T5 Energy transfer in and between organisms

Question 1

1 mark

In photosynthesis, which chemicals are needed for the light-dependent reaction?

Answer 1

☑ NADP, ADP, Pi and water;

Question 2

2 marks

Describe what happens during photoionisation in the light-dependent reaction.

Answer 2

1.   Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll;
Ignore photosystems.
2. Electron/s are lost
OR
(Chlorophyll) becomes positively charged;
Ignore site/molecule from where electrons are lost.
Accept electrons go to electron transport/carrier chain for ‘electrons lost’.

Question 3

A student obtained a solution of pigments from the leaves of a plant. Then the student used paper chromatography to separate the pigments. Explain why the student marked the origin using a pencil rather than using ink. 1 mark

Describe the method the student used to separate the pigments after the solution of
pigments had been applied to the origin. 2 marks

Answer 3

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;

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 4

1 mark

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

Answer 4

(Absorb) different/more wavelengths (of light) for photosynthesis;
Accept wider/larger range of wavelengths.
Accept frequency for wavelength.
Accept light-dependent reaction /photophosphorylation /photoionisation
for photosynthesis.

Question 5

2 marks

Heat stress is a condition that often occurs in plants exposed to high temperatures for a
prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.
Heat stress decreases the light-dependent reaction in photosynthesis.
Explain why this decreases the light-independent reaction. 2 marks

Answer 5

1. (Less/no) ATP;
2. (Less/no) reduced NADP;
   Accept NADPH, NADPH + H, NADPH2 NADPH + H+
   Reject reduced NAD, NADH etc,

Question 6

2 marks

Heat stress is a condition that often occurs in plants exposed to high temperatures for a
prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.
Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A
decrease in the activity of an enzyme means that the rate of the reaction it catalyses
becomes slower.
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

1 mark

Where precisely is rubisco found in a cell?

Answer 7

1. Stroma (of/in chloroplast);
   Reject: stoma
   Reject stroma of cytoplasm/chlorophyll
   Reject stroma of mitochondrion
   Ignore references to Calvin cycle or the light-independent reaction

Question 8

4 marks + 1 mark

Atrazine 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 4 marks

When treated with Atrazine, weeds have been shown to give off small amounts of heat.
Suggest an explanation for this observation.

Answer 8

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 / NADPH2 / NADPH+
   Reject reduced NAD
4. (So) light-independent reaction slows / stops;
   OR
   Less reduction of GP to triose phosphate.

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

Question 9

Crops use light energy to produce photosynthetic products.
Describe how crop plants use light energy during the light-dependent reaction 5 marks

Answer 9

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.
   Accept: energy used for phosphorylation of ADP to ATP
   Do not accept P as Pi but accept phosphate.
4. Photolysis of water produces protons, electrons and oxygen;
5. NADP reduced by electrons / electrons and protons / hydrogen;
   Accept: NADP to NADPH (or equivalent) by addition of
   electrons/hydrogen.
   Do not accept NADP reduced by protons on its own

Question 10

After harvesting, the remains of crop plants are often ploughed into the soil.
Explain how microorganisms in the soil produce a source of nitrates from these remains 5 marks

Answer 10

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;
   Reject: nitrifying bacteria in root nodules.
   1, 3 and 4. Accept: marks for conversion even if incorrect type of
   bacteria named as being involved.
   2 and 5. Reject: marks for type of bacteria if linked to incorrect
   process e.g. nitrite converted to nitrate by saprobionts.
   3 and 4. Accept: for one mark ammonia/ammonium into nitrate if
   neither mark point 3 or 4 awarded.
   Note: there are no marks for the role of nitrogen-fixing bacteria as
   the question refers to producing a source of nitrates from the remains of crops.

Question 11

Explain the relationship between stomatal opening and photosynthesis. 2 marks

Answer 11

1. Stomata allow uptake of carbon dioxide;
2. Carbon dioxide used in / required for photosynthesis;

Question 12

Describe the process of glycolysis. 4 marks

Answer 12

1. Phosphorylation of glucose using ATP;
2. Oxidation of triose phosphate to pyruvate;
   Accept removal of hydrogen from triose phosphate for oxidation.
3. Net gain of ATP;
   Accept any description that indicates a net gain e.g., 4 produced, 2
   used.
4. NAD reduced;
   Accept NADH/NADH2/NADH + H+
   produced.
   Accept all mark points in diagrams.

Question 13

Malonate inhibits a reaction in the Krebs cycle.
Explain why malonate would decrease the uptake of oxygen in a respiring cell. 2 marks

Answer 13

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 14

Where in a cell does glucose turn into pyruvate occur?

