# Recall the Limiting Factors of Photosynthesis

In this worksheet, students will recall the limiting factors of photosynthesis and their effects.

Key stage:  KS 4

Difficulty level:

### QUESTION 1 of 10

Photosynthesis is the process plants use to produce glucose.

Any factor that slows down the rate of photosynthesis is called a limiting factor. These factors include:

Temperature

Amount of carbon dioxide

Light intensity

Amount of chlorophyll

They are called limiting factors because they “limit” the reaction that is taking place.

Light Intensity

As you might already know, light is needed for photosynthesis. At night, there is no light for plants to photosynthesise with, so plants respire at this time. During the day, plants photosynthesise and respire.

The more light there is, the greater the rate of photosynthesis. If the rate of photosynthesis stops increasing even though there's still lots of light, something else must be limiting photosynthesis. Carbon dioxide, the temperature or the amount of chlorophyll could be the limiting factors. Graphs are useful to demonstrate this:

The graph above shows that as the light intensity increases, so does the rate of photosynthesis. The rate of reaction begins to level off because another factor is limiting the reaction e.g. carbon dioxide or temperature.
This means that increasing the light intensity will have no further effect because another factor is preventing the reaction from happening any faster.

Carbon dioxide concentration

Carbon dioxide is also essential for photosynthesis. If there is plenty of carbon dioxide, photosynthesis can occur. But if there isn't much light, or the temperature is too high, or there's not enough chlorophyll, the rate of photosynthesis will decrease.

The graph above shows that as the carbon dioxide concentration increases, so does the rate of photosynthesis. The rate of reaction begins to level off because another factor is limiting the reaction e.g. light or temperature.
This means that any further increases in carbon dioxide will have no effect because another factor is preventing the reaction from happening any faster.

Temperature

As the temperature increases, so does the rate of reaction. This is because more collisions occur between particles and enzymes when the temperature is warmer. The highest point on the graph is the optimum temperature - this is the best temperature for enzymes to work at, so photosynthesis is at its fastest (this is usually around 30 - 40ºC). Any further increases in temperature will cause enzymes to change shape (denature), so the rate of reaction will quickly fall.

Chlorophyll

Chlorophyll found in chloroplasts, absorbs light energy in order to power photosynthesis. The amount of chlorophyll affects the rate of photosynthesis. Plants in darker conditions will produce more chlorophyll, so that the plant can absorb the required amount of light in order to photosynthesise.

In the following activity, you will be looking at the factors limiting photosynthesis.

The concentration of carbon dioxide affects the rate of photosynthesis - it is a limiting factor.

The graph below shows the effect of carbon dioxide on the rate of photosynthesis.

Describe what is happening at 'X' by filling in the blanks.

The graph below shows how temperature affects the rate of photosynthesis.

What is happening at X?

Label the axes on the following graph:

A - Rate of temperature

A - Rate of photosynthesis

B - Rate of photosynthesis

B - Temperature

How does the amount of chlorophyll affect photosynthesis?

More chlorophyll allows better absorption of light

More chlorophyll allows enzymes to work better

More chlorophyll allows more carbon dioxide to be absorbed

Are these statements true or false?

What is meant by the term 'limiting factor'?

Something that limits growth

Something that limits respiration

Something that limits photosynthesis

A farmer in the UK wants to grow carrots in a greenhouse. He wants to sell the carrots he produces.

He decides to heat the greenhouse to 35°C.

Explain why he should not heat the greenhouse to a temperature higher than 35°C.

He will produce too many carrots

Enzymes in the carrots will denature and won’t photosynthesise

He will have high energy bills

One of the limiting factors of photosynthesis is a green pigment that traps light.

What is the name of this pigment?

Match up the definitions to the keywords below.

## Column B

Something that limits photosynthesis
Light
The process in which plants use sunlight to make ...
Carbon dioxide
The green pigment that absorbs sunlight
Photosynthesis
The source of energy needed by plants for photosy...
Glucose
The gas needed by plants for photosynthesis
Limiting factor
The sugar made by plants during photosynthesis
Water
The liquid needed by plants for photosynthesis
Chlorophyll

Any factor that slows down the rate of photosynthesis is called a limiting factor. These include carbon dioxide concentration and light intensity.

Which other two factors affect photosynthesis?

Temperature

pH

Enzyme

Amount of chlorophyll

• Question 1

The concentration of carbon dioxide affects the rate of photosynthesis - it is a limiting factor.

