Sec 3 Biology Biological Molecules topical questions

State the chemical elements present in carbohydrates and in proteins.

Name the reagent and the positive result for testing starch, protein and fats.

Name the small units from which starch and polypeptides are each built.

State what is meant by a catalyst, and why enzymes are catalysts.

State the chemical elements present in fats, and give two roles of fats in the human body.

Use the ‘lock and key’ hypothesis to explain why amylase digests starch but not protein.

Describe and explain the shape of the graph of enzyme rate against temperature, from 0 °C to 60 °C, for a human enzyme.

Amylase digests a standard starch sample in 50 s at 30 °C and in 25 s at 40 °C. Calculate the rate at each temperature and state the effect of the temperature rise.

Explain why human cells could not rely on uncatalysed reactions at 37 °C.

Four food samples are tested. W gives a blue-black colour with iodine; X turns biuret violet; Y turns heated Benedict’s brick-red; Z gives a cloudy white emulsion with ethanol. Identify what each sample contains, and name the small units from which W and X are each built.

Explain why the rate of an enzyme-catalysed reaction falls when the pH moves several units below the enzyme’s optimum.

Amylase digests standard starch samples in 60 s at 20 °C, 30 s at 30 °C and 12 s at 40 °C. Calculate the reaction rate at each temperature and state how many times faster the enzyme works at 40 °C than at 20 °C.

Design an investigation to find the optimum pH for amylase digestion of starch. State the variables and outline the method.

A table gives amylase digestion end-points of 120 s at pH 4, 40 s at pH 6, 20 s at pH 7 and 80 s at pH 8. Identify the optimum pH and explain the pattern either side of it.

Explain what denaturation does to an enzyme at the molecular level, and why its effect differs from simply cooling an enzyme below its optimum.

An unknown food sample gives these results: iodine stays brown; heated Benedict’s turns brick-red; biuret stays blue; the ethanol emulsion test gives a cloudy white layer. Identify every food substance present and absent, justifying each conclusion.

Plan an investigation to find how temperature affects the rate at which amylase digests starch. State the independent and dependent variables, the controls, and how the rate would be measured.

A described graph shows the rate of a protein-digesting enzyme peaking sharply at pH 2 and falling to zero by pH 6, while an amylase graph peaks near pH 7. Explain why the two enzymes have different pH optima, and what happens to each enzyme far from its optimum.