O LevelBiologyCambridgeTopic Questions4. Biological Molecules4.1 Biological Molecules

Biological Molecules (Cambridge O Level Biology)

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1a
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Table 1 lists a number of chemical substances.

Table 1

hydrogen  
water  
sulfur  
silicon  
titanium  
nitrogen  
 carbon  


Place a tick (✓) in the boxes next to the chemical elements that are found naturally in living organisms.

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1b
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Name a group of biological molecules that contain carbon, hydrogen and oxygen only.

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1c
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Table 2 lists some carbohydrates.

Place a tick (✓) in the boxes that classify each carbohydrate as either a monosaccharide, a disaccharide or a polysaccharide. 

 Table 2

Carbohydrate Monosaccharide Disaccharide Polysaccharide
 Glycogen      
 Glucose      
 Starch      

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1d
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Name the molecule that, in certain fats, binds to three fatty acid molecules.

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2a
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Describe the colour change that is observed when a sample of food has tested positive in the Benedict's test.

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2b
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.

(i)

Describe two safety precautions that need to be taken when performing the Benedict's test on a sample of food.

[2]

(ii)

Describe one additional safety precaution when performing the ethanol emulsion test on a sample of food.

[1]

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2c
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A student tested a sample of three different foods for starch.

The student's partial results are shown in Table 1.

Table 1

food sample colour of test sample after testing
lasagne blue/black
fish  
 bread  

Complete Table 1 to predict the results that would be obtained.

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3a
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A student processed a sample of food into an aqueous solution and tested it with a test solution. The test solution changed from blue to violet.

Name the solution used in this test.

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3b
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State the food group that the experiment in part (a) showed a positive result for.

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3c
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A sample of butter was shaken with ethanol, followed by an equal volume of cold water.

Predict the appearance of the mixture after the addition of water.

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3d
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A sample of freshly-squeezed orange juice was mixed with DCPIP solution.

Predict the result of this food test, and explain your prediction. 

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1
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This question is about biological molecules.

Choose words or phrases from the list to complete the sentences.

Each word or phrase may be used once, more than once, or not at all.

calcium  carbon  carbon dioxide carbohydrate
cellulose  chloroplasts  fat  glycerol
glycogen  iron  methane  nitrogen
oxygen  protein  starch  

Fats are composed of the elements .............................................. , hydrogen and .............................................. only. All proteins contain these three elements and the element .............................................. .

Glucose is a type of ............................................... . Animals store excess glucose as .............................................. in the liver.

Plants store excess glucose as .............................................. . Plants also convert glucose to .............................................. which is used to make cell walls. 

[7 marks]

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2a
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Table 1 contains some statements about biological molecules.

Table 1

  Correct? (✓)
 They contain carbon, hydrogen and oxygen only  
 All are sugars  
 They are all formed from long chains of glucose molecules   
 They are the principal energy source in the animal diet  
 They include starch, cellulose and triglycerides  
 They form solids at room temperature but melt into liquids when warmer  
 The sequence of the building blocks determines their function  

Place ticks (✓) in Table 1 to indicate statements that apply to carbohydrates.

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2b
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Compare the chemical elements found in carbohydrates and proteins.

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2c
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Fig. 3 shows groups of biological molecules and the building blocks that make them up.


ZXnLEs-f_building-blocks-join-boxes

Fig. 3

Join the boxes in an appropriate manner using straight lines. 

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3a
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Fig. 1 shows the components of fats and oils as shapes.

Using these shapes, sketch the appearance of a triglyceride molecule that would be found in fats and oils.

yeECsqJ~_fa-and-glycerol---sq

Fig. 1

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3b
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Describe the test that would be used to show a positive result for the presence of protein in a sample of food.

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4a
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Table 1 shows four samples of food that were tested for glucose (reducing sugar) using the Benedict's test. 

Table 1

test number contents
1  Water
2  Potato juice
3  Dilute orange juice
4  Glucose sports drink e.g. Lucozade™

Explain the purpose of the test tube containing just water in the experiment shown in Table. 1.

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4b
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Explain why the test for lipids is known as an emulsion test.

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4c
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Predict the colour changes (if any) of the iodine test on the food samples shown in Table 2.


Table 2

food sample iodine test result
Bagel  
Eggs  
Fish  
Rice  
Grapefruit  

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54 marks

DNA controls cell function by controlling the production of proteins.

These proteins determine the phenotype of an organism, including blood group in humans.

Describe the structure of a DNA molecule.

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