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A-level Biology > 5A - Photosynthesis > Flashcards

5A - Photosynthesis Flashcards

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1
Q

Where does photosynthesis take place?

A

In the chloroplasts of plant cells.

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2
Q

What are chloroplasts?

A

Flattened organelles surrounded by a double membrane found in plant cells.

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3
Q

What are thylakoids?

A

Fluid filled sacs that are stacked up into grana which are then linked together by bits of thylakoid membrane called lamellae.

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4
Q

How are thylakoids arranged in a chloroplast?

A

They are stacked up into grana which are then linked together by bits of thylakoid membrane called lamellae.

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5
Q

What is the singular for grana?

A

Granum

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6
Q

What is the singular for lamellae?

A

Lamella

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7
Q

Chloroplasts contain photosynthetic pigments, what are some examples?

A

Chlorophyll a, chlorophyll b and carotene.

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8
Q

What are photosynthetic pigments?

A

Coloured substances that absorb the light energy needed for photosynthesis.

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9
Q

Where are the photosynthetic pigments found in the chloroplast?

A

In the thylakoid membranes - they’re attached to proteins.

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10
Q

What is a protein and pigment called in a chloroplast?

A

A photosystem.

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11
Q

How many photosystems are there that are used by plants to capture light energy?

A

2

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12
Q

What is a photosystem?

A

A protein and pigment used by plants to capture light energy.

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13
Q

What are the 2 photosystems that are used by plants?

A

Photosystem I (PSI) and photosystem II (PSII).

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14
Q

When does photosystem I absorb light best?

A

At a wavelength of 700 nm.

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15
Q

When does photosystem II absorb light best?

A

At a wavelength of 680 nm.

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16
Q

What is the gel-like substance surrounding the thylakoids contained within the inner membrane of the chloroplasts?

A

The stroma.

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17
Q

What is the stroma?

A

The gel-like substance surrounding the thylakoids contained within the inner membrane of the chloroplasts

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18
Q

What does the stroma contain?

A

Enzymes, sugars and organic acids.

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19
Q

What happens to carbohydrates produced by photosynthesis in the chloroplasts?

A

They are not all used straight away so can be stored as starch grains in the stroma.

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20
Q

How are carbohydrates produced by photosynthesis stored within the chloroplasts?

A

As starch grains within the stroma.

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21
Q

How many stages are there to photosynthesis?

A

2

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22
Q

What are the 2 stages of photosynthesis?

A

The light-dependent reaction.

The light-independent reaction.

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23
Q

What is the first stage of photosynthesis?

A

The light-dependent reaction.

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24
Q

What is the second stage of photosynthesis?

A

The light-independent reaction.

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25
Q

Where does the first stage of photosynthesis take place?

A

In the thylakoid membranes of the chloroplasts.

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26
Q

What happens in the first stage of photosynthesis?

A
  • The reaction needs light and takes place in the thylakoid membranes of the chloroplasts.
  • Here, light energy is absorbed by chlorophyll (and other photosynthetic pigments) in the photosystems.
  • The light energy excites the electrons in the chlorophyll, leading to their eventual release from the molecule.
  • The chlorophyll has been photoionised.
  • Some of the energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to form reduced NADP.
  • ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction.
  • During the process H2O is oxidised to O2.
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27
Q

What happens to the energy from the released electrons during the first stage of photosynthesis?

A

Some of the energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to form reduced NADP.

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28
Q

What does the ATP formed from the first stage of photosynthesis do?

A

Transfers energy.

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29
Q

What does the reduced NADP formed from the first stage of photosynthesis do?

A

Transfers hydrogen to the light-independent reaction.

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30
Q

During the first stage of photosynthesis, what happens to the water?

A

It is oxidised into O2.

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31
Q

Where does the second stage of photosynthesis take place?

A

In the stroma of the chloroplast.

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32
Q

What is the second stage of photosynthesis also known as apart from the ‘light-independent reaction’?

A

The Calvin cycle.

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33
Q

What does the second stage of photosynthesis rely on?

A

Doesn’t use light energy directly but does rely on the products of the light-dependent reaction.

34
Q

What do the products of the first stage of photosynthesis do in the second stage of photosynthesis?

A

Here, the ATP and reduced NADP from the light-dependent reaction supply the energy and hydrogen to make simple sugars from carbon dioxide.

35
Q

In the second stage of photosynthesis, what do ATP and reduced NADP supply the energy and hydrogen for?

A

To make simple sugars from carbon dioxide.

36
Q

How is ATP made in the light-dependent reaction in photosynthesis?

A

By phosphorylation.

