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biochemistry > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

What part of the light spectrum is primarily used in photosynthesis?

A

red and blue

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2
Q

Why is green light less effective for photosynthesis?

A

chlorophyl reflects green light

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3
Q

How does chlorophyll a differ from chlorophyll b in light absorption?

A

Chlorophyll a absorbs mostly red light, while chlorophyll b absorbs more blue light

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4
Q

Which color of light has the highest energy and why?

A

blue because it has the shortest wavelength

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5
Q

What is the role of carotenoids in photosynthesis?

A

absorb blue and green light

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6
Q

Why is the absorption of red and blue light crucial for photosynthesis?

A

provides energy for light dependent reactions

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7
Q

What happens to the absorbed light energy in chlorophyll?

A

The energy excites electrons, initiating the process of converting light into chemical energy.

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8
Q

What is the main function of chloroplasts?

A

site of photosynthesis

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9
Q

What is the outer structure of the chloroplast composed of?

A

double membrane

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10
Q

What is the fluid-filled space inside the chloroplast called?

A

stroma

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11
Q

What are the disk-shaped structures in chloroplasts called?

A

Thylakoids

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12
Q

Where do the light-dependent reactions of photosynthesis take place?

A

thylakoid membrane

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13
Q

Where do the light-independent (Calvin cycle) reactions occur in the chloroplast?

A

stroma

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14
Q

What is the role of the thylakoid membrane in photosynthesis?

A

It contains chlorophyll and other pigments to capture light energy and generate ATP and NADPH.

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15
Q

What is the purpose of the thylakoid lumen?

A

proton gradient needed for ATP synthesis.

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16
Q

What pigment is embedded in the thylakoid membranes?

A

chlorophyl

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17
Q

What is Photosystem II (PSII) and where is it located?

A

PSII is a protein complex in the thylakoid membrane that initiates photosynthesis by absorbing light and splitting water molecules.

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18
Q

What is Photosystem I (PSI) and where is it located?

A

PSI is a protein complex also located in the thylakoid membrane, responsible for producing NADPH by transferring electrons to NADP+.

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19
Q

What is the primary role of PSII?

A

splits water to produce oxygen and passes electrons to ETC

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20
Q

What is the primary role of PSI?

A

reduce NADP+ to NADPH

21
Q

What is Förster resonant energy transfer (FRET)?

A

energy from an excited molecule (donor) is transferred to a nearby pigment molecule (acceptor) without the movement of electrons.

22
Q

How is FRET important in photosynthesis?

A

allows for transfer of energy to chloroplast

23
Q

What is the efficiency of FRET dependent on?

A

distance between donor and acceptor

24
Q

What is charge separation in photosynthesis?

A

Charge separation occurs when an electron in the chlorophyll reaction center becomes excited by light and is transferred to an electron acceptor, leaving behind a positively charged chlorophyll.

25
Q

In PSII, which molecules participate in charge separation?

A

The chlorophyll molecule P680 absorbs light and transfers an excited electron to a nearby plastoquinone molecule, initiating the electron transport chain.

26
Q

What is the result of charge separation in PSI?

A

PSI’s P700 chlorophyll transfers an excited electron to ferredoxin, which is then used to reduce NADP+ to NADPH.

27
Q

How is the H+ gradient generated in photosynthesis?

A

The movement of electrons through the electron transport chain causes protons (H+) to be pumped from the stroma into the thylakoid lumen, creating a proton gradient.

28
Q

What role does the H+ gradient play in photosynthesis?

A

drives ATP synthesis

29
Q

In which part of the thylakoid membrane is the H+ gradient the highest?

A

thylakoid lumen

30
Q

What is the electron transport chain in photosynthesis?

A

The ETC is a series of protein complexes in the thylakoid membrane that transfer electrons from PSII to PSI and ultimately to NADP+ to form NADPH.

31
Q

What role does plastoquinone (PQ) play in the electron transport chain?

A

PQ shuttles electrons from PSII to the cytochrome b6f complex and helps move protons into the thylakoid lumen

32
Q

How does the cytochrome b6f complex contribute to the H+ gradient?

A

It transfers electrons from plastoquinone to plastocyanin and simultaneously pumps protons (H+) into the thylakoid lumen, strengthening the proton gradient.

33
Q

What role does plastocyanin (PC) play in electron transport

A

transfers electrons from the cytochrome b6f complex to PSI.

34
Q

How does ferredoxin (Fd) function in the electron transport chain?

A

Ferredoxin transfers electrons from PSI to the enzyme ferredoxin-NADP+ reductase (FNR), which reduces NADP+ to NADPH.

35
Q

What is the final electron acceptor in photosynthesis?

A

NADP+

36
Q

How do photosystem II (PSII) inhibitors work as herbicides?

A

block transfer of electrons

37
Q

What is the effect of blocking electron transport in PSII?

A

causes a build up of reactive oxygen species that damages cell

38
Q

How do Photosystem I (PSI) inhibitors work as herbicides?

A

They accept electrons from PSI and produce toxic reactive oxygen species (ROS), causing oxidative damage to the plant.

39
Q

Name a herbicide that targets PSI.

A

paraquat

40
Q

Which herbicide class inhibits Photosystem II (PSII)?

A

Triazines

41
Q

What is the effect of inhibiting carotenoid synthesis in herbicide action?

A

plant cannot be protected from excess light leading to photo damage

42
Q

How do chloroplasts respond to high light intensity?

A

NPQ dissipates excess light

43
Q

What role do carotenoids play in protecting chloroplasts?

A

protects from ROS and dissipates excess light

44
Q

how do chloroplasts deal with low light conditions?

A

increase LHC

45
Q

What is photoinhibition, and how do chloroplasts cope with it?

A

Photoinhibition occurs when excess light damages PSII. Chloroplasts repair damaged D1 proteins in PSII to recover from this damage.

46
Q

What is the role of chloroplast movement in coping with environmental changes?

A

In high light conditions, chloroplasts move to the sides of cells to minimize light absorption; in low light, they spread out to maximize exposure.

47
Q

How do chloroplasts adjust to changes in temperature?

A

modulation of fluid and heat shock proteins

48
Q

How does photorespiration help chloroplasts cope with low CO₂ conditions?

A

Photorespiration allows the chloroplast to process oxygen when CO₂ levels are low, though it reduces photosynthetic efficiency.

49
Q

How do chloroplasts cope with water stress?

A

close stroma

biochemistry (9 decks)

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