DP Biology (first assessment 2025)
Question SPM.2.HL.TZ0.9
| Date | May Specimen-2023 | Marks available | [Maximum mark: 15] | Reference code | SPM.2.HL.TZ0.9 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Compare and contrast, Describe, Outline | Question number | 9 | Adapted from | N/A |
9.
[Maximum mark: 15]
SPM.2.HL.TZ0.9
Various mechanisms can lead to inhibition in biological systems. A toxin is a substance capable of disrupting metabolic processes in organisms.
(a)
Describe how toxins such as DDT might concentrate in the bodies of birds.
[4]
Markscheme
- some toxins/DDT are persistent/degrade slowly (once released into the environment);
- (some toxins/DDT) enter the food chain through producers/lower trophic levels;
- (some toxins/DDT) are passed on to higher trophic levels in the food chain;
- (they are) difficult to excrete / are not excreted;
- (they) accumulate in fatty tissues of animals;
- higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;
- they bioaccumulate/biomagnify;
(b)
Toxins often act as inhibitors. Compare and contrast competitive and non-competitive enzyme inhibition.
[7]
Markscheme
a valid example of each;
Answers must have at least one similarity for 7 max.
(c)
Rotenone is a naturally occurring toxin that blocks the electron transport chain in insects and fish. Outline the consequences of exposure to a toxin like rotenone for cell respiration.
[4]
Markscheme
- lower rate of aerobic respiration / inhibits aerobic respiration;
- reduced NAD (not oxidised) accumulates;
- fewer/no electrons (from reduced NAD and FADH) to be transported by carriers;
- less/no energy to transfer protons (from matrix to intermembrane space);
- proton gradient cannot be maintained;
- less/no diffusion of protons through ATP synthase;
- ADP is not phosphorylated / less ATP produced / no energy to produce ATP;
- oxygen not binding to protons / accepting electrons / no water formed;