Unit 5 - Energy Transfers

Question 1

Light dependant reaction - describe the process (6)

Answer 1

1. Excites electrons and electrons are removed from chlorophyll
2. Electrons move along carriers/etc releasing energy
3. Energy used to join ADP and pi to form ATP
4. Photolysis of water produces protons, electrons and oxygen
5. NADP is reduced by electrons

Question 2

Light independent reaction. Describe the Calvin cycle (6)

Answer 2

1. Carbon dioxide combines with RuBP
2. Produces two GP
3. GP reduced to TP
4. Using reduced NADP
5. Using energy from ATP
6. TP converted to glucose

Question 3

Why weed killers cause plants to give off heat? (2)

Answer 3

1. Energy is released from high energy electrons (that were lost from chlorophyll)
2. This energy which should be used to form ATP, cannot do this as the weed killer blocks the ETC (so the energy is lost as heat)

Question 4

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

Answer 4

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 5

How is ATP produced (11)
- respiration

Answer 5

1. ATP produced in glycolysis
2. Involving the oxidation of glucose to Pyruvate
3. ATP production directly from krebs cycle
4. Glycolysis produce reduced NAD/FAD
5. Reduced NAD/FAD transfer electrons to electron transport chain
6. Electrons transferred down chain of carriers
7. 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
10. ATP synthase

Question 6

Describe chemiosmosis (4)

Answer 6

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

Question 7

Why is there less ATP produced in anaerobic respiration? (4)

Answer 7

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 8

Describe anaerobic respiration in animals? (5)

Answer 8

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

Question 9

Why is energy transfer along food chain not 100% efficient? (9)

Answer 9

1. Some light energy fails to strike photosynthetic tissues / not the appropriate wavelength
2. Efficiency of photosynthesis in plants is low
3. Respiratory loss / excretion/ faeces/ not eaten
4. Loss as heat
5. Carbon dioxide/ excretion
6. Inedible parts
   7.efficiency of transfer to consumers greater than transfer to producers
7. Efficiency lower in older animals
8. Carnivores use more of their food than herbivores

Question 10

How do we improve productivity during farming of animals? (5)

Answer 10

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 11

How are nitrogen compounds in animals made available for plants? (8)

Answer 11

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 nitrite
7. Nitrate can be absorbed by roots
8. Nitrogen fixation forms ammonium compounds

Question 12

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

Answer 12

1. Protein/ amino acids/ DNA into ammonium compounds
2. By saprobionts
3. Ammonia into nitrite
4. Nitrite into nitrate
5. By nitrifying bacteria
6. Nitrogen to ammonia
   7.by nitrogen-fixing bacteria in soil

Question 13

Describe the phosphorous cycle (10)

Answer 13

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

Question 14

Describe the importance of phosphorylation (2)

Answer 14

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

Question 15

Describe eutrophication (6)

Answer 15

1. Growth of algae blocks light/ algal bloom
2. Reduced/no photosynthesis so plants die
3. Saprobiotic bacteria
4. Respires aerobically
5. Less oxygen for fish
6. So they die

Question 16

Describe the function of saprobionts releasing carbon dioxide (6)

Answer 16

1. Microorganisms are saprobionts
2. Secrete enzymes onto dead tissue
3. Absorb products of digestion
4. Synthesis of structural compounds
5. Respiration provides energy for growth
6. Respiration produces carbon dioxide

Question 17

Evaluate use of fertilisers for mycorrhizas (4)

Answer 17

Should not use fertilisers because;
1. Fertilisers prevent development of mycorrhizae
2. Mycorrhizae help plants to take up nitrates/ phosphates (increases crop yield)

Should use fertilisers because;
1. Fertilisers containing phosphate and nitrate increase gross primary production so increase yield
2. Most soil is poor in phosphate so without fertiliser plant might not get enough phosphate

Question 18

Equation for net primary production

Answer 18

NPP = GPP - R

Question 19

Net production of consumers

Answer 19

N = I - (F + R)

Where N = net production of consumers
I = chemical energy store in ingested food
F = chemical energy lost to environment in faeces
R = respiration losses