Answer 14

Cytoplasm/cytosol;

Question 15

The Respiratory Quotient (RQ) can provide information on the type of respiration taking
place in an organism. The following equation is used to calculate the RQ.
RQ=Vol of CO2 produced during respiration/Vol of O2 used during respiration

What would be the RQ for aerobic respiration of glucose? 1 mark

A student calculated that the RQ of germinating seeds was 1.8.
Use the information provided to explain this result. 2 marks

Answer 15

1/one/1.0;
​
1. Aerobic and anaerobic respiration occurring;
Accept: some/mainly anaerobic respiration occurring.
2. More carbon dioxide produced than oxygen uptake;

Question 16

Aerobic respiration produces more ATP per molecule of glucose than anaerobic respiration. Explain why. 2 marks

Answer 16

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;
   Ignore: number of ATP produced.
4. Accept: without oxygen.
5. Ignore: converse.

Question 17

Describe how acetylcoenzyme A is formed in the link reaction 2 marks

Answer 17

1. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released;
2. Addition of coenzyme A.
   Accept: NAD reduced for oxidationDescribe how acetylcoenzyme A is formed in the link reaction 2 marks

Question 18

In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form
six-carbon citrate. This reaction is catalysed by the enzyme citrate synthase.
(i) Oxaloacetate 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. 2 marks

Answer 18

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.
   Neutral: references to two active sites

Question 19

In muscles, pyruvate is converted to lactate during anaerobic respiration.
(i) Explain why converting pyruvate to lactate allows the continued production of ATP
during anaerobic respiration. 2 marks

In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this. 1 mark

Answer 19

1. Regenerates / produces NAD / oxidises reduced NAD;
2. (NAD used) in glycolysis.
   Accept: description of glycolysis
   Accept: glycolysis can continue / begin

(Pyruvate used) in aerobic respiration / (lactate / lactic acid) is toxic / harmful /
causes cramp / (muscle) fatigue.
Accept: (pyruvate) can enter link reaction
Accept: reduces cramp / (muscle) fatigue
Neutral: ‘reduces muscle aches’

Question 20

Freshwater marshes have one of the highest rates of gross primary production (GPP) and net
primary production (NPP) of all ecosystems.
Carbon use efficiency (CUE) is the ratio of NPP:GPP. Freshwater marshes have a high CUE.
1.
(a)  Use your knowledge of NPP to explain why freshwater marshes have a high CUE and the
advantage of this.
Do not refer to abiotic factors in your answer.
Explanation:
Advantage: 2 marks

Answer 20

1. Low respiration;
   Accept less energy lost in respiration
2. More growth/biomass/colonisation;
   Allow examples of more carbon-containing molecules eg glucose

Question 21

  Succession occurs in natural ecosystems. Describe and explain how succession occurs. 4 marls

Answer 21

1.   (Colonisation by) pioneer species;
2.   Pioneers/species/organisms change the environment/habitat/conditions/factors;
Accept example of change e.g. forms soil/humus/organic matter/nutrients.
Must convey idea of change being caused by pioneers/species
/organisms
3.   (Environment becomes) less hostile for other/new species
OR
(Environment becomes) more suitable for other/new species
OR
(Environment becomes) less suitable for previous species;
Accept previous species out-competed.
4.   Change/increase in diversity/biodiversity;
Ignore increase in genetic diversity.
5.   (To) climax community;

Question 22

Biofuels are fuels which can be produced from plants. Scientists have developed a standard
method called net life-cycle carbon dioxide production (NLP) to find the overall effect of
producing and using particular biofuels on carbon dioxide production.
(a) Petroleum is used as a comparison when evaluating NLPs of biofuels. Suggest two reasons why. 2 marks

Biofuels are produced by a variety of different companies. The scientists who developed
the method of calculating NLPs are funded by the government’s environmental agency.
Suggest two advantages of this method being developed by these scientists. 2 marks

Answer 22

1. Is widely / commonly used;
2. Provides a standard / benchmark / reference;
   Allow a variety of descriptors for marking point 2 e.g. ‘provides a
   base line’,
   ‘produces known amount of carbon dioxide’
   Mark point 2, do not accept ‘for comparison’ on its own as
   ‘comparison’ is in stem of question
3. Produces large amount of carbon dioxide;
4. Is a decreasing resource / could be replaced by biofuel;
   Ignore reference to a control

Independent / no bias / trustworthy;
2. Non-profit making;
3. (Focused on) effect on environment / climate;

Question 23

Producing and using biofuels from corn ethanol results in a negative percentage change in
carbon dioxide production. Explain why.
2 marks

Answer 23

1. CO2 taken up in photosynthesis;
2. More taken up than produced (when it is used) with less CO2 produced than
   petrol;

