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Biology > Photosynthesis A2 > Flashcards

Photosynthesis A2 Flashcards

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1
Q

Describe the light dependent reaction
(5 marks)

A

● Chlorophyll absorbs light energy via
photoionisation;
● Excites electrons / electrons removed (from
chlorophyll);
● Electrons move along carriers/electron
transport chain releasing energy;
● Energy released (by electrons) used to form
proton gradient;
● H+ ions move through ATP synthase;
● providing energy to join ADP and Pi to form ATP;
● Photolysis of water produces 2 protons, 2
electrons and ½ oxygen;
● NADP reduced by electrons / electrons and
protons / hydrogen;

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2
Q

Describe the light independent reaction
(6 Marks)

A

● Carbon dioxide combines with ribulose
bisphosphate/RuBP;
● Produces two glycerate (3-)phosphate/GP;
● GP reduced to triose phosphate/TP;
● Using reduced NADP;
● Using energy from ATP;
● Triose phosphate converted to
glucose/hexose/RuBP/ ribulose
bisphosphate/named organic substance;
● In light independent reaction / Calvin cycle

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3
Q

ATP is produced in the light dependant reaction, suggest why this is not plants only source of ATP. (4)

A

● Plants don’t photosynthesis in the dark;
● Not all the parts of the plants photosynthesise;
● Plants require more ATP than is produced in the
light dependant reaction;
● ATP used in Active Transport (accept other
named processes)

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4
Q

Describe the effect of introducing a
herbicide on the electron transport
chain (4 Marks)

A

● Reduced transfer of protons across thylakoid
membrane
OR
● Reduced chemiosmotic gradient/proton
gradient across thylakoid membrane;
● (So) less ATP produced;
● (So) less reduced NADP produced;
● (So) light-independent reaction slows/stops
OR
● Less reduction of GP to triose phosphate;

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5
Q

Describe how a lack of phosphates in
the soil surrounding a plant can affect
its growth.

A

● (Required to) make ATP/glucose phosphate, so
less respiration/less energy for growth;
● (Required to) make nucleotides, so less
DNA/mRNA/tRNA for cell division/production of
protein (for growth);
● (Required to) make RuBP/NADP, so less CO2
fixed/reduced into sugar;
● (Required to) make phospholipids for
membranes;

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6
Q

Where does the light independent reaction occur?

A

Stroma

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7
Q

Where does the light dependent reaction occur?

A

Thylakoid stacks (granum)

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8
Q

Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP?

A
  • Excitation of chlorophyll molecule/electrons/ energy of electrons raised to higher energy level;
  • Electron(s) emitted from chlorophyll molecule;
  • Electron(s) to electron transport chain;
  • Loss of energy by electron(s) along electron transport chain;
  • Energy lost by electron(s) is used to synthesise ATP;
  • From ADP + Pi;
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9
Q

What is photolysis?

A

Photolysis is the splitting of water molecules in the presence of light into proton, electron and oxygen.

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10
Q

Describe how ATP is produced?

A
  • excited electron loses energy
  • along electron transfer chain
  • energy from electrons used to combine ADP + Pi
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11
Q

How is reduced NADP recycled into NADP in a light independent reaction?

A

used to reduce GP to TP

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12
Q

Explain the part played by water in the production of ATP during photosynthesis. (2)

A
  • Photolysis/water is split using light energy
    -Provides electrons/hydrogen ions;
    -Replaces electrons lost by chlorophyll;
    -Provides hydrogen ions for ATP production;
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13
Q

How do herbicides cause a reduction in the production of oxygen? (application)

A
  • Binds to chlorophyll molecules;
  • Stops release/absorption of electrons by chlorophyll;
  • Named effect on compounds in (first) transport chain;
  • Stops movement of electrons down first transport chain;
  • (So) break down of water reduces;
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14
Q

How do herbicides cause the death of plants? (application)

A
  • Less ATP;
  • for light-independent reaction/named reaction;
  • (So) less sugars produced for respiration;
  • Rate of respiration is greater than rate of photosynthesis;
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15
Q

Two products of the light-dependent reaction of photosynthesis are used in the light-independent reaction. Name and explain the importance if these products. (4)

A
  1. ATP - supplies extra energy for reaction
  2. NADP - reduced NADP reduces G3P to sugar
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16
Q

Suggest what hydrogen sulphide is used for in photosynthesis?

