5.6: Photosynthesis

Question 1

Describe two ways in which the structure of part C(granum/ grana/ granal stack) is adapted to its function. (2mks) [f214 june 15 q1aii]

Answer 1

1 contain, (named) pigment (molecules) / photosystems;
2 contain, (named) electron carriers/ ETC/ ATP synth(et)ase;
3 idea that has a large surface area (in a small volume)
for, light absorption / light dependent reaction (s)/ light dependent stage / electron transport;
[ ‘the membranes containing the pigments have a large
surface area for absorbing light’ = 2 mks;
‘there is a large surface area for electron transport
chain’ = 2 mks ]

Question 2

explain why the theoretical rate of photosynthesis is not achieved at higher light intensities. (2mks) [f214 june 15 q1b]

Answer 2

1 at high light intensity other (temperature/ CO2 conc.) factor becomes a limiting factor; [light is no longer the limiting factor]
2 temperature becomes limiting as, Calvin cycle / light independent reaction, involves enzymes/ relies on kinetic energy of molecules; [ref to Rubisco being limited by temp (as a named enzyme being in the Calvin cycle)]
3 CO2 (concentration) becomes limiting as it is required for, Calvin cycle/ light independent reaction/ formation of (named) Calvin cycle compound/ reaction with RuBP/ fixation by Rubisco; [GP/ TP/ RuBP]

Question 3

Using the information in Fig. 1.3, explain which of the two species, D or E, is better adapted to living in shady conditions. graph shows light intensity against rate of photosynthesis, E starts phtosynthesis earlier, reaches plateau quicker and remains lower levele. (2mks) [f214 june 15 q1ci]

Answer 3

species E because
1 E starts photosynthesising at low(er) light intensity;
2 E reaches its maximum rate at low(er) light intensity;
3 E steep(er) increase in rate of photosynthesis
(with small increase in light intensity);
4 E has a, higher/ greater / faster, rate of photosynthesis (than D) at low light intensities; [E has a faster increase in the rate of photosynthesis at low light intensities’ = 2 marks ]

Question 4

The leaf of a plant that is adapted to living in shade will differ from the leaf of a plant that is adapted to living in sunlight.
Suggest one way in which the structure of these leaves will differ [f214 june 15 q1cii]

Answer 4

shade leaf will have
1 large(r) / more, chloroplast(s)/ (palisade) mesophyll; [more, chlorophyll/ photosystems]
2 more, grana/ thylakoids (in chloroplast);
3 large(r) surface area (of leaves);

Question 5

Plants are autotrophs. Most other organisms are heterotrophs. Outline the ways in which heterotrophic organisms are dependent on plants (3mks) [f214 june 15 q1d]

Answer 5

1 animals / heterotrophs (need to), eat/ obtain organic material from, plants / autotrophs;
2 (plants / autotrophs) produce (named) organic molecules during, photosynthesis/ Calvin cycle/ light independent stage;
3(plants / autotrophs) produce oxygen during, photosynthesis/ photolysis/ light dependent stage;
4 glucose / carbohydrate / oxygen, (produced in photosynthesis) are used in respiration by, animals/ heterotrophs;

Question 6

Name the primary photosynthetic pigment in photosystems I and II. [F214 June 14 q1ai]

Answer 6

chlorophyll, a/ A;

Question 7

Name an accessory pigment. [F214 June 14 q1aii]

Answer 7

chlorophyll b/ xanthophyll(s)/ carotenoid(s)/ (/ beta-) carotene; [

Question 8

State the advantage to the plant of having a range of accessory pigments in photosystems. [F214 June 14 q1aiii]

Answer 8

able to , absorb / use , a range of / different / more / other , (light) wavelengths;

Question 9

Name the compound that is synthesised in the light-dependent stage as a result of the generation of an electrical and pH gradient across the thylakoid membrane. [F214 June 14 q1aiv]

Answer 9

ATP

Question 10

Identify the enzyme that catalyses the fixation of carbon dioxide. [F214 June 14 q1bi]

Answer 10

rubisco / RuBP carboxylase / ribulose bisphosphate carboxylase; [ribulose biphosphate carboxylase]

Question 11

Identify the first stable product of carbon dioxide fixation. [F214 June 14 q1bii]

Answer 11

GP / glycerate(3-)phosphate ;

Question 12

Identify the compound that is regenerated in the Calvin cycle so that more carbon dioxide
can be fixed. [F214 June 14 q1biii]

Answer 12

RuBP / ribulose bisphosphate ;

Question 13

Name two different polysaccharides that can be synthesised from the end products of the light-independent stage of photosynthesis. [F214 June 14 q1biv]

