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Date November 2018 Marks available 2 Reference code 18N.2.SL.TZ0.2
Level Standard level Paper Paper 2 Time zone TZ0 / no time zone
Command term Explain Question number 2 Adapted from N/A

Question

Label the area where cellulose is found in the micrograph of a plant cell.

[Source: BIOPHOTO ASSOCIATES/Getty Images]

[1]
a.i.

Cellulose is the most abundant organic polymer on Earth. Describe the structure of cellulose.

[3]
a.ii.

Outline one reason for humans being unable to digest cellulose.

[1]
b.

Explain the advantages of having both lipid and carbohydrate as energy stores in the human body.

[2]
c.

Markscheme

label placed anywhere along outside perimeter/cell wall of plant cell ✔

a.i.

a. unbranched/straight chain of glucose molecules
OR
unbranched/straight-chain polysaccharide ✔

b. formed of beta glucose;

c. formed by condensation reactions/glycosidic bonds
OR
1, 4 linkage ✔

 

d. hydrogen bonds form between cellulose chains 

e. form microfibrils ✔

 

Award marks to an accurate annotated diagram

Do not allow carbohydrate

a.ii.

humans lack cellulase/appropriate enzyme ✔

b.

a. lipid is long-term energy storage
OR
carbohydrate is short-term energy storage/readily available ✔

b. lipids are insoluble, so easier to store
OR
carbohydrates/sugars are soluble, so easy to transport by blood ✔

c. lipids store more energy «per gram»
OR
lipids occupy less space «per energy/kJ» ✔

OWTTE

c.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.
[N/A]
c.

Syllabus sections

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