Unit 5

Question 1

Light Dependent Reaction –

Describe the process (6)

Answer 1

1.     Excites electrons / electrons removed from chlorophyll;

2.      Electrons move along carriers/electron transfer chain releasing energy;

Accept: movement of H+/protons across membrane releases energy.

Reject: ‘produces energy’ for either mark but not for both.

3.      Energy used to join ADP and Pi to form ATP;.

4.      Photolysis of water produces protons, electrons and oxygen;

5.      NADP reduced by electrons and protons / hydrogen;

Question 2

Light Dependent Reaction. Describe the electron transport chain (5)

Answer 2

1. Excites electrons (from chlorophyll);
2. Electrons move along carriers/electron transfer chain releasing energy;
3. Energy used to join ADP and Pi to form ATP;
4. Photolysis of water produces protons, electrons and oxygen;
5. NADP reduced by electrons and protons;

Question 3

Light Independent Reaction. Describe the Calvin Cycle (6)

Answer 3

1. Carbon dioxide combines with RuBP;
2. Produces two GP;
3. GP reduced to Triose Phosphate;
4. Using reduced NADP;
5. Using energy from ATP;
6. TP converted to glucose / hexose / RuBP / ribulose bisphosphate / named organic substance;

Question 4

Why weedkillers cause plants to

give off heat? (2)

Answer 4

Energy is released from high energy/excited electron/s (that were lost from chlorophyll

This energy which should be used to form ATP, cannot do this as the weedkiller blocks the ETC, (so the energy is lost as heat)

Question 5

Why does increased light intensity stimulate plant growth? (5)

Answer 5

1. Have faster production of ATP and reduced NADP;
2. (So) have faster/more light-independent reaction;
3. (So) produce more sugars that can be used in respiration;
4. (So) have more energy for growth;
5. Have faster/more synthesis of new organic materials;

Question 6

How is ATP produced? (11)

Answer 6

1. ATP produced in glycolysis;
2. Involving the oxidation of glucose/TP to pyruvate;
3. ATP production/ Substrate level phosphorylation directly from Krebs cycle;
4. Glycolysis/Krebs cycle produce reduced NAD/FAD;
5. Reduced NAD/FAD transfer electrons to electron transport chain;
6. Electrons transferred down a chain of carriers;
7. (Carriers) at decreasing energy levels;
8. Energy (lost by electrons) used to produce ATP;
9. From ADP and (inorganic) phosphate;
10. Protons move into intermembrane space;
11. ATP synthase;

Question 7

Describe chemiosmosis. (4)

Answer 7

1. Electrons transferred down electron transfer chain;
2. Provide energy to transport protons into space between membranes;
3. Protons diffuse/pass back, through membrane/into matrix/through ATP synthase;
4. Energy (from H+ movement) used to combine ADP and phosphate to form ATP

Question 8

Why is there less

ATP produced in anaerobic respiration? (4)

Answer 8

1. ATP formed as electrons pass along transport chain;
2. Oxygen is terminal electron acceptor
3. Forms H2O;
4. Electrons cannot be passed along electron transport chain if no O2 to accept them;

Question 9

Describe anaerobic respiration in

animals. (5)

Answer 9

1. Forms lactate;
2. Use of NADH;
3. Regenerates NAD;
4. NAD allows glycolysis to continue;
5. Can still release energy from ATP when no oxygen;

Question 10

What is energy transfer along

food chain not 100% efficient?

(9)

Answer 10

1. Some light energy fails to strike/is reflected/not of appropriate wavelength;
2. Efficiency of photosynthesis in plants is low
3. Respiratory loss / excretion / faeces / not eaten;
4. Loss as heat;
5. In excreta / excretion / urine / carbon dioxide;
6. Inedible parts / indigestible parts / egestion / to decomposers
7. Efficiency of transfer to consumers greater than transfer to producers;
8. Efficiency lower in older animals/herbivores/ primary consumers/warm blooded animals/homoiotherms;
9. Carnivores use more of their food than herbivores

Question 11

How do we improve

productivity during farming of

animals? (5)

Answer 11

1. Slaughtered while young so more energy transferred to biomass;
2. Fed on controlled diet so higher proportion of food absorbed/lower proportion lost in faeces;
3. Movement restricted so less respiratory loss;
4. Heating/Kept inside so less heat/respiratory loss;
5. Genetically selected / selective breeding (for high productivity)

Question 12

How are nitrogen

compounds in animals made

available for plants? (8)

Answer 12

1. Proteins/amino acids broken down;
2. by saprophytes/decomposers;
3. deamination/ammonium compounds/ammonia formed;
4. Ammonia converted to nitrite;
5. by nitrifying bacteria;
6. Nitrite converted to nitrate;
7. Nitrate can be absorbed by roots;
8. Nitrogen fixation forms ammonium compounds;

Question 13

Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants. (5)

Answer 13

1.      Protein / amino acids / DNA into ammonium compounds / ammonia;

2.      By saprobionts;

3.      Ammonium / ammonia into nitrite;

4.      Nitrite into nitrate;

5.      By nitrifying bacteria / microorganisms;

6.      Nitrogen to ammonia / ammonium;

7.      By nitrogen-fixing bacteria / microorganisms in soil;

Question 14

Describe the phosphorus cycle. (10)

