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1. 1993/I/2aiii

Certain cells in the lymphatic system are important in body defence. Briefly describe how these cells carry

out this function. (3 marks)

2. 1995/I/2bAbout 200 years ago, many people died of an infectious disease called smallpox. If a patient suffers from

smallpox, a lot of small boils will appear on the skin. A British doctor, Edward Jenner, noticed that

milkmaids often caught a similar but mild disease called cowpox. However, they never seemed to catch

small pox.

The following diagrams show two consecutive experiments performed by Jenner :

(i) With reference to the first experiment, explain why James caught cowpox and in a few days he was

well again. (4 marks)

(ii) With reference to the second experiment, explain why James did not catch smallpox. (4 marks)

(iii) At the end of the second experiment, would James become immune to other infectious diseases ?

Why ? (2 marks)

3. 1996/I/2bii

Explain the following :

Vaccination can protect our body against certain diseases. (4 marks)

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4. 1998/I/2b

Hepatitis B is a disease of the liver caused by a virus. Three members of a family, P, Q and R, took a blood

test to find out if they are immune to this disease. The results of the blood test are shown in the table below :

P Q R

Hepatitis B antigen in the blood Absent Absent PresentLevel of antibody against hepatitis B in the blood

(unit per dm3)

0 297 0

(i) (1) P was advised to have a hepatitis B vaccination. Explain how P could become immune against

the disease after vaccination. (4 marks)

(2) Would this vaccination allow P to become immune to other types of hepatitis ? Why ?

(2 marks)

(ii) Both Q and R have not received any hepatitis B vaccination before. Suggest a reason to explain the

difference in their blood test results. (2 marks)

(iii) Hepatitis B is transmitted through contact with the body fluid of an infected person. Apart from

vaccination, suggest twomeasures that can prevent the transmission of this disease. (2 marks)

5. 2003/I/4c

Cholera is a human disease caused by a type of bacteria. It is transmitted through contaminated water and

food. A vaccine against this disease is made up of killed cholera bacteria. To study the effectiveness of the

vaccine, a mouse was first injected with the vaccine and then with live cholera bacteria 20 days later. During

the study, the mouse showed no sign of cholera. The changes in the antibody level in the plasma of the

mouse are shown in the graph below :

(i) Explain the rise in the antibody level between day 5 and day 7. (2 marks)

(ii) State twodifferences between the patterns of antibody production as induced by the two injections.

Suggest an explanation for such differences. (5 marks)

(iii) People may be infected with cholera through eating contaminated seafood. Besides vaccination,

suggest twoways to reduce the risk of cholera infection through eating seafood. (2 marks)

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6. 2004/I/1ciii,iv

(iii) One method to confirm a patient is infected with the SARS virus is to test for the presence of

antibodies against this virus in the patient's blood.

Explain why these antibodies will be produced by a SARS patient. (2 marks)

(iv) Suggest a method that can help the body develop immunity against SARS. Explain how theimmunity is developed. (4 marks)

7. 2007/I/7b

Antibiotic is a drug commonly used to treat bacterial infections. In recent years, there have been more

reported cases of resistant forms of bacteria strains found in hospitals. The graph below shows the

percentage of the resistant form in a particular bacterial population and the amount of antibiotics used in one

particular hospital each year from 1995 to 2004:

(i) Explain why the increased amount of antibiotics used will lead to the rise in the percentage of the

resistant form in the bacterial population. (4 marks)

(ii) Some patients in hospitals will have a higher death rate if infected with resistant forms of bacteria.

Suggest onegroup of these patients and give an explanation. (2 marks)

(iii) If you were a doctor, suggest twopractices that you could adopt to slow down the rise of the resistant

forms of bacteria. (2 marks)

HKCEE BIOLOGY | 6.4 Defence against diseases | P.3