(i)

Function of labelled parts

I → Carries blood from the heart/left ventricle to the circulatory system
II → Brings (oxygenated) blood from lungs to heart/left auricle/atrium
IX → Brings (deoxygenated) blood from the body to heart/right atrium/right side of heart
X → Carry (oxygen deficient) blood from heart to lungs/right side of heart/right ventricle to lungs

(ii)

Why the left lower part of the heart has a thicker muscle

Contracts to pump (oxygenated) blood with high pressure to all parts of the body

OR

To generate high pressure to allow blood to reach all parts of the body

(iii)

Ways by which the flow of blood to and from the mammalian heart can be kept at acceptable levels

1. Exercising
2. Not smoking
3. Taking iron rich foods/balanced diet
4. Regulating one's blood pressure
5. Stress management
6. Get enough sleep
7. Healthy weight
8. Limit alcohol consumption
9. Manage diabetes
10. Regular health check-up

(iv)

Parts of the heart where oxygenated blood can be found

1. Aorta
2. Pulmonary vein
3. Left atrium
4. Left ventricle