Hold a cracker on your tongue long enough and it turns sweet. That is amylase at work — a protein in your saliva quietly taking starch apart, one bond at a time. This practical heats it up and times how fast it goes.
Amylase is an enzyme — a protein that speeds up a reaction without being consumed by it. Its job is to break down starch, a long chain of glucose units coiled up tight.
Starch is its substrate: the molecule the enzyme acts on. Amylase grips the chain at a precisely shaped pocket called the active site and snips it with water into shorter sugars — mostly maltose.
Here is the part that surprises people. The enzyme is a catalyst. It comes out of the reaction unchanged, ready to grab the next strand of starch and the next. One amylase molecule works thousands of times.
Some people simply make more of it. The gene for salivary amylase is copied a different number of times in different people — more copies, more enzyme, faster starch breakdown.
You can't see starch vanish. So you add iodine, which turns blue-black only when starch is present. Drag the slider to watch the reaction run, and find the moment the colour says the starch is gone.
Amylase finds the starch chain, locks onto it at the active site, and breaks one bond. The chain falls into shorter sugars. Then the enzyme lets go — unchanged — and goes looking for the next one.
In the practical you run the same reaction cold, at room temperature, and hot. Warmth makes molecules move faster and collide more often, so going from cold to warm speeds things up.
So picture pushing the temperature higher and higher — towards 60, 70, 80 degrees. Before you read on, commit to an answer.
As you keep heating the amylase, what happens to the rate of starch breakdown?
It speeds up, peaks, then crashes. More heat means faster collisions, so the rate climbs — but only to the optimum temperature. Push past it and the heat shakes the protein apart. The active site loses its shape, starch no longer fits, and the reaction stops. The enzyme is now denatured.
This is why a fried egg never turns runny again. Heat unfolds proteins, and that change does not reverse when it cools.
Exam tip: A question asking you to explain this needs both halves — faster collisions raising the rate and denaturation lowering it. A question asking you to describe the graph only needs the shape: rise, peak, fall.
Temperature pulls in two directions at once: it makes collisions faster, and it threatens the enzyme's shape. The result is a peak.
Drag the slider through cold, warm, and hot. Watch the particles, the rate, and where you sit on the curve.
The rate-temperature curve has a story at each point. Drag each label to the region it explains.
It is easy to think the colour change is the reaction. It isn't. Iodine slips inside the coiled starch and that trapped iodine is what looks blue-black.
Once amylase has cut the starch into maltose, there is no coil left to trap the iodine. So it stays amber. The colour marks the endpoint — the point where the starch is gone — not the reaction itself.
The tube that goes pale isn't empty. It is full of maltose. You are watching one molecule become another, read through a dye that only notices one of them.
Use the results below. The mark scheme is hidden — try each part first, then check.
| Temperature / °C | 10 | 20 | 40 | 60 |
|---|---|---|---|---|
| Time to clear / min | 12.0 | 6.0 | 2.0 | no change after 30 |
OUTLINE = a brief account of the main points. Award 1 mark per point, max 2.
Accept: "1/time" or "reciprocal of time". Do not accept: "faster colour" with no link to time.
Accept: 0.5 min⁻¹ with or without unit. Do not accept: answer with no working that gives a wrong value.
EXPLAIN = give reasons, both what happens and why. Award 1 mark per point, max 3.
Accept: "active site no longer complementary to substrate". Do not accept: "the enzyme is killed" (enzymes are not alive).
One sentence holds the whole practical. Stuck? Tap Reveal answers.
Amylase is a that breaks down its substrate, , into . The reaction speeds up as temperature rises, until the temperature. Beyond it, the active site loses its shape and the enzyme becomes .
Amylase breaks starch into maltose faster as it warms — but only up to the point where heat starts to wreck the very tool doing the work.
Amylase speeds up starch breakdown without being used up. One molecule cuts chain after chain into maltose.
Warmth means faster collisions, so the rate climbs — peaking at the optimum temperature, where the curve is highest.
Too much heat distorts the active site. Starch no longer fits, the reaction stops, and the change does not reverse.