B2: Photosynthesis

Green plants use light energy to make food, the raw materials are obtained from the air and soil

Equation for photosynthesis

carbon dioxide + water (light energy) -> glucose + energy

During Photosynthesis:

• light energy is absorbed by the chlorophyll
• the light energy is used to convert CO2 and H2O into glucose
• oxygen is released as a by-product
• glucose is converted and stored as insoluble starch to later use for respiration as glucose again

There are 3 limiting factors for photosynthesis:

• Light intensity
• Carbon dioxide concentration
• Temperature

Limiting Factors = Factors which slow down the rate of reaction (in this case photosynthesis)

Stage 1:

The rate of photosynthesis increases as the temperature increases

This means that it temperature is a limiting factor

Stage 2:

The temperature stops increasing and decreases as the temperature is too high

The enzymes controlling photosynthesis become denatured and photosynthesis falls to 0

Stage 1:

The rate of photosynthesis increases as the light intensity increases

Light intensity is a limiting factor

Stage 2:

Light intensity is no longer a limiting factor as the rate of reaction becomes steady

Now it is either the CO2 concentration or the temperature which is the limiting factor

Stage 1:

The rate of photosynthesis increases as the carbon dioxide concentration increases

This means that carbon dioxide concentration is a limiting factor

Stage 2:

Rise in Carbon Dioxide levels now has no effect so it is no longer a limiting factor

Carbon Dioxide and Light intensity Graphs:

The line will slowly increase at a steady rate and then start to flattten out to form a steady horizontal line

Temperature Graph:

The line will increase at a steady rate until the tmeperature reaches its highest before enzymes are denaturede

the graph then decreases suddenly to 0

Note: This applies when the rate of photosynthesis is on the Y axis and the limiting factor is on the X axis

People can use these limiting factor to their advantage to maximise the growth of vegetables, fruits and crops.

People can use artificial light to increase the light intensity

Heaters can be used to regulate temperature

Paraffin lamps increase the rate of photosynthesis as the burning paraffin produces CO2 and also heat