Date | November 2011 | Marks available | 4 | Reference code | 11N.2.HL.TZ0.8 |
Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
Command term | Draw | Question number | 8 | Adapted from | N/A |
Question
Draw the absorption spectrum of chlorophyll.
Explain the process of photophosphorylation in chloroplasts.
Outline how the glucose produced as a result of photosynthesis is transported and stored in plants.
Markscheme
labelled x-axis: wavelength / colour;
labelled y-axis: absorbance / % absorption;
peak between 400 and 500 nm / blue light;
peak between 600 and 700 nm / red light;
blue peak higher than red peak;
using energy from light to provide energy;
absorbing light/photoactivation produces an excited/high energy/free electron;
absorption of light in photosystem II gives electron to chain of carriers;
photolysis;
H+ pumped across thylakoid membrane;
protons pass through ATP synthetase/synthase;
producing ATP;
chemiosmosis;
(chlorophyll/antenna of) photosystem I absorbs light;
cyclic and non-cyclic photophosphorylation;
(in non-cyclic photophosphorylation) photolysis of water produces H+/O2/e–;
in cyclic photophosphorylation electron returns to photosystem I;
Accept any of the above points shown in a clearly annotated diagram.
glucose transformed to sucrose;
translocation of sugars/sucrose;
by phloem;
active process / requires energy;
from source to sink;
source is photosynthetic tissue/leaves;
sink is fruits/seeds/roots/storage organs;
(sucrose) converted to starch;
stored in storage organs/roots/tubers;
Examiners report
The syllabus statement for 8.2.7 does say "explain‟ as a command term for absorption spectrum. Draw is a lower level skill, and students should be able to draw the typical absorption spectrum. The x-axis is commonly not understood conceptually. If the axis is "wavelength‟, then red should be shown as longer wavelength than blue. This was commonly reversed. The y-axis was often insufficiently labelled as absorption. Absorbance or percent absorption was required.
Most of the better students who attempted this question explained photophosphorylation very well. Students who had done poorly on the rest of the paper avoided this question.
As mentioned before, some centres seem to have regarded the plant topic as optional, so the function of phloem was not well known. Many did not demonstrate awareness that sugars are translocated as sucrose, not glucose.