AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), June 2025: Question 2

✅ Correct Answer

Any one of the following:

• Direct physical contact / touch (e.g. touching blisters or contaminated skin)
• Touching contaminated surfaces
• Inhaling airborne droplets from coughs or sneezes

🧠 Exam Technique

Look at the clue in the question stem: "blisters on the skin". Direct physical touch or touching fluid from the blisters is the most direct application here.

❌ Common Errors

• Writing "sexual contact" (explicitly ignored by the mark scheme).
• Writing vague terms like "air" without specifying airborne droplets or coughs/sneezes.

✅ Correct Answer

• Chickenpox is caused by a virus (not a bacterium).
• OR: Antibiotics only kill/treat bacteria.

💡 Key Knowledge

Viruses reproduce inside host cells. Antibiotics target bacterial structures (such as cell walls or bacterial ribosomes) and have no effect on viruses. Treating viral infections with antibiotics also increases the risk of antibiotic resistance in harmless bacteria.

❌ Common Errors

• Stating that "the pathogen is resistant to antibiotics" — chickenpox is a virus, so it was never susceptible in the first place!
• Confusing antibodies with antibiotics.

✅ Correct Answer

Any one of the following:

• Dead or inactive / weakened pathogen (or virus / microorganism)
• Antigens (or viral proteins) from the pathogen
• mRNA from the pathogen

🧠 Exam Technique

Never just write "the pathogen" or "the disease". You must qualify it: it has to be dead, weakened, or inactive so that it triggers an immune response without causing the actual illness.

✅ Correct Answers (Give all 3)

1. To check for toxicity (to ensure it is safe / check for harmful side effects)
2. To check for efficacy (to verify that it works / stimulates immunity)
3. To find the optimum dose (how much is needed)

💡 The "TED" Rule

Always remember TED for any clinical drug trial question in GCSE Biology:

• T – Toxicity (Is it safe? What are the side effects?)
• E – Efficacy (Does it do its job?)
• D – Dose (What concentration is most effective with minimum side effects?)

❌ Examiner Trap

The mark scheme allows "to check it is safe", but explicitly states ignore "to check it is not dangerous". Use precise scientific vocabulary: toxicity, efficacy, and dose.

✅ Model Full-Mark Response

Response to the vaccine (Primary Response):

1. The vaccine introduces dead or weakened chickenpox viruses displaying specific antigens.
2. White blood cells are stimulated to produce specific antibodies that bind to these antigens.
3. Some white blood cells develop into memory cells that remain in the bloodstream.

Response upon future reinfection (Secondary Response):

1. If the live chickenpox virus enters the body later, memory cells recognise the antigens immediately.
2. White blood cells produce specific antibodies much faster and in larger quantities.
3. The virus is destroyed before it can reproduce enough to cause disease symptoms, giving the person immunity.

❌ Misconceptions that Cost Marks

• Saying "the vaccine fights the disease": The vaccine does not destroy anything; it simply trains the immune system.
• Confusing antigens and antibodies:
  • Antigen: Marker molecule on the pathogen.
  • Antibody: Protein made by white blood cells.
• Claiming the virus is prevented from entering: Immunity doesn't stop viruses from entering your body; it allows your body to destroy them rapidly after they enter before symptoms develop.
• Omitting "specific": Antibodies must match the shape of the antigens.