Question 19M.2.HL.TZ2.a
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.2.HL.TZ2.a |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Distinguish | Question number | a | Adapted from | N/A |
Organisms often release chemicals when attacked as part of their defence system. Scientists studied lima bean plants (Phaseolus lunatus) infested with either an armyworm, Spodoptera exigua, or a herbivorous mite, Tetranychus urticae. Both organisms feed on lima bean leaves, causing the leaves to release chemicals.
[Source: https://commons.wikimedia.org/wiki/File:Phaseolus_lunatus_Blanco2.369.png]
![https://commons.wikimedia.org/wiki/File:Phaseolus_lunatus_Blanco2.369.png]](https://commons.wikimedia.org/wiki/File:Phaseolus_lunatus_Blanco2.369.png%5D){kind=link}
The study was conducted to see which defence chemicals were produced by lima bean leaves when infested by armyworms or herbivorous mites. The scientists identified a mixture of compounds (C) released by the plant when attacked. Two of the chemicals in this mixture were identified (C1 and C2).
The scientists hypothesized that the defence chemicals in C act as signals to produce other chemicals (X, Y and Z) that are also involved in the defence of the plant.
The graphs show the amounts of chemicals X, Y and Z produced when the plants were infested by either one of the two herbivores or treated with the different chemicals C1 or C2.
[Source: R Ozawa and G Arimura, Involvement of Jasmonate- and Salicylate-Related Signaling Pathways for the
Production of Specific Herbivore-Induced Volatiles in Plants, Plant and Cell Physiology, 2000, 41, 4, 391–398,
by permission of Oxford University Press]
Distinguish between the data for the leaves infested with the armyworm and the leaves infested with the herbivorous mite.
[3]
a. armyworm «infestation» produced more X than Y than Z/decreasing amounts AND herbivorous mite showed the opposite pattern/more Z than Y than X ✔
b. armyworm «infestation» produced more X than herbivorous mite ✔
c. armyworm «infestation» produced more Y than herbivorous mite / Y is the middle value for both ✔ Accept OWTTE.
d. armyworm «infestation» produced less Z than the herbivorous mite ✔
e. other valid distinction ✔
Clear distinction required not simple lists of values.
For mp b-d accept vice versa.
It was common for students to earn three marks for this question. At the same time, students often outlined individual graphs separately rather than using comparative terms.
