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Edexcel IGCSE Biology 2.63B vaccination and memory cells

Practise vaccination questions by explaining memory-cell formation, interpreting antibody graphs and evaluating vaccine data in disease contexts.

Syllabus
First assessment 2019
Course
Biology 4BI1

Exam points

  • Explain how dead or weakened pathogens trigger lymphocytes and memory-cell formation.
  • Use antibody graphs to compare primary and secondary responses after vaccination.
  • Evaluate vaccine effects from data on antibodies, disease cases, immunity or infection spread.

2.63B Vaccination and memory cells question 1

[Maximum number: 3]

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Schistosomiasis

Schistosomiasis is an infection caused by a parasitic worm called a schistosome. The immature or larvae of the worm live in rivers and lakes in tropical parts of the world.

The diagram shows the life cycle of the schistosome worm.

Figure for Question 2.63B Vaccination and memory cells question 1 — Edexcel IGCSE Biology

5 Some people in tropical parts of the world use water from these rivers and lakes for their daily lives. These people risk infection because the larvae burrow into their skin. The larvae are then transported to other parts of the body where they damage organs such as the kidneys, intestines, lungs and brain. The larvae develop into adult worms.

10 The adult worms lay eggs in the human body. Some of these eggs are destroyed by the immune system, but most eggs survive. These eggs can get into water if faeces or urine from infected people pass into rivers or lakes. In the water, the eggs develop into small larvae which grow inside freshwater snails. Larvae are released from the snails and infect any person they contact. These larvae develop into adult worms inside the human body.

Doctors diagnose schistosomiasis when they find eggs in the faeces or urine of infected people. Infected people also have blood cells in their urine and antibodies for the pathogen in their blood.

At present, the drug praziquantel is used to kill the worms. A dose of 0.040 g per kg of body mass is usually effective. With no treatment, affected organs can be permanently damaged, leading to death. It is estimated that 240 million people (in the world) have schistosomiasis. Every year 8×10−48 \times 10^{-4} per cent of infected people die from the disease.

A vaccine is being developed using a plasmid. The plasmid has DNA inserted that makes a protein found on the body surface of the adult schistosome worm.

In one investigation, a vaccine made using the DNA plasmid was given to a group of infected people. The results showed a mean number of 21.53 worms per person in this group. In the control group, a mean number of 40.53 worms per person was found.

Explain how a vaccine could protect people from schistosomiasis (lines 24 to 25).

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