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2 The Cell > 10 Photosynthesis > Flashcards

10 Photosynthesis Flashcards

1
Q

What term describes an organism that makes its own food?

A

Autotroph

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2
Q

What term describes an organism that makes its own food using sunlight?

A

Photoautotroph

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3
Q

What term describes an organism that gains energy from eating other organisms?

A

Heterotroph

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4
Q

What is the structure of a chloroplast?

A

It has a double membrane with disks named thylakoids that are in stacks named grana.

The thylakoids are hollow, forming a hollow interior named the thylakoid.

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5
Q

Where does the oxygen in CO2 end up after photosynthesis?

A

In glucose and water

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6
Q

Where does the oxygen in H2O end up after photosynthesis?

A

Oxygen (not water)

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7
Q

Is photosynthesis a redox reaction?

A

Yes…
CO2 is reduced to form glucose
Water is oxidised to form oxygen

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8
Q

How do the light reactions extract energy?

A

By forming NADPH and by chemiosmosis in which ATP is generated, in a process known as photophosphorylation

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9
Q

What are inputs/outputs of the light reaction?

A

Input: NADP+, ADP and P, Water.
Outputs: ATP, NADPH, Oxygen

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10
Q

What are the inputs/outputs of the calvin cycle?

A

Input: CO2, ATP, NADPH, sugar in the form of CH2O

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11
Q

What is the incorporation of carbon into and organism named?

A

Carbon fixation

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12
Q

With what is the ability of a pigment to absorb light measured?

A

A spectrophotometer which measures the rate of reflection under different conditions.

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13
Q

What represents the how much of each wavelength a pigment can absorb?

A

An absorption spectrum

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14
Q

What represents the rate of a light dependent reaction across various wavelengths?

A

An action spectrum

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15
Q

What is the wavelength of purple?

A

400-450

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16
Q

What is the wavelength of blue?

A

450-500

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17
Q

What is the wavelength of green?

A

500-575

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18
Q

What is the wavelength of yellow/orange?

A

575 to 650

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19
Q

What is the wavelength of red?

A

650 to 750+

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20
Q

What are the common forms of chlorophyll?

A

Chlorophyll a and chlorophyll b

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21
Q

What are the common photopigments common in plants?

A

Carotenoids, Chlorophyll a and chlorophyll b

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22
Q

What is the absorption spectrum of chlorophyll?

A

High at blue/purple, drops at green and peaks again at orange/red.

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23
Q

How do the absorption spectra chlorophyll a, chlorophyll b and carotenoid differ?

A

On a graph from 400-700nm:

Chlorophyll-a peaks first, then chlorophyll b then carotenoids.

Only the two forms of chlorophyll peak gain after green with chlorophyll b peaking first.

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24
Q

What is the structure of chlorophyll?

A

It has a hydrocarbon head on a porphyrin ring as a head which has a magnesium atom at the centre.

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25
Q

How does chlorophyll a differ from chlorophyll b?

A

chlorophyll a has a CH3 in a specific place of the porphyrin whereas chlorophyll b has a CHO group at that location

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26
Q

Why are carotenoids found in plants?

A

They offer photoprotection (protection from too bright light) by absorbing some light wavelengths that would otherwise damage chlorophyll.

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27
Q

Where do the light reactions take place?

A

In the membrane of the thylakoid so that H+ ions are pumped out into the stroma and diffuse back to generate ATP.

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28
Q

What are the structures of the light reaction?

A

There are two photosystems (PSII) and (PS I). Between them,and after PS I, is an electron transport chain.

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29
Q

What are the photosystems of photosynthesis?

A

In order: Photosystem II (PS II) then Photosystem I (PS I)

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30
Q

How do the photosystems collect light energy?

A

The photons increase the energy levels of the electrons.

This energy is then collected as the electrons drop down to their original.

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31
Q

What is the structure of a photosystem?

A

It has a reaction-center complex that is surrounded by the light harvesting complex.

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32
Q

Where is chlorophyll found specifically?

A

In the light-harvesting complexes of both PS I and PS II

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33
Q

In what ways do the photosystems package light energy?

A

In the forms of ATP and NADPH

Also during step 3 (splitting H2O) H+ is formed in the stroma as a form of potential energy.

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34
Q

Which electron transporter does photosynthesis use?

A

NADP+

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35
Q

What is the reduced form of NAD?

A

NADH

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36
Q

How does photosystem II differ internally from photosystem I?

A

Photosystem II uses the P680 form of chlorophyll whereas photosystem I uses P700 as the electron donor

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37
Q

How many steps are there of photophosphorylation?

A

8

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38
Q

What is step 1 of photophosphorylation?

A

A photon hits a chlorophyll molecule in the light harvesting complex of PS II causing one of its electrons to jump to a higher energy state. As it falls back down it excites another electron in a chain that continues until a P680 in the reaction complex is excited.

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39
Q

What is step 2 of photophosphorylation?

A

An electron is transferred from P680, the electron donor, to the ‘primary electron acceptor’ of the reaction complex.

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40
Q

What are P680 and P700?

A

Special forms of chlorophyll that act as electron donors.

