An Amoeba is a single-celled organism that lives in pond water. It has no lungs and no blood. All of the oxygen it needs diffuses in across its outer surface.
The table gives data for an Amoeba and for an adult human.
Table: The surface area, the volume and the surface area to volume ratio of an Amoeba and of an adult human
| Organism | Surface area in m2 | Volume in m3 | Surface area to volume ratio |
|---|---|---|---|
| Amoeba | 0.000 000 03 | 0.000 000 000 001 | 30 000 : 1 |
| Adult human | 1.8 | 0.070 | to be calculated |
Calculate the surface area to volume ratio of the adult human. Give your answer in the form n : 1.
Explain why an Amoeba does not need a gas exchange system but an adult human does.
The alveoli of an adult human give a total gas exchange surface of about 70 m2 , which is far larger than the surface area of the skin. Suggest how the lungs achieve this.
179 exam-style questions on AQA GCSE Biology 2.2 Animal tissues, organs and organ systems, covering 2.2.1 The human digestive system, 2.2.2 The heart and blood vessels, 2.2.3 Blood, 2.2.4 Coronary heart disease: a non-communicable disease, 2.2.5 Health issues, 2.2.6 The effect of lifestyle on some non-communicable diseases, and 2.2.7 Cancer. Each one has a worked solution and a mark scheme showing where the marks go.