# Explain how the cardiac cycle produces the pressure changes that drive blood through the heart and into the aorta.

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

## Mark scheme (4 marks)

1. Contraction of the atria (atrial systole) raises pressure in the atria, forcing blood through the atrioventricular valves into the ventricles.
2. Contraction of the ventricles (ventricular systole) greatly increases ventricular pressure, which exceeds aortic/pulmonary pressure, causing the semilunar valves to open.
3. During ventricular diastole (relaxation), ventricular pressure falls below aortic pressure, causing the semilunar valves to close, preventing backflow into the ventricles.
4. The atrioventricular (bicuspid/tricuspid) valves close during ventricular systole when ventricular pressure exceeds atrial pressure, preventing backflow into the atria.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-cardiac-cycle-produces-a0d6973c) · Published by Druglandscape Ltd.