GCSE Biology Enzymes & digestion questions by topic

This question is about enzymes.

1. (a)State what type of molecule enzymes are.[1]
2. (b)Name the region where the substrate binds.[1]
3. (c)Explain why each enzyme usually catalyses only one reaction.[1]

An enzyme was tested at different temperatures; the times below were recorded.

1. (a)Describe the trend in the times between 10 °C and 40 °C.[1]
2. (b)State what happened at 50 °C and name the cause.[1]
3. (c)Suggest why the fastest temperature recorded may not be the true optimum.[1]
4. (d)State one variable that should be controlled.[1]

Name the reagent and the positive result for each food test.

1. (a)Reagent used to test for starch.[1]
2. (b)Positive result of the starch test.[1]
3. (c)Reagent used to test for protein.[1]
4. (d)Positive result of the protein test.[1]

This question is about bile.

1. (a)Name the organ that makes bile.[1]
2. (b)Name the organ that stores bile.[1]
3. (c)State the pH of bile and explain why that helps digestion.[1]
4. (d)State what emulsification means.[1]

A cheese sandwich travels through the digestive system.

1. (a)Name the structures that add amylase to the food in the mouth.[1]
2. (b)Give the order of the organs the sandwich passes through: stomach, mouth, small intestine, oesophagus.[1]
3. (c)Name the enzyme made in the stomach.[1]
4. (d)Name the organ where water is absorbed back into the body from the remaining food.[1]

A student tests a milkshake sample for four nutrients.

1. (a)Name the reagent used to test for glucose and state the positive colour.[1]
2. (b)Iodine solution stays orange-brown with the sample. What does this show?[1]
3. (c)Biuret reagent turns purple. Which nutrient is present?[1]
4. (d)Which nutrient would give a cloudy white emulsion with ethanol?[1]

Complete the table about digestive enzymes.

1. (a)Substrate of amylase.[1]
2. (b)Products of amylase.[1]
3. (c)Missing enzyme name.[1]
4. (d)Products of lipase.[1]

A student investigates the effect of pH on amylase.

1. (a)State the independent variable.[1]
2. (b)State the dependent variable.[1]
3. (c)State two variables that must be controlled.[2]
4. (d)Explain why iodine samples are taken every 30 seconds rather than once at the end.[1]

Amylase digested all the starch in these times: pH 5 — 150 s; pH 6 — 75 s; pH 7 — 50 s.

1. (a)Calculate the rate of reaction at pH 7, giving your answer to 2 significant figures.[2]
2. (b)State which pH gave the fastest reaction and how many times faster it was than pH 5.[2]
3. (c)Explain why the rate at pH 5 is slower than at pH 7.[2]

A meal contains bread (starch), chicken (protein) and butter (fat).

1. (a)Name the enzyme that digests the starch and the products formed.[2]
2. (b)Name the products of protein digestion.[1]
3. (c)Name the enzyme that digests fat and explain how bile helps it.[2]
4. (d)Name the structures where the digested products are absorbed.[1]

Amylase was tested at four temperatures; the time to digest all the starch was recorded each time.

1. (a)Calculate the rate of reaction at 40 °C, giving your answer to 2 significant figures.[2]
2. (b)How many times faster was the reaction at 40 °C than at 30 °C?[1]
3. (c)Explain the result at 50 °C.[2]

Starch digestion was timed at three pH values, with temperature held at 30 °C throughout.

1. (a)Calculate the rate of reaction at pH 7, giving your answer to 2 significant figures.[2]
2. (b)Explain why the rate falls on either side of pH 7.[2]
3. (c)Buffers were used to set each pH. Explain why the temperature was still controlled as well.[2]

Pepsin (a stomach protease) has an optimum pH of about 2; amylase’s optimum is about 7.

1. (a)Explain why pepsin works well in the stomach.[1]
2. (b)Explain what happens to pepsin when it reaches the small intestine and bile has raised the pH to about 8.[2]
3. (c)State why the two enzymes have different optima.[1]

Design an investigation into the effect of temperature on the time taken for amylase to digest starch.

1. (a)Describe a method using at least four temperatures.[3]
2. (b)State the independent and dependent variables.[2]
3. (c)State one safety precaution.[1]

Four tubes of glucose solution of different concentrations were tested with Benedict’s solution and heated equally.

1. (a)Rank tubes X, Y and Z by glucose concentration, lowest first.[1]
2. (b)State what tube W shows and what it is called.[2]
3. (c)Explain why the colour deepens along the run from green to brick-red.[2]
4. (d)State why the tubes were heated in a water bath rather than over a direct flame.[1]

Amylase was tested at five pH values; the times for complete starch digestion are shown.

1. (a)Identify the optimum pH and justify the choice.[2]
2. (b)Calculate the rate at pH 6, giving units.[2]
3. (c)Explain the result at pH 4.[2]
4. (d)Sketch the shape of the rate–pH graph this table implies.[1]

Explain how the digestive system breaks down and absorbs a fatty meal.

1. (a)Write a full explanation, covering bile, lipase, the products and absorption.[6]

A student reads that a human enzyme “works best at 37 °C and is killed at 60 °C”. Evaluate the student’s wording using your knowledge of enzymes.

1. (a)Explain why human enzymes usually work fastest at about 37 °C.[2]
2. (b)Describe what happens to the enzyme at 60 °C and give the correct scientific term.[2]
3. (c)Explain the error in saying the enzyme is “killed”, and state whether cooling it back down restores the rate.[2]