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BLG 143 Chapter 1 > Chapter 5 > Flashcards

Chapter 5 Flashcards

1
Q

Photosynthesis produces carbohydrate using

A

sunlight, carbon dioxide, and water

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2
Q

In photosynthesis, oxygen is a

A

By-product

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3
Q

6 CO2 + 12 H2O + light energy 

A

C6H12O6 + 6 O2 + 6 H2O

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4
Q

Photosynthesis contrasts with cellular
respiration:

A

– Photosynthesis is endergonic.
 Reduces CO2 to glucose or other sugars
– Cellular respiration is exergonic.
 Oxidizes sugars to CO2

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5
Q

Two Linked Sets of Reactions in photosynthesis are

A
  1. Light dependent reactions or “light reactions”
  2. Light independent reactions or “dark reactions”
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6
Q

Light dependent reactions or “light reactions” involve

A

Energy from photons causes release of electrons from chlorophyll.
These electrons replaced by splitting water; produce O2. Electrons
transferred to NADP+ forming NADPH. Electron transport also produces some ATP

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7
Q

Light independent reactions or “dark reactions” involve

A

The Calvin cycle – NADPH and ATP is used to reduce CO2 to carbohydrates.

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8
Q

Photosynthesis occurs in the

A

Chloroplast - green organelles of plants

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9
Q

The chloroplast has how many membranes

A

Two

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10
Q

Thylakoid membranes contain

A

Pigments

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11
Q

the most common pigment is

A

Chloroplasts

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12
Q

Why do plants appear green

A

Chlorophyll reflects (does not absorb) green light, thus plants appear green

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13
Q

The fluid-filled space between the thylakoids and the inner membrane is the

A

stroma

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14
Q

How many chloroplasts does a typical plant cell contain

A

40-50

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15
Q

The thylakoids structure is

A

flattened sacs

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16
Q

the granum are

A

stack of thylakoids

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17
Q

The stroma is

A

Liquid matrix

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18
Q

Photons are

A

discrete packets of electromagnetic energy

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19
Q

Electromagnetic energy travels in

A

Waves

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20
Q

Visible light (400 – 700 nm) is used by

A

photosynthetic organisms

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21
Q

Pigments are molecules that

A

absorb only certain wavelengths of light

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22
Q

There are two major classes of pigment in plant leaves:

A

chlorophylls and
carotenoids

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23
Q

The chlorophylls (a and b) absorb

A

red and blue light and reflect and transmit green light

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24
Q

The carotenoids

A
  • accessory pigments because
    the absorb light and pass energy to chlorophylls
  • absorb blue and green light and reflect and transmit yellow, orange, and red light
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25
Q

Different pigments absorb different

A

wavelengths of light

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26
Q

Each pigment has an absorption spectrum which is

A

Plot of the wavelength of light absorbed by that pigment

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27
Q

An action spectrum shows

A

The rate of photosynthesis at each wavelength

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28
Q

Which pigments are the most effective at driving photosynthesis

A

Pigments that absorb blue and red photons

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29
Q

The main photosynthetic pigments are

A

Chlorophylls

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30
Q

There Is a Strong Correlation between
the Absorption Spectra of Pigments and the

A

Action Spectrum for Photosynthesis

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31
Q

describe the structure of chlorophylls

A
  • Chlorophylls have a long “tail” made of isoprene subunits, and a “head” consisting of a large ring structure with a magnesium atom in the middle.
    – The tail keeps the molecule embedded in the thylakoid membrane.
    – Light is absorbed in the head.
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32
Q

What occurs when a pigment
absorbs a photon and the electron gets
excited, but then falls back to its ground state. Some of the absorbed energy is released as heat and the rest is released as electromagnetic radiation (light)

A

Fluorescence

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33
Q

approximately how much blue and red light produce fluorescence

A

Only approximately 2% of red and blue
photons produce fluorescence. The
remaining 98% drive photosynthesis

