Unit 5 - Energy Transfers

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 / 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;

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

Question 4

Why weedkillers cause plants to give off heat? (2)

Answer 4

1. Energy is released from high energy/excited electron/s (that were lost from chlorophyll
2. 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/ Triose phosphate 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 Pi 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 plant might not get enough phosphate;

Question 19

Acetylcoenzyme A is made in the link the reaction. Describe how. (2)

Answer 19

1. Oxidation of pyruvate AND carbon dioxide released to form acetate
2. Coenzyme A is added to acetate