Part 4: Diffusion In Living Organisms

Question 1

What is the definition of surface area to volume ratio?

Answer 1

How many times larger or smaller the surface area is compared to the volume.

Question 2

How does surface area to volume ratio relate to Biology? (4)

Answer 2

1. The bigger the volume, the smaller surface area to volume ratio
2. Shapes with a smaller surface area to volume ratio will have slower rates of diffusion
3. Shapes with a larger surface area to volume ratio will have faster rates of diffusion
4. Shapes with a large volume can increase their rate of diffusion by increasing the surface area (e.g. plants- root hair cells)

Question 3

Define the term ‘exchange surface’

Answer 3

A location where the materials are transferred between an organism and its environment.

Question 4

Define the term ‘transport system’

Answer 4

A structure that moves materials around the body of a multicellular organism

Question 5

Explain why large organisms require exchange surfaces and transport systems (5)

Answer 5

1. Large organisms have a small SA:V ratio.
2. This means a large distance from the outside to the centre if the organism.
3. If diffusion distsnce is large, then diffusion will be too slow.
4. Exchange surfaces increase the rate of diffusion.
5. Transport systems reduce the distance over which diffusion has to take place.

Question 6

Explain why single-celled organisms are able to rely on diffusion (3)

Answer 6

1. Single-celled organisms have a large SA:V ratio.
2. This means a small distance from the outside to the centre of the organism.
3. If diffusion distance is small, then diffusion will be quicker than in large organisms and quick enough for single-celled organisms.