The graph below shows the effect of carbon dioxide on the rate of photosynthesis.

Describe what is happening at 'X' by filling in the blanks.

EDDIE SAYS
There are four limiting factors, including the concentration of carbon dioxide. If photosynthesis has levelled off despite there being a high concentration of carbon dioxide, then something else must be limiting the reaction. This could be light intensity, temperature or the amount of chlorophyll.
• Question 2

The graph below shows how temperature affects the rate of photosynthesis.

What is happening at X?

EDDIE SAYS
As the temperature increases, so does the rate of photosynthesis because enzymes work best in warmer temperatures. However, if the temperature becomes too high, bonds in the enzymes will break and they will become denatured. Once this has happened, the enzymes cannot work any more and the process of photosynthesis will stop.
• Question 3

Label the axes on the following graph:

A - Rate of photosynthesis
B - Temperature
EDDIE SAYS
The tell-tale sign that this graph is to do with temperature is the peak and then decrease to zero. The peak represents the optimum temperature (30 - 40°C) and the fall to zero represents the enzyme denaturing. The bottom (x axis) is showing the temperature and the left (y axis) is showing the rate of photosynthesis.
• Question 4

How does the amount of chlorophyll affect photosynthesis?

More chlorophyll allows better absorption of light
EDDIE SAYS
More chlorophyll allows plants to absorb the required amount of light to photosynthesise. It doesn't necessarily mean that more photosynthesis will occur, however. There could be other limiting factors at work such as light intensity, temperature or carbon dioxide concentrations.
• Question 5

Are these statements true or false?

EDDIE SAYS
Enzymes denature at high temperatures between 30 - 40°C, not at low temperatures. Light is essential for photosynthesis, a greater intensity means a higher rate of photosynthesis. You've reached the end of this activity. Hopefully, you've got this topic cracked now!
• Question 6

What is meant by the term 'limiting factor'?

Something that limits photosynthesis
EDDIE SAYS
A limiting factor is something that will restrict or limit something or someones' ability to do something. For example, lack of revision could be a limiting factor to doing well in your exams!! In this topic, the term limiting factor refers to the process of photosynthesis. It means any factor that limits a plant's ability to perform the process of photosynthesis.
• Question 7

A farmer in the UK wants to grow carrots in a greenhouse. He wants to sell the carrots he produces.

He decides to heat the greenhouse to 35°C.

Explain why he should not heat the greenhouse to a temperature higher than 35°C.

Enzymes in the carrots will denature and won’t photosynthesise
EDDIE SAYS
It is true that his energy bills could be high if he increases the temperature of his greenhouse, but this is not the reason why he shouldn't do it! Generally, temperatures above 35°C will cause enzymes in plants to break down or become denatured. If this were to happen, the carrots wouldn't be able to photosynthesise or grow.
• Question 8

One of the limiting factors of photosynthesis is a green pigment that traps light.

What is the name of this pigment?

chlorophyll
EDDIE SAYS
Did you get the spelling right?! Chlorophyll is needed to absorb light energy. This energy is essential to start the process of photosynthesis. Chlorophyll can be found in structures called the chloroplasts.
• Question 9

Match up the definitions to the keywords below.

## Column B

Something that limits photosynthe...
Limiting factor
The process in which plants use ...
Photosynthesis
The green pigment that absorbs s...
Chlorophyll
The source of energy needed by p...
Light
The gas needed by plants for pho...
Carbon dioxide
The sugar made by plants during p...
Glucose
The liquid needed by plants for ...
Water
EDDIE SAYS
This is a quick summary activity to test your knowledge of the key terms found in this topic. How did you do with it? You can always have a few attempts to try to improve your score if you found this tricky.
• Question 10

Any factor that slows down the rate of photosynthesis is called a limiting factor. These include carbon dioxide concentration and light intensity.

Which other two factors affect photosynthesis?

Temperature
Amount of chlorophyll
EDDIE SAYS
This was quite a tricky question because of the choices on offer. Did you hesitate over the option of enzymes? If so, you are correct that enzymes do play a part in photosynthesis. They are catalysts that speed up the process, and it is also true that enzymes need an optimum pH as well as temperature to work. However, these two are not actually limiting factors. The two you needed here were temperature and chlorophyll levels. Try to memorise all the four limiting factors - you will often be asked about them in your exams and they will help you get easy marks!
---- OR ----