Rate of photosynthesis

The rate of photosynthesis is influenced by four key factors:

1. Temperature:

   • Photosynthesis is controlled by enzymes, which work best at their optimum temperature.

   • Below the optimum temperature, the enzymes and substrates have less kinetic energy and move more slowly, resulting in fewer successful collisions and a slower rate of reaction.

   • Above the optimum temperature, the enzymes risk denaturing, meaning their shape changes, and they can no longer function, causing the rate of photosynthesis to slow down or stop.

   • At the optimum temperature, the enzymes and substrates have the right amount of kinetic energy for the maximum rate of photosynthesis.

2. Light Intensity:

   • Photosynthesis requires light energy, so increasing light intensity increases the rate of reaction. However, this only continues up to a certain point, after which light is no longer the limiting factor.

3. Carbon Dioxide Concentration:

   • Carbon dioxide (CO₂) is a reactant in photosynthesis. A higher concentration of CO₂ increases the rate of photosynthesis, but again, only until another factor becomes limiting.

4. Amount of Chlorophyll:

   • Chlorophyll is the pigment in plants where photosynthesis takes place. The more chlorophyll available, the faster the rate of photosynthesis.

Effect of temperature, light intensity and carbondioxide concentration on rate of photosythesis

The rate of photosynthesis can be measured by:

• The rate at which the plant uses up carbon dioxide.

• The rate at which the plant produces glucose.

• Most commonly, the rate at which the plant produces oxygen. This is often measured by counting the oxygen bubbles released, as shown in required practical 6.

Limiting factors (Higher tier only)

At first, increasing light intensity, carbon dioxide concentration, or the amount of chlorophyll will directly increase the rate of photosynthesis. However, eventually, the rate stops increasing because another factor becomes limiting. This factor is called the limiting factor. For example:

• If the light intensity is increased but the temperature or CO₂ concentration is low, then one of these will become the limiting factor.

Interpreting graphs (Higher tier only)

Graphs are often used to show how factors like light intensity, temperature, and CO₂ concentration affect the rate of photosynthesis. These graphs can be used to identify which factor is the limiting one. 

The rate of photosynthesis and light intensity are related by inverse proportion, meaning that as the distance from a light source increases, the light intensity decreases by the inverse square law. This is important when studying how light affects photosynthesis.

Greenhouse economics (Higher tier only)