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Introduction to Genetics & Biochemistry > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

Where in plants does photosynthesis mostly take place?

A

In the leaves, although photosynthesis can take place in other green tissues in plants as well.

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2
Q

Chloroplasts can move in the cell. Why?

A

They will try and find more light if they are in a darker place.

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3
Q

Why might a plant have bigger thylakoid stacks?

A

To try and gain more light if they are in a shady place.

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4
Q

What does this describe?:

‘Individual pairs of parallel membranes which frequently associate into granal stacks. They are the site of the light-dependent reaction of photosynthesis’.

A

Thylakoids.

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5
Q

What interconnects thylakoid/granal stacks?

A

Single thylakoids.

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6
Q

What does appressed and non-appressed mean, in terms of thylakoids.

A

Stacked or non-stacked.

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7
Q

The thylakoid form a ……………………. ……. …………………… between the grana.

A

Network of interconnections.

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8
Q

Which pigments are contained in the thylakoid?

A

Carotenoids and chlorophyll.

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9
Q

What do carotenoids and chlorophyll absorb?

A

Light (for photosynthesis).

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10
Q

Plants use light in the ………………. ………………. of 400nm-700nm.

A

Visible spectrum.

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11
Q

What colour is the light that plants use for photosynthesis?

A

Blue and red-orange.

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12
Q

What colour light does carotenoid absorb?

A

Blue-green and violet.

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13
Q

What colour light does chlorophyll absorb?

A

Blue and red.

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14
Q

Carotenoids reflect red-orange light. What benefit is this for the plant?

A

It dissipates excess energy out of the cell.

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15
Q

Photosynthesis is a series of ………………. reactions.

A

Redox.

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16
Q

Why is it important to remember OIL RIG in photosynthesis?

A

Photosynthesis is a series of redox reactions and Oxidation Is Loss, Reduction Is Gain.

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17
Q

What is oxidised in photosynthesis?

A

Water.

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18
Q

What is reduced in photosynthesis?

A

CO2.

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19
Q

Which comes first in the thylakoid membrane, photosystem I or photosystem II?

A

Photosystem II comes first in the thylakoid membrane.

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20
Q

When light reaches photosystem II, an electron is transferred to…?

A

…the primary electron acceptor.

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21
Q

Name the four major structural compartments of chloroplasts.

A
  1. Envelope.
  2. Stroma.
  3. Thylakoids.
  4. Lumen.
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22
Q

Are the inner and outer membranes of the chloroplast involved in photosynthesis?

A

No.

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23
Q

What is the unstructured background matrix of the chloroplast called?

A

The stroma.

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24
Q

The intra-thylakoid space is also called…

A

…the lumen.

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25
Q

What are the four major protein complexes of the thylakoid membrane?

A
  1. Photosystem II.
  2. Cytochrome b6f complex.
  3. Photosystem I.
  4. ATP synthase.
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26
Q

Where are these four protein complexes found?

  1. Photosystem II.
  2. Cytochrome b6f complex.
  3. Photosystem I.
  4. ATP synthase.
A

In the thylakoid membrane.

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27
Q

Why are the protein complexes of the thylakoid membrane arranged in a specific way?

A

To allow the plant to harvest the maximum light energy.

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28
Q

In photosynthesis, the light-dependent reaction produces ………….. and …………. .

This is used in the dark reaction to make sugars from ………….. .

A

ATP and NADPH.

CO2.

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29
Q

What does light liberate from water, which end up as the ATP and NADPH used in the dark reaction to make sugar from CO2?

A

Two electrons.

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30
Q

In the light reaction, what enters the thylakoid to produce oxygen?

A

Water.

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31
Q

In the dark reaction, what is produced when carbon dioxide enters the calvin cycle.

A

Sugars.

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32
Q

Which part of the protein complexes photosystem I and photosystem II receives light?

A

The light harvesting complex / antenna.

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33
Q

Where is the light harvesting complex / antenna found?

A

In photosystem I and photosystem II.

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34
Q

Photosystem I and photosystem II contain a ‘special pair’ of chlorophyll molecules called P680. What do they do?

A

They are in the reaction centre and absorb light at 680nm. This light excites them so they lose electrons and become oxidised. These electrons are replaced by ones produced in the splitting of water in the oxygen-evolving complex.

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35
Q

What wavelength of light does the P680 complex of photosystem I absorb?

A

680nm.

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36
Q

In the oxygen-evolving centre, manganese is the catalyst for which reaction?

A

Water-splitting.

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37
Q

Where in photosystem II does water-splitting occur? What is the catalyst?

A

In the oxygen-evolving centre.

Manganese is the catalyst.

