How does the immune system destroy pathogens, and how do vaccines and antibodies protect us?
The role of white blood cells in the immune response (phagocytosis, antibodies and antitoxins), how vaccination produces immunity and protects populations, the action and limits of antibiotics including resistance, and the production and uses of monoclonal antibodies.
A focused answer to the OCR Gateway GCSE Biology A topic B6 on the immune system, covering white blood cells and phagocytosis, antibodies and antitoxins, how vaccination produces immunity and protects populations, antibiotics and resistance, and the production and uses of monoclonal antibodies.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
OCR wants you to explain how white blood cells fight pathogens, how vaccination produces immunity and protects a population, how antibiotics work and why resistance is a problem, and (at Higher tier) how monoclonal antibodies are produced and used.
The immune response and white blood cells
If a pathogen gets past the non-specific barriers, the immune system destroys it, mainly using white blood cells. There are two key actions:
- Phagocytosis. Some white blood cells (phagocytes) engulf and digest pathogens, breaking them down. This is non-specific, working against any pathogen.
- Antibodies and antitoxins. Other white blood cells (lymphocytes) produce antibodies, proteins that lock onto the specific antigens (markers) on the surface of a particular pathogen, clumping them together and marking them for destruction. Lymphocytes also produce antitoxins that neutralise the toxins released by some bacteria.
Vaccination
When a vaccine is given, white blood cells make the correct antibodies and, crucially, memory cells. If the live pathogen is met later, the memory cells produce the right antibodies quickly and in large numbers, destroying it before the person becomes ill (immunity).
If a large enough proportion of a population is vaccinated, the pathogen cannot spread easily because there are too few susceptible people to pass it on, so even those who are not vaccinated are protected. This is herd immunity. It protects people who cannot be vaccinated, such as very young babies or people who are ill.
Antibiotics and resistance
Antibiotics (such as penicillin) kill bacteria inside the body and have greatly reduced deaths from bacterial disease. But they do not kill viruses, because viruses live inside the body's own cells.
Overusing or misusing antibiotics has led to antibiotic-resistant bacteria (such as MRSA) by natural selection: a chance mutation makes a bacterium resistant, the antibiotic kills the rest, and the resistant survivor reproduces and spreads. To slow this, doctors prescribe antibiotics only when needed, and patients should finish the full course so all the bacteria are killed.
Monoclonal antibodies (Higher tier)
They are produced by:
- Injecting a mouse with the antigen, so its lymphocytes make the desired antibody.
- Removing those lymphocytes and fusing them with a tumour (myeloma) cell to make a hybridoma cell, which both divides rapidly and makes the antibody.
- Cloning the hybridoma cells and collecting the identical (monoclonal) antibodies they produce.
Uses include pregnancy tests (detecting a hormone in urine), detecting or measuring specific molecules such as pathogens or hormones in blood, identifying or locating specific cells (such as cancer cells), and delivering drugs directly to cancer cells while sparing healthy ones.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20186 marksExplain how vaccination protects an individual from a disease, and how vaccinating a large proportion of a population protects those who are not vaccinated.Show worked answer →
A 6-mark extended response, marked on levels.
Individual: a vaccine contains a dead or inactive (weakened) form of a pathogen, or its antigens. When injected, the antigens are recognised by white blood cells (lymphocytes), which respond by producing the correct antibodies, and importantly memory cells are made. If the live pathogen is met later, the memory cells let the body produce the right antibodies quickly and in large numbers, destroying the pathogen before the person becomes ill (immunity).
Population: if a large enough proportion of the population is vaccinated, the pathogen cannot spread easily because there are few susceptible people to pass it on, so even unvaccinated people are unlikely to catch it. This is herd immunity. Top answers name antigens, antibodies and memory cells, explain the faster secondary response, and explain herd immunity.
OCR 20214 marksDescribe how monoclonal antibodies are produced, and give one use of monoclonal antibodies. This is a Higher tier question.Show worked answer →
A Higher tier B6 question on monoclonal antibodies.
Production: a mouse is injected with the antigen so that its lymphocytes make the desired antibody. These lymphocytes are removed and fused with a tumour (myeloma) cell to make a hybridoma cell, which can both divide rapidly and produce the antibody. The hybridoma cells are cloned, and the identical (monoclonal) antibodies they make are collected and purified.
Use (any one): in pregnancy tests (to detect a hormone in urine); to detect or measure specific molecules such as pathogens, hormones or chemicals in blood; to identify or locate specific cells, for example cancer cells; and to deliver drugs directly to cancer cells. Reward the steps antigen into mouse, lymphocytes fused with tumour cells to form hybridomas, cloned to make identical antibodies, plus one valid use.
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