3.1 - Exchange Surfaces and Breathing

Question 1

What are the 3 main factors that affect the need of an exchange system?

Answer 1

1. The SIZE of an organism
2. Level of Activity
3. The Surface Area to Volume Ratio

Question 2

How does Size affect the exchange of gases/substances?

Answer 2

A single-celled organism has the cytoplasm very close to the external environment so the diffusion will supply enough oxygen and nutrients.

However, multi-cellular organsims have several layers of cells so there is a longer diffusion pathway so diffusion is too slow to enable a sufficient supply to the innermost cells.

Question 3

How does the Level of Activity affect the exchange of gases/substances?

Answer 3

If you have an active organsim. e.g. a spider, it’s going to need much more oxygen because it’s respiring more.

If you have a slightly less active organism, e.g. a snail, then it’s going to need less oxygen so there’s less need of a specialised exchange system.

Question 4

Define Surface Area to Volume Ratio.

Answer 4

The surface area of an organism, divided by its volume, expressed as a ratio.

Question 5

The LARGER the organism, the….

The SMALLER the organism, the…

Answer 5

…SMALLER its SA:V ratio.

…LARGER its SA:V ratio.

Question 6

How does a large Surface Area benefit an organism?

Answer 6

A large SA means more efficient gas exchange, more gas exchange in general, so more tissues are being kept alive.

Question 7

How is Volume proportional to Metabolism?

Answer 7

The more volume there is, the more cells there are that need to consume oxygen.