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Topic 5 key terminologies > Mark Scheme Answers > Flashcards

Mark Scheme Answers Flashcards

1
Q

During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how (6)

A
  • Carbon dioxide reacts with ribulose biphosphate/ RuBP using rubisco
  • Produces two glycerate 3-phosphate/ GP
  • GP reduced to two triose phosphate
  • Using reduced NaDP
  • Using energy from hydrolysis of ATP
  • Triose phosphate converted to useful organic substances e.g glucose/ hexose or regenerated RuBP
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2
Q

Describe how plants use light energy during the light-dependent reaction (6)

A
  • Excites electrons/ electrons removed from chlorophyll
  • Electrons move along carriers/ electron transfer chain in series of redox reactions releasing energy
  • Energy is used to pump H+ across thylakoid membrane
  • H+ move back across thylakoid membrane through ATP Synthase releasing energy used to join ADP and Pi to form ATP
  • Photolysis of water produces protons, electrons and oxygen
  • Electron from end of chain combines with proton from photolysis to form hydrogen
  • NADP reduced by hydrogen to produce reduced NADP
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3
Q

How is a leaf adapted to carry out photosynthesis (6)

A
  • Large surface area for absorption of light
    -Transparent cuticle to let light pass through the mesophyll cells for photosynthesis
  • Long narrow tightly packed mesophyll cells packed with chloroplasts for light absorption
  • Many stomata for gas exchange, which can open and close in different light intensities
  • Many air spaces allow short diffusion pathway for CO2 and O2
  • Network of xylem which brings water to leaf for photosynthesis and phloem which transport sugars made in photosynthesis away
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4
Q

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

A
  • Chlorophyll absorbs light/ electrons are excited
  • Electrons are lost, chlorophyll becomes positively charged
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5
Q

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

A

Ink and leaf pigments wExplain why the student marked the origin using a pencil rather than using
ink.ill mix

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6
Q

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

A
  • Level of solvent below origin/line
  • Remove/stop before (solvent) reaches top/end
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7
Q

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

A
  1. (Less/no) ATP;
  2. (Less/no) reduced NADP;
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8
Q

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

A
  1. (Less/no) carbon dioxide (reacts) with RuBP;
  2. (Less/no) GP;
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9
Q

Why does a potometer apparatus need to be air tight

A
  • Air bubbles might enter/ gases may escape so the rate of photosynthesis would be affected
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10
Q

How does temperature affect the rate of photosynthesis

A

Temperature would affect the enzymes which would affect the rate of photosynthesis

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11
Q

Suggest why the investigation of photosynthesis takes place in the dark with one light source and why the plant tissue is kept in the dark before the experiment

A
  • Light intensity affects photosynthesis so only one light source
  • Plant is kept in the dark so no residual product is formed
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12
Q

How is starch stored in plants

A
  • Amylose and amylopectin which is synthesized from glucose
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13
Q

Where in the thylakoid is chlorophyll stored?

A

In the outer membrane

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14
Q

Describe the process of glycolysis (4)

A
  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.
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15
Q

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

A
  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
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16
Q

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 (2)

A
  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;
    Accept description of glycolysis e.g. glucose to pyruvate.
    Accept ‘for oxidising/converting triose phosphate to
    pyruvate’.
17
Q

Many yeast cells die during the death phase.
Suggest one reason why

A
  • Decrease/no glucose/substrate
    OR
    Increase in ethanol/carbon dioxide/acidity;
  • Accept decrease/no oxygen as Figure 2 is not
    linked to Figure 1.
  • Accept competition for glucose/oxygen.
  • Accept any named sugar
  • Accept decrease in pH
  • Accept increase in toxin
18
Q

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.
(a) Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction (2)

A
  1. (Less/no) ATP;
  2. (Less/no) reduced NADP
19
Q

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. (2)

A
  1. (Less/no) carbon dioxide (reacts) with RuBP;
  2. (Less/no) GP;
20
Q

Explain why the student set up a control when testing for respiration

A
  1. To show light does not affect DCPIP;
  2. To show chloroplasts are required;
21
Q

The student evaluated the effectiveness of different chemicals as
weed-killers by assessing their ability to prevent the decolourisation of
DCPIP in chloroplast suspensions.
He added different concentrations of each chemical to illuminated
chloroplast suspensions containing DCPIP. He then determined the IC50 for
each chemical. The IC50 is the concentration of chemical which inhibits the
decolourisation of DCPIP by 50%.
Explain the advantage of the student using the IC50 in this investigation. (1)

A
  • Provides a standard / reference point
    OR
  • Can compare different chemicals/weed-killers
    OR
  • Can compare different concentrations of chemicals / weed-killers;
22
Q

A teacher studying these data with her students told her class that no
definite conclusions could be drawn when comparing the mean values in
the graph.
Suggest why the teacher said this (2)