Answer 14

1. Phosphate ions in rocks released to soil by erosion/weathering;
2. Phosphate ions taken into plants by roots/root hair cells;
3. Phosphate ions assimilated into DNA/RNA/phospholipids/NADP/RuBP;
4. Rate of absorption increased by mycorrhizae;
5. Phosphate ions transferred through food chain;
6. Some phosphate ions lost by excretion/when plants and animals die;
7. Phosphorus containing compounds are decomposed by saprobionts/fungi;
8. Weathering of rocks releases phosphate ions into seas and taken up by aquatic producers/algae;
9. Phosphate ions passed along food chain to birds;
10. Guano returns phosphate ions to soils

Question 15

Describe the importance of phosphorylation

(2)

Answer 15

1. Makes substrates more reactive;
2. Lowers activation energy for the reaction

Question 16

Describe

eutrophication (6)

Answer 16

1. Growth of algae / algal bloom blocks light;
2. Reduced / no photosynthesis so (submerged) plants die;
3. Saprobiotic (microorganisms / bacteria);
4. Aerobically respire / use oxygen in respiration;
5. Less oxygen for fish / aerobic organisms to respire;
6. (So) they die;

Question 17

Describe the function of saprobionts

releasing carbon dioxide (6)

Answer 17

1. Microorganisms are saprobionts/saprophytes;
2. Secrete enzymes (onto dead tissue) / extracellular digestion;
3. Absorb products of digestion/smaller molecules/named relevant substance;
4. Synthesis of structural compounds/named compound;.
5. Respiration provides energy for growth
6. Respiration (by microorganisms) produces carbon dioxide;

Question 18

Evaluate use of fertilisers for

mycorrhizas (4)

Answer 18

(Should not use fertilisers because)

1. Fertilisers prevent development of mycorrhizae;
2. Mycorrhizae help plants to take up nitrates/phosphates (causing an increase in crop yield);

(Should use fertilisers because)

3. Fertilisers containing phosphate and nitrate increase gross primary production so increase yield;
4. Most soil is poor in phosphate so without fertiliser so plant might not get enough phosphate;

Question 19

Describe the light-independent reaction of photosynthesis.

Answer 19

1. Carbon dioxide combines/reacts with ribulose bisphosphate/RuBP;
2. Produces two glycerate (3-)phosphate/GP using (enzyme) Rubisco;

Accept: any answer which indicates that 2 × as much GP produced from one RuBP catalysed by Rubisco.

Reject GP once if incorrectly named e.g., glucose 3- phosphate.

3. GP reduced to triose phosphate;

Reject GP once if incorrectly named e.g., glucose 3- phosphate.

Must have idea of reduction.

4. Using reduced NADP;

Accept NADPH or NADPH2 or NADPH + H for reduced NADP.

Reject: Any reference to reduced NAD for mp4 but allow reference to reduction for mp3.

Must be in context of GP to triose phosphate.

5. Using energy from ATP;

Must be in context of GP to triose phosphate.

6. Triose phosphate converted to glucose/hexose/RuBP/ribulose bisphosphate/named organic substance;

Question 20

Put a Tick (✓) in the box next to the process that occurs in anaerobic respiration but does not occur in aerobic respiration.

Phosphorylation of glucose

Reduction of NAD

Reduction of pyruvate

Substrate-level phosphorylation

Answer 20

Reduction of pyruvate

(Box 3)

Question 21

Apart from time, give two measurements the student would have to make to determine the rate of aerobic respiration of these seeds in cm3 hour –1

Answer 21

c)  1. Distance (drop/liquid moves);

Accept description of distance, e.g. ‘start and end position’.

2. Diameter/radius/bore of tubing/lumen

Accept (cross-sectional) area of tubing/lumen.

Question 22

Mature leaves from slow-growing, shade-tolerant plants produce poisonous chemicals that are a defence against being eaten by herbivores.

Suggest how this benefits slow-growing, shade-tolerant plants.

Answer 22

1. (In the shade, so) less/slower rate of photosynthesis;

Accept any named aspect of photosynthesis that uses light, eg LDR, photoionisation

2. (Slow-growing, so) would take a long time to replace (mature leaves)

OR

Leaves more likely to reach maturity

OR

Leaves take a long time to mature;

Accept would take a long time to make cellulose or any other correct named compound

3. Plants can maintain (a large enough) surface area for photosynthesis

OR

Plants can absorb enough light;

2

Question 23

Malonate inhibits a reaction in the Krebs cycle.

Explain why malonate would decrease the uptake of oxygen in a respiring cell.

Answer 23

1. Less/no reduced NAD/coenzymes

OR

Fewer/no hydrogens/electrons removed (and passed to electron transfer chain);

Accept less/no FAD reduced.

2. Oxygen is the final/terminal (electron) acceptor;

Question 24

Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions.

Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions.

Answer 24

1. Less nitrification OR Fewer/less active nitrifying bacteria;

OR Nitrification/nitrifying bacteria require oxygen/aerobic conditions;

2. (Less) oxidation/conversion of ammonium (ions) to nitrite (ions) and to nitrate (ions);

Order must be nitrite then nitrate

Accept correct chemical formulae for ions, eg there will be little
oxidation/conversion of NH4+ → NO2- → NO3-

Ignore ‘breakdown’ for
oxidation/conversion

3. More denitrification

OR More/more active denitrifying bacteria

OR Denitrification/denitrifying bacteria do not require oxygen

OR Denitrification/denitrifying bacteria require anaerobic conditions;

4. (So more) nitrate (ions) reduced/converted to nitrogen (gas);

Accept correct chemical formulae eg So more NO3-reduced/converted to N2;