3.1 Surface area to volume ratio

Question 1

How does an organism’s size relate to their surface area to volume ratio?

Answer 1

The larger the organism, the lower the surface area to volume ratio

Question 2

How does an organism’s surface area to volume ratio relate to their metabolic rate?

Answer 2

The smaller the surface area to volume ratio, the higher the metabolic rate

Question 3

How might a large organism adapt to compensate for its small surface area to volume ratio?

Answer 3

Changes that increase surface area, e.g. folding; body parts become larger (elephant’s ear), elongating shape; developing a specialised gas exchange surface

Question 4

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 4

The smaller the surface area to volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism

Question 5

Name three features of an efficient gas exchange surface

Answer 5

1. Large surface area, e.g. folded membranes in mitochondria
2. Thin/short distance, e.g. wall of capillaries
3. Steep concentration gradient, maintained by blood supply or ventilation, e.g. alveoli

Question 6

State Fick’s Law

Answer 6

rate of diffusion = surface area x diffusion in concentration gradient / length of diffusion pathway