A
  1. No error bars / SD;
  2. To show if overlap occurs so difference (in means) is not significant /
    due to chance
    OR
    To show if no overlap occurs so difference (in means) is significant /
    is not due to chance
23
Q

When treated with Atrazine, weeds have been shown to give off small
amounts of heat.
Suggest an explanation for this observation (1)

A

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

24
Q

Give one piece of evidence from the diagram which suggests that the conversion of pyruvate to ethanol involves production (2)

A
  • Oxygen removed from pyruvate
  • Reduced NAD is oxidised/ donates electrons/donates hydrogens
25
Q

Give two ways in which anaerobic respiration of glucose in yeast is similar to anaerobic respiration of glucose in a muscle cell (4)

A
  • ATP formed
  • Pyruvate formed
  • NAD is regenerated
  • Glycolysis involved
26
Q

Give two ways in which anaerobic respiration of glucose in yeast is different from anaerobic respiration from glucose in a muscle cell (2) (comparative statements_

A
  • Ethanol/ alcohol formed by yeast and lactate my muscle cell
  • Glycolysis involved
27
Q

If aerobic respiration had been investigated rather than anaerobic respiration, how would you expect the volumes of gas collected at 30°C to differ from these results?

Explain your answer. (2)

A
  • Volume less
  • So volume of CO2 evolved equals the volume of oxygen taken in
28
Q

The student closed the tap. After thirty minutes the drop of coloured liquid had moved to the left. Explain why the drop of coloured liquid moved to the left (3) of a woodlouse

A
  • Oxygen taken up/ used by woodlouse
  • Carbon dioxide is given out and is absorbed by the solution/ potassium hydroxide
  • Decrease in pressure
29
Q

What measurements should the student have taken to calculate the rate of aerobic respiration in mm3 of oxygen g–1 h–1? (3) in a woodlouse

A
  • Distance drops and moved and time
  • Mass of woodlouse
  • Diameter/ radius of tubing
30
Q

DNP inhibits respiration by preventing a proton gradient being maintained across membranes. When DNP was added to isolated mitochondria the following changes were observed

  • less ATP was produced
  • more heat was produced
  • the uptake of oxygen remained constant.

Explain how DNP caused these changes. (3)

A
  • Less/no proton/ H+ movement so less/ no ATP produced
  • Heat released from electron transport/ redox reactions/ energy not used to pump protons across inner membrane so is released as heat
  • Oxygen used as final electron acceptor/ combines with electrons (and protons)
31
Q

Explain why scientists measure the rate of production of oxygen in an investigation that deals with the rate of photosynthesis (1)

A
  • Oxygen is produced in the light-dependent reaction
32
Q

The scientists suggested that mutant plants producing more chlorophyll b would grow faster than normal plants in all light intensities (4)

A
  1. Have faster/ more production of ATP and reduced NADP;
  2. (So) have faster / more light-independent reaction/ GP reduced to triose phosphate;
  3. (So) produce more sugars that can be used in respiration;
  4. (So) have more energy/ATP for growth;
  5. Have faster / more synthesis of new organic materials/example e.g. more phospholipids for cell membranes/ more proteins for enzymes.
33
Q

During the light-dependent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how (6)

A
  1. Carbon dioxide reacts 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.

  1. GP reduced to triose phosphate;

Must have idea of reduction. This may be conveyed by stating m.p. 4.

  1. Using REDUCED NADP;

Reject: Any reference to reduced NAD for m.p.4 but allow reference to reduction for m.p. 3.

  1. Using energy from ATP;

Must be in context of GP to Triose Phosphate.

  1. Triose phosphate converted to glucose / RuBP / ribulose bisphosphate / named organic substance;
34
Q

The scientist carried out a similar experiment but increased the carbon dioxide concentration from 1% to 2%. The relative amounts of GP and RuBP remained the same. Suggests two reasons why (4)

A
  1. Temperature is a limiting factor/below optimum;
  2. Light intensity is a limiting factor/below optimum;

Accept: limited by reduced NADP or ATP.

  1. Limited by RuBP (available/produced);

Accept: RuBP will always give 2 GP (at high CO2).

  1. Limited by enzyme;

Accept: limited by Rubisco.

35
Q

Suggest what hydrogen sulfide is used for in bacteria (4)

A
  1. (Provides) hydrogen / protons/H+ and electrons/e-;
  2. For reduction (for NADP);

Reject: reduction of NAD.

  1. For production of ATP
  2. Source of electrons for (to replace) chlorophyll/electron transfer chain;

Accept: electrons for photophosphorylation.

36
Q

The student did not use a buffer to maintain the pH of the solution. Explain what would happen to the pH of the solution during this investigation

A
  1. (pH) increases;

Neutral: becomes more alkaline / less acidic

  1. As (more) carbon dioxide removed (for photosynthesis)

Topic 5 key terminologies (5 decks)

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