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

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

## Mark scheme (4 marks)

1. During diastole, the relaxation of the left ventricle causes pressure to fall below that in the left atrium, so the atrioventricular (bicuspid/mitral) valve opens and blood flows from the atrium into the ventricle.
2. Contraction of the left ventricle during systole raises ventricular pressure above atrial pressure, which closes the AV valve (preventing backflow into the atrium).
3. When ventricular pressure exceeds aortic pressure, the semilunar (aortic) valve opens and blood is ejected into the aorta.
4. At the end of systole, ventricular pressure falls below aortic pressure, causing the semilunar valve to close, preventing backflow of blood from the aorta into the ventricle.

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-cardiac-cycle-produces-d1b6523f) · Published by Druglandscape Ltd.