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Module 4: Biodiversity, evolution and disease
Quick questions on The immune system and vaccination: lymphocytes, antibodies, immunity types and antibiotic resistance - OCR A-Level Biology A
6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are antibodies?Show answer
An antibody is a globular protein (immunoglobulin) with quaternary structure: two heavy and two light polypeptide chains arranged in a Y shape, held by disulfide bonds. The variable region at the tips has a specific shape complementary to one antigen, so each antibody binds only one antigen, forming an antigen-antibody complex. The constant region is the same within a class of antibody and determines its function (for example binding to phagocytes). Antibodies work by agglutination (clumping pathogens), acting as opsonins (marking pathogens for phagocytosis), and neutralising toxins.
What is types of immunity?Show answer
Active immunity makes its own antibodies and memory cells (slow but long-lasting); passive immunity uses ready-made antibodies (immediate but short-lived, no memory).
What is antibiotic resistance?Show answer
Antibiotics kill bacteria or inhibit their growth but do not affect viruses. Resistance evolves by natural selection: a random mutation gives a bacterium resistance; when the antibiotic is present it acts as a selection pressure, killing non-resistant bacteria while resistant bacteria survive and reproduce, passing on the resistance allele (often on plasmids). Over generations the allele frequency increases. Overuse and misuse accelerate this, which is why finishing prescribed courses and reserving antibiotics for bacterial infections matter.
What is q1?Show answer
Describe the role of T helper cells in the specific immune response. [2 marks]
What is q2?Show answer
Explain why passive immunity does not give long-term protection. [2 marks]
What is q3?Show answer
State what is meant by herd immunity. [1 mark]
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