DP Biology (first assessment 2025)
Question 21N.2.SL.TZ0.b.ii
| Date | November 2021 | Marks available | [Maximum mark: 3] | Reference code | 21N.2.SL.TZ0.b.ii |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | b.ii | Adapted from | N/A |
b.ii.
[Maximum mark: 3]
21N.2.SL.TZ0.b.ii
Explain the reasons for food chains rarely containing more than four or five trophic levels.
[3]
Markscheme
a. energy is lost between the trophic levels;
b. transfer between levels is only usually 10% efficient
OR
energy transformations take place in living organisms / the process is never 100% efficient;
c. energy is lost by the organism/used in respiration / released as heat/movement;
d. energy is lost as waste/feces/urine/undigested food/uneaten parts;
e. as energy is lost between trophic levels and so (higher ones) have less biomass / less biomass available for next level;
Examiners report
Most were able to gain at least two marks for the explanation of energy loss through the trophic levels.