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38
Q

The electrons produced in the splitting of water in the oxygen-evolving complex are absorbed where?

A

P680, to reduce the electrons donated when P680 is excited by light.

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39
Q

Complete this equation:

2H2O + light =

A

= O2 + 4H+ + 4e-.

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40
Q

Where does the high energy electron produced in the reaction centre chlorophyll go?

A

To a primary electron acceptor and onwardly along an electron transport chain.

41
Q

Where does the ‘photolytic oxidation of water’ happen?

A

In photosystem II.

42
Q

The oxygen evolving complex joined to photosystem II is located on the inside of which membrane?

A

The thylakoid membrane.

43
Q

Is a lot of energy generated from charge separation in photosystem II?

A

Yes.

44
Q

Complete this reaction, wich takes place in the oxygen evolving complex:

2H2O =

A

= O2 + 4H+ + 4e-.

45
Q

In the oxygen-evolving complex, the …………….. are formed on the inside of the thylakoid membrane and thus contribute to building a pH gradient in …………… concentration across the membrane.

A

Proton, proton.

46
Q

In the oxygen evolving complex, the electrons generated from charge separation are used to …………….. the core of PSII.

A

Reduce.

47
Q

What happens to the oxygen produced in charge separation in the oxygen evolving complex?

A

It diffuses out of the chloroplast stomata eventually into the air (where we can breathe it in).

48
Q

As protons and electrons are produced from the splitting of water, acidic protons build up in the lumen and the stroma becomes more alkaline, creating…

A

…a pH gradient.

49
Q

Outline the first step when light excites electrons in PSI.

A

When light is absorbed by PSI, electrons in the reaction centre chlorophyll are excited and then donated to the electron acceptor ferrodoxin.

50
Q

What is the name of the electron acceptor that takes on electrons excited in the reaction centre chlorophyll when light is absorbed by PSI?

A

Ferrodoxin.

51
Q

When electrons are transferred to the electron acceptor ferrodoxin in PSI, where do the electrons go next?

A

The electrons are stored in high energy NADPH to be used in a multitude of possible reactions.

52
Q

What is the overall product of the electron transport chain?

A

High energy NADPH and a high energy proton concentration gradient across the thylakoid membrane.

53
Q

What is the purpose of the proton concentration gradient formed by the electron transport chain?

A

The protons can flow down the gradient through ATP synthase, generating ATP (as in respiration).

54
Q

What is the similarity between the electron transport chains in photosynthesis and respiration?

HINT: ATP synthase!

A

In both cases, protons flow down a concentration gradient, driving ATP synthase and creating ATP.

55
Q

What is the whole process of ATP generation called?

A

Oxidative phosphorylation.

56
Q

True or false? Electrons maintain the same amount of energy all the way along the electron transport chain.

A

False. Electrons lose a bit of energy as they progress along the electron transport chain.

57
Q

Which two processes increase the concentration of protons in the thylakoid lumen?

A
  1. Proton pump.
  2. Photolysis on the thylakoid lumen.
58
Q

The proton concentration gradient across the thylakoid membrane means that the lumen is more (acidic) / (alkaline) than the stroma.

A

The lumen is approximately 1,000x more acidic than the stroma.

59
Q

What are the two main results of the electron transport chain?:

A
  1. The production of high-energy NADPH.
  2. Creation of a proton concentration gradient across the thylakoid membrane, allowing protons to flow down the gradient through ATP synthase, thus generating ATP.
60
Q

The dark reactions of photosynthesis are also known as the ……………. cycle, where …………. is ‘fixed’.

A

Calvin, carbon.

61
Q

Does carbon fixing and processing the products require energy input?

A

Yes, the high energy ATP and NADPH made in the light reaction are used for this.

62
Q

Plants grow by taking ………….. from the atmosphere, sequestering the ……………….. and using it to build large organic molecules such as ……………… and ………………. .

A

Carbon dioxide, carbon, starch and cellulose.

63
Q

What is carbon dioxide fixed into in the Calvin cycle?

A

Carbohydrates.

64
Q

What are the three stages of the Calvin cycle?

A
  1. Carbon fixation / carboxylation.
  2. Reduction of 3-PGA.
  3. Regeneration of RuBP.
65
Q

Which stage of the Calvin cycle is this?:

‘The enzyme Rubisco incorporates CO2 into an organic molecule, 3-PGA’.

A

Carbon fixation / carboxylation.

66
Q

Which stage of the Calvin cycle is this?:

‘3-PGA is reduced using electrons supplied by NADPH’.

A

Reduction of NADPH.

67
Q

What supplies the electrons that reduce 3-PGA in the Calvin cycle?

HINT: It is made in the light reaction.

