AQA A-Level Biology - Topic 5: Bioenergetics LRQs

A Collection of Common Longer-Response Questions

Describe why phosphates are needed by a growing plant. (4)

1.      Production of phospholipids;

2.      In cell membranes;

3.      Synthesis of ATP;

4.      Production of DNA;

5.      Production of RNA;

6.      Production of NADP;

4 max

Explain how the decay of dead plants results in reduced oxygen concentration and increased nitrate production. (6)

1.      Bacteria / fungi feed on dead matter saprobiotically;

2.      Respiration uses up oxygen;

3.      Converts proteins to amino acids

4.      then to ammonium compounds;

5.      Nitrifying bacteria convert ammonium compounds

6.      via nitrates;

6

Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP. (3)

1.      NAD / FAD reduced / hydrogen attached to NAD / FAD;

2.      H⁺ ions / electrons transferred from coenzyme to coenzyme / carrier to carrier / series of redox reactions;

3.      Energy made available as electrons passed on;

4.      Energy used to synthesise ATP from ADP and phosphate / using ATPase;

5.      H⁺ / protons passed into intermembrane space;

6.      H⁺ / protons flow back through stalked particles / enzyme;

3 max

Describe the role of chlorophyll in photosynthesis. (3)

1.      Light (energy) absorbed by chlorophyll;

2.      Raises energy level of electrons / electrons are excited / emitted;

3.      ATP formed;

3

Explain the role of chlorophyll in photolysis. (3)

1.      Absorbs light / energy;

2.      Loses electrons / becomes positively charged / is oxidised;

3.      Accepts electrons from water / from OH^– which causes more water to dissociate / pulls equilibrium to the right;

3

Explain how the energy of light is converted into chemical energy in the light-dependent reactions. (3)

1.      Electrons raised to higher energy level / electrons excited;

2.      Use of electron carriers / cytochromes / acceptors;

3.      For production of ACT;

3

Explain the roles of the decomposers and the nitrifying bacteria in converting nitrogen in organic compounds in the sewage into a soluble, inorganic form. (3)

1.      Decomposers convert (nitrogen in organic compounds) into ammonia / ammonium;

2.      Nitrifying bacteria / correctly named convert ammonium to nitrate;

3.      Via nitrite;

3

Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP. (5)

1.      Excitation of chlorophyll molecule / electrons / energy of (pairs of) electrons raised to higher energy level;

2.      Electron(s) emitted from chlorophyll molecule;

3.      Electron(s) to electron transport chain;

4.      Loss of energy by electron(s) along electron transport chain;

5.      Energy lost by electron(s) is used to synthesise ATP;

6.      From ADP + Pi;

5 max

Explain why respiration yields more ATP per molecule of glucose in the presence of oxygen than it does in the absence of oxygen. (3)

1.     Oxygen as terminal hydrogen / electron acceptor allowing operation of electron transport chain / oxidative phosphorylation;

2.      Fate of pyruvate;

3.      Significance of ATP formed in glycolysis;

3

Describe and explain the effect of increasing carbon dioxide concentration on the rate of photosynthesis. (3)

1.     Carbon dioxide increases rate of photosynthesis;

2.     Up to a maximum;

3.     Something else is then a limiting factor;

3

Describe the light-independent reactions of photosynthesis and explain how they allow the continued synthesis of hexose sugars. (6)

1.       5C / RuBP combines with CO₂

2.       to form 3C compound / TP / GP

3.       using ATP

4.       and reduced NADP / eq;

5.       2 molecules of 3C compound / TP / GP form hexose;

6.       All RuBP is regenerated;

7.       10 molecules of 3C / TP / GP form 6 molecules of 5C / RuBP;

6 max

Describe the role of electron transport chains in the light-dependent reactions of photosynthesis. (6)

1.       Electron transport chain accepts excited electrons

2.       from chlorophyll / photosystem;

3.       Electrons lose energy along chain;

4.       ATP produced

5.       from ADP and Pi;

6.       Reduced NADP formed

7.       when electrons (from transport chain) and H⁺ combine with NADP;

8.       H⁺ from photolysis;

6 max

Explain why the increase in the dry mass of a plant over twelve months is less than the mass of hexose produced over the same period. (3)

1.       Some hexose / biomass / eq. used in respiration;

2.       CO₂ produced (is lost to air);

3.       Some parts of the plant are eaten / some parts lost to decomposers /  in leaf fall;

3

Describe how the light-dependent reaction of photosynthesis generates ATP. (5)

1.      Light (energy) excites / raises energy level of electrons in chlorophyll;

2.      Electrons pass down electron transfer chain;

3.      (Electrons) reduce carriers / passage involves redox reactions;

4.      Electron transfer chain / role of chain associated with chloroplast membranes / in thylakoids / grana;

5.      Energy released / carriers at decreasing energy levels;

6.      ATP generated from ADP and phosphate / P_i  / phosphorylation of ATP;

5

Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion. (3)

