Question 18M.2.HL.TZ2.b
| Date | May 2018 | Marks available | [Maximum mark: 2] | Reference code | 18M.2.HL.TZ2.b |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Distinguish | Question number | b | Adapted from | N/A |
Arabidopsis is a small flowering plant in the mustard family (Brassicaceae) that is widely used in basic research. It has a short life cycle, flowers quickly producing a large number of seeds and is easy to cultivate. It forms a circle of leaves known as a rosette that lies close to the soil. Flowers form at the end of short stems.
A study was carried out of differences in development between Arabidopsis plants grown in long days (16 hours light, 8 hours dark) or short days (8 hours light, 16 hours dark). The sixth leaf (L6) to emerge in the rosette of each plant was used in all investigations.
New leaves are initiated by the meristem and go through four stages as they develop.
• Stage 1 (S1) – rapid cell division
• Stage 2 (S2) – cell division has ceased, cell expansion continues
• Stage 3 (S3) – decreasing cell expansion rate
• Stage 4 (S4) – leaf growth complete
The start of each stage of leaf development for plants grown in long days and short days is shown above the first graph.
Distinguish between plants grown in long days and short days in the mean number of leaves per rosette during the experimental period.
[2]
a. rosette of plant grown in long day has fewer leaves. Accept vice versa.
b. rosette leaf number of plant grown in long day plateaus/stays constant while the number continues to increase for plants grown in short days. OWTTE.
