Biomolecules and enzymes for N(A)-Level Science (Biology): the elements and building blocks of carbohydrates, proteins and fats, how enzymes work as biological catalysts, and the food tests

What this module covers

Biomolecules and enzymes is about the chemistry of life. You need to know what carbohydrates, proteins and fats are made of and what the body uses each for, how enzymes speed up reactions and why temperature and pH change how well they work, and how to test a food sample to find out which molecules it contains. These ideas connect directly to digestion, respiration and nutrition later in the syllabus.

This overview links every dot point in the module. Work through them in order, then check yourself with the questions at the end. See the full set at /sg-n-level/biology/syllabus.

The main food molecules

Start with what food is made of. The page on carbohydrates, proteins and fats sets out the elements and building blocks of each: carbohydrates are built from simple sugars such as glucose, proteins from amino acids, and fats from fatty acids and glycerol. It also gives the role of each in the body, with carbohydrates and fats as energy stores and proteins for growth and repair.

Enzymes as biological catalysts

Next, the molecules that make reactions fast enough for life. The page on enzymes and how they work explains that an enzyme is a biological catalyst that speeds up a reaction without being used up, describes the lock and key model, and explains how temperature and pH change enzyme activity, including denaturing at high temperatures and extreme pH.

The food tests

Finally, the practical skill. The page on food tests sets out the reagent, the method and the colour change for starch, reducing sugars, proteins and fats. These are reliable marks if you learn the reagent and the positive result for each test.

How this module is examined

At N(A) level there is no standalone pure Biology paper. Biology is taken as part of a combined Science subject, either Science (Physics, Biology) syllabus 5106 or Science (Chemistry, Biology) syllabus 5107, so this module is examined within whichever combination your school offers.

• Match molecule to building block. Learn glucose for carbohydrates, amino acids for proteins, and fatty acids and glycerol for fats.
• Use the word denatured. Enzyme questions reward explaining the change in shape of the active site, not just saying the enzyme stops.
• Learn the colour changes. Food test questions reward naming the reagent and stating the colour change from negative to positive.

Check your knowledge

A mix of recall, explanation and practical questions. Attempt them, then check against the solutions.

1. State the building blocks of proteins and of fats. (2 marks)
2. Explain why an enzyme stops working at a very high temperature. (2 marks)
3. A food sample turns Benedict's solution brick-red when heated. What does this show? (1 mark)
4. Describe how you would test a food sample for starch and state the positive result. (2 marks)