Specialised exchange surfaces

Question 1

why do substances diffuse quickly between single celled organisms

Answer 1

1) short diffusion distance

Question 2

is diffusion slow or fast in multicellular animals and why

Answer 2

slow

• some cells are deep within the body( large diffusion distance)
• low SA:V
• multicellular organisms have higher metabolic rates so use up oxygen and glucose much faster

SO multicellular animals need specialised exchange surfaces- E.g alveoli

Question 3

what 3 things do specialised exchange surfaces have

Answer 3

1) large SA- eg roots have a large SA helps them to increase absorption of roots and mineral ions from the soil
2) short diffusion distance- Alveoli are very thin ( one cell thick)- increasing the rate of diffusion

3) Good blood supply/ well ventilated - eg alveoli have heir own blood supply
- blood constantly takes oxygen away from the alveoli and bring more CO2 in
- lungs are well ventilated so air is constantly replaced- maintaining in the concentration gradient between O2 and CO2.