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BIO 2 > PHOTOSYNTHESIS (LECTURE 4) > Flashcards

PHOTOSYNTHESIS (LECTURE 4) Flashcards

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1
Q

What energy transformation occurs in photosynthesis?

A

It is the transformation of solar energy to chemical energy.

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2
Q

Photosynthesis is what type of reaction?

A

Photosynthesis is REDOX reaction.

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3
Q

Describe the overall path of electrons in photosynthesis.

A

Electrons are transferred from H2O to CO2.

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4
Q

Why is photosynthesis an endergonic reaction? Justify using the energy state of electrons in photosynthesis.

A

Photosynthesis is an endergonic reaction because the electrons being transferred experience an increase in potential energy during the transfer, thus an input of energy is required to make the transfer happen.

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5
Q

What are the energy and carbon sources for photosynthesis?

A

The sun (solar energy) is the energy source and carbon dioxide (CO2) is the carbon source.

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6
Q

In photosynthesis, which molecule is oxidized and which molecule is reduced?

A

In photosynthesis, water (H2O) is oxidized and carbon dioxide (CO2) is reduced.

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7
Q

Photosynthesis is all about the transfer of what?

A

The transfer of electrons.

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8
Q

Where exactly is photosynthesis taking place?

A

In the chloroplast within mesophyll cells within plants.

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9
Q

What are the 3 structural components of chloroplasts?

A

The outer membrane, the inner membrane and the stroma.

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10
Q

Describe the chloroplast’s outer membrane. (1)

A

The chloroplasts outer membrane is very permeable.

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11
Q

Describe the chloroplast’s inner membrane. (2)

A

It is selectively permeable and surrounds the stroma (fluid).

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12
Q

Describe the stroma. (3)

A

The stroma fluid contains photosynthetic enzymes (for the Calvin cycle), the thylakoid membranes (stacked grana containing chlorophyll) and also contains DNA and ribosomes.

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13
Q

What are the two parts to photosynthesis? Where do they occur?

A

The light dependent reactions (in thylakoids) and the Calvin cycle (in stroma).

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14
Q

What are the two types of electron flow in light reactions?

A

Non-cyclic electron flow and cyclic electron flow.

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15
Q

What are the products of non-cyclic electron flow? (3)

A

ATP, NADPH and O2.

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16
Q

What are the products of cyclic electron flow?

A

ATP.

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17
Q

Non-cyclic electron flow requires which photosystem?

A

PSII and PSI.

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18
Q

Cyclic electron flow requires which photosystem?

A

PSI.

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19
Q

What is the full name for NADPH/NADP+? What can it do? What role does it play in the Calvin cycle?

A

Nicotinamide adenine dinucleotide phosphate acts as an electron shuttle. It can accept electrons (reduced to NADPH) or donate them (oxidized to NADP+). NADPH is the reducing power for the Calvin cycle (transfers electrons to CO2).

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20
Q

What are the two possible interpretations of light?

A

Light as a wave and light as photons.

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21
Q

What are photons? (2)

A

Photons are discrete packages of light, for which the energy is inversely proportional to wavelength.

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22
Q

What wavelengths of light are utilized by photosynthesis?

A

Photosynthesis utilizes visible light (400-700 nm).

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23
Q

How is light captured to be used by photosynthesis? Where does this absorption of light occur?

A

Light is captured (absorbed) by pigments embedded in the thylakoid membrane.

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24
Q

What three pigments can be found embedded in the thylakoid membrane?

A

Chlorophyll a, chlorophyll b and carotenoids.

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25
Q

Which pigment used to absorb light for photosynthesis is the most important? Where is it located within a photosystem?

A

Chlorophyll a is the most important for photosynthesis and it is located at the reaction center.

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26
Q

Describe the activity of a chlorophyll’s electrons. (3)

A

A chlorophyll’s electrons can be excited to a higher energy state, which requires an input of energy (endergonic). The electrons can also move back to a lower energy ground state, which releases energy (exergonic). Plant cells can harness this released energy to synthesize organic molecules.

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27
Q

What are photosystems and where are they located?

A

These are light harvesting complexes embedded in the thylakoid membrane.

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28
Q

What are the photosystem’s structural components? (2)

A

The antenna complex and the reaction center.

