AQA GCSE (9-1) Biology: Infection and Response

Key Takeaways for Infection and Response

1. Pathogens and Diseases

Key Concepts:

• 4 Types of Pathogens:
  1. Viruses (e.g., measles, HIV).
  2. Bacteria (e.g., salmonella, gonorrhoea).
  3. Fungi (e.g., athlete’s foot).
  4. Protists (e.g., malaria).
• Transmission Examples:
  • Airborne: Measles (droplets from sneezing).
  • Waterborne: Cholera (contaminated water).
  • Vectors: Malaria (mosquitoes).
  • Direct Contact: Gonorrhoea (sexual transmission).

Key Rules:

• Viruses replicate inside host cells; bacteria reproduce via binary fission.
• Antibiotics work on bacteria/fungi, not viruses.

Tips:

• Use flashcards to memorise examples of diseases and their pathogens.
• Mnemonic: VBF-P (Viruses, Bacteria, Fungi, Protists).

2. Human Defence Systems

Three Lines of Defence:

1. First Line (Physical/Chemical Barriers):
   • Skin, stomach acid, lysozymes (tears/saliva), mucus and cilia in the trachea.
2. Second Line (Phagocytosis):
   • Phagocytes engulf pathogens. Process:
     • Engulf → Enzymes digest → Antigens displayed.
3. Third Line (Lymphocytes):
   • Antibodies produced by lymphocytes bind to antigens.
   • Memory cells provide long-term immunity.

Key Terms:

• Antigen: Protein on pathogen’s surface.
• Antibody: Y-shaped protein that neutralises pathogens.

Tips:

• Draw a diagram of phagocytosis and antibody-antigen binding.
• Exam question focus: Explain why memory cells prevent reinfection (e.g., faster antibody production).

3. Vaccination

How Vaccines Work:

• Contain dead/inactive pathogens with antigens.
• Triggers primary immune response (memory cells created).
• Booster shots strengthen immunity.

Key Concepts:

• Herd Immunity: High vaccination rates protect unvaccinated individuals.
• Example: MMR vaccine (measles, mumps, rubella).

Exam Tip:

• Link vaccination to specific immune response (lymphocytes and antibodies).

4. Antibiotics and Drug Development

Antibiotics:

• Penicillin (discovered by Fleming) weakens bacterial cell walls.
• Antibiotic Resistance: Caused by overuse/misuse (e.g., not finishing a course).

Painkillers vs. Antibiotics:

• Painkillers (e.g., aspirin) relieve symptoms but don’t kill pathogens.
• Antiseptics kill pathogens on surfaces; antibiotics work internally.

Drug Development Stages:

1. Preclinical Testing: Lab/animal trials.
2. Clinical Trials:
   • Phase 1: Safety on healthy volunteers.
   • Phase 2: Efficacy on patients.
   • Phase 3: Large-scale testing.
3. Double-Blind Trials: Patients/doctors unaware of placebo/drug allocation.

Math Tip:

• Bacterial growth: If a culture divides every 30 minutes, population after 3 hours = Initial×2(180/30)=Initial×26Initial×2(180/30)=Initial×26.

5. Monoclonal Antibodies (Higher Tier)

Production:

1. Antigen injected into mouse → spleen cells produce antibodies.
2. Fuse spleen cells with myeloma cells → hybridoma cells.
3. Hybridomas cloned to produce identical antibodies.

Uses:

• Pregnancy tests: Detect HCG hormone.
• Cancer treatment: Deliver drugs directly to cancer cells.

Limitations:

• Side effects (e.g., fever, allergic reactions).

Exam Tip:

• Explain why monoclonal antibodies are “specific” (bind to one antigen).

6. Practical Skills

Aseptic Techniques:

• Flame inoculating loops, lid agar plates, sterilise equipment.
• Zone of Inhibition: Measure effectiveness of antiseptics using Area=πr2Area=πr2.

Example Experiment:

• Testing antibiotic resistance: Larger zones = more effective.

Common Mistakes to Avoid:

• Confusing antibiotics (kill bacteria) with antiseptics (surface disinfectants).
• Stating viruses are “alive” (they don’t carry out all life processes).

Revision Tricks:

• Use flowcharts for immune response stages.
• Practice data analysis (e.g., interpreting vaccine efficacy graphs).

Need More Help?

• Watch: Animations on phagocytosis/vaccination.
• Quiz Yourself: Past paper questions on antibiotic resistance.

50 GCSE Infection and Response Questions

Section 1: Pathogens and Diseases

1. Name four types of pathogens and give an example of a disease caused by each.
2. Explain why viruses are not classified as living organisms.
3. How is cholera transmitted?
4. Describe two symptoms of malaria.
5. What is a vector? Give an example.
6. How does athlete’s foot spread?
7. Why is gonorrhoea becoming harder to treat?
8. Compare how viruses and bacteria reproduce.
9. State two ways the spread of malaria can be reduced.
10. What is the role of lysozymes in the human body?

Section 2: Human Defence Systems

11. Outline the three lines of defence against pathogens.
12. Describe how cilia and mucus protect the body.
13. Explain the process of phagocytosis.
14. What is the difference between antigens and antibodies?
15. How do memory lymphocytes provide long-term immunity?
16. Why does stomach acid act as a chemical barrier?
17. What happens when the skin is cut?
18. How do antitoxins neutralise harmful substances?
19. Explain why the third line of defence is described as “specific”.
20. What role do platelets play in wound healing?

