C1.3 Photosynthesis

a. plants/producers/autotrophs convert light to chemical energy by photosynthesis

b. chlorophyll/photosynthetic pigments absorb light

c. electrons are excited/raised to higher energy level

d. excited electrons pass along chain of electron carriers

e. energy from electrons used to pump protons across thylakoid membrane/into thylakoid space

f. chemiosmosis/proton gradient used to make ATP

g. ATP synthase generates ATP

h. pigments arranged in photosystems

i. electrons from Photosystem II flow via the electron chain to Photosystem I

j. electrons from Photosystem I are used to reduce NADP

k. ATP and reduced NADP used in the light independent reactions/Calvin cycle

I. carbohydrate/glucose/carbon compounds produced containing energy

Marking guidance:

Award marking points for any point made on a clearly annotated diagram.

8 max

a. solar/light energy is converted to chemical energy

b. energy needed to produce glucose

c. only specific wavelengths are absorbed by chlorophyll OR

red and blue absorbed most strongly.

OR

chlorophyll is the pigment that absorbs light energy

d. $\mathrm{H}^{(+)} /$electrons from water are used to reduce compounds

e $\quad \mathrm{CO}_{2}$ is absorbed/used/reduced to produce carbohydrates

f. correct word/balanced symbol equation of photosynthesis

Marking guidance:

Accept correct reference to NADPH/ATP from AHL.

B

a. crush/blend algae with organic solvent/alcohol/other valid solvent;

b. place drop of extracted algal pigments/ obtained liquid on thin layer

OR

mark the origin;

c. place slide (with pigments) in solvent ensuring the pigment spot does not touch the solvent

OR

solvent moves up carrying pigments

OR

different pigments move at different rates/distances (so can be distinguished);

Thin layer could be
(chromotography) paper, slide,
column etc.

3 max

Outline how plants make use of the different wavelengths of light.

a. light used in photosynthesis/light-dependent reactions/ photolysis/photosystems/photophosphorylation/excitation of electrons/switch to flowering

b. chlorophyll absorbs red AND blue light (more)

c. chlorophyll/leaf/plant reflects/does not absorb/does not use green light

d. absorption spectrum of chlorophyll has peaks in the red and blue/sketch graph to show this

e. action spectrum shows which wavelengths plants use in photosynthesis/sketch graph of action spectrum showing peaks in the blue and red

f. accessory/other (named) photosynthetic pigments absorb different wavelengths/colours

g. violet is the shortest wavelength and red the longest

h. red light and far red/infra-red absorbed to measure length of light/dark periods

4 max

a. axes correctly labelled «wavelength and 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

Accept rate of oxygen production for rate of photosynthesis.

3 max

measuring oxygen release;
measuring volume / counting rising oxygen bubbles / counting rising disks; measuring carbon dioxide intake/uptake;
$\mathrm{CO}_{2}$ can be measured by change in pH / increase in pH shows an increase in $\mathrm{CO}_{2}$ fixation;
increase in biomass would be an indirect measure of photosynthesis / measure of net photosynthesis;
measure starch production / dry organic mass;
increasing temperature would increase the rate of photosynthesis; provided the temperature did not go above optimum temperature of enzymes;
increasing carbon dioxide concentration would increase the rate of photosynthesis; higher light intensity would increase the rate of photosynthesis;
light of different wavelengths / blue and red light can affect photosynthesis / green wavelength usually not absorbed;

data does not support idea that rising $\mathrm{CO}_{2}$ levels will increase growth rates in maize;
(at all temperatures) there appears to be no difference between exchange rate at current or elevated $\mathrm{CO}_{2}$ levels;
temperature has larger effect on growth of maize;
so if rising $\mathrm{CO}_{2}$ levels causes more of a greenhouse effect/larger temperature increase, this will affect growth of maize;

a. photosystems embedded/located in chloroplast/thylakoid membranes;

b. two types of photosystems, (Photosystem I and Photosystem II/PSI and PSII);

c. structure allows light energy to be captured;

d. (energy used) to emit excited electron;

e. molecular arrays of chlorophyll (and accessory pigments)

