Explain chemiosmosis as it occurs in photophosphorylation.

Draw an annotated graph of the effects of light intensity on the rate of photosynthesis.

Using a named example of a genetically modified crop, discuss the specific ethical issues of its use.

Remember, up to TWO “quality of construction” marks per essay.

a. photophosphorylation is the production of ATP;
b. (some of the) light absorbed by chlorophyll / photosystem II;
c. photolysis/splitting of water separation of hydrogen ion from its electron;
d. the electron transport system moves the electrons through a series of carriers;
e. (electron transport system occurs) in the thylakoid membrane;
f. electron transport linked to movement of protons into thylakoid space;
g. a proton gradient builds up (in the thylakoid space);
h. small thylakoid space enhances the gradient;
i. hydrogen ions move by diffusion through the ATP synthase;
j. ADP + inorganic phosphate (Pi) forms ATP;
k. (the kinetic energy from) movement of hydrogen ions (through ATP synthase) generates ATP;
l. ATP synthase is a protein complex in the thylakoid membrane;
m. formation of proton gradient / ATP synthesis linked to electron transport is chemiosmosis;

Award marks for a clearly drawn correctly annotated diagram.

a. vertical axis labelled as “rate of photosynthesis” and horizontal axis labelled as “light intensity”;
b. drawn showing that at low light intensities, increased intensity leads to increased rate of photosynthesis (sharply);
c. drawn with plateau formed at high light intensities;
d. plateau annotated as maximum rate of photosynthesis;
e. curve intersecting horizontal axis at a value above zero;
f. arrows added to axes or student annotates axis with “rate of photosynthesis increases” and “light intensity increases”

Remember, up to TWO “quality of construction” marks per essay.

a. named example of verified genetically modified crop; eg, Bt corn / golden rice;
Example must be verifiable.
b. specific gene added / new protein synthesized by the crop plant / specific modification; eg gene from Bacillus thuringiensis / cry protein;
c. biological effect of the modification; eg, makes the plant toxic to (herbivorous) insects / insect pests / corn borers;
[2 max] for benefits and [2 max] for harmful effects / costs;

d. a benefit of specific genetic modification; eg, increased crop yields / less land needed;
e. a second benefit of this specific modification; eg, reduced need for use of chemical pesticides;
f. a harmful effect of specific genetic modification; ingestion of toxin by nontarget species;
g. another specific harmful effect; eg, concerns about contamination of neighbouring non-GMO crops affecting trade;

To award [6] responses need to address the name, description and the effect of the modification. Effects have to be linked to the specific example discussed. Marks have to be all linked to one example. Assistant examiners are required to research examples.

Students appear to have a general understanding of mechanisms but make a number of errors in terms of the location of events such as where the proton gradient builds up.

This was well answered by most students. Many did not draw the curve intersecting the horizontal axis at a value above zero. Many constructed a diagram of the curve but provided text below the curve in a paragraph rather than annotating the curve itself with explanations of what was occurring at various levels of light intensity.

The best answers outlined the biology of the example well though a very large number dealt in hypothetical or speculative costs and benefits of genetic modification.