Clock the enzyme, read the hump

Science · Organisms & Life Processes · ages 15-16

Name ______________________ Date ____________

Why does heating usually speed a reaction?
- Particles collide more often and with more energy
- Heat lowers the activation energy that the reaction needs
- Heating makes more enzyme molecules form in the mixture
A colour-change experiment defines its rate score as 1000 divided by seconds. The change takes 50 seconds. What is the rate score?
Answer: ______________
The rate falls after the optimum because the enzyme gets used up.
Circle one: True False
You count 30 bubbles in 60 seconds. What is the rate in bubbles per second?
Answer: ______________
On a rate-against-temperature graph, where is the optimum?
- Where the curve begins before the rate rises
- Where the horizontal and vertical axes cross
- Where the curve reaches its highest point
Pepsin works best in the stomach and amylase works best in the mouth. What follows?
- Both enzymes share one pH optimum even though they work in different digestive organs
- Their pH optima differ: acidic for pepsin and near neutral for amylase
- pH does not affect enzyme rate or the shape of its active site in any condition
Two amount-against-time runs differ only in temperature. Run B has a steeper initial slope. What can you conclude?
- Run B has the higher initial rate under these controlled conditions
- Run B must have used more enzyme even though the other conditions matched
- A steeper initial slope means a slower reaction rate on this graph
An enzyme is heated until it denatures, then cooled before testing. The rate stays near zero. Why?
- Cooling was too slow to bring the enzyme back to its original working state
- The active site changed shape, so cooling did not restore the reaction
- The heating removed every substrate permanently from the mixture

Answer key

For grown-ups. Fold this page away before handing over the rest.

Clock the enzyme, read the hump W1-mt_Rmz54ICmRC-s1

Particles collide more often and with more energy · Warming makes particles move faster. They collide more often and with more energy, so more collisions lead to a reaction.
20 · Use the stated rule: 1000 divided by 50 equals a rate score of 20 per second.
False · The fall comes from heat changing the active site's shape, not from the enzyme being used up.
0.5 · Rate is amount divided by time: 30 bubbles divided by 60 seconds equals 0.5 bubbles per second.
Where the curve reaches its highest point · The optimum is the temperature at the top of the hump, where the rate is highest.
Their pH optima differ: acidic for pepsin and near neutral for amylase · Different active sites work best in different conditions. Pepsin has an acidic optimum, while mouth amylase has a near-neutral optimum.
Run B has the higher initial rate under these controlled conditions · On an amount-against-time graph, slope is amount divided by time. A steeper initial slope therefore shows a higher initial rate. Since temperature was the tested difference, it is the likely cause in this comparison.
The active site changed shape, so cooling did not restore the reaction · Denaturation can change the active site permanently. Cooling does not necessarily restore its working shape.