AQA Biology Biological molecules Grasp IT A level PDF

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exam practice questions for a level biology...

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GraspIT – AQA A level Biology - Biological molecules A. Biological molecules part 1 – Carbohydrates.

1. Describe the difference between α- glucose and β-glucose. (2)

2. The monosaccharides glucose and fructose can join to form a disaccharide. Complete the diagram to show how this happens. Name the disaccharide which is formed. Name the bond which is formed. Explain what kind of reaction this is. (5)

3. What are the two components of the polysaccharide, starch? How does the structure of these components contribute to the properties of starch? (5).

4. Cellulose is a polysaccharide of β-glucose molecules. Describe how two β-glucose molecules are able to join together. (4)

5. Extended response question: Describe the structure of glycogen and explain how its structure makes it suitable for its function (6)

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GraspIT – AQA A level Biology - Biological molecules B. Biological molecules part 2 – Lipids. 1. Describe the structure of a triglyceride. What type of bond links the components of a triglyceride? (3) 2. Explain the difference between a saturated and unsaturated fatty acid. (1)

3. Describe the difference between a triglyceride and a phospholipid. Why do phospholipids form bilayers in biological systems? (4).

4. Extended response question: Name of fatty acid lauric acid palmitic acid stearic acid oleic acid linoleic acid linolenic acid

Formula CH3(CH2)10CO2H CH3(CH2)14CO2H CH3(CH2)16CO2H CH3(CH2)7CH=CH(CH2)7 CO2H CH3(CH2)4CH=CHCH2CH=CH(CH2)7CO2H CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7CO2H

Saturated / unsaturated saturated saturated saturated unsaturated unsaturated unsaturated

Melting Point / oC 45 63 69 13 -5 -11

The table displays information about a number of fatty acids. Describe and explain the pattern shown by the melting points of the fatty acids. (6)

C. Biological molecules part 3 – Proteins. 1. Draw the generalised structure of an amino acid and label the main groups of the molecule (3).

2. Using a diagram, describe how two amino acids join together. Label and name the bond which is formed (3).

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GraspIT – AQA A level Biology - Biological molecules 3. The diagram shows the structure of a protein.

The black strips represent disulfide bonds which help stabalise the tertiary structure. (a) Name two other types of bond that stabalise the tertiary structure of proteins (2).

(b) Region A is a secondary structure. Describe the nature of region A (2).

4. Extended response question: Milk powder was made up to standard solutions of 1%, 2%, 3%, 4% and 5% protein. 5cm3 of 1% trypsin enzyme solution was added to 10cm3 samples of each standard solution. The time it took the milk solution to become clear at room temperature was recorded. The average of 10 trials is shown in the table below: Standard solutions Average time for milk solution to clear (s)

1% 44

2% 56

3% 65

4% 82

5% 102

A 45

B 81

Plot a calibration curve using the results for the standard solutions and use the curve to estimate the concentration of the unknown solutions A and B.

(6)

D. Biological molecules part 4 – Enzymes. 1. Why are enzymes sometimes referred to as ‘biological catalysts’? (2) 2. How do enzymes reduce the activation energy of a reaction? (2) 3. Why do different enzymes have a different optimum pH? (2)

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GraspIT – AQA A level Biology - Biological molecules 4. Explain the importance of tertiary structure to the functioning of an enzyme. (4) 5. The diagram shows an enzyme, the substrate and a non-competitive inhibitor.

substrate enzyme inhibitor

Label the active site and explain how the inhibitor has its effect. (4)

6. Extended response question: State two factors that can cause an enzyme to denature and explain how this denaturation occurs in each case (6).

E. Biological molecules part 5 – Enzyme kinetics. 1. The graph shows the effect of substrate concentration on an enzyme-catalysed reaction. 2.

C B

A

Explain the shape of the graph at points A, B and C. (3)

3. A reduction in enzyme activity above the optimum temperature for a particular enzyme can be explained by the idea of denaturation. Explain what causes a reduction in enzyme activity below the optimum temperature. (3)

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GraspIT – AQA A level Biology - Biological molecules

4. Extended response question: The enzyme amylase catalyses the hydrolysis of starch to maltose. The graph shows the results of an investigation into the production of maltose at two temperatures.

(a) Suggest why the quantity of maltose produced became constant over time. (1) (b) Explain the difference in the amount of maltose produced after 4 minutes at 18oC and 23oC. (2) (c) Sketch a curve onto the graph above to show the expected results if the experiment were repeated at 23oC but with a higher concentration of starch. All other factors are kept constant. (2)

F. Biological molecules parts 6 & 7 – Nucleic acids and DNA replication. 1. Name parts labelled on the nucleotide below:

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GraspIT – AQA A level Biology - Biological molecules

2. DNA is a double helix made up of two polynucleotide chains. Describe how the three parts of the nucleotide identified in Question 1 are joined together and how the polynucleotide chains are bonded. (4)

3. Extended response question: Explain how the structure of DNA is related to its functions (6).

G. Biological molecules part 8 - ATP. 1. Extended response question: Explain the role of ATP in biological systems.

H. Biological molecules part 9 - Water. 1. Extended response question: Outline the importance of water to living organisms (6).

I. Biological molecules part 10 – Inorganic ions. 1. Extended response question: Explain the importance of inorganic ions to living organisms. Using named examples, describe the consequences of inorganic ion deficiency (6).

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