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Date	May 2021	Marks available	2	Reference code	21M.2.HL.TZ2.3
Level	Higher level	Paper	Paper 2	Time zone	Time zone 2
Command term	Compare and contrast	Question number	3	Adapted from	N/A

Question

A broad bean is the seed of a species, Vicia faba, in the Fabaceae, a family of flowering plants. This family contains many species that are used as sources of food.

On the diagram, label the testa and the radicle.

[2]

An experiment was done to test the hypothesis that temperature affects the rate of germination of the broad bean. Outline two factors apart from temperature that should be controlled in this experiment.

[2]

State the genus of the broad bean.

[1]

Broad beans are rich in starch and cellulose. Compare and contrast the structure of starch and cellulose.

[2]

Once the germinated bean grows above the ground, state the process used by the bean in the production of starch.

[1]

Markscheme

a. testa labelled ✔

b. radicle labelled ✔ (must point to the bottom half of the embryo or the tip).

a. same amount/type of soil/substrate / pH of soil ✔ e.g.: heater

b. same amount of water / humidity ✔

c. oxygen/aeration ✔

d. same measurement of germination / time ✔ e.g.: emergence of radicle

e. same number/source/age of seeds ✔

Accept discussion of light only in as much as it relates to temperature.

Vicia ✔

No mark if the species name is included.

Mark can be awarded if the genus is not capitalized.

a. both polymers of glucose molecules / polysaccharides
OR
both form 1,4 glycosidic bond ✔

b. starch is formed by alpha glucose while cellulose is formed by beta glucose
OR
in starch C1 hydroxyl groups are found in same plane while in cellulose on different planes
OR
in cellulose, alternatively the beta glucose needs to be placed upside-down in order to have C1 hydroxyl groups on the same plane
OR
two types of starch (amylose and amylopectin) but one type of cellulose ✔

One similarity and one difference.

Comparison to cellulose needed.

photosynthesis

Do not accept condensation or polymerization; if list of processes given, mark the first answer.

Examiners report

Many candidates did not correctly label the testa and in many cases the radicle was labelled too high up, pointing at the hypocotyl.

Several answers considered how light is needed for germination without any reference to its relationship to temperature.

This question presented some confusion to Spanish speaking candidates since the word "género" is the same for "genus" and "gender", so some candidates write "male/female" in their answers.

Candidates seemed to find it difficult to find similarities and differences in structure between starch and cellulose, and many wrote about their functions, or simply mentioned that both were made of "glucose" without referencing that they are both polymers. There was limited recognition that there are two forms of starch: amylose and amylopectin that differ in their degree of branching.

[N/A]

Syllabus sections

Core » Topic 2: Molecular biology » 2.3 Carbohydrates and lipids

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