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34
Q

Blue photons excite electrons to an even

A

an even higher energy state

35
Q

Red photons excite electrons to a

A

high-energy state

36
Q

If an electron is excited by photons but then returns to its ground state

A

the energy it absorbed is released as heat and fluorescence

37
Q

Chlorophyll molecules work together in
groups, forming a complex called a

A

photosystem

38
Q

Two major elements of the photosystem

A
  1. antenna complex – accessory pigments and carotenoids
  2. reaction centre – contains a chlorophyll a molecule
    - as well as proteins that capture and process excited electrons.
39
Q

Chlorophyll molecules transmit energy from excited electrons in the antenna complex to

A

a reaction center

40
Q

At the reaction center, excited electrons are

A

passed to an electron acceptor

41
Q

Chlorophyll at reaction
centre can not perform
another excitation reaction
until the

A

lost electron
is replaced

42
Q

Replacement electron
comes from

A

hydrolysis
of water molecule

43
Q

Energy released by excited electrons in
chlorophyll can

A
  1. Drop back down to a low energy state, causing fluorescence
  2. Drop back down to a low energy state, releasing heat
  3. Excite an electron in a nearby pigment, inducing resonance
  4. Be transferred to an electron acceptor in a redox reaction
44
Q

Four fates for excited electrons in photosynthetic pigments

A

When sunlight promotes electrons in pigments to a high-energy state, four things happen: they can fluorescence, release heat, pass energy to a nearby pigment via resonance, or transfer the electron acceptor

45
Q

There are two types of reaction centre

A

photosystem I and photosystem II

46
Q

Photosynthesis is found to be

A

moderate at red light (680 nm) and at far red light (700 nm)

47
Q

Photosynthesis greatly enhanced

A

when red and far-red light combined. This Led to recognition of two separate
photosystems that work in concert, one with absorption max at 680 nm and one with absorption max at 700 nm

48
Q

how does photosystem II work

A

Energy reaches the reaction centre
* Chlorophyll is oxidized when an electron is donated to the electron acceptor pheophytin
* The electron is passed to an electron
transport chain (ETC) in the thylakoid
membrane
* Produces a proton gradient
 ATP production
* Photosystem II triggers chemiosmosis and ATP synthesis in the chloroplast.

49
Q

Photosystem II and the cytochrome complex are located in the

A

thylakoid membranes

50
Q

Phrophytin

A

Higher electronegativity,
therefore accepts electrons
Missing magnesium

51
Q

Oxygenic and Anoxygenic
Photosynthesis

A

This process is called oxygenic
photosynthesis. Photosystem II is the only known protein complex able to oxidize water in this way.
H2O –> 2 H+ + 2 e– + ½ O2

52
Q

How Does Photosystem I Work?

A

Excited electrons from the reaction centre of photosystem I are passed down an ETC of iron- and sulphur-containing proteins to ferredoxin.
– Does not generate proton motive force and ATP
* A proton and two electrons from ferredoxin to NADP+, forming NADPH.

53
Q

Photosystem II produces a

A

proton gradient
that drives the synthesis of ATP

54
Q

Photosystem I yields

A

reducing power in the
form of NADPH

55
Q

Photosystems I and II perform functions during

A

These occur during light-dependent
reactions

56
Q

What happens after photosystems I and II have performed their functions

A

Ultimately, the ATP and NADPH will be used to reduce CO2 into glucose involving light- independent reactions

57
Q

The Z scheme is a model of

A

how photosystems II and I interact

58
Q

Describe the Z-scheme

A

First, the electrons of photosystem II will be replaced by electrons stripped from water, producing oxygen gas as a by-product.
* A special pair of reaction-centre chlorophyll molecules named P680 passes the excited electron to pheophytin
* At the end of photosystem II’s ETC, the electron is passed to a protein called plastocyanin.
* Plastocyanin carries the electron back across the thylakoid membrane and donates it to photosystem I,
* Electrons from PC replace electrons from the P700 pair of chlorophyll molecules in the photosystem I reaction centre.
* These electrons enter an ETC, then are eventually passed to ferredoxin and used to reduce NADP+ to NADPH.

