Exam code: 4XSD1
Bread contains starch.
Describe how you would test a piece of bread to show it contains starch.
The diagram shows the mycelium of an organism growing on a piece of bread.
Which type of organism is shown growing on the bread?
Bacterium
Fungus
Protoctist
Virus
Which enzyme is released by the organism to digest starch?
Amylase
Ligase
Lipase
Protease
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Starch is a carbohydrate which contains glucose.
(i) Give the chemical formula for glucose
[1]
(ii) Starch is a polysaccharide, while some other carbohydrates are disaccharides.
Name the disaccharide which contains glucose and fructose
[1]
The pancreas, small intestines and salivary glands produce the enzymes involved in the digestion of starch.
(i) Describe what an enzyme is.
[2]
(ii) State the name of the enzyme responsible for the digestion of starch.
[1]
The diagram below shows the mechanism of enzyme action.
State the name given to molecule X and location Y in a chemical reaction.
The image shows the action of an enzyme on a molecule of starch.
(i) State the name of the product of starch digestion as shown in the diagram.
[1]
(ii) Some students used iodine solution to show the rate of the above reaction at different temperatures.
They mixed a starch solution with the enzyme at a range of different temperatures between 20 °C and 60 °C, then added 2 drops of iodine. They timed how long it took for the solution to change from black to brown.
Identify the independent variable and dependent variable in this investigation.
[2]
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The table shows a list of positive and negative results for some tests that can be used to detect the presence of food substances.
Test reagent | Substance being tested | Result if positive | Result if negative |
|---|---|---|---|
|
| Purple | Blue |
|
| Blue/black | Orange/brown |
|
| Green/orange/red | Blue |
Complete the table to identify the test reagent and substance being tested.
A balanced diet should contain a variety of different biological molecules, each of which is digested by a specific set of enzymes.
Draw lines to match up the molecule to the specific enzyme involved in its digestion.
The graph below shows the effect of temperature on an enzyme controlled reaction.
Explain the rate of reaction at 41 °C.
Enzymes are examples of proteins.
Which of the following combinations of chemical elements shows the correct four elements found in proteins?
Carbon, hydrogen, oxygen and amino acids
Carbon, hydrogen, oxygen and nitrogen
Carbon, oxygen, calcium and nitrogen
Hydrogen, oxygen, nitrogen and sulfur
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Some cosmetic companies claim that adding argan oil to their shampoo increases the strength of human hair.
Design an investigation to find out if argan oil shampoo does increase the strength of human hair.
Include experimental details in your answer and write in full sentences.
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Describe the structure of a protein such as an enzyme.
The mechanism of enzyme action is often described as being like a 'lock and key'.
Describe the mechanism of enzyme action.
During the digestive process, digestive enzymes break down larger molecules into smaller molecules.
Explain the role that digestive enzymes play in sustaining respiration in cells of the body.
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Yeast cells are often used when making bread.
A student uses this method to investigate the effect of temperature on the height that bread dough rises.
Place dough containing flour, sugar, water and yeast into a measuring cylinder
Measure the height of the dough
Place the measuring cylinder in a 25 °C water bath
Measure the height of the dough after two hours
Repeat the experiment at temperatures of 35 °C and 65 °C
The diagram shows the student’s apparatus.
The table shows the student’s results.
Temperature in °C | Height of dough in mm | Percentage (%) increase in height of dough | |
|---|---|---|---|
At start | After two hours | ||
25 | 25 | 35 | 40 |
35 | 25 | 45 |
|
65 | 25 | 27 | 8 |
Calculate the percentage increase in the height of the dough after two hours at a temperature of 35 °C.
Explain why yeast causes the bread dough to increase in height.
Explain why the dough rises to a different height at 25 °C compared with the height at 35 °C.
Explain why the dough rises to a different height at 35 °C compared with the height at 65 °C.
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The graph shows the effect of temperature on the activity of an enzyme.
Describe and explain the trend of the graph.
Explain how the evidence from the graph in part (a) indicates that the enzyme being studied is not likely to be one found in the human body.
A group of students wanted to investigate the effect that temperature has on the activity of pepsin, a protease found in the human digestive system.
They used the following method:
Put 4 cm3 of 1% protein solution into a boiling tube.
Put 4 cm3 of pepsin solution into a second boiling tube. Put both boiling tubes into a water bath at 20 °C.
After 4 minutes, add the pepsin solution to the protein solution together in one boiling tube, mixing together with a stirring rod.
After 20 seconds, add a drop of the mixture to a drop of Biuret solution in one well of a spotting tile.
Repeat step 5 until the Biuret solution no longer changes colour.
Repeat steps 1 – 6 at 10 °C (using an ice water bath), 30 °C, 40 °C and 50 °C.
Explain why the student left the protein and pepsin solutions in the water bath for 4 minutes in step 3.
The image below shows the incomplete results of the experiment carried out in part (c).
Complete the image below to show the results you would expect at 30 °C and at 40 °C
You should write a tick or a cross in each well of the spotting tile.
State where in the digestive system protease is secreted.
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The table shows four samples of food that were tested for glucose (reducing sugar) using the Benedict's test.
Test number | Contents |
|---|---|
1 | Water |
2 | Potato juice |
3 | Dilute orange juice |
4 | Glucose sports drink e.g. Lucozade™ |
The results were observed as follows:
The Benedict's test is referred to as being semi-quantitative.
Use the information provided to suggest what the term 'semi-quantitative' means.
Explain the purpose of the test tube containing just water in the experiment shown in part (a).
Explain why the test for lipids is known as an emulsion test.
Predict the colour changes (if any) of the iodine test on the food samples shown below:
Food sample | Iodine test result |
|---|---|
Bagel |
|
Eggs |
|
Fish |
|
Rice |
|
Grapefruit |
|
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Food items can often be spoiled if saprotrophic microorganisms such as mould fungi grow on them.
Describe how a saprotrophic fungus such as mould obtains its food.
A student uses this method to investigate ways of preventing peas from being spoiled.
Place three peas in each of three test tubes as shown in the diagram
Cover the peas in test tube A with water and keep at 37 °C
Cover the peas in test tube B with water and keep at 4 °C
Cover the peas in test tube C with vinegar, which is a weak acid, and keep at 37 °C
Leave the peas for 24 hours
The student observes the level of cloudiness of the solution to determine how spoiled the peas have become. The level of cloudiness can be used as a measure of fungal growth.
The table shows the student’s results.
Test tube | Conditions peas are kept in | Level of cloudiness |
|---|---|---|
A | Water at 37 °C | Very cloudy |
B | Water at 4 °C | Slightly cloudy |
C | Vinegar at 37 °C | No cloudiness |
(i) Suggest a problem with using the level of cloudiness of the solution to determine how spoiled the peas have become.
[1]
(ii) Explain the appearance of the peas in water at 4 °C.
[2]
(iii) Explain the appearance of the peas in vinegar at 37 °C.
[2]
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The protein Rubisco is an enzyme.
Identify where, in a cell, Rubisco would be made.
Rubisco has a unique 3D shape that enables it to carry out its roles in living organisms.
Describe how the 3D shape of rubisco is determined.
Extreme hyperthermia is a condition in which human body temperature rises above the normal body temperature of 37 °C. Body temperatures above 40 °C can be life threatening.
Use your knowledge of proteins to suggest why body temperatures above 40 °C can be life threatening.
Sketch a graph to show how the rate of reaction of an enzyme such as Rubisco would change over a range of temperatures from 0 to 60 °C.
Use the axes provided below.
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