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BISC 101 Mid2 > Photosynthesis > Flashcards

Photosynthesis Flashcards

Lecture 9

1
Q

(photo) autotrophs function

A

use light energy to drive the synthesis of organic molecules from CO2 and water

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2
Q

where is the site of photosynthesis

A

chloroplasts

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3
Q

what is photosynthesis

A

harnesses sunlight to make carbohydrate (sugar)

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4
Q

what do the light-capturing reactions do?

A

convert solar energy to ATP and NADPH in photosystems using chlorophyll

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5
Q

Calvin cycle does what?

A

uses chemical energy of ATP and NADPH to reduce CO2 to sugar

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6
Q

where have alternative mechanisms of carbon fixation evolved

A

hot, arid climates

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7
Q

Redox reaction of photosynthesis

A

carbon is reduced and oxygen is oxidised

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8
Q

what happens to the potential energy in photosynthesis

A

electrons are held more loosely in products than reactants so their potential energy increases; requires energy

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9
Q

what do plants take in with the help of sunlight?

A

CO2 and H2O

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10
Q

chloroplasts characteristics

A
  • double membrane
  • inside has fluid-filled stroma
  • contains thylakoids
  • contains enzymes and pigments (chlorophyll)
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11
Q

thylakoids characteristics

A

stacked “pancake-like” in grana

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12
Q

enzymes and pigments (chlorophyll) function and characteristics

A

they run photosynthesis and are embedded in thylakoid membrane or stroma

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13
Q

pigments

A

substances that absorb visible light

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14
Q

why does chlorophyll (and leaves) appear green?

A

because chlorophyll absorbs violet-blue and red wavelength light while reflecting green light

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15
Q

spectrophotometer measures what?

A

the ability of a pigment to absorb various wavelengths of light

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16
Q

what happens when a photon of light strikes a chlorophyll molecule?

A

energy is transferred to an electron [in the chlorophyll]

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17
Q

if the excited electron falls back to its “ground” or unexcited state what happens?

A

it emits extra energy as heat and light

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18
Q

what happens to the energy from the electron in chloroplasts?

A

passed around: Antenna complex -> reaction centre -> electron acceptor

it can be passed among many chlorophyll molecules of an antenna complex then to a reaction center and then an electron can be transferred to an electron acceptor

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19
Q

how do chlorophyll molecules work?

A

they work in groups within chloroplasts

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20
Q

where do the antenna complex, reaction centre, and electron acceptor occur?

A

in photosystems on the thylakoid membrane

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21
Q

What are the 2 types of photosystem

A

PS 2 and PS 1

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22
Q

Photosystem 2 does what?

A

feeds high-energy electrons to an electron transport chain

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23
Q

what does energy reaching the reaction centre do?

A

excites an electron within a specialized chlorophyll molecule

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24
Q

what does the excited electron bind to in PS 2

A

electron acceptor = pheophytin

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25
Q

“high energy” electrons that reach pheophytin are passed where?

A

to an electron transport chain in the thylakoid membrane

26
Q

ETC function

A

generates a proton-motive force and produces ATP by chemisosmosis

27
Q

plastoquinone in ETC function

A

carriers electrons to a cytochrome complex

28
Q

energy is used to transport what in photosystem 2

A

transport protons from the stroma to the thylakoid lumen

29
Q

the transport of protons does what across the thylakoid membrane

A

creates a large proton gradient

30
Q

How do Proton’s flow in the thylakoid membrane? What do they drive?

A

flow down their concentration gradient. Drives photophosphorylation of ADP to ATP by ATP synthase

31
Q

Photosystem 1 does what?

A

produces NADPH via an electron transport chain not coupled to chemiosmosis

32
Q

what does ferrodoxin move in PS 1?

A

high-energy electrons are passed through an electron transport chain by this molecule

33
Q

NADP+ reductase function

A

transfers 2 electrons + 1H+ to NADP+ reducing it to NADPH

34
Q

ATP production in PS 2

A

generates a proton-motive force and produces ATP by chemisosmosis

35
Q

ATP production in PS 1

A

this ETC does not involve chemiosmosis so ATP is not produced. NADPH is produced by PS1

36
Q

How is PS 1 energy stored

A

this photosystem stores energy as NADPH

37
Q

what happens to the electrons lost from PS 2

A

they are replaced by the splitting of water. The H+ ions are released into thylakoid lumen

38
Q

Plastocyanin function

A

transfers electrons from cytochrome of PS 2 to PS 1

39
Q

what are the outputs of light-capturing reaction

A

ATP and NADPH (and O2)

40
Q

How does the Calvin cycle fix carbon?

A

by addition of CO2 to an existing organic compound (RuBP)

41
Q

what kind of reaction is the Calvin cycle

A

anabolic. It builds complex CHO from smaller molecules and consumes energy

42
Q

rubisco function

A

catalyses reaction between CO2 and RuBP

43
Q

what is the first phase of the Calvin cycle and what does it do?

A

CO2 fixation. It uses ATP and NADHP and regenerates RuBP

44
Q

What does one turn of the Calvin cycle do?

A

fixes 1 CO2

45
Q

what do three turns of the Calvin cycle do?

A

produces 1 x G3P

46
Q

What does photosynthesis require?

A

CO2 that enters via stomata on the leaf

47
Q

what is the stomata the main route of?

A

for evaporative loss of water via transpiration

48
Q

why do plants on hot, dry days close their stomata?

A

to conserve water

49
Q

what happens when the stomata is closed?

A

limits access to CO2 and reduces photosynthetic yield and causes build up of O2 in air spaces of leaf from light reactions

50
Q

Why are most plants called C3 plants

A

because rubisco initially fixes carbon as a 3C molecule

51
Q

what type of enzyme is rubisco?

A

a slow and inefficient enzyme

52
Q

what will rubisco bind together?

A

will bind O2 to RuBP equally as well as CO2 (when CO2 is scarce)

53
Q

Photorespiration

A

consumes ATP and releases “fixed” CO2 so it decreases the efficiency of photosynthesis

54
Q

C4 and CAM plants trick

A

store CO2 when its available to maintain constant supply for Calvin cycle when stomata are closed

55
Q

C4 photosynthesis

A

CO2 is fixed initially as a 4C-compound in outer mesophyll cells

56
Q

PEP carboxylase has high affinity for…

A

CO2

57
Q

PEP carboxylase does NOT have high affinity for…

A

O2 so carbon fixation occurs even at low CO2

58
Q

where are 4C products exported

A

bundle-sheath cells

59
Q

4C products in bundle-sheath cells maintain what?

A

a supply of CO2 for the Calvin cycle

60
Q

Why do CAM plants take up CO2 at night?

A

when the stomata can be open and incorporate it into organic acids

61
Q

where do CAM plants store taken up CO2?

A

In vacuole of mesophyll cells

62
Q

When is the stored CO2 in CAM plants released

A

during the day

BISC 101 Mid2 (5 decks)

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