Tuesday 11 January 2011

Question 1

What structures that are in an epithelial cell aren’t in a cholera bacterium? 2 Marks

Answer 1

• Nucleus

- Mitochondria

Question 2

Give one advantage of using a TEM than a SEM. 1 mark

Answer 2

• Higher-resolution so a higher level of detail

- Allows structures within the cell to be seen

Question 3

Give one advantage of using a SEM rather than a TEM. 1 mark

Answer 3

• Thin sections do not need to be prepared.

- Can have 3D images

Question 4

Describe the induced fit model of enzyme action. 2 marks

Answer 4

• Active site not complementary
• Active site changes shape
• Change in enzyme allows the substrate to fit and E-S complexes are produced

Question 5

Describe one way that the lock and key model is different from the induced fit model. 1 mark

Answer 5

• Active site is complementary before binding.

Question 6

The diagram shows the structure of a molecule of PABA. It also shows the structure of a molecule of a drug called sulfanilamide, which can be used to treat bacterial infections. Sulfanilamide prevents bacteria producing folic acid. Use the diagram and your knowledge of enzymes to explain how sulfanilamide prevents bacteria producing folic acid. 3 marks

Answer 6

• Similar structure
• It is a competitive inhibitor
• Less PABA bind so less E-S complexes are produced

Question 7

Explain, in terms of pressure, why the semilunar valves open. 1 mark

Answer 7

• Pressure is greater below valve/ in ventricle than artery

Question 8

When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay. 2 marks

Answer 8

• Allows atria to empty + ventricles fill

- Before ventricles contract

Question 9

Use information from the table to explain how training has caused the resting heart rate of this athlete to be lower. 2 marks

Answer 9

• Increase in size or volume of heart
• Cardiac output is the same before and after training
• More blood leaves the heart in each beat

Question 10

Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? 2 marks

Answer 10

• Double bonds

- Between carbon

Question 11

A triglyceride does not contain sucrose or glycosidic bonds.

Give one other way in which the structure of a triglyceride is different to olestra. 1 mark

Answer 11

• Contains glycerol
• Three fatty acids
• Forms 3 ester bonds

Question 12

Before reweighing, the student blotted dry the outside of each cylinder. Explain why. 2 marks

Answer 12

• Only want to measure water taken up or lost;

- Ensures the same amount of water on outside

Question 13

The student calculated the percentage change in mass rather than the change in mass.
Explain the advantage of this. 2 marks

Answer 13

• Allow comparison

- Idea that cylinders have different starting masses / weights

Question 14

The student carried out several repeats at each concentration of sodium chloride solution. Explain why the repeats were important. 2 marks

Answer 14

• Allows anomalies to be found

- Produce a mean

Question 15

HPV vaccine is offered to girls aged 12 to 13 (line 5). Suggest why it is offered to this age group. 1 mark

Answer 15

• Girls aren’t sexually active

- Not likely to carry HPV

Question 16

The vaccine is made from HPV types 16 and 18 (line 5). Explain why this vaccine may not protect against other types of this virus. 2 marks

Answer 16

• Other HPV types have different antigens
• Memory cells not activated
• Antibodies aren’t complementary

Question 17

Three injections of the vaccine are given (lines 5 to 6). Use your knowledge of immunity to suggest why. 2 marks

Answer 17

• More antigens
• More memory cells
• So more antibodies produced at a faster rate

Question 18

t will be many years before it can be shown that this vaccination programme has reduced cases of cervical cancer (lines 7 to 9). Suggest two reasons why. 2 marks

Answer 18

• Cancer takes years to develop
• Females must be sexually active to obtain data
• Only teenagers vaccinated - small

Question 19

Smear tests will continue to be offered to women, even if they have been vaccinated (lines 9 to 10). Suggest why women who have been vaccinated still need to be offered smear tests. 1 mark

Answer 19

• As a precaution in case, the vaccine doesn’t work

- (Some) women may have been infected (with HPV) before receiving the vaccine;

Question 20

Suggest one reason why vaccinating a large number of people would reduce significantly the spread of HPV through the population (lines 14 to 16). 2 marks

Answer 20

• Virus cannot replicate

- Non-vaccinated people more likely to contact vaccinated people;

Question 21

Pulmonary tuberculosis is a disease of the lungs.

Describe the transmission and course of infection of pulmonary tuberculosis. 5 marks

Answer 21

• Bacteria transmitted in droplets
• Ingested by phagocytes
• Bacteria encases in wall
• Bacteria not active
• If immunosuppressed, bacteria activate
• Bacteria destroy alveoli
• (Leads to) fibrosis/scar tissue
• (Damage) leads to less diffusion
• damage allows bacteria) to enter the blood

Question 22

Emphysema is another disease of the lungs. People with emphysema may feel weak and tired. Explain why. 5 marks

Answer 22

• Alveoli break down
• Less surface area so less diffusion
• Loss of elastic tissue
• Reduced elasticity in the lungs
• Reduced diffusion gradient
• Less oxygen enters blood
• Less respiration