Kerboodle 5

Question 1

2 Describe two differences between:

a active transport and facilitated diffusion

Answer 1

Any two from: Active transport uses energy / ATP but facilitated diffusion does not ü Active transport can move substances against a diffusion gradient (from low to high concentration) but in facilitated diffusion movement is always down the gradient (from high to low) ü In active transport the carrier protein changes shape, but in facilitated diffusion it does not ü

Question 2

2 Describe two differences between: b bulk transport and osmosis

Answer 2

Bulk transport can move various soluble and insoluble substances but osmosis refers to movement of water only ü Bulk transport can move substances against a diffusion gradient (from low to high concentration) but in osmosis movement is always down the water potential gradient (from high ψ to low ψ) ü Bulk transport involves fusion or formation of vesicles at the cell surface membrane, changing its size, but osmosis does not ü

Question 3

2 Describe two differences between: c the structure of a cell-surface membrane at 20 °C and 80 °C.

Answer 3

Proteins are intact at 20 °C but denatured at 80 °C ü Phospholipids form a stable bilayer at 20 °C but move more and break apart making gaps in the membrane at 80 °C ü

Question 4

a Identify, with reasons, the membrane or membranes that is / are: ii most likely to be the site of chemical reactions

Answer 4

Mitochondrion inner membrane ü High protein content due to membrane-bound enzymes ü

Question 5

b Suggest a reason for the differences in percentage composition between the two cell-surface membranes. liver cell-surface
membrane unicellular protoctist
cell-surface membrane

Answer 5

Liver cell part of a multicellular organism so needs to communicate / has more protein receptors ü Protoctist proteins may detect chemicals in environment or act as channels ü

Question 6

b A leaf of Canadian pondweed, which had been kept out of water for a short time, was seen to have wilted (its cells were no longer turgid).
Explain, in terms of water potential, what would happen to its cells if the leaf was then placed in distilled water with a water potential (ψ) of 0.

Answer 6

Any four points from: Water will enter by osmosis ü Down water potential gradient / from high ψ to low ψ ü Because ψ of cells is lower / more negative ü Cells / vacuoles expand ü Cell membrane presses against cell wall ü ψ increases until equilibrium ü Cell wall resists expansion / prevents bursting ü