Topic 3:surface Area

Question 1

What substances may need to be exchanged between an organism and its environment?

Answer 1

Oxygen
Carbon dioxide
Ions
Water
Urea
Glucose
Amino acids

Question 2

Single celled organisms and gas exchange

Answer 2

They are small, so they have a large surface area to volume ratio
Oxygen is absorbed by diffusion across their body surface through a cell surface membrane
Carbon dioxide from respiration diffuses out across their body surface
If a cell wall is present, it is fully permeable to gases and doesnt act as a barrier

Question 3

What can affect the rate of exchange?

Answer 3

Surface area to volume ratio
As the size of an organism increases, its surface area:volume ration decreases

Question 4

Why do mammals or larger organisms need gas exchange systems?

Answer 4

It is difficult to exchange materials and heat with the environment fast enough to maintain conditions inside organisms at constant levels

Question 5

Ficks law

Answer 5

SA x Difference in concentration/ length of diffusion pathway

Question 6

How can the body shape affect the SA:volume ratio

Answer 6

Flattening or elongation the body increases the SA: Volume ration
Animals like lugworms, have thin skin and blood vessels close to the surface so there is a short diffusion pathway

Question 7

Give 4 features of specialised exchange surfaces

Answer 7

1. A large SA to Vol ration increases the rate of exchange
2. Very thin, so short diffusion pathway, materials cross at a faster rate
3. Permeable to allow selected materials across without obstruction
4. Movement/ventilation of air and water and blood maintains a diffusion gradient