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41
Q

What is the electron donor of photophosphorylation?

A

P680 (PS II) and P700 (PS I)

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42
Q

What is step 3 of photophosphorylation?

A

An enzyme catalyses the splitting of H2O into O2 and H+. This provides electrons to replace that lost by P680 (it is highly electronegative so grabs the electron)

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43
Q

What does P680+ refer to?

A

A P680 molecule which has donated its electron and thus has a + 1 charge.

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44
Q

What is step 4 of photophosphorylation?

A

The ‘photoexcited’ high energy electrons enter the electron transport chain between PS II and PS I

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45
Q

What does the first electron transport chain of photophosphorylation include?

A

Pq (plastoquinone), Cytochrome complex, and Pc (plastocyanin)

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46
Q

What is step 5 of photophosphorylation?

A

As the electrons travel through the electron transport chain they drop back down to a lower energy level. This provides the energy for the cytochrome complex to synthesis ATP.

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47
Q

Where is ATP formed during photophosphorylation?

A

In the cytochrome complex of the first electron transport chain.

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48
Q

Where is H2O used in photophosphylation and why?

A

Only by PS II to regenerate the electrons donated by P680.

PS I does not need these electrons as it replaces P700’s donated electrons using those from the electron transport chain.

49
Q

What is step 6 of photophosphorylation?

A

A photon hits a pigment in the light harvesting complex of PS I and through a chain of excited electrons dropping back and exciting others, P700 is excited causing it to donate a high energy electron to the primary receptor.

50
Q

How is P700+’s donated electron replaced?

A

Using electrons from the first electron transport chain.

51
Q

What is step 7 of photophosphorylation?

A

The photoexcited electrons travels from the primary acceptor to the second electron transport chain.

52
Q

What is does the second electron transport chain include?

A

Fd (ferredoxin) and NADP+ reductase

53
Q

What is step 8 of photophosphorylation?

A

Electrons of the second electron transport chain pass through Fd (ferredoxin) and then, using NADP+ reductase reduce NADP+ to NADPH to be used as energy

54
Q

What occurs after photophosphorylation?

A

Chemiosmosis

55
Q

Describe chemiosmosis in photosynthesis.

A

Electrons send into the storm during photophosphorylation reenter the thylakoid space through ATP synthase and thus generate ATP

56
Q

What is an alternative form of photophosphorylation?

A

Cyclic electron flow

57
Q

Describe cyclic electron flow.

A

It uses only PS I.

Electrons move in the path of:
Primary acceptor → Fd → Cytochrome complex → Pc (plastocyanin) → Pigment → Primary acceptor again

58
Q

How does cyclic electron flow differ from normal photophosphorylation in terms of input and output?

A

Cyclic electron flow does split water or reduce NADP+ to NADPH.

The cytochrome complex does still generate ATP.

59
Q

What organism tend to use cyclic electron flow?

A

Many prokaryotes such as cyanobacteria perform it exclusively.

However most plants can do it as it appears to have a photo protective role.

60
Q

What are the inputs/outputs of the light reactions?

A

In: Light, H2O, ADP, NADP+
Out: oxygen, H+, ATP, NADPH

61
Q

What are the inputs/outputs of the dark reactions?

A

In: CO2, ATP and NADPH
Out: ADP, NADP+ and sugar (G3P)

62
Q

What does [CH2O] refer to?

A

A sugar as this represents its ratio (1 carbon to 2 hydrogens to 1 oxygen)

63
Q

What is the input to the Calvin Cycle?

A

3 Carbon dioxide molecules at a time.

64
Q

What are the stages of the Calvin Cycle?

A

1: Carbon fixation
2: Reduction
3: Regenration of the CO2 acceptor (RuBP)

65
Q

How many steps are there of the Calvin Cycle?

A

6

66
Q

What is step 1 of the Calvin Cycle?

A

3 molecules of CO2 and 3 molecules of Ribulose biphosphate (RuBP) combine to form 3 molecules of a short live intermediate.

This is catalysed by the enzyme Rubiso

67
Q

What is step 2 of the Calvin Cycle?

A

3 of Short lived intermediates → 6 of 3-phosphoglycerate

68
Q

What is step 3 of the Calvin Cycle?

A

6 of 3-phosphoglyercate → 6 of 1,3-biphosphoglycerate using ATP

69
Q

What is step 4 of the Calvin Cycle?

A

6 of 1,3-biphosphoglycerate → 6 of G3P using NADPH

70
Q

What is step 5 of the Calvin Cycle?

A

One G3P is outputted resulting in 5 G3P remaining

71
Q

What is step 6 of the Calvin Cycle?

A

An ATP is used to regenerate 5 G3P into 3 ribulose biphosphate

72
Q

What does RuBP stand for?

A

Ribulose biphosphate

73
Q

What does Rubisco catalyse?

A

Carbon fixation i.e. RuBP + CO2

74
Q

What does G3P stand for?

A

Glyceraldehyde 3-phosphate

75
Q

What is Glyceraldehyde 3-phosphate also known as?

A

G3P

76
Q

What is ribulose biphosphate also known as?

A

RuBP

77
Q

Which steps of the Calvin Cycle use ATP and how much?

