3.3.1 Surface area to volume ratio

Question 1

What happens to the surface area to volume ratio as an organism increases in size and how does it affect exchange of gases?

Answer 1

As an organism increases in size, the surface area to volume ratio decreases. This makes it harder for sufficient exchange of substances to occur across the surface as simple diffusion would take too long.

Question 1

Why is a large surface area to volume ratio beneficial for single-celled organisms?

Answer 1

Substances can diffuse directly through the cell membrane so do not require specialised adaptations to meet metabolic demands

Question 2

Why do multicellular organisms need specialised exchange surfaces?

Answer 2

Multicellular organisms have a low surface area to volume ratio, so diffusion alone would occur to slow so have specialised exchange surfaces to increase efficiency.

Question 3

What are the three main features for maximising rate of diffusion?

Answer 3

Large surface area
Thin surface for a short diffusion pathway
Steep concentration gradient

Question 4

How is the surface area to volume ratio related to diffusion distance?

Answer 4

A high SA:V ratio is associated with shorter diffusion distances, facilitating faster exchange of substances.

Question 5

How is the distance between internal and external environment different in a single celled organism than a multicellular one ?

Answer 5

Large surface area to volume ratio so short distance between internal and external environment.
Gases can be exchanged directly through cell membrane through diffusion