AQA GCSE Limiting factors interacting (Biology)

Limiting factors interacting

Make sure you have read through the page on single limiting factors first, it can be found here.

A limiting factor is a factor that is in short supply, increasing the limiting factors will increase the rate of photosynthesis.

There are four limiting factors for photosynthesis

1.Temperature

2.Carbon dioxide concentration

3. Light intensity

4. Amount of chlorophyll

Photosynthesis depends on all factors at the same time. Increasing one factor only increases the rate if the others are not limiting.

Changing one factor can change which factor is limiting

Two-factor graphs

On the graph below each line shows how rate of photosynthesis changes with light intensity at a specific CO₂ concentration.

Differences between the lines show the effect of CO₂ concentration on the rate of photosynthesis.

Green part of the line

Light intensity is the limiting factor during the green part of the line. This is because as light intensity increases, so does the rate of photosynthesis.

Red part of the line.

Light intensity is no longer a limiting factor during either of the red parts of the graph line, because as light intensity increases, rate of photosynthesis is constant.

During the lower red line (0.01% carbon dioxide)

Carbon dioxide is the limiting factor, because as carbon dioxide increases, to 0.04% then rate of photosynthesis increases

During the higher red line (0.04% carbon dioxide)

Neither carbon dioxide concentration or light intensity are a limiting factor. Another factor, possible temperature is now limiting.

Three-factor graphs

In the graph below in the rising green line section:

In the green section of all the graph lines, light intensity is the limiting factor.

Increasing light provides more energy for the light-dependent reactions, increasing the rate of photosynthesis. Carbon dioxide concentration and temperature do not limit the rate at this stage, as the rate continues to increase when light intensity increases.

In the graph below at the plateau section (in red):

In all of the red lines, light intensity is no longer a limiting factor because as light intensity increases, rate of photosynthesis is constant.

Line 1: 0.01% CO₂, 15 °C to line 2 0.01% CO₂, 25 °C

The same carbon dioxide concentration is present, but temperature has increased, causing rate of photosynthesis to increase, so temperature is the limiting factor here during line 1.

Line 2: 0.01% CO₂, 25 °C to line 4 0.04% CO₂, 25 °C

Same temperature, but carbon dioxide concentration has increased, causing rate of photosynthesis to increase. So, carbon dioxide concentration will be a limiting factor during line 2.

Line 4:

High CO₂ concentration & optimum temperature

Rate of photosynthesis is highest possible rate on the graph.

In the red section of the highest line, light intensity, temperature and carbon dioxide are not limiting because all are at high levels.

The rate has reached a maximum for these conditions. It is not possible to conclude from the data that chlorophyll is the limiting factor, as the amount of chlorophyll was not varied. Additional data would be required.