Problems With Size In Gas Exchange

Question 1

State three adaptations for gas exchange of unicellular organisms

Answer 1

They have a large SA:V ratio
They have a thing cell membrane so diffusion is rapid
They are thin so diffusion distances inside the cell are short

Question 2

What do a unicellular organisms adaptations allow it to do?

Answer 2

Absorb enough oxygen across it membrane to meet it needs for respiration.
Remove CO2 fast enough to prevent the build up of it, stopping the cytoplasm getting to acidic for the enzymes to not be able to function.

Question 3

In multicellular organisms why is it beneficial to be flat e.g. the flatworm?

Answer 3

The diffusion pathway to the centre of the organism is shorter than if it was spherical.

Question 4

Give two features of a flatworm

Answer 4

Smaller SA:V ratio than unicellular organisms but greater than a cylindrical organism because it is flat.
Shorter diffusion pathway than a cylindrical organism.

Question 5

Give three features of an earthworm

Answer 5

It’s skin is it’s respiratory surface so it secretes mucus onto it to keep it moist.
Low oxygen requirement as it is slow moving and has a low metabolic rate
Haemoglobin is present in its blood carrying oxygen around its body in blood vessels

Question 6

Give three special feature that multicellular organisms have over unicellular organisms

Answer 6

They have a higher metabolic rate as they need to deliver more oxygen to respiring cells and remove more carbon dioxide
They have to actively maintain a steep concentration gradient across their respiratory surfaces by keeping the environmental medium moving (blood, air or water).
Respiratory surfaces must be thin so are fragile but in multicellular organisms they are inside the organism so are protected.