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Year 9 iGSCE - Biology

Factors affecting enzyme performance

We’ve established that enzymes are like the workers in a factory, and like workers in a factory, they have specific working requirements.

The first requirement is temperature. The graph to the right shows how an enzyme acts in different temperatures.

When it’s too cold, enzymes work really slowly. When the temperature is right (40 deg in the graph to the right) they work as fast as the can. However if the temperature gets too hot, they denature and can’t work.

pH affects enzymes much in the same way as temperature does.

As the pH increases, the enzyme will reach its optimum point and function as fast as it can. However as the pH continues to rise, the enzyme will be Denatured and unable to work.

Every enzyme has its perfect pH range, depending on where it lives. Enzymes in the intestines have an optimum pH of 7.5, while those in the stomach have an optimum pH of 2.

The amount of substrates in a reaction will obviously affect the amounts of products created.

Think of it as a car manufacturing plant. You can have 100 workers (enzymes), but if you only have enough parts to make one car, then that’s all you can make.

You can see in the graph to the right, once all the products are formed, no matter how much time you give, there won’t be any more products, unless you add more substrates.

On the other side, if we continue to increase the amount of substrates, eventually, it’ll get to the point where all the enzymes are full and working at max capacity.

Using the car manufacturing plant again as the example, if we have 50 workers and keep adding car parts.

Eventually we’ll get more car parts than cars, because all the workers are busy.

You can see this in the graph to the left. Notice how we continue to increase substrate concentration, but the reaction rate eventually plateaus.


1. List 3 things that would describe an enzyme

2. Explain the term optimum temperature

3. What happens at critical temperature

4. How does denaturing affect the enzyme?

5. Why is it incorrect to say ‘heat kills enzymes’.

6. Observe the graph to the right.

   What is the enzyme optimum temperature.

7. Explain what is happening to the enzyme at

    35 degrees

8. Observe the graph to the right. Why is there

a plateau?

9. How would you fix it, so the graph continues

to rise?

10. In terms of what was placed into the reaction
what is the difference between graph A and B?

11. What happened at the 1 minute mark on
Graph A