What role do characteristic cell-surface molecules, including proteins, play in immune recognition?
They help the immune system distinguish body cells from foreign or abnormal material.
AQA A-Level Biology - (7402) · 3.2.4
Revise AQA A-Level Biology - (7402) specification point 3.2.4, Cell recognition and the immune system, with free active-recall flashcards. Flip through the set or review every question and answer below.
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What role do characteristic cell-surface molecules, including proteins, play in immune recognition?
They help the immune system distinguish body cells from foreign or abnormal material.
What three kinds of material can surface molecules help the immune system identify?
Can toxins be recognised as foreign even though they are not cells?
Yes. Toxins can be recognised as foreign.
What is an antigen?
A molecule or molecular structure recognised by a specific antibody or lymphocyte receptor.
What can antigens on cells and other foreign material initiate?
An immune response.
What allows antigens to be specifically recognised?
Differences in their molecular structures.
How can pathogen antigens vary?
They can differ between pathogen variants and change over time.
Why may antibodies or memory cells against one pathogen variant be less effective against another?
Immune recognition is specific to antigen structure, which may differ between variants.
What can antigen variability allow to happen after a previous infection?
It can allow repeated disease.
How can antigen variability reduce vaccine protection?
Vaccine protection may not recognise all variants or may become less effective as antigens change.
How does a phagocyte take in a pathogen?
It recognises and engulfs the pathogen, enclosing it in a vesicle within the cell.
How is an engulfed pathogen destroyed inside a phagocyte?
Lysosomes fuse with the vesicle and release lysozymes, which digest and destroy the pathogen.
Why is phagocytosis considered a non-specific defence?
A phagocyte can engulf different kinds of pathogen rather than responding to only one specific antigen.
What is an antibody?
A specific protein that binds to an antigen.
What chains make up an antibody molecule, and what bonds join them?
Two heavy chains and two light chains, joined by disulfide bonds.
How do an antibody’s variable regions enable it to bind a particular antigen?
They form antigen-binding sites with shapes complementary to the antigen.
How do constant regions compare between antibodies?
They have a more similar structure between antibodies.
What is formed when an antibody binds to an antigen?
An antigen-antibody complex.
How can antibodies cause bacterial cells to agglutinate?
Their multiple binding sites allow them to link bacterial cells together.
How does agglutination affect the destruction of bacteria by phagocytes?
Agglutinated bacteria are more readily engulfed and destroyed by phagocytes.
What happens to specific B cells during a primary response to an antigen?
They are selected and divide.
What do plasma cells produce during an immune response?
Antibodies.
What long-lived cells develop from some activated cells during a primary immune response?
Memory cells.
How do memory cells respond to subsequent exposure to the same antigen?
They respond rapidly and produce many plasma cells.
How does the antibody concentration in a secondary response compare with that in a primary response?
It rises more quickly and generally reaches a higher level.
What can a secondary immune response do before significant symptoms develop?
Control the pathogen.
How does vaccination use antigens to stimulate an immune response?
It introduces antigens in a form intended to stimulate a response without causing the disease.
How does vaccination affect the immune response to later exposure to a pathogen?
It produces immunological memory, enabling a faster and stronger response.
How can vaccination affect disease in the vaccinated individual?
It can reduce the likelihood or severity of disease.
Why does herd immunity reduce pathogen transmission?
When a sufficiently large proportion of the population is immune, an infected person is less likely to encounter a susceptible person.
Who can be indirectly protected by herd immunity?
Susceptible individuals, including some who cannot be vaccinated.
What factors affect the effectiveness of herd immunity?
The level and distribution of immunity and how readily the pathogen spreads.
How does active immunity develop?
An individual's own immune system responds to an antigen, producing specific antibodies and memory cells.
What are the two ways active immunity can arise?
Through infection or vaccination.
What do memory cells enable in active immunity?
Long-lasting protection and a secondary response on re-exposure.
What is passive immunity?
Immunity gained by receiving antibodies made by another individual.
How quickly can passive immunity provide protection?
It can provide immediate protection.
Does receiving antibodies through passive immunity cause the recipient to produce memory cells?
No. Receiving the antibodies does not cause memory cells to be produced.
Why is protection from passive immunity temporary?
The transferred antibodies are broken down.
How does HIV infection affect helper T cells over time?
It reduces their number and function.
Why does the loss of helper T cells weaken immune responses?
Helper T cells stimulate other immune cells.
What is AIDS?
The advanced stage of HIV infection, in which severe immune deficiency allows opportunistic infections and other illnesses to cause serious symptoms.
Why do antibiotics not treat HIV or other viral infections?
Viruses lack the bacterial structures or processes targeted by antibiotics and reproduce using host-cell machinery.
Why might a person with AIDS be given antibiotics?
To treat a bacterial infection occurring alongside AIDS.
Why do monoclonal antibodies have the same antigen specificity?
They originate from a single clone of antibody-producing cells.
How can a monoclonal antibody direct a therapeutic drug towards target cells?
The drug is attached to an antibody that binds an antigen on the target cells.
How can a monoclonal antibody detect a particular antigen in a diagnostic sample?
It binds the antigen, and a detectable label or reaction reveals whether the target is present.
What does ELISA detect, and what specific interaction does it rely on?
It detects an antigen or antibody in a sample using specific antibody–antigen binding.
What is immobilised on a surface in an ELISA?
A target or binding molecule.
What is the role of the enzyme-linked antibody in an ELISA?
It reveals a bound target.
What is the purpose of washing during an ELISA?
To remove unbound material.
What happens after a substrate is added in an ELISA?
The enzyme produces a detectable colour change.
What indicates a positive ELISA result?
The appropriate colour change.
What is the role of controls in interpreting an ELISA result?
They provide a basis for interpreting the result.
How can a quantitative ELISA estimate the amount of target?
By measuring the amount of colour.
What should an ethical assessment of vaccines or monoclonal antibodies weigh and consider?
Weigh potential benefits against risks and consider whose interests are affected.
What four ethical considerations apply to vaccines and monoclonal antibodies?
Why can vaccination decisions affect both personal autonomy and population health?
Reduced transmission can benefit people beyond the vaccinated individual, so an individual’s choice can affect others’ health.
What access issue can arise with monoclonal antibody treatments?
Costly treatments may not be accessible fairly.
What ethical concern about animals can arise with monoclonal antibodies?
Animals may be used in their research or production.
What should a well-reasoned ethical judgement make explicit and acknowledge?
It should make its reasons explicit and acknowledge relevant uncertainty and competing interests.
What is the central question when evaluating a method used to study vaccines or monoclonal antibodies?
Whether the method supports the conclusions drawn from its results.
Which three features of study design should be checked when evaluating the groups or samples used?
The comparison or control group, sample size, and selection of participants or samples.
Which three features should be checked when assessing the reliability of study results?
Possible confounding variables, measurement methods, and whether results can be repeated.
What can blinding and random allocation reduce when appropriate to a study?
Bias.
What three perspectives should be considered when interpreting data on vaccines or monoclonal antibodies?
What distinction should a sound conclusion make about study results?
It should distinguish what the results show from claims the method or data cannot establish.
What limitations should a sound conclusion identify?
Limitations affecting confidence in the results or their generalisation.