# Explain how the structural features of the atrioventricular (AV) valves prevent backflow of blood during ventricular systole.

> IB DP Biology Higher Level (2023 syllabus) — B3.2 Transport · Explain · 4 marks

## Mark scheme (4 marks)

1. AV valves have flap-like cusps / leaflets that are pushed closed when ventricular pressure exceeds atrial pressure
2. Chordae tendineae (heart strings) attach the cusps to the papillary muscles and prevent the cusps inverting / being pushed back into the atrium
3. Papillary muscles contract during ventricular systole, tensioning the chordae tendineae to hold the valve closed under pressure
4. The sealed, closed valve ensures blood is directed through the semilunar valves into the aorta / pulmonary artery rather than back into the atrium, maintaining unidirectional flow

## Key terms

- [atrioventricular (AV) valve](https://www.gradenine.co.uk/glossary/atrioventricular-av-valve)
- [ventricular systole](https://www.gradenine.co.uk/glossary/ventricular-systole)

## 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-the-structural-features-of-0e29bf0c) · Published by Druglandscape Ltd.