# Explain how viruses can be transmitted between hosts, with reference to at least two distinct transmission routes.

> IB DP Biology Higher Level (2023 syllabus) — A2.3 Viruses (HL only) · Explain · 4 marks

## Mark scheme (4 marks)

1. Direct contact transmission: viruses can be passed from one host to another through physical contact, such as touching, kissing, or sexual intercourse, allowing viral particles on body surfaces or in secretions to enter a new host.
2. Airborne or droplet transmission: respiratory droplets or aerosols expelled during coughing, sneezing, or breathing carry viral particles that can be inhaled by a new host.
3. Vector-borne or indirect transmission: some viruses are transmitted via biological vectors (e.g. arthropods such as mosquitoes) or via contaminated fomites / water / food, transferring viral particles to a new host without direct host-to-host contact.
4. Viral particles must successfully enter host cells via receptor-mediated attachment; transmission is only effective if sufficient viral load reaches susceptible (non-immune) cells in the new host.

## Key terms

- [transmission](https://www.gradenine.co.uk/glossary/transmission)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-viruses-can-be-transmitted-3c2c2208) · Published by Druglandscape Ltd.