Biological molecules and enzymes covers what living things are made of and how enzymes speed up the reactions that keep them alive. It matters beyond this topic, because digestion, respiration and photosynthesis all rely on enzymes.
For the exact wording of the content you are examined on, check the subject page on the Cambridge website for your exam year. This page gives the learning route, and the lessons give the detail.
What should you know before you start?
You should be comfortable with cells and with how particles move. The topics cells and microscopy and movement across membranes help, since enzymes act inside and around cells. You do not need any chemistry beyond the idea that substances are made of particles that can join and separate.
An orienting example
An enzyme test on a potato extract gives three results, and the lesson skills show up in each.
An iodine test turns blue-black, so starch is present (food test inference). Starch is a polymer of glucose, so the enzyme amylase can break it into smaller units (monomers and polymers). Amylase acts on starch but not on protein, because its active site is complementary to starch only (specificity).
If the reaction runs faster at 35 °C than at 15 °C, collisions explain it. If it stops at 80 °C, the enzyme has been denatured. Two slow reactions, two different reasons.
In what order should you study the lessons?
- Connect a food-test observation with a limited inference: it teaches the wording discipline used in every data question.
- Distinguish a monomer from a polymer: it gives you the building blocks that enzymes act on.
- Explain enzyme specificity using a model: it introduces the active site, which everything later relies on.
- Interpret temperature and pH response graphs: it turns the model into data and rates.
- Separate denaturation from a slower collision rate: it resolves the most common explanation error.
What are the common traps?
- Writing “sugar” or “glucose” when the test only shows a reducing sugar.
- Calling a large molecule a monomer, or swapping glucose and amino acids.
- Saying the enzyme and substrate have the same shape, instead of a complementary active site.
- Saying “the optimum is exactly” a value that the data only approximate.
- Saying cold temperatures denature an enzyme, or that an enzyme is killed.
How should you use the practice set?
Attempt the mixed practice set after the lessons, on paper, and write full sentences. Afterwards mark the error type and go back to the matching lesson, then try a fresh question on the same skill a few days later.
The later topics plant nutrition and human nutrition and digestion build directly on this one, so the time spent here returns quickly.
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