topic 5

Question 1

Which chemicals are needed for the
light-dependent reaction?

Answer 1

-NADP
-ADP
-Pi
-water

Question 2

Describe how crop plants use light
energy during the light-dependent
reaction.

Answer 2

1. Excites electrons / electrons removed (from chlorophyll);
   Accept: higher energy level as ‘excites’.
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;
   Reject: ‘produces energy’ for either mark but not for both.
4. Photolysis of water produces protons, electrons and oxygen;
5. NADP reduced by electrons / electrons and protons /
   hydrogen;

Question 3

Describe what happens during
photoionisation in the light-
dependent reaction

Answer 3

1. Chlorophyll absorbs light
   OR
   Light excites/moves electrons in chlorophyll;
   Ignore photosystems.
2. Electron/s are lost
   OR
   (Chlorophyll) becomes positively charged

Question 4

Heat stress decreases the light-
dependent reaction of
photosynthesis.
Explain why this leads to a decrease
in the light-independent reaction.

Answer 4

1. (Less/no) ATP;
2. (Less/no) reduced NADP

Question 5

During the light-independent
reaction of photosynthesis, carbon
dioxide is converted into organic
substances. Describe how.

Answer 5

1. Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. Produces two glycerate (3-)phosphate / GP;
   Accept: any answer which indicates that 2 x as much GP produced
   from one RuBP.
3. GP reduced to triose phosphate / TP;
   Must have idea of reduction. This may be conveyed by stating m.p.
   4.
4. Using reduced NADP;
   Reject: Any reference to reduced NAD for m.p.4 but allow
   reference to reduction for m.p. 3.
5. Using energy from ATP;
   Must be in context of GP to TP.
6. Triose phosphate converted to glucose / hexose / RuBP / ribulose bisphosphate / named organic substance;

Question 6

A decrease in the activity of the
enzyme rubisco would limit the rate
of photosynthesis.
Explain why.

Answer 6

1. (Less/no) carbon dioxide (reacts) with RuBP;
2. (Less/no) GP

Question 7

Where precisely is rubisco found in a
cell?

Answer 7

Stroma

Question 8

Where precisely in a cell does the
Calvin cycle take place?

Answer 8

Stroma

Question 9

A herbicide binds to proteins in the
electron transfer chain in
chloroplasts of weeds, reducing the
transfer of electrons down the chain.
Explain how this reduces the rate of
photosynthesis in weeds.

Answer 9

1. Reduced transfer of protons across thylakoid membrane
   OR
   Reduced chemiosomotic gradient / proton gradient across
   thylakoid membrane;
2. (So) less ATP produced;
3. (So) less reduced NADP produced;
   Accept NADPH / NADPH 2 / NADPH +
   Reject reduced NAD
4. (So) light-independent reaction slows / stops;
   OR
   Less reduction of GP to triose phosphate.

Question 10

Chromatography - Explain why the
student marked the origin using a
pencil rather than using ink

Answer 10

Ink and (leaf) pigments would mix
OR
(With ink) origin/line in different position
OR
(With pencil) origin/line in same position
OR
(With pencil) origin/line still visible;

Question 11

Describe the method the student
used to separate the pigments after
the solution of pigments had been
applied to the origin.

Answer 11

1. Level of solvent below origin/line;
   Reject water or any named aqueous solution.
   Accept named organic solvent.
2. Remove/stop before (solvent) reaches top/end;

Question 12

The pigments in leaves are different
colours. Suggest and explain the
advantage of having different
coloured pigments in leaves.

Answer 12

(Absorb) different/more wavelengths (of light) for
photosynthesis;

Question 13

Other than temperature and pH,
give two factors which should be
kept constant during a
photosynthesis investigation.

Answer 13

1. Intensity of light;
   Accept: distance from light
2. Amount / number / mass / species of algae /
   photosynthesising cells;
3. Carbon dioxide (concentration / partial pressure);
4. Time.

Question 14

Explain why the scientists measured
the rate of production of oxygen in a
photosynthesis investigation.

Answer 14

1. Oxygen produced in light-dependent reaction;
2. The faster (oxygen) is produced, the faster the light-
   dependent reaction.

Question 15

Describe how acetylcoenzyme A is
formed in the link reaction.

Answer 15

1. Oxidation of / hydrogen removed from pyruvate and carbon
   dioxide released;
2. Addition of coenzyme A.

Question 16

In Krebs cycle, oxaloacetate (4C) is the first substrate to bind with the enzyme citrate synthase. This induces a change in the enzyme, which enables the acetylcoenzyme A to bind.
Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme.

Answer 16

1. Change (in shape) of active site / active site moulds around
   the substrate;
   Reject: reference to inhibitor
   Accept: change in tertiary structure affecting active site
2. (Substrate / active site) now COMPLEMENTARY

Question 17

In muscles, pyruvate is converted to
lactate during prolonged exercise.
Explain why converting pyruvate to
lactate allows the continued
production of ATP by anaerobic
respiration.

Answer 17

1. Regenerates/produces NAD
   OR
   oxidises reduced NAD;
   Reject NADP and any reference to FAD.
   Accept descriptions of oxidation e.g. loss of hydrogen.
2. (So) glycolysis continues

Question 18

Where in a cell
does glycolysis occur?

Answer 18

Cytoplasm

Question 19

Explain how anaerobic
respiration enables glycolysis to
continue.