A
  • source of hydrogen / use instead of water
  • for light-dependent reaction / reducing NADP
  • source of electrons for chlorophyll / electron transport chain
17
Q

Describe how NADP is reduced in the light-dependant reaction of photosynthesis?

A
  • electrons;
  • from chlorophyll / photolysis;
18
Q

Explain why there is twice the amount of glycerate 3-phosphate as ribulose bisphosphate when the carbon dioxide concentration is high?

A

RuBP combines with carbon dioxide to produce 2x GP

19
Q

Explain the rise in the amount of ribulose bisphosphate after the carbon dioxide concentration is reduced.

A
  • less used to combine with CO2 / less used to form glycerate-3 phosphate
20
Q

Explain why radioactively labelled CO2 may be used in an experiment with the cells?

A

used in photosynthesis, allows detection of products.

21
Q

explain how lack of light caused the amount of radioactively labelled glycerate 3-phosphate to rise?

A
  • ATP and reduced NADP not formed;
  • GP is not being used to form RuBP / is being formed from RuBP;
22
Q

Explain what caused the amount of radioactively labelled glucose to decrease after the light was switched off?

A

used in respiration / formation of starch / cellulose;

23
Q

Explain why light-independent reaction slows down at low temperatures?

A
  • enzymes are involved
  • fewer collisions / less kinetic energy
24
Q

The production of phosphoglycolate could lead to a reduction in the rate of photosynthesis. Explain how.

A
  • less GP
  • so reduced amount of TP
  • less RuBP regenerated
  • so less carbon dioxide taken up
25
Q

Describe and explain the effect of oxygen concentration on the rate of photosynthesis. (2)

A
  • High levels of oxygen reduce photosynthetic rate, effect greater at higher temperatures;
  • Higher concentration more effective competitor / more RuBP combines with oxygen (instead of carbon dioxide) / greater chance of binding with the active site / colliding with the enzyme;
26
Q

The suspension of chloroplast in blue reagent was exposed to sunlight. The colour blue disappeared. Use your knowledge of the light-dependent reactions of photosynthesis to explain why. (2)

A
  • chlorophyll excited / reduced NADP formed;
  • electrons from chlorophyll / reduced NADP changes the dye
    colour;
27
Q

Another suspension of chloroplast was set up as before. Small quantities of ADP and phosphate ions were added and then the tube was exposed to light. The blue colour disappeared more quickly. Explain why. (2)

A
  • ADP and phosphate needed to produce ATP / ATP is a product of the light dependent reactions;
  • ADP levels are a limiting factor;
28
Q

Describe the need for plants to both
photosynthesise AND respire? (6)

A

● In the dark no ATP production in
photosynthesis;
● Some tissues unable to
photosynthesise/produce ATP;
● ATP cannot be moved from cell to cell/stored;
● Plant uses more ATP than produced in
photosynthesis;
● ATP for active transport;
● ATP for synthesis (of named substance);

29
Q

The concentrations of carbon dioxide in
the air at different heights above
ground in a forest changes over a
period of 24 hours. Use your knowledge
of photosynthesis to describe these
changes and explain why they occur. (6)

A

● High concentration of carbon dioxide linked with night/darkness;
● No photosynthesis in dark/night / light required for photosynthesis/light-dependent reaction;
● (In dark) plants (and other organisms) respire;
● In light net uptake of carbon dioxide by plants/plants use more carbon dioxide than they produce/ rate of photosynthesis greater than rate of respiration;
● Decrease in carbon dioxide concentration with height;
● At ground level fewer leaves/less
photosynthesising tissue/more animals/less light;

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