A

Step 3 (3-phosphoglycerate → 1,3-biphosphoglycerate) uses 6 ATP molecules and Step 6 (G3P to RuBP) uses 3 ATP molecules

78
Q

What step of the Calvin Cycle uses NADPH and how much?

A

Step 4 (1,3biphosphoglycerate → G3P) uses 6 molecules

79
Q

How many carbon atoms does the short lived intermediate have?

A

6

80
Q

How many carbon atoms does 3-phosphoglycerate have?

A

3

81
Q

How many carbon atoms does 1,3 biphosphoglycerate have?

A

3

82
Q

How many carbon atoms does G3P have?

A

3

83
Q

How many carbon atoms does RuBP have?

A

6

84
Q

Which reaction of the Calvin Cycle is a reduction?

A

Step 4 (1,3-biphosphoglycerate to G3P) as is demonstrated by it using NADPH

85
Q

To synthesis one molecule of G3P how much ATP and NADPH is used?

A

9 ATP and 6 NADPH

86
Q

How many CO2 molecules enter the Calvin Cycle per ‘turn’?

A

3

87
Q

What is the output of the Calvin Cycle?

A

1 G3P which can be converted to Glucose etc. (2 G3P = 1 glucose)

88
Q

What are the main types of photosynthesis?

A

C3, C4 and CAM.

89
Q

What is the “normal” and most common method of photosynthesis?

A

C3

90
Q

What does the 3 in C3 and the 4 in C4 refer to?

A

The number of carbon atoms in the substance which fixes CO2

91
Q

What does CAM photosynthesis stand for?

A

crassulacean acid metabolism

92
Q

What is a major inefficiency of photosynthesis?

A

Photorespiration.

93
Q

What does C4 respiration attempt to overcome?

A

Photorespiration

94
Q

What triggers photorespiration?

A

Hot, dry days as this triggers the stomata to close and thus leaves the plant with low carbon dioxide for photosynthesis

95
Q

What causes photorespiration chemically?

A

Under low CO2 concentrations Rubicso binds O2 instead of CO2 to RuBP.

This result splits, forming a 2-carbon sugar which is broken down by peroxisomes and the mitochondria to form CO2

96
Q

Why is photorespiration disadvantageous?

A

It does not release ATP but uses some i.e. active transport.

It also wastes products i.e RuBP that could otherwise be used productively.

97
Q

Why can photorespiration be advantageous?

A

It is photo-protective

98
Q

How do C4 plants differ structurally from C3 plants?

A

They have two distinct photosynthetic cells: Mesophyll cells and bundle-sheath cells.

99
Q

Where are bundle sheet cells found?

A

C4 plants

100
Q

How do C4 plants differ physiologically?

A

They fix carbon in the mesophyll cells so that CO2 is concentrated for use in the calvin cycle which occurs in the bundle sheath cells.

101
Q

How many steps are there of CO2 fixation in C4 plants?

A

4

102
Q

What is step 1 of carbon fixation in C4 plants?

A

CO2 enters the mesophyll cell where the enzyme PEP carboxylase adds it to PEP. This forms oxaloacetate

103
Q

What is step 2 of carbon fixation in C4 plants?

A

The oxaloacetate is converted into malate which travels through plasmodesmata to the bundle sheath cells.

104
Q

What is step 3 of carbon fixation in C4 plants?

A

The oxaloacetate in the bundle sheet cell is broken down into pyruvate and CO2 for use in the calvin cycle.

105
Q

What is step 4 of carbon fixation in C4 plants?

A

The pyruvate reenters the mesophyll cell where ATP is added to it. This regenerates PEP

106
Q

Which plant would benefit if the global CO2 concentration increased?

A

C3 plants as less photorespiration would occur.

107
Q

Why is C4 carbon fixation not always the best?

A

It requires ATP to regenerate PEP so reduces the net output.

108
Q

In what conditions would one typically find a C3 plant?

A

Normal i.e. not too hot, not too dry

109
Q

In what conditions would one typically find a C4 plant?

A

Mildly hot and quite dry

110
Q

In what conditions would one typically find a CAM plant?

A

Extremely hot and dry i.e. dessert where water loss must absolutely be minimised.

111
Q

What is an example of a C4 plant?

A

Sugar cane, corn and some grasses

112
Q

What is an example of a CAM plant?

A

Pineapple

113
Q

What do CAM plants tend to be?

A

Succulent (water storing)

114
Q

Describe CAM photosynthesis.

A

During the night CO2 is fixed into a four-carbon organic acid.

During the day this store CO2 is used for the Calvin Cycle.

115
Q

Why does the Calvin cycle still occur during the day?

A

It requires the ATP and NADPH provide by the light-dependant reactions which can only occur during the day.

116
Q

Which forms of photosynthesis use the Calvin Cycle?

A

All of them (C3, C4 and CAM)

117
Q

What is the advantage of CAM photosynthesis?

A

The desert plants that use it down’t have to open their stomata for CO2 which would lead to excessive water loss.

118
Q

Where do CAM plants store the acid?

A

In their vacuole.

2 The Cell (7 decks)

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