Immunity: Biology 9700 (Cambridge International AS & A Level)
Syllabus 11.1, 11.2 · Strand 4 Health, disease and immunity
- Questions
- 10
- Total marks
- 61
- Tier mix
- 10 Core
0 of 10 questions completed
Syllabus coverage
- 11.1 8 questions completed
- 11.2 3 questions completed
The immune system defends the body against pathogens and remembers past infections, and this topic (syllabus 11.1 and 11.2) explains how its cells and molecules achieve this. The first line of cellular defence is phagocytosis, in which macrophages and neutrophils engulf and digest invaders in a non-specific response. The specific response depends on recognising antigens, the molecules that mark a cell as self or non-self. During a primary immune response, macrophages, B-lymphocytes that become antibody-secreting plasma cells, and T-lymphocytes acting as helper and killer cells work together to destroy the pathogen. Memory cells then remain, allowing a faster and larger secondary response and giving long-term immunity.
The topic also relates the structure of an antibody to its function and outlines how the hybridoma method produces monoclonal antibodies for use in diagnosis and treatment. Finally, it distinguishes the different kinds of immunity: active immunity, in which the body makes its own antibodies, versus passive immunity, in which antibodies are received ready-made; and natural immunity, gained through everyday exposure, versus artificial immunity, gained through medical intervention. This leads to vaccination, where harmless antigens prime the immune system, and to how vaccination programmes can control the spread of infectious disease across a population.
The exam-style questions below are original, written to match these objectives, each with a full worked solution so you can check your reasoning step by step.
Question 1
A neutrophil in an infected wound comes into contact with a bacterium and destroys it by phagocytosis.
Which statement correctly describes how the neutrophil destroys the bacterium?
Question 2
A patient recovering from a bacterial infection has antibodies against the bacterium circulating in their blood plasma.
(a) Describe the structure of an antibody molecule. [3]
(b) Using your answer to (a), explain why a particular antibody will bind to only one specific type of antigen. [2]
(c) Describe two different ways in which these antibodies could help to destroy or remove the bacterium from the patient's body. [4]
Question 3
A person is infected for the first time with a bacterium that is able to survive and multiply inside body cells. Doctors monitor the concentration of antibodies against this bacterium in the person's blood plasma. Several weeks after recovering, the same person is accidentally exposed to the same bacterium a second time, and their antibody concentration is monitored again.
(a) Describe how the pattern of antibody concentration in the blood plasma after the second exposure would differ from the pattern after the first exposure, and explain these differences in terms of B-lymphocytes. [4]
(b) Name the type of cell that B-lymphocytes differentiate into once activated, and state what this cell type produces. [2]
(c) T-lymphocytes are also essential in defending the body against this bacterium. Describe the different roles of T-helper cells and T-killer (cytotoxic T) cells in this response. [4]
Question 4
A new viral disease is spreading in a country. Public health officials introduce a vaccination programme, and doctors also give some newborn babies antibodies against the virus obtained from their mother's breast milk.
(a) State the type of immunity a baby gains from antibodies in its mother's breast milk. In your answer, use both of the terms active/passive and natural/artificial, with a brief justification for each. [2]
(b) Explain how vaccinating an older child against the virus can give them long-term protection, referring to memory cells in your answer. [3]
(c) Explain why the immunity gained from breast milk in (a) does not give the baby long-term protection, unlike the immunity gained from vaccination in (b). [2]
(d) After several years, a high percentage of the country's population has been vaccinated against the virus. Unvaccinated individuals in this population also become much less likely to catch the virus. Explain this observation. [3]
Question 5
Monoclonal antibodies are used in many diagnostic tests and treatments, for example in pregnancy testing kits and in some cancer treatments.
Which statement correctly describes monoclonal antibodies?
Question 6
A macrophage engulfs a virus particle by phagocytosis and partially digests it inside a phagolysosome.
Which statement correctly describes what the macrophage does next to help trigger the specific immune response?
Question 7
Before a person is ever exposed to a particular new pathogen, their body already contains an enormous variety of different B-lymphocytes, each with a slightly different-shaped receptor (a form of antibody) on its cell-surface membrane.
(a) Explain why the body already contains so many different types of B-lymphocyte before ever encountering this new pathogen. [2]
(b) When the new pathogen enters the body, describe how one specific type of B-lymphocyte is selected and increases greatly in number. Your answer should refer to clonal selection and clonal expansion. [4]
(c) State two types of cell that these activated B-lymphocytes differentiate into, and give the function of each. [3]
Question 8
A person bitten by a venomous snake is given an injection of antivenom. The antivenom contains antibodies against the snake's venom that were produced in the blood of another animal, such as a horse, and then extracted and purified for medical use.
Which type of immunity does the bitten person gain from this injection?
Question 9
Clostridium tetani bacteria can infect a deep wound and release a toxin that damages the nervous system, causing the disease tetanus. A patient who has never been vaccinated against tetanus receives a deep, dirty wound. Doctors immediately give the patient an injection of tetanus antitoxin, which contains ready-made antibodies against the toxin, produced in another organism. They also recommend that the patient later be vaccinated with tetanus toxoid, which is an inactivated (harmless) form of the toxin.
(a) Explain how the antibodies in the antitoxin injection protect the patient from the harmful effects of the toxin. Use the term neutralisation in your answer. [3]
(b) State and explain the type of immunity provided by the antitoxin injection. [2]
(c) Explain why vaccination with tetanus toxoid, unlike the antitoxin injection, can give the patient long-term protection against tetanus. [3]
(d) Suggest one reason why doctors give the patient both the antitoxin injection and, later, the toxoid vaccine, rather than the toxoid vaccine alone. [2]
Question 10
The specific immune response can be divided into two cooperating parts: humoral immunity and cell-mediated immunity.
(a) State which type of lymphocyte is mainly responsible for humoral immunity, and outline how this type of immunity helps to destroy or remove pathogens. [3]
(b) State which type of lymphocyte is mainly responsible for cell-mediated immunity, and outline how this type of immunity destroys pathogens. [3]
(c) A virus enters a person's body and then enters and replicates inside their body cells. Explain why cell-mediated immunity, rather than humoral immunity alone, is especially important once this virus is inside the body cells. [3]