exchanging substances

Question 1

why can gases diffuse directly into the cell in a single-cellular organism?

Answer 1

they have a large surface area to volume ratio so enough substances can be exchanged to supply the volume of the cell

Question 2

why do multicellular organisms needed an exchange surface?

Answer 2

they have a smaller surface area to volume ratio so not enough substances can diffuse in to supply their entire volume

Question 3

how are most exchange surfaces adapted?

Answer 3

1. thin membrane so substances have a short distance to diffuse
2. large surface area so lots of a substance can diffuse at once
3. good blood supply to maintain concentration gradient as blood is constantly replaced
4. ventilated so air moves in and out, constantly replaced
5. permeable so substances can pass in and out

Question 4

gas exchange in lungs

Answer 4

1. lots of alveoli which increase surface area
2. good blood supply which maintains concentration gradient
3. thin membranes for short diffusion distance
4. a moist lining for dissolving gases

Question 5

villi in small intestine

Answer 5

1. lots of villi with each villi having many microvilli, increase the surface area so lots of molecules can diffuse across at the same time
2. good blood supply to maintain concentration gradient
3. single layer of surface cells for short diffusion distance

Question 6

leaves

Answer 6

1. stomata allow gas to diffuse (CO2 in, O2 and water vapour out)
2. flattened shape of leaf increases surface area to absorb more light
3. thin so short diffusion distance
4. air spaces inside leaf increase surface area so more chance of CO2 diffusing in

Question 7

fish gills

Answer 7

1. gill made of thin plates called gill filaments which increase surface area for gas exchange
2. gill filaments covered in lamellae which also increase surface area
3. lamellae have lots of blood capillaries to speed up diffusion
4. lamellae have a thin surface area for short diffusion distance
5. large concentration gradient as blood flows in one direction and water flows in other direction in lamellae

Question 8

root hair cells

Answer 8

1. increase surface area
2. absorb water and minerals

Question 9

what is surface area?

Answer 9

the amount of contact an object has with its environment

Question 10

what is the surface area : volume ratio?

Answer 10

the size of an object compared with the amount of area where it contacts its environment