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Date November 2016 Marks available 4 Reference code 16N.2.HL.TZ0.8
Level Higher level Paper Paper 2 Time zone TZ0 / no time zone
Command term Describe Question number 8 Adapted from N/A

Question

In ecosystems, energy is used to convert inorganic compounds into organic matter. Energy enters ecosystems through producers.
 

Explain the processes by which light energy is converted into chemical energy.

[8]
a.

Describe how energy flows through and is used by organisms in ecosystems.

[4]
c.

Markscheme

a. plants/producers/autotrophs convert light to chemical energy by photosynthesis

b. chlorophyll/photosynthetic pigments absorb light

c. electrons are excited/raised to higher energy level

d. excited electrons pass along chain of electron carriers

e. energy from electrons used to pump protons across thylakoid membrane/into thylakoid space

f. chemiosmosis/proton gradient used to make ATP

g. ATP synthase generates ATP

h. pigments arranged in photosystems

i. electrons from Photosystem II flow via the electron chain to Photosystem I

j. electrons from Photosystem I are used to reduce NADP

k. ATP and reduced NADP used in the light independent reactions/Calvin cycle

l. carbohydrate/glucose/carbon compounds produced containing energy

Award marking points for any point made on a clearly annotated diagram.

a.

a. producers/plants/autotrophs obtain energy from light/sun/inorganic sources

b. food contains energy / energy passed in the form of food/carbon compounds (along food chains/between trophic levels)

c. consumers obtain energy from other organisms/from previous trophic level 

This mark point distinguishes consumers from producers.

d. energy released (in organisms) by (cell) respiration 

Reject energy used in respiration.

e. ATP produced

f. energy/ATP used for biosynthesis/movement/active transport/other valid use of ATP

g. less energy available / energy lost at each trophic level

c.

Examiners report

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

Syllabus sections

Core » Topic 4: Ecology » 4.2 Energy flow
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