Section 3: Vaccination

21. Define vaccination and explain how it works.
22. What is herd immunity?
23. Why are booster injections given?
24. Name the diseases prevented by the MMR vaccine.
25. Describe the primary and secondary immune responses.
26. How does a vaccine differ from an antibiotic?
27. Why might someone still get ill after receiving a vaccine?
28. Explain the term immunisation.
29. What is the significance of antigens in vaccines?
30. How do vaccines reduce the spread of diseases in a population?

Section 4: Antibiotics and Drug Development

31. Who discovered penicillin, and how was it discovered?
32. Why are antibiotics ineffective against viral infections?
33. Explain the term antibiotic resistance.
34. What is the difference between antiseptics and antibiotics?
35. Describe the three phases of clinical trials.
36. What is a double-blind trial, and why is it used?
37. How does aspirin differ from paracetamol?
38. Why is it important to finish a course of antibiotics?
39. What is a placebo, and how does it affect trial results?
40. Calculate the bacterial population after 4 hours if bacteria divide every 20 minutes.

Section 5: Monoclonal Antibodies (Higher Tier)

41. Define monoclonal antibodies.
42. Describe how hybridoma cells are produced.
43. Give two uses of monoclonal antibodies in medicine.
44. How are monoclonal antibodies used in pregnancy tests?
45. Why are monoclonal antibodies described as specific?
46. What are the limitations of using monoclonal antibodies?
47. Explain how Herceptin treats breast cancer.
48. What is the role of myeloma cells in antibody production?
49. Why might monoclonal antibodies cause side effects?
50. Name one diagnostic test that uses monoclonal antibodies.

Answers

Section 1: Pathogens and Diseases

1. Viruses (e.g., measles), bacteria (e.g., salmonella), fungi (e.g., athlete’s foot), protists (e.g., malaria).
2. Viruses cannot carry out all life processes (e.g., respiration) and require a host to replicate.
3. Cholera spreads via contaminated water.
4. Fever, vomiting, headaches, and fatigue.
5. A vector is an animal that transmits pathogens (e.g., mosquitoes transmit malaria).
6. Through direct contact in communal areas (e.g., swimming pools).
7. Due to antibiotic-resistant strains of Neisseria gonorrhoeae.
8. Viruses replicate inside host cells; bacteria reproduce via binary fission.
9. Use mosquito nets, destroy stagnant water, and take antimalarial drugs.
10. Lysozymes in tears/saliva break down bacterial cell walls.

Section 2: Human Defence Systems

11. 1st: Physical/chemical barriers; 2nd: Phagocytosis; 3rd: Antibodies/lymphocytes.
12. Cilia waft mucus (trapping pathogens) to the throat to be swallowed.
13. Phagocytes engulf pathogens, digest them with enzymes, and display antigens.
14. Antigens are pathogen surface proteins; antibodies bind to them.
15. Memory lymphocytes recognise antigens and trigger a faster response.
16. Stomach acid kills pathogens ingested via food/water.
17. Platelets form a scab; skin regrows underneath.
18. Antitoxins bind to toxins, neutralising their effects.
19. The third line targets specific pathogens (via antibodies).
20. Platelets clot blood to seal wounds.

Section 3: Vaccination

21. Vaccines contain antigens to trigger immune memory without causing disease.
22. Herd immunity occurs when most are vaccinated, reducing disease spread.
23. Boosters refresh memory cell production.
24. Measles, mumps, rubella.
25. Primary: Slow antibody production; Secondary: Rapid, stronger response.
26. Vaccines prevent disease; antibiotics treat bacterial infections.
27. They might encounter a new pathogen strain.
28. Immunisation is becoming immune via vaccination or infection.
29. Antigens trigger antibody production.
30. Vaccines reduce transmission rates by limiting susceptible hosts.

Section 4: Antibiotics and Drug Development

31. Alexander Fleming discovered penicillin after noticing fungus inhibited bacterial growth.
32. Viruses lack cell structures (e.g., cell walls) targeted by antibiotics.
33. Resistance occurs when bacteria evolve to survive antibiotic exposure.
34. Antiseptics kill pathogens on surfaces; antibiotics work internally.
35. Phase 1: Safety; Phase 2: Efficacy; Phase 3: Large-scale testing.
36. Neither patients nor doctors know who receives the drug/placebo to avoid bias.
37. Aspirin reduces inflammation; paracetamol only relieves pain/fever.
38. To ensure all bacteria are killed, preventing resistance.
39. A placebo is a fake treatment; it tests psychological effects.
40. Population=2(240/20)=212=4096 bacteriaPopulation=2(240/20)=212=4096 bacteria.

Section 5: Monoclonal Antibodies

41. Identical antibodies produced by cloned hybridoma cells.
42. Mouse spleen cells (antibody-producing) fused with myeloma cells (cancerous).
43. Diagnostic tests (e.g., pregnancy) and cancer treatment.
44. Antibodies bind to HCG hormone in urine, causing a colour change.
45. They bind to one specific antigen.
46. Side effects include allergic reactions and high production costs.
47. Herceptin blocks receptors on cancer cells, stopping growth.
48. Myeloma cells allow continuous division of hybridomas.
49. They may trigger immune responses against mouse proteins.
50. HIV/AIDS diagnostic tests.

Need More Practice? Try drawing diagrams for processes like phagocytosis or monoclonal antibody production!