Answer 13

starch / amylose / amylopectin
and
cellulose ;

Question 14

Respiration can be aerobic or anaerobic. Certain parasites live in the blood of mammals. Suggest why, even though blood carries oxygen, these parasites are adapted to respire anaerobically. (2mks) [F214 June 14 q5bi]

Answer 14

1 idea that parasites have little access to oxygen ;
2 (inaccessible because) little oxygen dissolved in plasma / oxygen not very soluble (in plasma) ;
3 (inaccessible because) idea that oxygen is , combined with haemoglobin / contained in red blood cells ; [in context of saturation]
4 idea that haemoglobin has greater affinity for oxygen than parasite (pigment) ; [‘because the oxygen is bound to haemoglobin, the parasite is unable to use it’ = 2 marks]

Question 15

[F214 June 14 q6] The molecules listed below are all associated with photosynthesis. amino acid, reduced NADP, ATP, ribulose bisphosphate (RuBP), carbon dioxide, rubisco, glycerate-3-phosphate (GP), triose phosphate (TP), oxygen, water
From these molecules, identify:
(a) the enzyme.
(b) a product of the light-dependent reaction that is used in the light-independent reaction.
(c) a 3-carbon compound.
(d) a compound that can be made from TP but is not part of the Calvin cycle.
(e) a 5-carbon compound.
(f) a product of the light-dependent reaction that is not used in the light-independent reaction.

Answer 15

a) rubisco ;
b) ATP / reduced NADP ;
c) glycerate-3-phosphate / GP / triose phosphate / TP ;
d) amino acid ;
e) ribulose bisphosphate / RuBP ;
f) oxygen ;

Question 16

Explain what is meant by the term autotroph [F214 Jan 13 q3a]

Answer 16

can make, organic molecule(s) / named organic molecule(s), from, inorganic molecule(s) / carbon dioxide ; [fixes carbon dioxide to produce (named)
carbohydrates / protein / lipid]

Question 17

Explain what is meant by the term heterotroph [F214 Jan 13 q3a]

Answer 17

relies on / needs to use / has to obtain / feeds on and digests , (named) organic molecules (that have been made by another organism) ; [idea of need or taking in and breaking down is important; has to get its organic molecules from another organism’ = 1 mark]

Question 18

The chloroplast contains fat droplets, as shown in Fig. 3.1. These act as a reserve of raw material for the chloroplast.
Suggest what this raw material might be used for in the chloroplast. [F214 Jan 13 q3bii]

Answer 18

for membrane formation or phospholipid / cholesterol / glycolipid , for membrane ;
fatty acid / (named) pigment , synthesis ; [ref to repair of membrane; ref to (chloroplast) envelope instead of membrane]

Question 19

Fig. 3.2 represents the light harvesting system found on the surface of the internal membranes
of the chloroplast. Use the information in Fig. 3.2 to describe how light is harvested in the chloroplast membranes. [F214 Jan 13 q3c] {picture shows surface of internal membrane with light energy going into blobs and arrows jumping from blob to blob}

Answer 19

1 (primary and accessory) pigments , are in / form a(n), photosystem / complex / antenna complex; [if pigments are named, state that chlorophyll a and at least 1 named accessory pigment are in a photosystem]
2 photon / light energy , absorbed by pigment (molecule(s)) ; [idea of absorption required in the context of this Q]electron , excited / moves to higher energy level / delocalised , and returned to pigment ;
4 (energy / photon) passed from one pigment to another ;
5 (energy / photon) passed to , reaction centre / chlorophyll a / P680 / P700 / PSI / PSII / primary pigment ;
6 range of / accessory , pigments allow range of wavelengths to be absorbed ; [‘photon energy’ for ‘wavelengths’]

Question 20

Triazine herbicide acts on the weeds by binding to a specific protein associated with photosystem II, blocking the movement of electrons between electron carriers.
Explain the effect that the herbicide binding to this protein will have on photosynthesis. (2mks) {table and questions} [F214 Jan 13 qdiii]

Answer 20

1 prevents non-cyclic photophosphorylation ;
2 no electron(s) available to form reduced NADP ;
3 idea that ATP production by cyclic
photophosphorylation is not prevented ;
4 no / less , ATP and no reduced NADP available for ,
Calvin cycle / light independent reaction /
conversion of GP to TP ;

Question 21

Plants treated with triazine herbicide can, when illuminated under experimental conditions, be seen to fluoresce (emit light) and give off small quantities of heat.
Suggest how this experimental finding could be explained. {table and questions} [F214 Jan 13 qdiv]

