3.1.1a) The need for specialised exchange surfaces

Question 1

The 2 main reasons why diffusion alone is enough to supply the needs of single-celled organisms

Answer 1

Metabolic activity
Surface area: Volume ratio

Question 2

Metabolic activity in single-celled organisms

Answer 2

Metabolic activity is usually low, so oxygen demands & carbon dioxide production of the cell are relatively low

Question 3

Metabolic activity in multicellular organisms

Answer 3

Metabolic activity is higher than in single-celled organisms
The amount of energy needed for movement means oxygen demands for muscle cells will be high and will produce a lot of carbon dioxide

Question 4

Diffusion distance in multicellular organisms

Answer 4

Distance between cells needed to transport and exchange oxygen is too far for effective diffusion
Bigger the organism, smaller the SA:V ratio
So gases cannot be exchanged fast enough or in large enough amounts for the organism to survive