Plant Structure and Function

YOU ARE LEARNING:

Limiting Factors

Conditions such as temperature, light intensity and carbon dioxide concentration are limiting factors on the rate of photosynthesis.

What would you think a logical name would be for a factor (such as temperature), that slows down the rate of photosynthesis?

A factor is something that affects the rate of a reaction - it could speed it up or slow it down. Photosynthesis is a type of chemical reaction. A limiting factor in photosynthesis is a factor that slows down the rate of the photosynthesis reaction.

Temperature is a limiting factor of photosynthesis. At which temperature do you think photosynthesis is faster?

So photosynthesis generally likes it warm. However if the temperature **** is too high - usually above $40^{\circ}C$ - the enzymes that help with the reaction denature (they are destroyed)! What would that mean for photosynthesis?

Light intensity is another term for "brightness" **** of light. It is also a limiting factor of photosynthesis, so how will a higher light intensity, affect the rate of photosynthesis?

Water is not a limiting factor, because plants can close stomata to prevent water loss. What is the other reactant of photosynthesis that could affect the rate of reaction?

Have a look at the very early part of this diagram. Before the two temperature graphs start to separate, what is the limiting factor for the rate of photosynthesis?

A) Light intensity B) Temperature

Now, have a look at the point where the two graphs for temperatures separate. What is the limiting factor on the rate of photosynthesis at that point?

A) Light intensity B) Temperature

So we see from these graphs that the limiting factor for photosynthesis changes.

Early on, it is the rate of light intensity that makes a difference for the rate of photosynthesis. But after a level of light intensity (after we have passed a certain point on the x-axis), the difference in temperature is all of a sudden the factor that makes the difference (the two graphs for temperature separate).

Now, have a look at this diagram. What is the factor that is initially limiting the rate of photosynthesis?

A) Light intensity B) Carbon dioxide concentration

Now, have a look at the point where the two graphs for temperatures and carbon dioxide concentration separate. What is the limiting factor on the rate of photosynthesis at that point?

A) Light intensity B) Carbon dioxide concentration C) Temperature

Apart from light intensity, temperature and carbon dioxide concentration, what is the other factor that affects the rate of photosynthesis?

Which horticultural building do farmers use to grow more crops?

A greenhouse allows a farmer to control the factors that affect photosynthesis. Which factors do you think a farmer can control?

You can select multiple answers

What is the main reason that a farmer would want to control the factors that affect photosynthesis?

So greenhouses are good for farmers because they allow them to grow more crops. However, the farmer must make sure the crops make enough of a profit. It costs money to use lamps to increase lighting **** and to use paraffin heaters to increase the temperature and carbon dioxide concentration. So the farmer must be careful that he covers these costs with the money from the plants he cell.