OCR GCSE Biology B (Twenty First Century)
OCR GCSE Biology B B2.2 How do organisms protect themselves against pathogens? Exam Questions
Free OCR GCSE Biology B exam questions for B2.2 How do organisms protect themselves against pathogens?, with a mark scheme for every pack. Covers non-specific defences, skin, mucus and cilia, the immune system, phagocytes, antigens, antibodies, memory cells and plant defences.
B2.2 How do organisms protect themselves against pathogens? exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR GCSE Biology B B2.2 How do organisms protect themselves against pathogens?
B2.2 explains how humans and plants defend themselves against pathogens. You need to describe the physical and chemical barriers that stop pathogens entering the body, then the specific immune response, where lymphocytes produce antibodies that match antigens on a pathogen. Memory cells explain why a second infection is dealt with faster, which links directly to vaccination in B2.3. Plants have their own physical and chemical defences. Examiners like graphs of antibody concentration against time, and they expect precise terms: antigen, antibody, lymphocyte, phagocyte and memory cell.
What you need to know
- Physical and chemical barriers The skin is a barrier and produces antimicrobial secretions. Mucus traps pathogens in the airways and cilia sweep it away; stomach acid kills pathogens in food; tears contain enzymes that kill bacteria. Platelets help clot blood to seal wounds.
- Phagocytes Phagocytes are white blood cells that engulf and digest pathogens. This is a non-specific response.
- Antigens and antibodies Antigens are molecules on the surface of a pathogen. Lymphocytes make antibodies with a shape complementary to one specific antigen; antibodies bind to it, clumping pathogens or marking them for destruction.
- Memory cells After an infection, memory lymphocytes remain in the blood. On reinfection they make antibodies faster and in greater quantities, so the pathogen is destroyed before symptoms develop. This is immunity.
- Primary and secondary response The primary response is slow and small; the secondary response is fast and large. Graphs of antibody level show a steeper, higher second peak.
- Plant defences Plants use cellulose cell walls, a waxy cuticle and bark as physical barriers, and produce antimicrobial chemicals. Some have mechanical defences such as thorns.
Common mistakes in B2.2 How do organisms protect themselves against pathogens?
- Saying antibodies kill pathogens on their own. Antibodies bind to antigens; this clumps pathogens and helps phagocytes destroy them.
- Writing that white blood cells eat or kill antigens. Antigens are markers on the pathogen; the whole pathogen is engulfed.
- Stating that antibodies are specific to a disease in general. Each antibody is specific to one antigen shape.
- Saying memory cells prevent infection. Pathogens still enter, but memory cells allow a quick response before symptoms appear.
- Saying cilia trap pathogens. Mucus traps them; cilia move the mucus away.
Try three B2.2 How do organisms protect themselves against pathogens? exam-style questions
1. State the function of a phagocyte. (1 mark)
Show the mark scheme answer
To engulf and digest pathogens.
2. Explain why antibodies made against the measles virus do not protect against the chickenpox virus. (2 marks)
Show the mark scheme answer
Antibodies are specific to one antigen; the chickenpox virus has antigens of a different shape so the measles antibodies cannot bind to them.
3. Explain why a person who has had chickenpox usually does not get ill from it a second time. (4 marks)
Show the mark scheme answer
During the first infection lymphocytes make antibodies against the chickenpox antigens; memory cells remain in the blood; on reinfection memory cells recognise the antigen and produce antibodies more rapidly and in larger amounts; the pathogen is destroyed before it can cause symptoms.
B2.2 How do organisms protect themselves against pathogens? FAQs
What does OCR GCSE Biology B B2.2 cover?
It covers human non-specific defences, the specific immune response involving antigens, antibodies and memory cells, and the defences plants use against pathogens.
Which paper is B2.2 examined in?
J257 has two papers at each tier, Breadth in Biology and Depth in Biology, and content from any chapter, including B2, can be assessed on either one. Expect it to be linked to ideas about science and to other chapters.
How do I interpret antibody graphs in B2.2?
Compare the speed of rise and the peak concentration of the first and second responses, quote values from the graph, and link the faster, larger second response to memory cells.