37
Q

The energy resulting from the photoionisation of chlorophyll in the light-dependent reaction in photosynthesis is used for what 3 things?

A
  1. Making ATP from ADP and inorganic phosphate. This reaction is called photophosphorylation.
  2. Making reduced NADP from NADP.
  3. Splitting water into protons (H+ ions), electrons and oxygen. This is called photolysis.
38
Q

How many types of photophosphorylation are used in the light-dependent reaction in photosynthesis?

A

2

39
Q

What are the 2 types of photophosphorylation that are used in the light-dependent reaction in photosynthesis?

A

Non-cyclic and cyclic.

40
Q

What is the primary difference between non-cyclic and cyclic photophosphorylation?

A

Non-cyclic photophosphorylation produces ATP, reduced NADP and oxygen.

Cyclic photophosphorylation only produces ATP.

41
Q

What are the photosystems in the thylakoid membranes of the chloroplasts linked by?

A

Electron carriers.

42
Q

What are electron carriers?

A

Proteins that transfer electron - they can be found linking the photosystems in the thylakoid membranes of the chloroplasts.

43
Q

What do the electron carriers and photosystems form?

A

An electron transport chain - a chain of proteins through which excited electrons flow.

44
Q

What is an electron transport chain?

A

A chain of proteins through which excited electrons flow.

45
Q

What are the different processes that occur during non-cyclic photophosphorylation?

A
  • Light energy excites electrons in chlorophyll.
  • Photolysis of water produces protons (H+ ions), electrons and oxygen.
  • Energy from the excited electrons makes ATP…
  • …and generates reduced NADP.
46
Q

Explain the process of ‘light energy excites electrons in chlorophyll’ that happens during non-cyclic photophosphorylation

A
  • Light energy is absorbed by PSII.
  • The light energy excites electrons in chlorophyll.
  • The electrons move to a higher energy level (i.e. they have more energy).
  • These high-energy electrons are released from the chlorophyll and move down the electron transport chain to PSI.
47
Q

Explain the process of ‘photolysis of water produces protons (H+ ions), electrons and oxygen’ that happens during non-cyclic photophosphorylation

A
  • As the excited electrons from chlorophyll leave PSII to move down the electron transport chain, they must be replaced.
  • Light energy splits water into protons (H+ ions), electrons and oxygen - photolysis.
  • The reaction is:
    H2O –> 2H+ + 1/2O2
48
Q

Explain the process of ‘energy from the excited electrons makes ATP…’ that happens during non-cyclic photophosphorylation

A
  • The excited electrons lose energy as they move down the electron transport chain.
  • This energy is used to transport protons into the thylakoid, so that the thylakoid has a higher concentration of protons than the stroma. This forms a proton gradient across the thylakoid membrane.
  • Protons move down their concentration gradient into the stroma, via the enzyme ATP synthase, which is embedded in the thylakoid membrane. The energy from this movement combines ADP and inorganic phosphate to form ATP.
49
Q

Explain the process of ‘energy from the excited electrons generates reduced NADP’ that happens during non-cyclic photophosphorylation

A
  • Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level.
  • Finally, the electrons are transferred to NADP, along with a proton (H+ ion) from the stroma, to form reduced NADP.
50
Q

What is chemiosmosis?

A

The process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis.

51
Q

What is the process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis called?

A

Chemiosmosis

52
Q

What is the process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis (chemiosmosis) described by?

A

The chemiosmotic theory.

53
Q

What does the chemiosmotic theory describe?

A

The process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis (chemiosmosis).

54
Q

What photosystem does cyclic photophosphorylation use?

A

PSI only.

55
Q

Why is cyclic photophosphorylation called ‘cyclic’?

A

Because the electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers meaning that the electrons are recycled and can repeatedly flow through PSI.

56
Q

What does cyclic photophosphorylation produce?

A

Small amounts of ATP only.

57
Q

What happens in cyclic photophosphorylation?

A
  • Uses PSI only.
  • The electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers meaning that the electrons are recycled and can repeatedly flow through PSI.
  • This process doesn’t produce any reduced NADP of O2 - it only produces small amounts of ATP.
58
Q

Where does the Calvin cycle take place?

A

In the stroma of the chloroplasts.

59
Q

What is the light-independent reaction of photosynthesis also called?

A

The Calvin cycle.

60
Q

What does the Calvin cycle do?

A

Makes a molecule called triose phosphate from CO2 and ribulose biphosphate (a 5-carbon compound).

61
Q

What is the Calvin cycle and the light-independent reaction of photosynthesis also known as?

A

Carbon dioxide fixation.

