Photosynthesis

• Photosynthesis is the process by which plants make carbohydrates from raw materials, using energy from light
• During photosynthesis:

  • light energy is absorbed by chlorophyll - a green substance found in chloroplasts in the palisade cells in the leaf
  • absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
  • oxygen is released as a by-product
• Photosynthesis is a chemical reaction that takes place inside photosynthetic organisms (e.g. green plants, algae) and converts light energy into chemical energy. It occurs within the chloroplasts of a cell.
• Photosynthesis requires:

  • Carbon dioxide - provides carbon (C) and oxygen (0) found in glucose
  • Water - provides hydrogen (H) found in glucose
  • Light - provides energy
  • Chlorophyll - green pigment found in chloroplasts that absorbs light
• Some glucose is used for respiration, while some is converted into insoluble starch for storage. The stored starch can later be turned back into glucose and used in respiration.
• Word equation - carbon dioxide + water ➡️ glucose + oxygen
• Photosynthesis involves a series of endothermic reactions in which carbon dioxide and water is converted to glucose and oxygen (the waste product) in the presence of light.
• Photosynthesis is important in organisms for a variety of reasons:

  • Produces glucose which is used in respiration to release energyGlucose used to make complex organic molecules which are used for growth in plants
  • These organic molecules are transferred between organisms through food chains
  • Produces oxygen which is required by organisms for respiration
• There are a number of factors which contribute towards the process of photosynthesis. The factor which is working at the lowest level will usually be the limiting factor of the process. There are several limiting factors which can reduce the rate of photosynthesis, eg temperature, light intensity and carbon dioxide concentration.
• Temperature - As with other chemical reactions, the rate of photosynthesis increases as the temperature rises. Photosynthesis is controlled by enzymes, which become denatured if the temperature is too high. As a result, the rate of photosynthesis reaches its maximum at an optimum temperature, then decreases. The maximum rate is determined by the other factors involved.
• Light intensity- Light provides the energy needed for photosynthesis. Increasing the light intensity increases the rate of photosynthesis, provided plenty of carbon dioxide and water are available. The maximum rate is determined by the other factors involved.
• Carbon dioxide - Carbon dioxide is needed for photosynthesis. Increasing the carbon dioxide concentration increases the rate of photosynthesis, provided the plant is warm enough, and has plenty of light and water. The maximum rate is determined by the other factors involved.
• Light intensity becomes a limiting factor at night and in the winter
• Temperature becomes a limiting factor when it drops too low on cold days
• The limiting factor, the variable that limits the rate of a particular reaction, determines the rate of photosynthesis.