3.1.1 Exchange surfaces – The need for a specialised exchange surface

Question 1

Calculate the surface area to volume ratio of a cube that is 5cm x 5cm x 5cm.

Answer 1

150:125 = 1.2 cm2/cm3

Question 2

State what happens to the surface area to volume ratio of organisms as they get larger.

Answer 2

The surface area to volume ratio gets smaller.

Question 3

How does surface area to volume ratio effect the rate of diffusion?

Answer 3

As the surface area to volume ratio gets smaller, the rate of diffusion gets slower.

Question 4

Why do single celled organisms not require a specialised exchange surface?

Answer 4

• They have a large surface area to volume
  ratio.
• They can obtain oxygen and nutrients through diffusion alone.

Question 5

Other than size of organism, what other factor could mean an organism needs a specialised exchange surface?

Answer 5

A high metabolic activity.

Question 6

Why are specialised exchange surfaces required in larger animals?

Answer 6

The diffusion of substances is too slow to meet the needs of the organism.

Question 7

List the 4 features that could make a good exchange surface.

Answer 7

1. A good blood supply
2. A thin barrier
3. A large surface area
4. Maintenance of a concentration gradient

Question 8

How does a good blood supply increase exchange of substances?

Answer 8

Maintains a steep/large concentration gradient.

Question 9

State a surface in a fish and a mammal that has a good blood supply.

Answer 9

• Gills (fish)
• Alveoli of lungs or villi of small intestine (mammal)

Question 10

How does a thin barrier increase exchange of substances?

Answer 10

Provides a shorter diffusion distance.

Question 11

State the structure in the mammalian lung that has a thin wall to maximise exchange of gases.

Answer 11

Alveolus (singular) or alveoli (plural)

Question 12

How does a large surface area increase exchange of substances?

Answer 12

It increases membrane surface for substances to exchange.

Question 13

State the specialised cell found in a plant that increases the surface area of roots to maximise water and mineral ion absorption.

Answer 13

Root hair cell.

Question 14

How does the maintenance of a concentration gradient increase exchange of substances?

Answer 14

Ensures there is a steep/large concentration gradient (so that equilibrium isn’t reached).

Question 15

State the process that maintains a steep concentration gradient in the lungs by bringing in oxygen and removing carbon dioxide.

Answer 15

Ventilation