Question 19M.2.HL.TZ1.a
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.HL.TZ1.a |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Outline | Question number | a | Adapted from | N/A |
Xylem and phloem contain structures that are adapted for transport. Outline the differences between these structures in xylem and phloem.
[2]
a. plasma membrane in phloem/sieve tubes but not in xylem/vessels
OR
xylem/vessels dead/acellular and phloem/sieve tubes alive ✔
b. xylem vessels have thicker walls «than phloem» ✔
c. xylem «vessel» walls are lignified «but phloem walls are not» ✔
d. phloem vessels have sieve plates «whereas xylem vessels have no cross walls» ✔
e. xylem/vessels are wider/larger than phloem/sieve tubes ✔
f. companion cells in phloem «but not in xylem» ✔
Many candidates knew nothing about the structure of the conducting tissues of plants and instead gave some rudimentary information on their functions. A common misconception is that phloem sieve tubes are wider than xylem vessels. This may have come from a failure to identify correctly the xylem and phloem tissue correctly in the micrograph. The most commonly known feature of xylem was the lignified wall and if phloem was the presence of companion cells.
