(a) Polio is a viral disease that can cause nerve damage in humans. In one area, polio vaccination began in 1957. Fig. 6.1 shows the number of cases of polio in this area between 1950 and 1970.
(i) Calculate the percentage change in the number of cases of polio between 1950 and 1952 in Fig. 6.1. Give your answer to two significant figures. Space for working.
(ii) Explain how vaccination causes the results shown between 1958 and 1970 in Fig. 6.1.
(iii) Explain why the polio vaccine does not protect you from other diseases.
(b) Blood clotting helps to prevent some infections. Outline how a blood clot is formed and how it can prevent infections.
(c) State the name of the component of blood responsible for transporting blood cells.
▶️ Answer/Explanation
Ans
(a)(i) – 64 (%) / 64 (%) decrease
Explanation: The percentage decrease is calculated using the formula: \[ \text{Percentage Change} = \left( \frac{\text{Final Value} – \text{Initial Value}}{\text{Initial Value}} \right) \times 100 \] From the graph, the number of cases in 1950 is ~1100 and in 1952 is ~400. Substituting: \[ \left( \frac{400 – 1100}{1100} \right) \times 100 = -63.63\% \approx -64\% \text{ (to 2 s.f.)} \]
(a)(ii) Vaccination introduces weakened/inactivated polio virus, stimulating an immune response. Lymphocytes produce antibodies and memory cells, providing long-term immunity. Herd immunity reduces transmission, leading to fewer cases.
(a)(iii) The polio vaccine is specific—antibodies produced only recognize polio antigens. Memory cells do not respond to other pathogens, so protection is limited to polio.
(b) Blood clotting involves fibrinogen conversion to fibrin, forming a mesh that traps platelets and seals wounds. The clot acts as a barrier, preventing pathogen entry.
(c) plasma
(a) HIV can be transmitted from mother to infant.
Describe how the risk of a mother transmitting HIV to their infant can be reduced.
(b) (i) Scientists investigated the effect of breastfeeding on the chance of infants getting an infection.
They studied two groups of 100 infants. One group was breastfed and one group was not breastfed.
Table 3.1 shows the data.
Using the data in Table 3.1, describe the effect of breastfeeding on the chance of getting an infection.
(ii) State the name of a blood cell involved in the immune response.
(iii) Describe how infants can gain passive immunity.
(iv) Describe how immunity gained by vaccination differs from passive immunity.
▶️ Answer/Explanation
(a) The risk of HIV transmission can be reduced by:
- Taking antiretroviral drugs during pregnancy and breastfeeding.
- Opting for a C-section delivery to avoid exposure during birth.
- Avoiding breastfeeding if safe alternatives are available.
Explanation: These measures minimize viral load and direct exposure, significantly lowering transmission risk.
(b)(i) Breastfeeding reduces infections:
- Gastroenteritis cases dropped from 18 (non-breastfed) to 4 (breastfed).
- Bronchitis decreased from 12 to 5 cases.
- No significant change in influenza/conjunctivitis rates.
Explanation: Breast milk contains antibodies that protect against specific pathogens, notably reducing gastrointestinal and respiratory infections.
(b)(ii) White blood cells (lymphocytes/phagocytes) are key to immune responses.
(b)(iii) Passive immunity in infants is gained through:
- Placental transfer of maternal antibodies during pregnancy.
- Breast milk, providing IgA antibodies post-birth.
Explanation: These antibodies offer temporary protection until the infant’s immune system matures.
3(b)(iv) Vaccination vs. passive immunity:
- Vaccination triggers active immunity (long-term, memory cell production).
- Passive immunity provides immediate but short-term protection (no memory cells).
Explanation: Active immunity involves the body’s own immune response, while passive immunity relies on externally acquired antibodies.