Question 19M.2.HL.TZ2.d
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.2.HL.TZ2.d |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Deduce | Question number | d | 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]
RNA was collected from leaves of the plants after each treatment (armyworm, herbivorous mite and the chemicals C1 and C2). DNA copies of the extracted RNA were made by a process called reverse transcription. Targeted genes in the DNA were then amplified.
The scientists then used the transcribed DNA of each treatment to study the activation of three genes of the plants’ defence system. The DNA was separated by gel electrophoresis. The activation was tested one hour after treatment and again after 24 hours.
[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]
Deduce, with a reason, which gene is first transcribed when exposed to C2.
[1]
gene 1 is first transcribed «after C2 treatment» as it shows activation after one hour ✔
It was common for students to correctly identify Gene 1 as the first gene being expressed. It was also common for students to correctly justify their answer making reference to the data.
