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Date	November 2019	Marks available	3	Reference code	19N.2.HL.TZ0.4
Level	Higher level	Paper	Paper 2	Time zone	TZ0 / no time zone
Command term	Explain	Question number	4	Adapted from	N/A

Question

During photosynthesis plants use water in the conversion of light energy to chemical energy.

State the property of amphipathic phospholipids that enables them to form a bilayer.

[1]

a.i.

State the reason cis and trans fatty acids are said to be unsaturated.

[1]

a.ii.

State the name of this process.

[1]

b.i.

Explain how water is used in photosynthesis.

[3]

b.ii.

Markscheme

have both a hydrophilic and a hydrophobic region
OR
have both a polar and a non-polar region ✔

a.i.

they have a double bond between carbon/C «atoms»
OR
they could hold more hydrogen ✔

Accept clearly annotated diagrams to that effect.
Do not accept double bonds between C and any other atom

a.ii.

photolysis / light-dependent «reactions/stages» / photophosphorylation ✔

b.i.

a. water is split/broken «up»/lysed/undergoes photolysis ✔ For mpa, reject “water is cut in half”. For mpa, accept photolysis only if the context shows that water is being split.

b. producing/providing electrons ✔

c. replaces electrons lost by Photosystem II / PSII / P680 / chlorophyll a ✔ For mpc, do not accept just chlorophyll.

d. allows electrons «to continue» to pass along the electron transport chain ✔

e. provides protons/H+ «inside thylakoid» to help generate a «proton» gradient/maintain high concentration inside thylakoid ✔ For mpe, reject pumping of protons into the thylakoid as photolysis produces them inside the thylakoid.

b.ii.