6.2 - Specialised Exchange Surfaces

Question 1

Why can’t substances diffuse directly across the cell membrane in multicellular organisms?

2 reasons

Answer 1

• Cells are not in direct contact with the environment
• Diffusion distances between cells and their environment are large.
• Larger organisms have higher metabolic rates, so they need more oxygen and glucose.

Question 2

What have multicellular organisms evolved to solve this problem?

Answer 2

Specialised exchange surfaces

Question 3

What are specialised exchange surfaces?

Answer 3

Structures for transferring materials between cells and the environment

Question 4

What features do specialised exchange surfaces have?

Name 2

Answer 4

• Large surface area
• Thin walls
• An extensive blood supply and/or ventilation
• Being surrounded by selectively permeable plasma membranes

Question 5

Why is a large surface area important?

Answer 5

Provides a larger area for exchange

Question 6

Why are thin walls important?

Answer 6

Minimises diffusion distance

Question 7

Why is an extensive blood supply/ventilation important?

Answer 7

Maintains steep concentration gradients

Question 8

Why are selectively permeable membranes important?

Answer 8

Controls what substances are exchanged