How do pathogens spread, and how do plants and people prevent disease?
Explain how pathogens are spread and how spread can be reduced, the lytic and lysogenic virus pathways, how STIs are spread and prevented, and how plants defend against and are tested for disease.
A focused answer to Edexcel GCSE Biology 5.6 to 5.11B, covering how pathogens spread and how spread is reduced, the lytic and lysogenic viral pathways, STIs, plant physical and chemical defences, and how plant diseases are detected.
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What this dot point is asking
Edexcel statements 5.6 to 5.11B want you to explain how pathogens spread and how spread can be reduced, describe the lytic and lysogenic pathways of a virus (5.7B Biology only), explain how STIs spread and are prevented, and describe how plants defend themselves and how plant diseases are detected (5.9B to 5.11B Biology only).
How pathogens spread
Reducing the spread
The spread of disease is reduced by breaking the route of transmission:
- Hygiene: hand washing, disinfectants and food safety remove pathogens.
- Isolation: keeping infected people away from others stops transmission.
- Vaccination: making people immune so the pathogen cannot spread (herd immunity).
- Vector control: killing or avoiding vectors, for example mosquito nets and insecticides.
- Clean water and sewage treatment: preventing water-borne diseases like cholera.
The lytic and lysogenic pathways (Biology only)
Viruses can only reproduce inside host cells, and they do so by two pathways:
- Lytic pathway: the virus injects its genetic material, the host cell makes many copies of the virus, and the cell then bursts (lyses), releasing the new viruses to infect more cells. This causes the symptoms of illness.
- Lysogenic pathway: the virus's genetic material is inserted into the host cell's own DNA and is copied every time the cell divides, but stays dormant, causing no symptoms. Later, a trigger can switch it to the lytic pathway.
Sexually transmitted infections
STIs are spread through sexual contact and body fluids. HIV is a key example: it is spread through blood, semen and vaginal fluids, and by sharing needles. Spread is reduced by using condoms (barrier protection), avoiding sharing needles, and screening blood. Reducing the number of sexual partners and getting tested also lowers transmission.
Plant defences and disease detection (Biology only)
Plants defend themselves with both physical and chemical defences:
- Physical defences: a waxy cuticle and the cellulose cell wall act as barriers, and layers of dead cells such as bark protect the surface.
- Chemical defences: some plants make antibacterial chemicals or poisons that kill or deter pathogens and pests; some of these are used as human medicines.
Plant diseases can be detected in the lab and in the field by looking at the distribution of affected plants, observing symptoms such as discoloured or spotted leaves and stunted growth, eliminating environmental causes (like a lack of minerals), and using laboratory tests such as testing for the pathogen's DNA or using monoclonal antibodies.
Try this
Q1. State two ways the spread of an airborne disease such as influenza can be reduced. [2 marks]
- Cue. Any two of: catching coughs and sneezes (tissues), isolating infected people, vaccination, good ventilation and hygiene.
Q2. Describe the difference between the lytic and lysogenic viral pathways. [2 marks]
- Cue. Lytic: the virus copies itself and bursts the host cell, causing symptoms. Lysogenic: the viral DNA hides in the host DNA and is copied silently, causing no symptoms until triggered.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksDescribe four ways that the spread of communicable diseases can be reduced.Show worked answer →
A 4-mark describe question rewards four distinct, sensible control measures.
- Improving hygiene, such as washing hands and using disinfectants, to remove pathogens.
- Isolating or quarantining infected individuals so they cannot pass the pathogen on.
- Vaccination, to make people immune so the pathogen cannot spread through the population.
- Controlling or removing vectors (such as mosquitoes) and providing clean water and proper sewage treatment.
Markers reward four different methods. Repeating one idea in different words (for example listing several kinds of hand washing) does not gain four separate marks.
Edexcel 20213 marksDescribe how a plant can defend itself against pathogens using physical and chemical defences.Show worked answer →
A 3-mark describe question (Biology only) rewards both a physical and a chemical defence.
Physical defences: a waxy cuticle and the cellulose cell wall act as barriers that pathogens find hard to get through, and layers of dead cells (such as bark) protect the surface.
Chemical defences: some plants produce antibacterial chemicals or poisons that kill or deter pathogens and pests; some of these chemicals are used by humans as medicines.
Markers reward at least one clear physical barrier (cuticle, cell wall or bark) and one chemical defence (antibacterial or poisonous chemicals). Listing only one type caps the marks.
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Sources & how we know this
- Pearson Edexcel GCSE (9-1) Biology (1BI0) specification — Pearson (2016)