Temperature and enzymes — questions

1. identify

Amylase and starch are mixed, and every 30 seconds a drop of the mixture is put onto iodine on a spotting tile. Which observation shows the end point?

Circle one answer.

• The first drop that turns the iodine blue-black
• The first drop that turns the iodine purple
• The moment the amylase is poured in
• The first drop that stays orange-brown, like iodine on its own

Nudge (only if you are stuck): What colour does iodine stay when there is no starch left?

2. calculate

At 20 °C the first drop that stayed orange-brown was taken at 150 s. Calculate the relative rate, using relative rate = 1000 ÷ time in seconds. Give your answer to one decimal place.

Relative rate (no unit): ______________ unit ________

Nudge (only if you are stuck): Divide 1000 by the time in seconds. The 1000 only makes the answer easy to read: 1 ÷ 150 would be 0.0067.

3. identify

In the temperature investigation, which of these must be kept the same in every run? Choose all that apply.

Tick every correct statement.

• Volume of starch suspension
• Concentration of the amylase solution
• Temperature of the water bath
• pH
• Time between samples

Nudge (only if you are stuck): Only one variable is changed on purpose. Which one is it?

4. explain

A tube of starch with water instead of amylase is sampled in the same way. Every drop stays blue-black for 5 minutes. What does this control show?

Circle one answer.

• That iodine does not work at 30 °C
• That the starch is broken down by the amylase, not by itself
• That 30 °C is the optimum temperature
• That water denatures starch

Nudge (only if you are stuck): What is missing from this tube?

5. explain

Between 10 °C and 40 °C the relative rate of the amylase reaction increases. Explain why.

Nudge (only if you are stuck): What happens to the speed of molecules when they get warmer, and what has to happen before starch can be broken down?

6. explain

At 70 °C the drops stayed blue-black for the whole 5 minutes. Explain why.

Nudge (only if you are stuck): What happens to the shape of the enzyme at high temperature?

7. calculate / identify

A group tested a different amylase. Time of the first orange-brown drop at each temperature: 25 °C: 200 s; 35 °C: 80 s; 45 °C: 50 s; 55 °C: 125 s. (a) Calculate the relative rate at 35 °C and at 55 °C, to one decimal place. (b) Which tested temperature was best?

Relative rate at 35 °C (no unit): ______________ unit ________

Relative rate at 55 °C (no unit): ______________ unit ________

Best tested temperature: ______________ unit ________

Nudge (only if you are stuck): Relative rate = 1000 ÷ time in seconds. The best temperature has the shortest time.

8. sequence

The water bath is warmed from 20 °C to 30 °C. Put the steps in order to explain why amylase then breaks down starch faster.

Write the number of each step in order.

1. The molecules gain kinetic energy
2. They move faster
3. They collide more often
4. More collisions are effective: starch fits the active site
5. More enzyme–substrate complexes form each second
6. Starch is broken down faster

• First: ______
• Second: ______
• Third: ______
• Fourth: ______
• Fifth: ______
• Last: ______

Nudge (only if you are stuck): Start with the energy the molecules gain, then their speed, and end with the rate.

9. predict / explain

Bacteria living in a hot spring at 75 °C make a protease whose optimum temperature is 75 °C. (a) Predict how its rate at 37 °C compares with its rate at 75 °C. (b) Explain why its rate at 95 °C is close to zero.

(a) Rate at 37 °C

(b) Rate at 95 °C

Nudge (only if you are stuck): Use the two halves of an enzyme graph: below the optimum, and above it.

10. explain

Fresh green beans contain enzymes that slowly spoil their colour and taste, even in a freezer at −18 °C. Before freezing, cooks blanch the beans: they dip them in boiling water for 2 minutes, then cool them quickly in iced water. (a) Explain why freezing alone slows the spoiling but does not stop it for good. (b) Explain why blanched beans stay green and tasty for months in the freezer, even after they are thawed.

(a) Freezing alone

(b) Blanching

Nudge (only if you are stuck): What does cold do to enzyme molecules, and what does boiling do to them? Which change lasts?