Question 21M.2.HL.TZ1.8c
| Date | May 2021 | Marks available | [Maximum mark: 7] | Reference code | 21M.2.HL.TZ1.8c |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Cellular processes at the molecular level are regulated by enzymes.
Explain the factors that affect the rate of enzyme-controlled reactions in cells.
[7]
a. temperature increases rate up to optimum and higher temperatures decrease rate / graph ✔
b. faster molecular movement as temperature rises (so more substrate-active site collisions) ✔
c. high temperature/heat causes denaturation/irreversible change to active site (so rate reduces) ✔
d. rate decreased if pH is above and below optimum/if pH is too high or low / graph ✔
e. pH affects shape/structure of enzyme/active site /affects ionization (of amino acids) ✔
f. increases in substrate concentration cause rate to rise towards a plateau/WTTE / graph ✔
g. greater chance of substrate-active site collisions with higher substrate concentration
OR
active sites saturated/all full at high substrate concentrations ✔
h. higher enzyme concentration increases rate (as there are more active sites) ✔
i. enzyme inhibitors/competitive inhibitors/non-competitive inhibitors reduce the rate ✔
j. end-product inhibitors switch off metabolic pathway / act on enzyme at start of pathway rate ✔
OR
allosteric site used to control enzyme activity by binding of (non-competitive) inhibitor
Graphs can be used for mpa, mpd mpf and mph but x-axis must have the variable indicated.
For mpa there must be exponential rise to optimum then faster drop.
For mpd there must be a bellshaped curve but it need not be exactly symmetrical.
For mpf and mph there must be decreasing increases in rate towards a plateau.
This was expected to be high-scoring, because it is such a standard topic, but candidates may have been running out of steam by the time they reached it and many answers were too brief, with significant points omitted.
