Infectious & non-infectious diseases

Year 9 answers

Fluency

Infectious: caused by a pathogen and can spread (e.g. influenza). Non-infectious: not caused by a pathogen, cannot spread (e.g. type 2 diabetes).
Bacteria (tuberculosis), viruses (flu), fungi (tinea), protists (malaria), prions (CJD).
Antibiotics target bacterial structures (cell walls, ribosomes) that viruses lack. Viruses replicate inside host cells using host machinery.
Physical: skin, mucous membranes, cilia in airways, tears washing eyes. Chemical: stomach acid, lysozyme in tears/saliva, antimicrobial peptides.
An antigen is a molecule (often on a pathogen surface) that the immune system recognises as foreign. An antibody is a Y-shaped protein produced by B-cells that binds to a specific antigen.
A memory cell is a long-lived lymphocyte formed after an infection or vaccination. If the same pathogen returns, memory cells mount a fast, strong response before illness develops.

Reasoning

Any three of: isolate the sick student; vaccinate those at risk; encourage hand washing; cover coughs and sneezes; wipe surfaces; keep non-immune students home.
Vaccination gives immunity without the illness, avoiding the risks of severe disease, complications (pneumonia, encephalitis), and death. It also protects others via herd immunity.
Salmonella is a food-borne pathogen; contamination is expected in food preparation areas, not living quarters. Inspection targets the transmission route.
Stopping early leaves the hardiest bacteria alive; they can multiply and pass on resistance. Finishing the course kills remaining bacteria and reduces the chance of resistance.
Smoking damages lung cell DNA, triggering cancer (uncontrolled division). It also paralyses cilia and irritates airways, making bacterial/viral lung infection more likely.

Problem solving

Expected number who still get sick: $5\% \times 10\,000 = 500$ . Herd immunity relies on the other 9500 being protected, which blocks most transmission chains and indirectly protects the 500 plus anyone who cannot be vaccinated.
Draining water: removes mosquito breeding sites (prevents vector population). Bed nets: prevent biting during peak mosquito activity (breaks transmission to human). Insecticide spraying: kills adult mosquitoes (reduces vector numbers and biting).
E.g.: lose weight through diet changes and portion control; increase physical activity to at least 150 min/week; reduce refined-sugar intake; regular blood-glucose monitoring with a doctor.
Quarantine interrupts person-to-person transmission, which infectious diseases need. Non-infectious diseases arise within an individual and do not spread, so isolation has no effect.

Reasoning

Selection pressure: every antibiotic course kills susceptible bacteria but allows resistant mutants to reproduce. Frequent, unnecessary use (viral infections, livestock growth promotion) intensifies selection, so resistance genes spread. Controls: prescribe antibiotics only when needed; finish full courses; restrict non-therapeutic use in animals.
Flu’s surface antigens (haemagglutinin, neuraminidase) mutate quickly, so memory cells from last year may not recognise this year’s strain — a new vaccine formulation is needed. Measles antigens barely change, so one vaccine gives decades of protection.
HIV destroys T-helper cells, which coordinate both B-cell and cytotoxic T-cell responses. Without them, adaptive immunity collapses, leaving the patient vulnerable to opportunistic infections (Pneumocystis pneumonia, Kaposi’s sarcoma) that a healthy immune system normally suppresses.
Primary response: slow (days to peak), low antibody level, mostly IgM. Secondary response: fast (hours to days), much higher antibody level, mostly IgG, due to memory cells. Sketch: low bump after first exposure; much higher, faster peak after second exposure.