and tubers
- In the production of cellulose, the structural material in cell walls
- Used in respiration, which creates energy
It is important for the glucose to be converted into starch in the cells if not being used immediently, as glucose is soluble, so dissolves in the cytoplasm. This will upset the osmotic balance, meaning the cells with more glucose in will become more concentrated, allowing water to flow into the cell. As the rate of osmosis cannot be stopped, this will cause the cells to burst. Starch is a larger molecule however, so is insoluble, and will keep the osmotic balance steady.
Rate of photosynthesis
The rate of photosynthesis is affected by four factors, light intensity, CO₂ concentration, amount of water and temperature. All of these factors are limiting factors, meaning they can stop a different factor having an affect on photosynthesis as it is in short supply, so has reached its maximum rate of photosynthesis.