Specialised Exchange Surfaces - The Alveoli

Question 1

What do single celled organisms have for exchange surface?

Answer 1

They have a large surface area compared to volume, so lots of substances can be exchanged across the membrane to supply the volume, out of the cell

Question 2

What do multicellular have for exchange surfaces?

Answer 2

Multicellular organisms have a smaller surface area compared to their volume

This makes it difficult to exchange enough substances to supply their entire volume across the outside surface alone.

Question 3

How does gas exchange in mammals,in alveoli?

Answer 3

1) the lungs transfer oxygen to the blood and to remove waste carbon dioxide
2) the lungs contain millions of little air sacs called alveoli, this is where gas exchange takes place
3) blood arriving at the alveoli has just returned to the lungs from the body , so it contains little CO2 , not much oxygen. This maximises the concentration gradient.
4) oxygen diffuses out of the air in the alveoli and into blood
5) CO2 diffuses in the opposite direction to be breathed out

Question 4

How are the alveoli adapted to their function?

Answer 4

A moist lining for dissolving gases
A good blood supply to maintain the gradient of oxygen and carbon dioxide
Very thin walls , minimising diffusion distance
Enormous surface area