1.      ATP formed as electrons pass along transport chain;

2.      Oxygen is terminal electron acceptor / accepts electrons from electron transport chain / electrons cannot be passed along electron transport chain if no O₂ to accept them;

3.      Forms H₂O / accepts H⁺ from reduced NAD / FAD / oxidises reduced NAD / FAD;

3

Explain how nitrate may cause the death of fish in fresh water. (5)

1.      Growth of algae / surface plants / 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 to respire / aerobic organisms die;

5

Describe how, in the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. (5)

1.      Carbon dioxide combines with ribulose bisphosphate / RuBP

2.      to produce two molecules of glycerate 3-phosphate / GP;

3.      Reduced to triose phosphate / TP;

4.      Requires reduced NADP;

5.      Energy from ATP;

5

Describe the part played by the inner membrane of a mitochondrion in producing ATP. (3)

1.      Electrons transferred down electron transport chain;

2.      Provide energy to take protons / H⁺ into space between membranes;

3.      Protons / H⁺ pass back, through membrane / into matrix / through ATPase;

4.     Energy used to combine ADP and phosphate / to produce ATP;

3 max

Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants. (5)

1.      Saprobionts / saprophytes

2.      digest / break down proteins / DNA / nitrogen-containing substances;

3.      Extracellular digestion / release of enzymes;

4.      Ammonia / ammonium produced;

5.      Ammonia converted to nitrite to nitrate / ammonia to nitrate;

6.      Nitrifying (bacteria) / nitrification;

7.      Oxidation;

5 max

Describe how ATP is made in mitochondria. (6)

1.      Substrate level phosphorylation / ATP produced in Krebs cycle;

2.      Krebs cycle / link reaction produces reduced coenzyme / reduced NAD / reduced FAD;

3.      Electrons released from reduced / coenzymes / NAD / FAD;

4.      (Electrons) pass along carriers / through electron transport chain / through series of redox reactions;

5.      Energy released;

6.      ADP / ADP + Pi;

7.      Protons move into intermembrane space;

8.      ATP synthase;

6 max

Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis. (5)

1.      In the dark no ATP production in photosynthesis;

2.      Some tissues unable to photosynthesise / produce ATP;

3.      ATP cannot be moved from cell to cell / stored;

4.      Plant uses more ATP than produced in photosynthesis;

5.      ATP for active transport / synthesis (of named substance);

5

Give three environmental factors that should be controlled when measuring the rate of photosynthesis in an investigation. (3)

1.      Intensity / brightness of light (at each wavelength);

2.      Carbon dioxide concentration;

3.      Temperature;

4.      Water;

OR

Humidity;

3 max

Describe how the products of the light-dependent reaction are used in the light-independent reaction to produce triose-phosphate. (3)

1.      ATP and reduced NADP;

2.      ATP provides energy;

3.      GP reduced to triose phosphate;

3

Explain why reducing light intensity would affect the amount of oxygen released by a plant. (3)

1.      (Light intensity) Limiting factor;

2.      Fewer electrons (released) from chlorophyll;

3.      Less photolysis therefore (less) oxygen from water;

3

Explain how farming practices increase the productivity of agricultural crops. (5)

1.      Fertilisers / minerals / named ion (added to soil);

2.      Role of named nutrient or element e.g. nitrate / nitrogen for proteins / phosphate / phosphorus for ATP / DNA;

3.      Selective breeding / genetic modification (of crops);

4.      Ploughing / aeration allows nitrification / decreases denitrification;

5.      Benefit of crop rotation in terms of soil nutrients / fertility / pest reduction;

5

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

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;

5 max

Describe what happens during the light-dependent reaction. (5)

1.      Chlorophyll absorbs light energy;

2.      Excites electrons / electrons removed (from chlorophyll);

3.      Electrons move along carriers / electron transport chain releasing energy;

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

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

6.      NADP reduced by electrons / electrons and protons / hydrogen;

5 max

Explain the decrease in production of triose phosphate in the iron-deficient plants. (4)

1.      (Less) ATP produced;

2.      (Less) reduced NADP produced;

3.      ATP / reduced NADP produced during light-dependent reaction;

4.      (Less) GP to triose phosphate / TP;

4

Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem. (3)

1.      Heat (loss) from respiration;

2.      (Food) not digested

OR

Not all eaten;

3.      Excretion;

3

Describe the light-independent reaction of photosynthesis. (6)

1.      Carbon dioxide combines / reacts with ribulose bisphosphate / RuBP;

2.      Produces two glycerate (3-)phosphate / GP using (enzyme) Rubisco;

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;

6

Describe the process of glycolysis. (4)

1.      Phosphorylation of glucose using ATP;

2.      Oxidation of triose phosphate to pyruvate;

3.      Net gain of ATP;

4.      NAD reduced;

4 max