CIE IGCSE Biology

Topic Questions

IGCSEBiologyCIETopic Questions4. Biological Molecules4.1 Biological Molecules

4.1 Biological Molecules

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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      
 Maltose      

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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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Fig.1 shows a partial view of the structure of an amino acid.

Using the appropriate chemical symbols, complete Fig. 1 to show the full structure of the amino acid.

xQoTbTN1_4-1-q1e---sq

Fig. 1

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2b
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State what the R group in Fig. 1 represents.

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2c
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Place these three chemical structures in size order, starting with the smallest.
  • Peptides
  • Proteins
  • Amino acids

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2d
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(d)

Read this passage:

There are only around ______ amino acids that are found in living organisms. They can be arranged in any order in proteins, creating a __________ of combinations. Even if one of the amino acids is altered or not present, a very __________ protein will be formed. This may result in a __________.

Complete the passage by using some of the phrases in the box below.

You may use each word once, more than once or not at all.  

               non-functioning protein             

three

carbohydrate being formed instead

hundreds of

small number

different

large number

twenty

large

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3a
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Fig. 1 shows five food tests and the food groups that those tests are designed to be used for. 


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Fig. 1

Using five straight lines, link each food test to the food group that the test is used for.

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3b
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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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3c
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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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3d
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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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4a
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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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4b
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State the food group that the experiment in part (a) showed a positive result for.

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4c
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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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4d
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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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5a
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Extended only

Fig. 1 shows a nucleotide. 

nucleotide-labelling-1

Fig.1

Label the parts of the nucleotide molecule shown as A, B, and C.

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5b
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Extended only

State the base pairings between A, C, G and T in a DNA molecule. 

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5c
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Define the term 'double helix' in the structure of DNA.

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5d
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State a part of the nucleotide shown in part (a) that occupies the outside of the DNA double helix.

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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. 1 shows the structure of glucose.


Structure of α-D-glucose

Fig. 1

Fig. 2 shows the structure of another sugar.


LXysu6k1_maltose---sq

Fig. 2

Identify the sugar depicted in Fig. 2. Explain your choice of answer.

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2d
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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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Fig. 2 shows the chemical structure of an amino acid called serine.

serine

Fig. 2

(i)

  Draw a label line to indicate serine's central carbon with an X on Fig. 2.

[1]

(ii)  

Draw a line around the R group of serine on Fig. 2.

[1]

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3c
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Table 1 contains some statements about the fate of proteins in an animal's body.

Table 1

 A.   Protein undergoes chemical digestion
B.  Amino acids circulate in the blood
C.  Food is ingested
D.  Peptides are put together in protein synthesis
E.  Peptides are synthesised

Place these events into a logical chronological order.

1st ➙ 2nd ➙ 3rd ➙ 4th ➙ 5th
                 

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3d
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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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Extended only

State the type of bonding that holds DNA bases together in base pairs. 

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4b
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Extended only

Fig. 1 shows the base sequence on one strand of DNA. 

A C G G A T C A
               

Fig. 1

Complete Fig.1 to show the base sequence of the opposite strand of DNA.

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4c
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Extended only

Fig. 2 shows outlines that represent the bases of DNA.


uTSmwKxL_4-bases-as-shapes

Fig. 2

Use your knowledge of base-pairing to label each one with the letter that each could represent.

Note: there is more than one possible correct answer. 

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4d
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The following are all aspects of the structure and organisation of an organ such as the liver.

  • Chromosome
  • Tissue
  • Base
  • DNA double helix
  • Nucleus
  • Cell
  • Nucleotide

Using an imaginary powerful microscope with a full zoom function, list the order in which the above structures would become visible when zooming in on a piece of liver tissue. 

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5a
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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™

The results are shown in Fig.1 


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Fig. 1

The Benedict's test is referred to as being semi-quantitative.

Use the information provided in Table 1 and Fig. 1 to suggest what the term 'semi-quantitative' means. 

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5b
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Explain the purpose of the test tube containing just water in the experiment shown in Fig. 1.

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5c
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Explain why the test for lipids is known as an emulsion test.

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5d
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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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