3.1.1 exchange surfaces

Question 1

which organisms require specialised exchange surfaces

Answer 1

larger organisms with more than 2 layers of cells

Question 2

which 3 factors affect the need for an exchange system

Answer 2

• size
• surface area to volume ratio
• level of activity

Question 3

why do small organisms (eg. unicellular) not require exchange surfaces

Answer 3

• cytoplasm is close to the environment
• diffusion supplys enough oxygen/nutrients

Question 4

small organisms: surface area to volume ratio

Answer 4

• small surface area & small volume
• surface area large compared to volume (large surface area to volume ratio)

Question 5

larger organisms: surface area to volume ratio

Answer 5

• large surface area & larger volume
• as size increases, volume increases quicker than surfac area
• surface area is small compared to volume (small surface area to volume ratio)

Question 6

examples of organisms adopting a different to increase surface area

Answer 6

• eg. flatworm has thin & flat body = larger SA:V ratio

Question 7

features of efficient exchange surface

Answer 7

• increased SA eg. root hair cells
• thin layer eg. alveoli
• good blood supply/ventilation to maintain gradient eg. gills

Question 8

example of large SA - root hair cells

Answer 8

• cells on plants grow into long ‘hairs’
• gives roots large SA
• helps increase rate of absorption of water by osmosis & mineral ions by active transport

Question 9

example of efficient exchange surface - alveoli

Answer 9

1. thin
   - each alveolus made from thin, flat cells = alveolar epithelium
   - O2 diffuses out of alveolar space into blood & CO2 diffuses opposite way
   - thin alveolar epithelium decreases diffusion distance = increases rate
2. good blood supply & ventilation
   - surrounded by large capillary network
   - each alveolus has own blood supply = blood constantly takes O2 away & brings more CO2
   - lungs are ventilated = maintain concentration gradient

Question 10

example of efficient exchange surface - fish gills

Answer 10

good blood supply & ventilated
- oxygen & carbon dioxide exchange between blood & water
- gills contain large network of capillaries = well supplied with blood
- well ventilated (fresh water constantly passes over) = maintain concentration gradient