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Date	May 2019	Marks available	3	Reference code	19M.2.HL.TZ2.8
Level	Higher level	Paper	Paper 2	Time zone	Time zone 2
Command term	Draw	Question number	8	Adapted from	N/A

Question

Outline energy flow through a food chain.

[4]

Draw a fully labelled graph of the action spectrum for photosynthesis.

[3]

Explain Calvin’s experiment and what was discovered about photosynthesis through his work.

[8]

Markscheme

a. energy from the sun/light energy is converted to chemical energy by photosynthesis ✔

b. «chemical» energy flows through the food chains by feeding ✔

c. energy is released «from carbon compounds» by respiration
OR
energy from respiration is used by living organisms and converted to heat ✔

d. heat is not recyclable / heat is lost from food chains
OR
heat cannot be converted to other forms of energy ✔

e. energy is lost in excretion/uneaten material/egestion/feces ✔

f. energy losses between trophic levels limits the length of food chains
OR
energy transfer is only 10 % between trophic levels ✔

a. axes correctly labelled «wavelength and rate of photosynthesis» ✔ Accept rate of oxygen production for rate of photosynthesis.

b. 400 and 700 nm as limits ✔

c. correct shape of curve involving two peaks at the correct places, broader in the blue-violet range not starting at zero and a narrower peak in the orange-red range with the trough in the green range that does not reach zero ✔

d. peaks of activity at 430 nm AND at 660 nm ✔

e. peaks indicated as «violet» blue light AND peak indicated as «orange» red light ✔

a. Calvin cycle is light-independent ✔

b. carbon fixation
OR
carboxylation of ribulose bisphosphate/RuBP occurs ✔

c. algae placed in thin glass container/“lollipop” apparatus ✔

d. given plenty of light and bicarbonate/ CO₂ ✔

e. at start of experiment algae supplied radioactive carbon/HCO₃-/¹⁴C ✔

f. samples taken at intervals / heat/alcohol killed samples ✔

g. C-compounds separated by chromatography ✔

h. ¹⁴C/radioactive-compounds identified by autoradiography ✔

i. showed that RuBP was phosphorylated ✔

j. after five seconds/immediately more glycerate-3-phosphate/3-PGA labelled than any other compound ✔

k. shows glycerate-3-phosphate/3-PGA first «carboxylated» compound/the first stable product ✔

l. next compound to be detected containing radioactive carbon was triose phosphate/G3P/glyceraldehyde 3 phosphate ✔

m. showed that a wide range of carbon compounds was quickly made in sequence ✔

n. showed that a cycle of reactions was used to regenerate RuBP ✔

Examiners report

Was well answered with most students being knowledgeable about ecology.

A number of students made errors in their sketches. Axes were commonly mis-labelled. The colors were commonly presented in the reverse order with red at the left end and blue at the right end. Showing red as a higher peak was another common error. The overall shape was often correctly drawn.

This question was commonly answered poorly with students showing a lack of knowledge of both the Calvin cycle as well as the Calving experiment.

Syllabus sections

Core » Topic 2: Molecular biology » 2.9 Photosynthesis

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