Question 19M.3.SL.TZ2.c.ii
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.SL.TZ2.c.ii |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Suggest | Question number | c.ii | Adapted from | N/A |
Two models of plasma membrane structure are shown.
[Source: diagram from article published in The American Journal of Pathology, 65, J Singer and G Nicolson,
The structure and chemistry of mammalian cell membranes, 427–437, Copyright Elsevier (1971)]
Phospholipase C is an enzyme that digests the polar heads of phospholipids. Scientists used phospholipase C to test these models of membrane structure. They found that the enzyme could digest the heads of phospholipids in the plasma membranes of red blood cells.
Suggest one reason for maintaining a pH of 7.5 throughout the experiment.
[2]
a. pH values away from optimum pH affect enzyme
OR
so enzyme can function properly
OR
pH 7.5 is the optimum pH for the enzyme ✔
b. sketch of enzyme activity versus pH ✔ Sketch of enzyme activity needs labels.
c. change in pH affects 3D structure of protein/active site
OR
change in pH denatures the enzyme / protein ✔
d. substrate does not fit in active site
OR
interaction of substrate and active site affected ✔
Most candidates answered correctly that a specific pH was necessary for the enzyme to function properly and that deviation from this pH could denature the enzyme.