62
Q

Why is the Calvin cycle and the light-independent reaction of photosynthesis also known as carbon dioxide fixation?

A

Because carbon from CO2 is ‘fixed’ into an organic molecule.

63
Q

What can triose phosphate made in the Calvin cycle be used for?

A

To make glucose and other useful organic substances.

64
Q

What does the Calvin cycle need to keep going?

A

ATP and H+ ions.

65
Q

The reactions in the light-dependent reaction of photosynthesis are linked in a cycle. What does this mean for the starting compound, ribulose bisphosphate?

A

It is regenerated.

66
Q

What is the starting compound in the Calvin cycle?

A

Ribulose bisphosphate.

67
Q

What happens to the starting compound, ribulose bisphosphate in the Calvin cycle?

A

It is regenerated.

68
Q

What are the stages of the Calvin cycle?

A
  1. Carbon dioxide is combined with ribulose bisphosphate to form two molecules of glycerate 3-phosphate.
  2. ATP and reduced NADP are required for the reduction of GP to triose phosphate.
  3. Ribulose bisphosphate is regenerated.
69
Q

What is the first stage of the Calvin cycle?

A
  1. Carbon dioxide is combined with ribulose bisphosphate to form two molecules of glycerate 3-phosphate.
70
Q

What is the second stage of the Calvin cycle?

A
  1. ATP and reduced NADP are required for the reduction of GP to triose phosphate.
71
Q

What is the third stage of the Calvin cycle?

A
  1. Ribulose bisphosphate is regenerated.
72
Q

Explain the first stage of the Calvin cycle - where carbon dioxide is combined with ribulose bisphosphate to form two molecules of glycerate 3-phosphate.

A
  • CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast.
  • Here, it’s combined with ribulose biphosphate (RuBP), a 5-carbon compound. This reaction is catalysed by the enzyme rubisco.
  • This gives an unstable 6-carbon compound, which quickly breaks down into two molecules of a 3-carbon compound called glycerate 3-phosphate (GP).
73
Q

Explain the second stage of the Calvin cycle - where ATP and reduced NADP are required for the reduction of GP to triose phosphate.

A
  • The hydrolysis of ATP (from the LD reaction) provides energy to turn the 3-carbon compound, GP, into a different 3-carbon compound called triose phosphate (TP).
  • This reaction also requires H+ ions, which come from the reduced NADP (also from the LD reaction). Reduced NADP is recycled to NADP.
  • Some triose phosphate is then converted into useful organic compounds (e.g. glucose) and some continues in the Calvin cycle to regenerate RuBP.

(Reduced NADP reduced GP to TP).

74
Q

Explain the third stage of the Calvin cycle - where ribulose bisphosphate is regenerated.

A
  • 5 out of every 6 molecules of TP produced in the cycle aren’t used to make hexose sugars, but to regenerate RuBP.
  • Regenerating RuBP uses the rest of the ATP produced by the LD reaction.
75
Q

What are TP and GP converted to in the light-independent reaction?

A

Useful organic substances like glucose.

Carbohydrates, lipids and amino acids.

76
Q

In the light-independent reaction, what are carbohydrates, lipids and amino acids made of?

A

Triose phosphate (TP) and glycerate 3-phosphate (GP) molecules.

77
Q

In the light-independent reaction, how are carbohydrates made?

A

Hexose sugars like glucose are made by joining two triose phosphate molecules together and larger carbohydrates like uscrose, starch and cellulose are made by joininghexose sugars together in different ways.

78
Q

In the light-independent reaction, how are lipids made?

A

Using glycerol, which is synthesised from triose phosphate, and fatty acids, which are synthesised from glycerate 3-phosphate.

79
Q

In the light-independent reaction, how are amino acids made?

A

Some are made from glycerate 3-phosphate.

80
Q

How many times does the Calvin Cycle need to turn to make one hexose sugar?

A

6

81
Q

Why does the Clavin Cycle need to turn 6 times to make one hexose sugar?

A
  • Three turns of the cycle produces 6 molecules of triose phosphate (TP), because 2 molecules of TP are made for every 1 molecule of CO2 molecule used.
  • 5 out of 6 of these TP molecules are used to regenerate ribulose biphosphate (RuBP).
  • This means that for 3 turns of the cycle only one TP is produced that’s used to make a hexose sugar.
  • A hexose sugar has 6 carbonds though, so two TP molecules are needed to form one hexose sugar.
  • This means the cycle must turn 6 times to produce 2 molecules of TP that can be used to make 1 hexose sugar.
  • 6 turns of the cycle need 18ATP and 12 reduced NADP from the light-dependent reaction.

A-level Biology (42 decks)

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