Answer 21

idea that energy given off from , high energy / excited , electron (emitted by , chlorophyll / reaction centre) ;

Question 22

State the precise location of the electron transport chain in the cell. [F214 June 12 3a]

Answer 22

crista(e) / inner mitochondrial membrane ; [thylakoid membrane / lamella(e) (of chloroplast)]

Question 23

If oxygen is not present or is in short supply, respiration can take an anaerobic pathway after

glycolysis. In plant cells, this pathway is the same as the one used in yeast cells.
(i) Name the hydrogen acceptor in this pathway.
(ii) Name the intermediate compound in this pathway.
(iii) Name the products of this pathway.
(iv) Explain why this pathway is important for the plant cell. [F214 June 12 3c]

Answer 23

i) ethanal ; [acetaldehyde]
ii) ethanal ; [acetaldehyde]
iii) ethanol and carbon dioxide ; [formulae]
iv) 1 releases NAD , to accept more H / to be reduced again / so glycolysis can continue or allows (some) ATP to be generated (in glycolysis) ;
2 (some ATP available) for named cellular process ; [ active transport/ endocytosis/ exocytosis/ pinocytosis/ mitosis / meiosis/ protein synthesis DNA replication/ Calvin cycle / light-independent stage of photosynthesis]
3 [eg stated situation where oxygen is in short supply (e.g. waterlogging / compacted soil / roots situated very deep in soil)]

Question 24

One way to determine the rate of photosynthesis is to measure the uptake of carbon dioxide.
(a) Discuss why measuring carbon dioxide uptake may or may not give a better indication of photosynthetic activity than measuring oxygen production. [F214 June 12 4a]

Answer 24

oxygen:
1 oxygen only produced in one (named) stage of photosynthesis ; [for O2 ‘only measures the rate of the light dependent stage / photolysis’]
2 oxygen produced might be used for respiration ;
carbon dioxide:
3 CO2 only used in one (named) stage of photosynthesis; [for CO2 ‘only measures the rate of the Calvin cycle’]
4 CO2 produced during respiration might be used for , photosynthesis / light independent reaction / Calvin cycle ;
5 O2 / CO2 / both , could be an underestimate or
represents net production (O2) or represents net use (CO2) ; [a description e.g. ‘measurement is less than expected because not all the oxygen produced can be measured’ (but not if expressed in terms of terms of experimental error – e.g. dissolves in the water)]

Question 25

Fig. 4.1 shows the relationship between light intensity and the relative carbon dioxide uptake
and production in a plant. State the factor that is limiting the rate of photosynthesis at A (when rate is stil increasing) on the graph. [F214 June 12 4bi]

Answer 25

light intensity;

Question 26

Fig. 4.1 shows the relationship between light intensity and the relative carbon dioxide uptake
and production in a plant. Suggest one factor that may limit the rate of photosynthesis at B. [F214 June 12 4bii]

Answer 26

carbon dioxide concentration / partial pressure of CO2 / temperature ; [eg stomatal density/ stomatal size/ chlorophyll conc./ no of chloroplasts/ enzyme turnover rate]

Question 27

Fig. 4.1 shows the relationship between light intensity and the relative carbon dioxide uptake
and production in a plant. Carbon dioxide is given off by the plant when the light intensity is lower than X.
Name the process that produces carbon dioxide in the plant. [F214 June 12 4biii]

Answer 27

(aerobic / anaerobic) respiration ; [Krebs cycle / link reaction / decarboxylation DO NOT CREDIT photorespiration (as light intensity stated as being low)]

Question 28

With reference to Fig. 4.1, explain the biochemical processes that are occurring in the
plant: (graph shows carbon uptake increasing as light intensity increases then plateau, X is when light intensity is 0)
• as light intensity increases from 0 (zero) to X.
• at light intensity X.
• at light intensities greater than X. (3mks) [F214 June 12 4biv]

Answer 28

1 at 0 , respiration only / no photosynthesis ; between 0 and X
2 idea that (rate of) respiration is greater than (rate of) photosynthesis ; at X
3 idea that (rate of) respiration equals (rate of) photosynthesis / at compensation point ;
after X
4 idea that (rate of) photosynthesis is greater than (rate of) respiration ;

Question 29

Name the products of the light-dependent stage of photosynthesis. (3mks) [F214 June 12 4ci]

Answer 29

reduced NADP / NADPH / NADPH2 / NADPH+ ;
ATP ;
oxygen ; [O2 (to be consistent with the other answers to this question)]

Question 30

Paraquat is a weedkiller. It binds with electrons in photosystem I. Suggest how paraquat results in the death of a plant. (2mks) [F214 June 12 4cii]

