# 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 if there is not enough of it is called a limiting factor. These factors include:

1. Temperature
2. Amount of carbon dioxide
3. Light
4. Amount of chlorophyll

It is called a limiting factor because it “limits” the reaction from 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 must be limiting photosynthesis. Carbon dioxide, the temperature or amount of chlorophyll may be the limiting factors here. 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 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 further increases in carbon dioxide 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 (usually around 30-40ºC). Any further increases in temperature causes enzymes to change shape (denature) so the rate of reaction quickly falls.

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 the plant can absorb the required amount of light in order to photosynthesise.

In the following activity, you will recall the factors limiting photosynthesis.

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

The graph shows the effect of carbon dioxide on the rate of photosynthesis. Describe what is happening at 'X' by filling in the blanks.

The above graph 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? Select one answer in each row.

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

Any factor that slows down the rate of photosynthesis if there is not enough of it is called a limiting factor. These include the concentration of carbon dioxide 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 shows the effect of carbon dioxide on the rate of photosynthesis. Describe what is happening at 'X' by filling in the blanks.

EDDIE SAYS
Light intensity, temperature or the amount of chlorophyll are the limiting factors here.
• Question 2

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

What is happening at X

EDDIE SAYS
As the temperature increases so does the rate because enzymes work best in the warmth. Too high temperatures, however, will break bonds in the enzyme and cause it to denature.
• 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.
• 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.
• Question 5

Are these statements true or false? Select one answer in each row.

EDDIE SAYS
Enzymes denature at high temperatures between 30-40°C. Light is essential for photosynthesis, a greater intensity means a higher rate of photosynthesis.
• Question 6

What is meant by the term 'limiting factor'?

Something that limits photosynthesis
EDDIE SAYS
The term limiting factor in your exams will refer to 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
Generally, temperatures above 35 °C will cause enzymes in plants to break down or become denatured. This means that carrots won't be able to 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
Chlorophyll is needed to absorb light energy. This energy is essential to start the process of photosynthesis. Chlorophyll can be found in a structure called the chloroplast.
• Question 9

Match up the definitions to the keywords below.

## Column B

Something that limits photosynthe...
Limiting factor
The process where plants use sun...
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
A quick summary activity to test your knowledge of the key terms found in this topic. Have a few go's if you didn't manage to get them all correct the first time round!
• Question 10

Any factor that slows down the rate of photosynthesis if there is not enough of it is called a limiting factor. These include the concentration of carbon dioxide and light intensity.

Which other two factors affect photosynthesis?

Temperature
Amount of chlorophyll
EDDIE SAYS
---- OR ----

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