Question 19M.2.HL.TZ2.8
| Date | May 2019 | Marks available | [Maximum mark: 15] | Reference code | 19M.2.HL.TZ2.8 |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Draw, Explain, Outline | Question number | 8 | Adapted from | N/A |
Outline energy flow through a food chain.
[4]
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 ✔
Was well answered with most students being knowledgeable about ecology.
Draw a fully labelled graph of the action spectrum for photosynthesis.
[3]
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 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.
Explain Calvin’s experiment and what was discovered about photosynthesis through his work.
[8]
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 ✔
This question was commonly answered poorly with students showing a lack of knowledge of both the Calvin cycle as well as the Calving experiment.