Exchange surfaces 3.1.1

Question 1

What substances need to be exchanged out of the body?

Answer 1

• Nutrients e.g. glucose
• Oxygen
• Waste products
• Hormones

Question 2

Why are specialised exchange systems not required in small organisms?

Answer 2

In very small organisms can take place over the surface of the body - specialised exchange systems are not required.
This is because the cytoplasm is very close to the environment, and diffusion is sufficient to supply enough oxygen and nutrients to keep the cell active and alive.

Question 3

Why are specialised exchange systems required in large organisms?

Answer 3

• They have several layers of cells, so the diffusion pathway would be longer
• Diffusion is too slow to allow a sufficient supply to the innermost cells

Question 4

Why can a unicellular organism like amoeba get its oxygen and nutrients via direct diffusion from its surface area and why can we not?

Answer 4

It has a large surface area to volume ratio

Question 5

Why may some cells require a higher/more sufficient supply of nutrients and oxygen?

Answer 5

Due to their high metabolic activity, therefore their energy demand is higher.
Warm blooded animals also require more energy

Question 6

Does a larger organism have a smaller or larger surface area to volume ratio?

Answer 6

Smaller, as its volume is much larger than its surface area

Question 7

State 3 features of a sufficient exchange surface

Answer 7

• Large surface area
• Short diffusion distance/thin barrier
• A good blood supply = steep concentration gradient