Answer 30

1 prevents photophosphorylation ;
2 cyclic and non-cyclic ;
3 no / less , ATP / reduced NADP , for , light-independent stage / Calvin cycle / GP to TP ;
4 no (named) substrate made for respiration ; [substrate eg glucose / starch / carbohydrate / sucrose / sugars]

Question 31

In addition to the structures seen in Fig. 3.1, a chloroplast also contains DNA and ribosomes.
Suggest the role of DNA and ribosomes in this organelle. (2mks) [F214 Jan 12 3aii]

Answer 31

1 (DNA) coding for , gene(s)/ protein/ enzyme
or (ribosome) protein / enzyme , synthesis;
2 (enzymes for production of / proteins for) chlorophyll synthesis / pigment synthesis/ photosystem ;
3 (protein for) electron , acceptor(s) / carrier(s); [named acceptor / carrier (e.g. NADP / cytochrome)]
4 ATP synth(et)ase ;
5 (enzyme / PSII) for , photolysis / splitting of water;
6 (enzymes for) Calvin cycle / light independent reaction; [Rubisco]

Question 32

ATP is produced [F214 Jan 12 3b]

Answer 32

B

Question 33

an electron leaves PSI [F214 Jan 12 3b]

Answer 33

B

Question 34

electrons are passed along an ECC [F214 Jan 12 3b]

Answer 34

B

Question 35

electrons leave both PSI and PSII [F214 Jan 12 3b]

Answer 35

N

Question 36

an electron from water molecule replaces the electron lost from the photosystem [F214 Jan 12 3b]

Answer 36

N

Question 37

the same electron returns to the photosystem [F214 Jan 12 3b]

Answer 37

C

Question 38

Suggest how the student supplied the aquatic plant with a source of carbon dioxide. [F214 June 11 2aiii]

Answer 38

1 (sodium) hydrogen carbonate ;
2 bubble in , CO2 / exhaled air ;
3 dry ice ;

Question 39

Certain assumptions are made when using the apparatus shown in Fig. 2.1 to measure the
rate of photosynthesis.
(i) One of these assumptions is that all of the oxygen produced by the plant during photosynthesis is collected.
Suggest why not all of the oxygen produced by the plant is collected. [F214 June 11 2bi]

Answer 39

idea that some of the oxygen:
1 would dissolve in the water ;
2 used in , respiration / oxidative phosphorylation ;
3 may escape the collection apparatus ;
4 trapped in , a bubble attached to / air spaces in , the leaf ;

Question 40

(ii) Another assumption is that all of the gas collected is oxygen. Analysis of the gas collected reveals that it has the following composition:
• oxygen 50%
• nitrogen 44%
• carbon dioxide 6%
Suggest a reason for the presence of nitrogen in the gas collected. [F214 June 11 2bii]

Answer 40

1 (nitrogen) was present in the air (spaces) in the , leaf / plant ;
2 (nitrogen) leaves the plant with the oxygen ;
3 idea that (nitrogen) comes out of solution / ‘undissolved’ (as less soluble in warm water) ;

Question 41

Comment on the percentage of carbon dioxide present in the gas collected and give reasons for this figure. [F214 June 11 2biii]

Answer 41

1 higher than , expected / normal / in atmosphere ;
2 (plant is) respiring / produces CO2 during respiration ;
3 CO2 , has been added to water / is present in excess ;
4 (CO2) comes out of solution / ‘undissolved’ (as less soluble in warm water) ;
5 less / low(er) , as some CO2 will dissolve in , water / solution ; [DO NOT CREDIT if in context of lower than O2 and N2]
6 less / low(er) , as CO2 used in photosynthesis ; [DO NOT CREDIT if in context of lower than O2 and N2]

Question 42

Some aquatic photosynthetic organisms, for example seaweeds, contain pigments such as fucoxanthin and phycoerythrin, in addition to chlorophyll. These pigments give seaweeds a brown or red colour and are produced in larger quantities in those seaweeds that live in deeper water.
Suggest why the presence of these pigments is an advantage to seaweeds that live in deeper
water. [F214 June 11 b]

Answer 42

intensity:
1) in deeper water there is , less / lower , light intensity ;
2) (these pigments) can absorb what (little) light there is ; [trap / harvest / capture]
wavelength:
3) not all wavelengths of light can penetrate
or mainly, shorter wavelengths/ higher frequency, can penetrate
or (mostly) blue light (450 – 520 nm) penetrates ;
4) (these pigments) can absorb wavelengths of light that can penetrate (deeper water) ; [trap / harvest / capture]