Structures and Functions in Living Organisms · 6 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 15% of your exam marks.
The heart, blood vessels, and blood components are regularly tested, particularly structure-function links.
A human body contains around 37 trillion cells, most of them buried deep inside organs many centimetres from the body's surface. Every one of these cells needs a constant supply of oxygen, glucose, water, mineral ions, hormones and other essentials, and a fast way to get rid of waste carbon dioxide, urea and heat. Diffusion alone is far too slow to do this on a body-wide scale, so humans (and most other large animals) have a circulatory system: a closed loop of vessels through which blood is pumped by the heart.
The system has three parts:
Together they deliver substances to every cell in the body and carry the waste products away to the organs that excrete them.