59
Q

The Z scheme explains which effect

A

the enhancement effect

60
Q

What is the enhancement effect

A

Photosynthesis is more efficient when both 680- nm and 700-nm wavelengths are present

61
Q

cyclic photophosphorylation is

A

Photosystem I occasionally transfers electrons to photosystem II’s electron transport chain to increase ATP production, instead of using them to
reduce NADP+.
This cyclic photophosphorylation coexists with the Z scheme and produces additional ATP.

62
Q

The energy transformation of the light-dependent reactions and the carbon dioxide reduction of the Calvin cycle are two

A

separate but linked
processes in photosynthesis

63
Q

ATP and NADPH are produced by photosystems I and II in

A

the presence of light

64
Q

The reactions that produce sugar from carbon dioxide in the Calvin cycle are

A

light-independent. These reactions require the ATP and NADPH
produced by the light-dependent reactions.

65
Q

The Calvin cycle has three phases
All three phases take place in the stroma of chloroplasts, they are

A
  1. Fixation
  2. Reduction
  3. Regeneration
66
Q

The CO2-fixing enzyme is called

A

ribulose 1,5- bisphosphate carboxylase/oxygenase
(rubisco). Has 8 active sites where CO2 is fixed

67
Q

Rubisco is found

A

in all photosynthetic organisms
that use the Calvin cycle to fix carbon and is thought to be the most abundant enzyme on Earth

68
Q

Rubisco is inefficient because

A

although it does catalyze the addition of CO2 to RuBP, it also catalyzes the addition of O2 to RuBP

69
Q

Oxygen and carbon dioxide compete at the enzyme’s active sites, which

A

slows the rate of CO2
reduction

70
Q

When O2 and RuBP react in rubisco’s active site, one of the products undergoes a process called

A

photorespiration

71
Q

Photorespiration “undoes” photosynthesis because

A

it consumes energy and releases fixed
CO2

72
Q

When photorespiration occurs, the rate of photosynthesis

A

declines drastically.

73
Q

Carbon fixation is favoured over

A

photorespiration

74
Q

Rubisco catalyzes competing reactions with

A

very different outcomes
- Reaction with carbon dioxide during photosynthesis:
RuBP + CO2 → 2 3-phosphoglycerate (used in Calvin cycle)
- Reaction with oxygen during “photorespiration”:
RuBP + O1 → 1 3-phosphoglycerate (used in Calvin cycle) + 1 2-phosphoglycolate (when processed, CO2 released and ATP used)

75
Q

The leaf structures where gas exchange occurs

A

Stomata

76
Q

Stomata consist of two guard cells that

A

change shape to open or close.

77
Q

When a leaf’s CO2 concentration is low during photosynthesis, stomata

A

open to allow atmospheric CO2 to diffuse into the leaf and its cells’
chloroplasts

78
Q

The calvin cycle maintains a concentration gradient favouring

A

Entry of co2, since the calvin cycle
constantly uses up the CO2 in chloroplasts.

79
Q

How is CO2 concentration increased in plants from hot, dry habitats

A

The C4 pathway spatially separates carbon fixation and the Calvin
cycle.
– During carbon fixation, C4 plants incorporate CO2 into 4-carbon (C4) organic acids instead of
3-phosphoglycerate (performed by C3 plants)

80
Q

In crassulacean acid metabolism (CAM)

A

plants, carbon fixation and the Calvin cycle are separated in time. These plants, which also live in hot,dry habitats keep their stomach closed all day and open them

81
Q

G3P molecules produced by the Calvin cycle are often used to

A

make glucose and fructose, which can
be combined to form sucrose

82
Q

In rapidly photosynthesizing cells where sucrose is abundant, glucose is

A

temporarily stored in the
chloroplast as starch

83
Q

Because starch is not water soluble, it is

A

broken down at night and used to make more sucrose for transport throughout the plant

BLG 143 Chapter 1 (5 decks)

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