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29
Q

What does the antenna complex consist of and how is energy transferred within it?

A

The antenna complex consists of several hundred pigment molecules (chlorophyll) that absorb photons. The energy from a photon is transferred from pigment to pigment.

30
Q

Describe the 2 components of the reaction center and the way in which they interact with each other.

A

The reaction center contains a pair of chlorophyll a molecules. Contains a primary electron acceptor, which removes the excited electron from the chlorophyll.

31
Q

What are the two types of photosystems?

A

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

32
Q

What are the characteristic of PSII?

A

The pair of chlorophyll a’s within a PSII’s reaction center is called P680, which absorbs energy at 680nm.

33
Q

What are the characteristics of PSI?

A

The pair of chlorophyll a’s within a PSI’s reaction center is called P700, which absorbs energy at 700nm.

34
Q

Describe non-cyclic electron flow in light reactions.

A

PSII and PSI absorb light, electrons from P680 and P700 are excited to higher energy state and the excited electrons are trapped by the primary electron acceptor. The excited electron in P680 is replaced by an electron from H2O (water splitting). Electrons pass from PSII to PSI’s reaction center via the electron transport chain (ETC). Electrons from primary electron acceptor of PSI is transferred to NADP+ via another ETC.

35
Q

What is water splitting? What is the chemical equation for water splitting?

A

When an H2O molecule grants an electron to replace the excited electron in P680 (PSII).
H2O –> (1/2)O2 + 2H+ + 2e-

36
Q

What occurs when the electron passes from PSII to PSI via the electron transport chain? (non-cyclic electron flow). Where does this electron end up?

A

The electron goes from a higher to a lower energy state (exergonic reaction) and the energy released is used to produce ATP (process called photophosphorylation). The electron then eventually takes the spot of the previous excited electron in P700.

37
Q

How many water molecules need to be split to reduce one NADP+ to NADPH?

A

1 water molecule required to reduce 1 NADPH.

38
Q

What is the formula for the reduction of NADP+?

A

(2e-) + (NADP+) + (H+) –> NADPH

39
Q

Describe the flow of electrons in cyclic electron flow (light reactions).

A

PSI absorbs solar energy and electrons from P700 (PSI) are excited to a higher energy state. The electrons then move along an electron transport chain back to the reaction center (P700), during which process they move to a lower energy state (exergonic).

40
Q

Describe the characteristic of cyclic electron flow.

A

When the electrons pass through the electron transport chain, they move to a lower energy state. The energy released from this exergonic process is used to produce ATP (photophosphorylation). Cyclic electron flow produces only ATP and only involves PSI.

41
Q

Why is cyclic electron flow (light reactions) significant if it only produces ATP?

A

Cyclic electron flow is important since the Calvin cycle uses more ATP than NADPH. The cyclic flow thus produces the extra ATP that is needed without using up any NADP+.

42
Q

What photosystems are involved in cyclic vs non-cyclic photophosphorylation?

A

PSI in cyclic photophosphorylation and PSII + PSI in non-cyclic photophosphorylation.

43
Q

What is the electron donor in cyclic photophosphorylation?

A

Chlorophyll a donates an electron (to itself).

44
Q

What is the (initial) electron donor in non-cyclic photophosphorylation?

A

H2O donates an electron (water splitting).

45
Q

What is the electron acceptor in cyclic photophosphorylation?

A

Chlorophyll a accepts an electron (from itself).

46
Q

What is the (final) electron acceptor in non-cyclic photophosphorylation?

A

NADP+ accepts an electron (to form NADPH).

47
Q

What are the products of cyclic photophosphorylation?

A

ATP.

48
Q

What are the products of non-cyclic photophosphorylation?

A

ATP, NADPH and O2.

49
Q

Are electrons in antenna pigments excited to a higher energy level by photons?

A

Yes.

50
Q

Are electrons “stripped” from antenna complex pigments?

A

No, there is only a transfer of energy between them.

51
Q

Are electrons excited to a higher energy level by photons in chlorophyll a molecules (P680 or P700) in the reaction center?

A

Yes.

52
Q

Are electrons stripped from chlorophyll a molecules (P680 or P700) in the reaction center?

A

Yes, and this electron is then replaced by another that is donated from H2O (PSII) or from P680 (PSI).

