Factors That Affect Photosynthesis

This lesson covers:

  1. Why chlorophyll is required for photosynthesis 
  2. How temperature, carbon dioxide concentration, and light intensity affect the rate of photosynthesis 
  3. How farmers can maximise the rate of photosynthesis 

What is the inverse square law?


  • The inverse square law states that the intensity of light decreases proportionally to the square of the distance from its source.
  • For example, if the distance is doubled, the light intensity decreases to 1/4 of its original value.
  • The formula is:


I ∝ d21​

Where:

I = light intensity

d = distance between light source and object

Example calculations


The table below shows how the distance from a lamp affects relative light intensity at distances of 1 m, 2 m, and 3 m.

Table showing the inverse square law with distances from light source and corresponding light intensities.

What is the role of chlorophyll?

To attract bees

To absorb light energy for photosynthesis

To provide strength to the leaf

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Illustration of a green droplet with a red prohibition symbol indicating chlorophyll deficiency.

Why may plants produce insufficient chlorophyll?

(Select all that apply)

They don't have enough oxygen

They have a disease like Tobacco Mosaic Virus

They grow too tall

They lack the required nutrients 

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In addition to the amount of chlorophyll that a plant has, there are three environmental factors that affect the rate of photosynthesis. List them below.

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Graph showing the rate of photosynthesis against an unknown variable on the x axis.

Given the shape of the graph above, which variable(s) could be on the x axis?

(Select all that apply)

Oxygen concentration 

Temperature 

Light intensity 

Carbon dioxide concentration 

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Graph showing the rate of photosynthesis with a peak and subsequent decline.

Using what you know about how different factors affect the rate of photosynthesis, which factor would give the above graph?

Temperature

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Graph showing the rate of photosynthesis against the concentration of CO2 with a labelled point indicating the limiting factor.

What is limiting the rate of photosynthesis at the point labelled in the graph? 

Light intensity 

Carbon dioxide concentration 

Temperature

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Graph showing the rate of photosynthesis leveling off with increasing concentration of CO2.

When a graph levels off like this we say that it has:

Stopped

Reached equilibrium

Plateaued

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Graph showing the rate of photosynthesis against light intensity with a highlighted area indicating a limiting factor.

At the point indicated on the graph above, what could be limiting the rate of photosynthesis?

(Select all that apply)

Carbon dioxide concentration 

Temperature

Light intensity 

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Describe and explain how the rate of photosynthesis varies with temperature. 

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Illustration of a greenhouse containing plants.

sunlight / lamps / greenhouses / pests / thieves / fertilisers


Farmers in cooler climates often use . These help trap the heat energy from , and so increase the temperature. They also keep out which could otherwise damage the plants. 

greenhouses
sunlight
pests

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How can farmers ensure that photosynthesis takes place 24 hours a day?

Use greenhouses

Use paraffin heaters

Use artificial lighting 

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Paraffin heaters have two benefits. As the paraffin (a type of fuel) is burned it releases lots of heat, and also lots of:

pesticides

carbon dioxide

oxygen 

light

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