Question 18M.2.HL.TZ2.a.ii
| Date | May 2018 | Marks available | [Maximum mark: 2] | Reference code | 18M.2.HL.TZ2.a.ii |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Distinguish | Question number | a.ii | 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 timing of the four stages of leaf development.
[2]
a. S1/S2 is longer in short day plants
OR
the stages in long day plants are more variable in length. Accept vice versa.
b. leaves of plants grown in long day reach S2 / S3 /S4 stages sooner
OR
S1/S2/S3 completed earlier in plants grown in long days
c. leaves of plants grown in long day reach S1 later than plants grown in short days