53
Q

What is chemiosmosis?

A

It is the movement of protons (H+) across a selectively permeable membrane by passive transport (exergonic).

54
Q

In what way is chemiosmosis significant to photophosphorylation?

A

Chemiosmosis (exergonic) is coupled to the production of ATP by ATP synthase (endergonic).

55
Q

Why do protons want to move across the thylakoid membrane into the stroma (why does chemiosmosis occur)?

A

Because the concentration of H+ in the thylakoid space is greater than the concentration of H+ in the stroma.

56
Q

Chemiosmosis depends on the proton gradient, which is generated in what 3 ways?

A

By water splitting, by the electron transport chain and by the reduction of NADP+ to NADPH.

57
Q

In what way does water splitting help create a proton gradient?

A

Protons from H2O are released into the thylakoid space when water splits (to donate an electron).

58
Q

In what way does the electron transport chain participate in the production of a proton gradient?

A

The movement of electrons from a higher to lower energy state via the ETC (exergonic) is coupled to the pumping of protons into the thylakoid space (endergonic).

59
Q

How does the reduction of NADP+ to NADPH help generate a proton gradient?

A

The reduction of NADP+ to NADPH uses a H+ from the stroma, meaning protons are removed from the stroma which further increases the gradient.

60
Q

Why do leaves change colour in the fall?

A

Because the chlorophyll pigments (green-ish) break down before the carotenoid pigments do (orange-ish) in the absence of sun.

61
Q

What does the Calvin cycle produce? From what starting components does it do this? What type of fixation occurs? What energy does it use?

A

It produces organic molecules from CO2, ATP and NADPH. Carbon fixation occurs (inorganic CO2 to organic molecules). It does not use solar energy directly, but rather the ATP and NADPH produced by light reactions.

62
Q

What are the three steps (phases) of the Calvin cycle?

A

(1) Carbon fixation, (2) reduction and (3) regeneration of RubBP.

63
Q

Describe the first phase of the Calvin cycle (carbon fixation). Assume 3 CO2’s enter the cycle.

A

3 CO2 molecules enter the cycle, each CO2 is attached to a 5-carbon sugar called ribulose bisphosphate (RubBP). This reaction is catalyzed by ribulose bisphosphate carboxylase (rubisco). Each now 6-carbon sugar splits into two 3-phosphoglycerate molecules (for a total of 6 such molecules).

64
Q

How many 3-phosphoglycerates do you get per CO2 molecule entering the Calvin cycling?

A

2.

65
Q

Describe the second phase of the Calvin cycle (reduction).

A

Each 3-phosphoglycerate receives a phosphate from ATP to become 1,3-bisphosphoglycerate. Each of these is then reduced by an NADPH (2e-) to become glyceraldehyde 3-phosphate (G3P), which can then be used to make glucose and other organic compounds.

66
Q

What equation best describes the reactions that take place in the first and second phase of the Calvin cycle (carbon fixation and reduction)?

A

3 CO2 + 3 Ribulose bisphosphate –> 6 G3P

67
Q

What 4 things are required for the first and second phase of the Calvin cycle to occur? (given 3 CO2 and 3 RuPB)

A

Rubisco enzyme, 6 NADPH, 6 ATP and other enzymes.

68
Q

Describe the 3rd phase of the Calvin cycle (regeneration of ribulose bisphosphate - RuBP).

A

Only 1 of the 6 G3P molecules exits the cycle to be used to make glucose and other organic molecules. The 5 other G3P molecules are used to regenerate RuBP. This process requires ATP.

69
Q

Why can only 1 G3P molecule (out of 6, when 3 CO2 enter the cycle) exit the Calvin cycle?

A

Because all 15 carbons (in the 5 G3Ps) are needed to regenerate 3 RuBPs (one for each CO2) so that the cycle can start again.

70
Q

How many CO2 molecules and G3P molecules are needed to make 1 glucose molecule?

A

6 CO2s are needed to produce 2 G3P’s to then produce a single glucose molecule.

71
Q

Why is the Calvin cycle called a cycle?

A

Because has been removed is limited to what has been added (input = output) and most the products are used as reactants for the same reaction to occur again.

BIO 2 (14 decks)

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