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Infection and Response

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Diagram of an antibody binding to antigens

Antibodies are specific to one antigen shape.

Key Facts

  • Antibiotics treat bacterial infections, not viral infections.
  • Monoclonal antibodies can target specific antigens.
  • Overuse of antibiotics increases resistant bacteria.
  • White blood cells include phagocytes and lymphocytes.

Topics Covered

Pathogens and Disease

What you need to know

  • Pathogens include bacteria, viruses, fungi, and protists.
  • Communicable diseases spread via air, water, contact, or vectors.

Exam Tips

  • State the pathogen type first, then the method of spread.

Human Defence Systems

What you need to know

  • Skin, mucus, and cilia act as physical barriers.
  • White blood cells engulf pathogens and produce antibodies.

Exam Tips

  • Use the words "antigen" and "antibody" in longer answers.

Immune Response and Vaccination

What you need to know

  • White blood cells engulf pathogens or produce antibodies.
  • Vaccination exposes antigens to trigger memory cells.

Exam Tips

  • Use the terms antigen and antibody in 4-6 mark questions.

Plant Disease and Defences

What you need to know

  • Plant diseases are caused by bacteria, viruses, and fungi.
  • Plants defend using physical barriers and chemical defences.

Exam Tips

  • Give a named example such as black spot or mosaic virus.

Key Terms

Pathogen

A microorganism that causes disease.

Antibody

A protein that binds to specific antigens.

Vector

An organism that carries a pathogen between hosts.

Communicable

A disease that can be spread between organisms.

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Common Exam Questions

Explain how a vaccine protects against disease.

4 marksmediumPaper 1

Model Answer

Vaccines contain antigens that trigger white blood cells to make antibodies and memory cells. If the pathogen returns, memory cells respond quickly to destroy it.

What examiners want to see

  • Mention antigens.
  • Mention memory cells.
  • Link to faster response on reinfection.

Explain how antibiotic resistance develops.

4 marksmediumPaper 1

Model Answer

Mutations create resistant bacteria. Antibiotics kill non-resistant bacteria, leaving resistant ones to survive and reproduce.

What examiners want to see

  • Mention mutation.
  • Link to survival and reproduction of resistant bacteria.

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