Question 24

Ethanol can be produced from cellulose. It is produced by anaerobic respiration of
cellulose-based biomass by microorganisms. The cellulose is pre-treated by adding
cellulose-digesting enzymes before it is used in anaerobic respiration. Suggest why
pre-treatment is necessary. 3 marks

Answer 24

1. (These microorganisms) don’t have (cellulose-digesting) enzymes;
   Accept ‘don’t make enough of these enzymes’ for mark point 1
2. (Cellulose) is a polysaccharide / polymer / long (molecule / chain);
   Accept ‘large’ for mark point 2
3. (Cellulose) is insoluble / glucose / product of digestion is soluble;
4. Broken down into glucose / monomers / monosaccharides;
   Ignore (alpha) glucose for mark point 4.
   Do not accept sugars for mark point 4
5. Sugars / glucose used in glycolysis / glucose can be converted to pyruvate;
6. Produces more ethanol / fuel produces ethanol / fuel quicker;
   Accept ‘speeds up process’ for mark point 6

Question 25

Large areas of land have to be used to grow the plants to make biofuels. Ecologists have
suggested that changes in land use could lead to a decrease in biodiversity.
Suggest how changes in land use could lead to a decrease in biodiversity.2 marks

Answer 25

1. Removes species / fewer species / growth of single crop / single plant species /
   monoculture;
   Deforestation or removal of hedges on its own should not be
   credited
2. Removes habitats / fewer habitats / niches / only one habitat;
3. Removes variety of food sources / fewer food sources / only one food source;

Question 26

Describe the role of saprobionts in the nitrogen cycle 2 marks

Answer 26

1.   (They use enzymes to) decompose proteins/DNA/RNA/urea;
Accept any named molecule containing nitrogen eg enzymes, NAD, ATP,
amino acids
Accept digest/breakdown/hydrolyse for decompose
Ignore ‘nitrogen -containing compounds’ unqualified
2.   Producing/releasing ammonia/ammonium compounds/ammonium ions;
Accept (they) perform ammonification
Accept named ammonium compound

Question 27

One environmental issue arising from the use of fertilisers is eutrophication.
Eutrophication can cause water to become cloudy.
You are given samples of water from three different rivers.
Describe how you would obtain a quantitative measurement of their cloudiness. 3 marks

Answer 27

Principle is
1. Named apparatus
2. What is measured
3. Standardisation of method
Accept any valid method, for example
1.   Use of colorimeter;
Reject calorimeter
2.   Measure the absorbance/transmission (of light);
Reject if samples are filtered unless filtering to remove debris
Accept descriptions
3.   Example of how method can be standardised eg same volume of water,
zeroing colorimeter, same wavelength of light, shaking the sample;
Ignore references to calibration curves

Question 28

Describe the role of microorganisms in producing nitrates from the remains of dead organisms. 3 marks

Answer 28

1. Saprobiotic (microorganisms / bacteria) break down remains / dead
   material / protein / DNA into ammonia / ammonium;
   Accept: saprobionts / saprophytes / saprotrophs
   Neutral: decomposer
2. Ammonia / ammonium ions into nitrite and then into nitrate;
   Allow correct chemical symbols.
   Accept: correct answers which use incorrect bacteria e.g. nitrogenfixing but then reject m.p. 3.
3. (By) Nitrifying bacteria / nitrification;

Question 29

Upwelling often results in high primary productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters. 2 marks

Answer 29

1. Nitrate / phosphate / named ion / nutrients for growth of / absorbed / used by
   plants / algae / producers;
2. More producers / consumers / food so more fish / fish reproduce more / fish
   grow more / fish move to area;
   Must have idea of more plants related to some increase in fish.

Question 30

Leguminous crop plants have nitrogen-fixing bacteria in nodules on their roots.
On soils with a low concentration of nitrate ions, leguminous crops often grow better than
other types of crop. Explain why.
2 marks

Answer 30

1. (Nitrogen) to ammonia / NH3 / ammonium;
2. Do not disqualify mark for any references to ammonia being
   converted to nitrite, nitrate etc
3. Produce protein / amino acids / named protein / DNA / RNA;
4. Do not disqualify mark for any references to protein being formed
   from nitrogen, nitrite or nitrate

Question 31

Applying very high concentrations of fertiliser to the soil can reduce plant growth. Use your knowledge of water potential to explain why. 2 marks

Answer 31

Soil has lower water potential so water moves out of the plants by osmosis

Question 32

Net production of consumers Formula

Answer 32

N = I - F+ R
I = Chemical energy stored in ingested food
F = Energy lost to the environment in faeces or urine
R = Respiratory losses

Question 33

Units for Rates of Productivity

Answer 33

KJha^-1year^-1