DP Biology (first assessment 2025)

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Question 19M.2.HL.TZ2.c

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Date May 2019 Marks available [Maximum mark: 8] Reference code 19M.2.HL.TZ2.c
Level HL Paper 2 Time zone TZ2
Command term Explain Question number c Adapted from N/A
c.
[Maximum mark: 8]
19M.2.HL.TZ2.c

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

[8]

Markscheme

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

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