A

NADPH.

68
Q

Why does RuBP need to be regenerated?

A

So that the Calvin cycle can continue.

69
Q

How many CO2 molecules are incorporated at a time in the Calvin cycle?

A

One, so the cycle must be completed three times to produce a single three carbon GA3P molecule and six times to produce a six carbon glucose molecule.

70
Q

How many times does the Calvin cycle need to be completed to produce a singe six carbon glucose molecule?

A

Six times.

71
Q

How many times must the Calvin cycle be completed to produce a single GA3P molecule?

A

Three times.

72
Q

How many ATP and NADPH are required for every CO2 fixed?

A

Three ATP and two NADPH.

73
Q

True or false? The light and dark reactions are independent of one another.

A

False, they are mutually dependent.

74
Q

Complete the reaction for carbon fixation:

RuBP + CO2 =

A

= 3PGA.

75
Q

Carbon fixation is catalysed by…?

A

…rubisco.

76
Q

In the Calvin cycle, is PGA oxidised or reduced?

A

It is oxidised, consuming the ATP and NADPH from the light reaction to produce 6GA3P.

77
Q

What happens to the six molecules of GA3P produced in the Calvin cycle?

A

One is used by the plant, the other five go round the Calvin cycle again.

78
Q

In the Calvin cycle, what consumes the ATP and NADPH from the light reaction?

A

PGA, when it is oxidised.

79
Q

True or false? Rubisco can catalyse CO2 or O2.

A

True. It is a carboxylase AND an oxygenase. In the Calvin cycle it catalyses CO2, in photorespiration it catalyses O2.

80
Q

What type of experiments discovered that the first molecule of the Calvin cycle that CO2 is incorporated into is 3PGA?

A

Radioisotope experiments.

81
Q

Is RuBisCo a fast or slow enzyme?

A

RuBisCo is a slow enzyme, catalysing around 3-10 reactions per second!

82
Q

What is the commonest protein in the world and makes up about 30% of the protein the chloroplasts of C3 plants?

HINT: It is a slow enzyme!

A

RuBisCo.

83
Q

RuBisCo can catalyse CO2 AND O2. In the Calvin cycle it should catalyse CO2. What happens if it catalyses O2? When does this happen?

A

RuBisCo catalyses O2 about 25% of the time. It produces PG which can be very damaging to the plant and must be removed as soon as possible in photorespiration.

84
Q

At 25c, about 80% of reactions of RuBisCo are carboxylase reactions and 20% are oxygenase reactions. What happens as the temperature increases?

A

The number of oxygenase reactions increases.

85
Q

In the Calvin cycle, the pentose sugar ………………….. joins with CO2 and cleaves to give two molecules of …………….. .

A

Ribulose 1, 5 bisphosphate (RuBP), 3-PGA.

86
Q

Which enzyme carries out the first step of the Calvin cycle, joining RuBP to CO2?

A

Ribulose 1,5 bisphosphate carboxylase (RuBisCo).

87
Q

In the Calvin cycle, where does the energy come from that converts 3PGA to G3P?

A

From ATP and NADPH from the electron transport chain of the light reaction.

88
Q

Six molecules of G3P are produced in the Calvin cycle. One is used to make…?

A

Hexose sugars.

89
Q

Five molecules of G3P are recycled back into the Calvin cycle from the six that are produced. Does this require energy input?

A

Yes, in the form of ATP.

90
Q

Where do the dark reactions take place? Using what energy?

A

In the stroma matrix, using energy from ATP and NADPH made in the light reaction.

91
Q

How is carbon fixation highly regulated?

A

The substrate of RuBisCo, RuBP, is not made in the dark.

92
Q

What is reduced in the Calvin cycle? To what? Using what energy?

A

3PGA is reduced to G3P using energy from ATP and NADPH made in the light reaction.

93
Q

What is G3P regenerated to to restart the Calvin cycle? What does this require?

A

RuBP. Energy (from ATP) and enzymes are required.

94
Q

True or false? The photorespiration cycle ony occurs in the chloroplasts.

A

False - it occurs in multiple organelles.

95
Q

What is the purpose of the photorespiration cycle?

A

To recover the carbon wasted during the oxygenase reaction of RuBisCo which produces PG.

96
Q

How does the oxygenase reaction compete with the fixation of CO2?

A

By adding oxygen instead of carbon at the active site of RuBP.

97
Q

How many ATP and NADPH are used in the photorespiration cycle?

A

One ATP and one NADPH.

98
Q

Is photorespiration costly in terms of energy?

A

Yes, recycling the two PG comes at a relatively high energy cost.

99
Q
A

Introduction to Genetics & Biochemistry (21 decks)

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