Date | May 2019 | Marks available | 2 | Reference code | 19M.3.HL.TZ2.1 |
Level | Higher level | Paper | Paper 3 | Time zone | Time zone 2 |
Command term | Outline | Question number | 1 | Adapted from | N/A |
Question
The drawing shows part of a Thunbergia grandiflora plant. It has been widely cultivated as an ornamental garden plant.
[Source: from Wight, R., Icones Plantarum Indiae Orientalis, vol. 3 (1846)]
The drawing shows a section through a T. grandiflora flower, which contains a honeybee (Apis mellifera).
[Source: © D G Mackean (www.biology-resources.com/drawing-plant-flower-tropical-06.html)]
Using the drawing, deduce which plant phylum T. grandiflora belongs to, giving one visible recognition feature of this phylum.
Identify the structure labelled X.
Outline the relationship the bee has with the T. grandiflora flower.
After fertilization, seeds of T. grandiflora form in a small pod. If you were provided with Petri dishes, absorbent cotton balls and seeds, suggest how one variable affecting germination of these seeds could be investigated.
Markscheme
Angiospermophyta/Angiosperms
AND
flowers «as reproductive organs» ✔
Both required.
ovule ✔
a. mutualistic relationship
OR
bee gets nectar/pollen «as food» AND flower is pollinated/fertilized ✔ Both needed.
b. when bee enters, pollen from anther sticks to it ✔
c. pollen is picked up by stigma «of same or other flower» ✔
a. different values for the named independent variable ✔ Name of the independent variable must be included, eg temperature.
b. large / equal number of seeds in each Petri dish ✔
c. control of other variables «than seeds» ✔
d. mentions how germination will be determined eg appearance of radicle.
OR
how germination rate/percentage will be measured ✔ eg number germinated over time/in a set time. Do not accept measurement of growth of stem/number of leaves.
e. includes a control giving seeds all factors needed ✔
Possible factors include water, oxygen, temperature, pH, light, salt concentration.
Examiners report
Most could use the flower as a recognition feature, but it was more difficult for some to deduce the phylum.
This question was derived from the skill of drawing half-views of animal pollinated flowers and the understanding of mutualistic relationships involved in plant reproduction. A large number could identify the ovule, but many incorrect answers, such as ovary, were also seen, as well as totally irrelevant answers.
Although some could not write "mutualistic/mutualist", the majority could outline the relationship, but some confused pollination, fertilization and seed dispersal; it was more difficult for most to name either the anther or the stigma.
This question was an open opportunity for candidates to display their understanding of experimental processes. Although a certain number of well-structured answers were seen, this was probably the most poorly handled question of this paper. Although most had understood that only one variable could be changed at a time, it was expected they should have the basic knowledge that water is essential for germination and would go beyond experiments involving one seed with water and one with no water, as too many suggested. The majority could not understand that, to draw valid conclusions, many seeds should be used in many repeats and that controls should be used. They also had much difficulty at suggesting how results could be gathered, often confusing germination with seedling growth. One can therefore wonder about how the practical programme is delivered in many schools.