Size and Surface Area

Question 1

How easy the exchange of substances is depends on an organism’s what?

Answer 1

Surface area to volume ratio

Question 2

How do single celled organisms exchange substances?

Answer 2

Substances can diffuse directly in and out the cell across the cell-surface membrane. The diffusion rate is quick due to the small distances the substances have to travel

Question 3

In multicellular organisms why is diffusion slow across the outer membrane?

Answer 3

1. Some cells are deep within the body - big distance between them and outside environment
2. Larger animals have a low SA to vol ratio - hard to exchange enough substances to supply a large volume though a small outer surface

Question 4

How do multicellular organisms exchange substances?

Answer 4

Specialised exchange organs

Question 5

What is mass transport?

Answer 5

System to carry substances to and from their individual cells

Question 6

What does man transport in mammals refer to?

Answer 6

The circulatory system

Question 7

How does size affect rate of heat loss from an organism?

Answer 7

Rate of heat loss depends on surface area. If an organism has large volume its SA is small - this makes it harder for it to lose heat. If an organism is small its SA is large - loses heat more easily. This means smaller organisms need a high metabolic rate, in order to generate enough heat to stay warm

Question 8

How does shape affect rate of heat loss from an organism?

Answer 8

1. Animals with a compact shape have a small SA to vol ratio - minimising heat loss
2. Animals with a less compact shape have a larger SA to vol ratio - increasing heat loss
3. Whether an animal is compact or not depends on the temp of its environment