OR

photosystem combines different types of pigments in one array;

f. a greater proportion of wavelengths can be absorbed / greater proportion of sunlight can be used

OR

a single molecule of chlorophyll would not be able to perform photosynthesis;

3

Marking guidance:

max

water only plays a role in non-cyclic photophosphorylation;
chlorophyll absorbs light/photons and activates electrons of photosystem II; excited/active electrons of photosystem II are passed to carriers; photolysis is the splitting of water;
produces $\mathrm{O}_{2}$ and $\mathrm{H}^{+}$/proton and electrons;
$\mathrm{O}_{2}$ released (as waste);
electrons (from water) replace lost electrons in photosystem II; electrons from photosystem II pass (through carriers) to photosystem I;
electrons from photosystem I pass to NADP ${ }^{+}$(in stroma);
NADP ${ }^{+}$accepts $\mathrm{H}^{+}$/proton (from water) to form NADPH;
electron flow causes protons pumped across thylakoid membranes/into the thylakoid space;
creating a proton concentration gradient;
chemiosmosis couples electron transport to ATP synthesis; protons pass through ATP synthase/synthetase;
$\mathrm{NADPH} / \mathrm{H}^{+} /$proton is passed to the light-independent reactions (to fix carbon);

Marking guidance:

[8 max]

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 ( $\mathrm{P}_{\mathrm{i}}$ ) forms ATP;
k. (the kinetic energy from) movement of hydrogen ions (through ATP synthase) generates ATP;
I. ATP synthase is a protein complex in the thylakoid membrane;
m. formation of proton gradient / ATP synthesis linked to electron transport is chemiosmosis;

Marking guidance:

Award marks for a clearly drawn correctly annotated diagram.

D

ATP and $\mathrm{NADPH}_{2} / \mathrm{NADPH}+\mathrm{H}^{+}$(both needed)

a. Calvin's experiment used algae/Chlorella in a round/thin/flat apparatus/"lollipop";

b. labelled carbon dioxide with radioactive carbon/ $\mathrm{C} 14 /{ }^{14} \mathrm{C}$ (supplied to algae);

c. exposed the algae to light to promote photosynthesis;

d. every 5/few seconds/at short time intervals, samples of algae were taken;

e. carbon compounds separated using chromatography;

f. radioactive carbon compounds/molecules with radioactive carbon/C14/ ${ }^{14} \mathrm{C}$ identified with x-rays (autoradiography) / molecules containing radioactive carbon/C14/ ${ }^{14} \mathrm{C}$ traced / glycerate 3-phosphate was the first compound detected/identified;

g. Calvin cycle/carbon fixation is the light-independent phase (of photosynthesis);

h. it takes place in the stroma (of the chloroplast);

i. ribulose bisphosphate/RuBP carboxylated to glycerate 3-phosphate/G3P;

j. catalysed by rubisco / (ribulose bisphosphate) carboxylase;

k. glycerate 3-phosphate/G3P is reduced to triose phosphate (using reduced NADP/NADPH and ATP);

I. triose phosphate is used to produce glucose;

m. triose phosphate is used to regenerate RuBP;

Marking guidance:

Allow clear annotated diagrams for
marking points mpi to mpm.

8 max

A

B

a light-dependent reactions produce ATP/reduced NADP;

b ATP generated by chemiosmosis/by photophosphorylation/by ATP synthase;

c reduced NADP produced by/using electrons from Photosystem I;

d RuBP $+\mathrm{CO}_{2}$ to glycerate 3-phosphate (in light independent reactions);

e glycerate 3-phosphate reduced to triose phosphate (in light independent reactions);

f ATP/reduced NADP used in the light-independent reactions;

g reduced NADP provides electrons/hydrogen / to reduce (glycerate 3phosphate)

OR

reduced NADP used to convert glycerate 3-phosphate to triose phosphate;

h ATP provides energy (for reduction of glycerate 3-phosphate);

i ATP needed to regenerate RuBP

j ATP/reduced NADP run out in darkness

k Calvin cycle only possible with light/in the day/is indirectly dependent on light;

7 max