biology 17

Question 1

explains why this pigment is orange-red to the human eye?

Answer 1

The pigment absorbs green and blue light.

Question 2

Outline the importance of photosynthetic pigments in photosynthesis.

Answer 2

(pigments) absorb , light / photons ✓

electrons , excited / raised to
higher energy level ✓

accessory pigments pass energy to , reaction centres / primary pigments ✓
primary pigments , become oxidised / lose electrons / pass electrons to ETC ✓
for light dependent reaction / photophosphorylation ✓

Question 3

The wavelengths of light absorbed by chlorophyll c are different from those wavelengths absorbed by chlorophyll a and chlorophyll b

Suggest why Chromista need pigments that are different from those of other photosynthetic organisms.

Answer 3

idea that they have to absorb light of short (er) wavelengths ✓

idea that some wavelengths (of light) don’t reach , depths / them

Question 4

State the precise location of photosynthetic pigments in a chloroplast.

Answer 4

photosystems ✓
(in) thylakoid (membranes) ✓

Question 5

The solvent used for the separation was non-polar.

Identify the spot corresponding to the least polar pigment. Give a reason for your choice.

Answer 5

spot 5 ✓ - the one furthest from origin
(because) is most soluble in , mobile phase / solvent ✓

Question 6

Explain why the method included the following precautions:
Hold the TLC plate carefully by the edges and avoid damaging the surface of the plate.

Answer 6

hold TLC plate carefully
(so that) movement of spots not affected (by damage)
OR
(so that) plates are not contaminated (by fingerprints / oils from skin) ✓

Question 7

Explain why the method included the following precautions:
Make sure the plate does not touch the sides of the jar anywhere else.

Answer 7

condensation / liquid / solvent , on walls of jar may affect movement of spots

Question 8

Suggest an advantage of working as quickly as possible in Step 1 (Hold the TLC plate carefully by the edges and avoid damaging the surface of the plate.)

Answer 8

to avoid , solvent / spots , travelling in wrong direction ✓

Question 9

State the name of the final electron acceptor in the light-dependent stage of photosynthesis.

Answer 9

NADP

Question 10

During the light-independent stage of photosynthesis, triose phosphate (TP) is synthesised in the chloroplasts of plant cells.
i.
State two possible uses of this molecule within the plant.

Answer 10

synthesis of:
(named) carbohydrate (1)

hexose sugars (1)

amino acids (1)

lipids (1)

Question 11

From which molecule is TP synthesised during the light-independent stage?

Answer 11

GP / glycerate-3-phosphate

Question 12

Moderate HT stress:
Effect:
Heat-induced deactivation of RuBisCO
No change in chlorophyll fluorescence in PSII
Reduction in stomatal aperture

Answer 12

deactivation of RuBisCO will reduce, carbon dioxide fixation / light independent reaction (1)

the light dependent reaction will reduce when the supply of NADP is reduced (1)

reduction in stomatal aperture will reduce carbon dioxide available for fixation (1)

Question 13

Suggest two ways in which the ultrastructure of the chloroplast can be altered by high
temperatures.

For each suggestion, explain the effect that it will have on photosynthesis.

Answer 13

damage to chlorophyll / reduction in pigment (1)
which will reduce the light dependent stage (1)

damage to membranes in chloroplast / reduction in sites for light capture (1)
which will reduce the light dependent stage (1)

damage to membranes in chloroplast / reduction in reaction sites for electron transfer (1) which will reduce, photophosphorylation / ATP production in the light dependent stage (1)

damage to membrane around chloroplast / release of enzymes (1)
which will reduce, light independent stage / Calvin cycle (1)

Question 14

Explain what is meant by a limiting factor.

Answer 14

the factor that will, determine / limit /the rate ✔
when at, low(er) / sub-optimal / AW, level ✔

Question 15

Describe how the student could improve their experimental method and the presentation of their dat

Answer 15

Improvements to presentation
* Units for light intensity should be shown
(e.g. AU or lux, etc.)
* The table should be presented to make comparisons of light intensity easier (example of improvement - e.g. separate tables for temperature and light intensity).
* The heading of column three could be improved (e.g. ‘rate of photosynthesis - bubbles min-1’)
* present data as a graph (e.g. light intensity / temperature vs, number of bubbles)
Improvements to method
* A more precise method for measuring photosynthetic rate (e.g. a (calibrated) oxygen sensor (rather than counting bubbles) use of a photosynthometer / gas syringe / burette / measuring cylinder (to measure volume of gas).
Control other variables in the experiment (named control variables e.g. same, size/age, pondweed /
same pH / change water surrounding pondweed for each measurement / time to acclimatise / same wavelength of light)
* Provide carbon dioxide source
(e.g. so carbon dioxide in excess / not limiting / add hydrogencarbonate)
* Smaller and more consistent intervals between light and temperature values should be used (e.g. intervals of 50 light intensity units or 10°C).
* repeats should be used. (e.g. to calculate mean or identify
anomalies)

Question 16

The students wanted to test whether there was a significant difference between the stem lengths of the seedlings in Group A and the seedlings in Group B.

State the name of the most appropriate statistical test for the students to use.
iii. Justify your choice of statistical test given in part (ii).

Answer 16

(unpaired) t-test ✓
idea of comparing two means ✓

Question 17

Describe two ways in which the structure of grana is adapted to its function.

Answer 17

1 contain , (named) pigment (molecules) / photosystems ;

2 contain ,
(named) electron carriers / ETC / ATP synth(et)ase ;

idea that has a large surface area (in a small volume) for , light absorption /
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light dependent reaction(s) / light dependent stage / electron transport ;