Author: Philip Colls
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Digestion booklet revision questions              NAME:
Q1. The diagram represents part of the human digestive system. The organs are labelled A−F.
 
(a)     Give the letter of the organ that produces amylase.
 
(1)
(b)     Give the letter of the organ that produces maltase.
 
(1)
(c)     Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction.
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Q2. The diagram outlines the digestion and absorption of lipids.
 
(a)     Tick (✔) the box by the name of the process by which fatty acids and glycerol enter the intestinal epithelial cell.
 
Active transport |
Diffusion |
Endocytosis |
Osmosis |
(1)

(b)     Explain the advantages of lipid droplet and micelle formation.
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(3)
(c)     Name structure Q in the diagram above and suggest how it is involved in the absorption of lipids.
Name _____________________________________________________________
How it is involved ____________________________________________________
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(4)
(Total 8 marks)
Q3.
(a)     Bacteria are often used in industry as a source of enzymes. One reason is because bacteria divide rapidly, producing a large number of them in a short time.
Describe how bacteria divide.
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(2)

(b)     Washing powders often contain enzymes from bacteria. These enzymes include proteases that hydrolyse proteins in clothing stains.
The graph shows the effect of temperature on a protease that could be used in washing powder.
 
Explain the shape of the curves at 50 °C and 60 °C.
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(4)

(c)     Some proteases are secreted as extracellular enzymes by bacteria.
Suggest one advantage to a bacterium of secreting an extracellular protease in its natural environment.
Explain your answer.
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(2)
(d)     Mammals have some cells that produce extracellular proteases. They also have cells with membrane-bound dipeptidases.
Describe the action of these membrane-bound dipeptidases and explain their importance.
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(2)
(Total 10 marks)
Q4.
(a)     Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how.
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A student set up the experiment shown in the diagram below.
 
The material from which Visking tubing is made is partially permeable.
After 15 minutes, the student removed samples from the liquid in the beaker and from the liquid inside the Visking tubing. She carried out biochemical tests on these samples. She drew the table below to record her results.
(b)     Complete the table by placing a tick (✔) in each box that you expect to have shown a positive result.
 
Biochemical test | Liquid from beaker | Liquid inside Visking tubing
Biuret reagent | |
Iodine in potassium iodide | |
Benedict’s solution | |
(3)
(c)     Justify your answers to part (b).
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(3)
(Total 9 marks)

Q5.
The figure below shows the processes involved in absorbing amino acids into a capillary from the small intestine.
 
(i)      Name processes A, B and C. In each case, give the evidence for your answer.
A       Process _______________________________________________________
Evidence ______________________________________________________
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B       Process _______________________________________________________
Evidence ______________________________________________________
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C       Process _______________________________________________________
Evidence ______________________________________________________
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(3)
(ii)      Explain how process B creates the conditions for process A to occur.
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(2)
(Total 5 marks)
Q6. Lipase is an enzyme that hydrolyses triglycerides. A student investigated the hydrolysis of triglycerides in milk by human lipase at 20 °C.
He recorded the pH of a sample of milk before and after adding lipase. He used a pH meter to record pH. His results are shown in the graph.
 
(a)     Suggest one advantage of using a pH meter rather than a pH indicator in this experiment.
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(b)     Explain why the pH decreases when the lipase is added to the milk.
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(c)     Suggest why the pH remained constant after 2 minutes.
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(d)     The student carried out his experiment at 20 °C. He then repeated the experiment at 15 °C.
Draw a line on the graph to show the results you would expect at 15 °C.
(2)
(Total 6 marks)
Q7.
Biological washing powders contain enzymes which hydrolyse substances that cause stains on clothes.
A manufacturer tested the ability of two types of the same brand of washing powder to remove different food substances that stain clothes.
•        Type A contained an enzyme.
•        Type B was identical to A except it did not contain the enzyme.
Figure 1 shows the results.
Figure 1
 
A scientist worked for a company that wanted to develop a biological washing powder that was effective over a range of temperatures. He investigated the effect of temperature on the rates of the reaction catalysed by two enzymes, P and S used in biological washing powders.
Figure 2 shows his results.
Figure 2
 
