AQA GCSE Biology (8461), Higher tier · Organisation › Animal tissues, organs and organ systems
Practise The human digestive system. 24 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Required practicals:Food tests · Enzymes (method, variables and exam tips)
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Name the type of enzyme that breaks down proteins into amino acids.
protease
A student tested some foods for the presence of different nutrients. Name the reagent used to test for starch.
iodine solution
The protease enzyme in the stomach works best at pH 2. Name the substance produced by the stomach that provides this pH.
hydrochloric acid
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Digestive enzymes break down large food molecules into small soluble molecules.
(a) Complete the sentence. Amylase breaks down starch into ____________ .[1]
(b) Name the type of enzyme that breaks down proteins into amino acids.[1]
(c) Lipase breaks down lipids. Name the two products.[2]
(d) Where is bile made? Tick (✓) one box.[1]
Gall bladder
Liver
Pancreas
Stomach
Show the answer and mark scheme
(a)
sugars / maltose
(b)Answer: protease
protease(s)
(c)
fatty acids
glycerol
(d)Answer: Liver
Question 2Medium6 marks
Enzymes are biological catalysts.
(a) Use the lock and key theory to explain why an enzyme can only catalyse one specific reaction.[2]
(b) Explain why the rate of an enzyme-controlled reaction decreases when the temperature rises above the optimum.[3]
(c) The protease enzyme in the stomach works best at pH 2. Name the substance produced by the stomach that provides this pH.[1]
Show the answer and mark scheme
(a)
the active site has a specific shape
only one substrate has a shape that fits / is complementary to the active site
(b)
the enzyme is denatured
the shape of the active site changes
so the substrate no longer fits (the active site)
(c)Answer: hydrochloric acid
hydrochloric acid
Question 3Hard7 marks
Amylase breaks down starch. A student wanted to investigate how pH affects the time taken for amylase to break down starch. The student was given starch solution, amylase solution, buffer solutions of different pH, iodine solution, a spotting tile and a water bath.
(a) Describe a method the student could use. Your method should produce valid results.[6]
(b) Give the reason why the solutions should be left in the water bath for a few minutes before they are mixed.[1]
Show the answer and mark scheme
(a)
put a drop of iodine solution into each well of a spotting tile
use a measuring cylinder / syringe to put the same volume of starch solution and buffer solution into a test tube
keep the temperature constant by placing the tubes of starch and amylase in a water bath, e.g. at 35 °C, and letting them reach that temperature
add a set volume of amylase to the starch and buffer, mix and start the stopwatch
every 30 s remove a drop of the mixture with a pipette and add it to a fresh drop of iodine
record the time when the iodine stays orange-brown (starch has all been digested)
repeat with buffers of different pH, e.g. pH 5, 6, 7, 8 and 9
repeat each pH and calculate a mean time; rate = 1 ÷ time
Marked with levels of response: the full level descriptors are in the app.
(b)
so the solutions reach the temperature of the water bath before the reaction starts