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Date May 2017 Marks available 3 Reference code 17M.2.SL.TZ2.6
Level Standard level Paper Paper 2 Time zone Time zone 2
Command term Describe Question number 6 Adapted from N/A

Question

Describe the structure and function of starch in plants.

[3]
a.

Outline the production of carbohydrates in photosynthesis.

[4]
b.

Discuss the processes in the carbon cycle that affect concentrations of carbon dioxide and methane in the atmosphere and the consequences for climate change.

[8]
c.

Markscheme

Structure:

a. «starch» is a polysaccharide/is composed of glucose molecules 

b. contains amylose which is a linear/helical molecule 

c. contains amylopectin which is a branched molecule 

Function:

d. storage of glucose/energy in plants 

e. storage form that does not draw water

a.

a. light is absorbed by chlorophyll
OR
chlorophyll absorbs more red and blue light 

b. «absorbed» light energy is converted to chemical energy 

c. some of the energy is used for production of ATP 

d. water molecules are split/photolysis 

e. produces oxygen «as waste product»/hydrogen/NADPH 

f. plants absorb/fix CO2 «from air or water» 

g. ATP/energy is needed to produce carbohydrates/starch

b.

a. CO2 is produced from respiration in organisms/combustion of biomass/fossil fuels 

b. CH4 is produced by anaerobic respiration of biomass/«methanogenic» bacteria 

c. CH4 is oxidized to CO2 and water 

d. CO2 is converted into carbohydrates/organic compounds by autotrophs/producers/photosynthesis 

e. CO2 can be converted to calcium carbonate/fossilized into limestone 

f. «partially» decomposed organic matter/biomass can be converted into peat/coal/oil/gas/fossil fuels 

g. CO2 and CH4 are both greenhouse gases/increase greenhouse effect 

h. both absorb long-wave radiation from the earth and retain the heat in the atmosphere 

i. increased CO2 concentrations in the atmosphere correlate with increased combustion of fossil fuels 

j. rising average global temperatures correlate with more greenhouse gases in the atmosphere 

k. cattle production/rice paddy/defrosting of tundra increase CH4 in the atmosphere
OR
increasing CO2 leads to acidification of marine/aquatic environments 

l. the global temperature increase influences/disrupts climate patterns

OWTTE

c.

Examiners report

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

Syllabus sections

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