(a)     Many of the substances causing the food stains are large, insoluble proteins.
Suggest how a biological washing powder removes this type of stain.
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(b)     The manufacturer of type A and type B washing powder claimed that these results showed that biological washing powders are better at removing stains from clothes. Use the information in Figure 1 to evaluate this claim.
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(c)     Most customers want a washing powder which removes stains from clothes over a range of temperatures. After obtaining the results shown in Figure 2, which enzyme should the scientist recommend for use in a biological powder?
Give reasons for your answer.
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 (3)
(d)     Biological washing powders often contain a number of different enzymes. This enables them to remove a wider range of stains from clothes.
Explain why a number of enzymes are required to remove a wider range of stains.
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 (3)
(Total 12 marks)
Q8.
Biologists divided new-born rats randomly into four groups.
They fed the rats in each group on a standard diet which only differed in the carbohydrate content. When these rats were adult, the biologists measured the activity of lactase in the digestive system of the rats. The following table shows the mean results for each group.

Diet

Mean lactase activity / µ mol of lactose digested per 
hour (± standard deviation)

Low sucrose | 57.9 (± 14.5)
High sucrose | 184.2 (± 30.8)
Low starch | 86.9 (± 13.3)
High starch | 221.4 (± 25.4)
(a)     Give one piece of evidence from the table that indicates lactase activity is affected by diet.
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(1)
(b)     Some students suggested from these data that increasing starch in the diet was the most effective way to increase lactase activity in lactase deficient people. Is this conclusion valid? Explain your answer.
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(2)
(Total 3 marks)

Mark schemes
Q1.
(a)     C.
Ignore name of organ
1
(b)     E.
Ignore name of organ
1
(c)     1.       Active site (of enzyme) has (specific) shape / tertiary structure / active site complementary to substrate / maltose;
Reject active site on substrate.
Must have idea of shape
Assume “it” = maltase
Accept (specific) 3D active site
Reject has same shape
2.       (Only) maltose can bind / fit;
Accept “substrate” for “maltose”
3.       To form enzyme substrate complex.
Accept E−S complex
3
[5]
Q2.
(a)    Diffusion
Automarker
1
(b)     1.      Droplets increase surface areas (for lipase / enzyme action);
2.      (So) faster hydrolysis / digestion (of triglycerides / lipids);
3.      Micelles carry fatty acids and glycerol / monoglycerides to / through membrane / to (intestinal epithelial) cell;
1.      Context is important
1.      Reject micelles increase surface area
2.      Ignore ‘breakdown’
3.      Ignore ‘small enough’
3.      Accept description of membrane
3.      Reject any movement through membrane proteins
3
(c)     1.      Golgi (apparatus);
2.      Modifies / processes triglycerides;
3.      Combines triglycerides with proteins;
4.      Packaged for release / exocytosis
OR
Forms vesicles;
Ignore ‘processes and packages’ unqualified
2.      Reject synthesises triglycerides
3.      Accept ‘forms / are lipoproteins’
4
[8]
Q3.
(a)     1.      Binary fission;
2.      Replication of (circular) DNA;
3.      Division of cytoplasm to produce 2 daughter cells;
4.      Each with single copy of (circular) DNA;
1.      Ignore reference to ‘chromosome’
2.      Ignore ‘copy’.
4.      Ignore references to number of plasmids.
2 max
(b)     1.      Both denatured (by high temperature);
2.      Denaturation faster at 60 °C due to more (kinetic) energy;
3.      Breaks hydrogen / ionic bonds (between amino acids / R groups);
4.      Change in shape of the active site / active site no longer complementary so fewer enzyme-substrate complexes formed / substrate does not fit;
3.      Ignore references to disulphide bonds
3.      Accept (at 60 °C) Change in shape of the active site / active site no longer complementary so no enzyme-substrate complexes formed / substrate does not fit;
4
(c)     1.      To digest protein;
2.      (So) they can absorb amino acids for growth / reproduction / protein synthesis / synthesis of named cell component;
OR
(So) they can destroy a toxic substance / protein;
1.      For ‘digest’ accept ‘break down’ here.
2.      Accept ‘(so) they can destroy antibodies / antibiotics / viral antigens / bacterial antigens’
2
(d)     1.      Hydrolyse (peptide bonds) to release amino acids;
2.      Amino acids can cross (cell) membrane;
OR
Dipeptides cannot cross (cell) membrane;
OR
Maintain concentration gradient of amino acids for absorption;
OR
Ensure (nearly) maximum yield from protein breakdown;
2.      Ignore references to crossing gut membranes.
2.      Accept ‘there are carrier proteins for amino acids’
2.      Accept ‘no carrier proteins for dipeptides’
2
[10]
Q4.
(a)     1.      Sodium ions actively transported from ileum cell to blood;
2.      Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
3.      Glucose enters by facilitated diffusion with sodium ions;
3
(b)
 