Answer 19

1. Regenerates/produces NAD / oxidises reduced NAD;
2. NAD reduced in glycolysis / NAD accepts hydrogen in
   glycolysis

Question 20

Aerobic respiration produces more
ATP per molecule of glucose than
anaerobic respiration.
Explain why

Answer 20

1. Oxygen is final/terminal (electron) acceptor / oxygen
   combines with electrons and protons;
2. (Aerobic respiration) oxidative phosphorylation / electron
   transfer chain;
3. Anaerobic (respiration) only glycolysis occurs / no Krebs / no link reaction;

Question 21

Explain why an increase in biomass
can be taken as a measurement
of net primary productivity.

Answer 21

1. Represents dry mass / mass of carbon;
2. Represents gross production minus respiratory losses;

Question 22

Explain why CO 2 uptake is a measure
of net productivity.

Answer 22

Shows (gross) photosynthesis / productivity minus respiration /
more carbon dioxide used in photosynthesis than produced in
respiration;

Question 23

Suggest appropriate units for gross
productivity.

Answer 23

Unit of energy / mass, per area, per year.

Question 24

Explain the decrease in gross
productivity as the woodland
matures

Answer 24

1. Less light / more shading / more competition for light;
   Neutral: references to animals
2. Reduced photosynthesis

Question 25

In a climax community biomass shows little increase after 100 years. Use your knowledge of net productivity to explain why.

Answer 25

1. Net productivity = gross productivity minus respiratory loss; 2. Decrease in gross productivity / photosynthesis / increase in respiration

Question 26

Why is most light falling on producers NOT used in photosynthesis

Answer 26

1. (Light is) reflected; 2. (Light is) wrong wavelength; 3. (Light) misses chlorophyll/ chloroplasts/photosynthetic tissue; 4. CO 2 concentration or temperature is a limiting factor.

Question 27

Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water.

Answer 27

1. Growth of algae / surface plants / algal bloom blocks light; 2. Reduced / no photosynthesis so (submerged) plants die; 3. Saprobiotic (microorganisms / bacteria); 3. Accept: Saprobiont / saprophyte / saprotroph 3. Neutral: decomposer 4. Aerobically respire / use oxygen in respiration; 5. Less oxygen for fish to respire / aerobic organisms die;

Question 28

Explain how microorganisms in the soil produce a source of nitrates from crop plant remains.

Answer 28

1. Protein/amino acids/DNA into ammonium compounds / ammonia; Accept: any named nitrogen containing compound e.g. urea. 2. By saprobionts; Accept: saprophytes. 3. Ammonium/ammonia into nitrite; 4. Nitrite into nitrate; 5. By nitrifying bacteria/microorganisms;

Question 29

Describe the role of saprobionts in the nitrogen cycle

Answer 29

1. (They use enzymes to) decompose proteins/DNA/RNA/urea; 2. Producing/releasing ammonia/ammonium compounds/ammonium ions;

Question 30

Give two examples of biological molecules containing nitrogen.

Answer 30

1. amino acid / protein / polypeptide / peptide; 2. nucleic acid / nucleotide / base; 3. DNA; 4. RNA; 5. ATP / ADP; 6. NAD / NADP (reduced or not); 7. Cyclic AMP / cAMP; 8. Chlorophyll;

Question 31

Describe the role of microorganisms in producing nitrates from the remains of dead organisms

Answer 31

1. Saprobiotic (microorganisms / bacteria) break down remains / dead material / protein / DNA into ammonia / ammonium; 2. Ammonia / ammonium ions into nitrite and then into nitrate; 3. (By) Nitrifying bacteria / nitrification;

Question 32

Leguminous plants have nodules containing nitrogen-fixing bacteria on their roots. Explain how nitrogen-fixing bacteria could increase the growth of maize.

Answer 32

1. Nitrogen-fixing bacteria convert nitrogen (in the air) into ammonium compounds (in the soil) which are converted into nitrates / nitrification occurs; 2. Maize uses nitrates (in soil) for amino acid / protein / ATP / nucleotide production;

Question 33

Explain how microorganisms contributed to the increase in temperature during processing of organic waste.

Answer 33

1.Respiration/metabolism/ammonification; 2. (Releases/produces) heat;

Question 34

Suggest one way in which an increase in the uptake of phosphate could increase plant growth.

Answer 34

Used to produce named phosphate compound in cells; e.g. ATP / ADP / phospholipids / DNA / RNA / RuBP / TP /GP etc

Question 35

Suggest and explain two reasons why a poor supply of phosphate ions results in poor growth of plants

Answer 35

1. (Required to) make ATP / glucose phosphate, so less respiration / less energy for growth; 2. (Required to) make nucleotides, so less DNA / mRNA / tRNA for cell division / production of protein (for growth); 3. (Required to) make RuBP / NADP, so less CO 2 fixed / reduced into sugar; 4. (Required to) make phospholipids for membranes;

Question 36

Calorimetry [5]

Answer 36

- Take the mass of the sample - Burn in pure oxygen in a sealed container surrounded by water - Measure the increase in temperature - Use specific heat capacity of water (amount of energy to increase 1kg of water by 1°C) - Energy released can be measure (kJkg-1)

Question 37

How to measure dry mass [4]

Answer 37

- Take the mass of the sample. - Heat for 1 hour at temperature that will evaporate water, but not burn the sample - Take the mass of the sample - Repeat heating and taking mass until mass remains constant

Question 38

Dry Mass [2]

Answer 38

- Dry mass often measured due to varying water content - measuring will kill the organism - Gives more accurate results