Biochemical test | Liquid from beaker | Liquid inside Visking tubing
Biuret reagent | | ✔
I_2/KI | | ✔ or blank
Benedict’s | ✔ | ✔
1 mark for each correct row
3
(c)     1.      Biuret: protein molecules too large to pass through tubing;
Neutral: enzyme molecules
2.      Iodine in potassium iodide solution: starch molecules too large to pass through tubing;
If no tick in 04.2, allow no starch hydrolysed
3.      Benedict’s: starch hydrolysed to maltose, which is able to pass through tubing.
Reject: glucose
3
[9]
Q5.
(i)      In all cases reject ‘energy’ unless qualified
A –  facilitated diffusion as transport protein needed but ATP not needed;
B –  active transport ‘energy’ unless as (transport protein and) ATP needed; qualified
C –  (simple) diffusion as neither ATP nor transport protein needed;
(Ignore all references to concentration gradients)
3
(ii)      creates low concentration of amino acids / Na^+ in cell concentration gradient established between lumen and cell (of amino acids or Na^+)
2
[5]
Q6.
(a)     Any one from:
1.      Numerical readings / not subjective / colour change subjective / gives quantitative data / not qualitative / gives continuous data;
2.      Greater accuracy;
Accept greater precision
1 max
(b)     Fatty acids produced;
1
(c)     1.       No more (fatty) acids produced;
2.       All triglycerides/fat//lipids/substrate used up / enzyme denatured;
2
(d)     1.       Line starting at same point and falling above original line;
2.       Levels off at same pH, but later;
Accept the line still falling at 4 minutes
Do not credit if levels off at higher pH
2
[6]
Q7.
(a)     1.      Enzyme hydrolyses / breaks down protein to amino acids;
2.      Products are soluble / can be washed away;
2
(b)     Arguments for biological washing powder:
3 max if only arguments against biological washing powder are referred to
1.      More effective with all stains;
Accept different ways of expressing ‘effective’ e.g. higher % of stain removed
2.      Greater improvement with salad dressing / chocolate milkshake / chocolate pudding;
Arguments against biological washing powder:
3.      Little / less improvement with raspberry sorbet / raspberry smoothie;
4.      Only tested 5 / a small number of stains;
5.      Only chose stains that would work / didn’t select stains that wouldn’t work;
6.      Only included results that did work / didn’t show results that didn’t work;
7.      Only one set of results / not repeated;
8.      Only compared against one washing powder / may not be true for other washing powders;
Ignore references to unknown masses of powder, temperature of washes or other aspects of technique or different fabrics
4 max
(c)     1.      Enzyme S effective across a wider range of temperatures;
2.      Enzyme S more active above 50 °C / active up to 80 °C / active above 60 °C;
3.      Enzyme S more active below (about) 37 °C temperature;
4.      (Although) Enzyme P has higher rate of reaction at optimum / 40 – 50 °C;
5.      Enzyme P denatured above 50 °C;
Answers should be in the context of choosing enzyme S but, if P is chosen, points 4 and 5 may still be awarded, if described
In points 2 and 3, a temperature must be stated. Allow ± 5 degrees of values shown
3 max
(d)     1.      Stains caused by different substances;
2.      Enzymes are specific;
3.      Active site specific to substrate / other substrates cannot fit active site;
This could be expressed in other ways e.g. ‘other substrates are not complementary to the active site’
3
[12]
Q8.
(a)     High sucrose / starch diet leads to increase in lactase activity;
1
(b)     Not valid / cannot be certain because overlap in SD between high sucrose and high starch;
Study based on rats (not human) so may not apply to human;
2
[3]