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Flashcards in Chapter 10 (Notes) Deck (132):
1

Photosynthesis is

the process that converts solar (light) energy into chemical energy

2

Directly or indirectly, photosynthesis

nourishes almost the entire living world

3

Autotrophs

sustain themselves without eating anything derived from other organisms.

4

Autotrophs are the producers of the biosphere, producing

organic molecules from CO2 and other inorganic molecules

5

Almost all plants are

photoautotrophs, using the energy of sunlight to make organic molecules

6

Photosynthesis occurs in

plants, algae, certain other protists, and some prokaryotes.

These organisms feed not only themselves but also most of the living world

7

Heterotrophs

obtain their organic material from other organisms

8

Heterotrophs are the

consumers of the biosphere

9

Almost all heterotrophs, including humans,

depend on photoautotrophs for food and O2.

10

The Earth's supply of fossil fuels was

formed from the remains of organisms that died hundreds of millions of years ago.

In a sense, fossil fuels represent stores of solar energy from the distant past.

11

Chloroplasts are structurally similar to and likely evolved from

photosynthetic bacteria.

The structural organization of these cells allows for the chemical reactions of photosynthesis.

12

Photosynthesis happens in

chloroplasts.

13

Chloroplasts aren't found in

every plant cell.
Found in Mesophyll.

14

Leaves are the major locations of

photosynthesis.

15

Leaves green color is from chlorophyll,

the green pigment within chloroplasts.

16

Chloroplasts are found mainly in cells of the

mesophyll, the interior tissue of the leaf.

17

Each mesophyll cell contains

30-40 chloroplasts

18

CO2 enters and O2 exits the leaf through microscopic pores called

stomata
(openings on leaf)

19

The chlorophyll is in the membranes of

thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana

20

Chloroplasts also contain stroma,

a dense interior fluid
(the goopy stuff inside)

21

Chlorophyll absorbs

light.

22

Photosynthesis is a complex series of reactions that can be summarized/simplified into the following equation

6 CO2 + 6 H2O + Light energy ----> C6H12O6 + 6 O2

3 things in- 6 Carbon dioxide, 6 water, light
2 things out- 1 glucose, 6 oxygen

23

Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into

sugar molecules and releasing oxygen as a by-product.

In photosynthesis, the oxygen comes from the water molecules.

24

Photosynthesis reverses the direction of

electron flow compared to respiration.

25

Photosynthesis is a

redox process in which H2O is oxidized and CO2 is reduced.

26

Photosynthesis is an

endergonic process; the energy boost is provided by light.

27

Photosynthesis consists of two stages;

the light reactions (the photo part) and the Calvin Cycle (the synthesis part)

28

The light reactions (in the thylakoids)

Split H2O
Release O2
Reduce NADP+ to NADPH
Generate ATP from ADP by photophosphorylation

29

The Calvin Cycle (in the stroma)

forms sugar from CO2, using ATP and NADPH.

30

The Calvin cycle begins with carbon fixation,

incorporating CO2 into organic molecules.

31

The calvin cycle is Sometimes mistakenly called the "dark-cycle" but

it can occur at any time of the day.

32

The light reactions convert solar energy to

the chemical energy of ATP and NADPH

33

Chloroplasts are

solar-powered chemical factories

34

Chloroplasts's thylakoids transform light energy into the

chemical energy of ATP and NADPH

35

Light is a form of

electromagnetic energy, also called electromagnetic radiation.

36

Like other electromagnetic energy, light travels in

rhythmic waves.

37

Light is a form of

kinetic energy.

38

Wavelength is the distance between

crests of waves

39

Wavelength determines the type of

electromagnetic energy

40

The electromagnetic spectrum is the

entire range of electromagnetic energy, or radiation

41

Visible light consists of

wavelengths (including those that drive photosynthesis) that produce colors we can see

42

Light also behaves as though it consists of

discrete particles, called photons (pieces of light)

43

Photosynthetic pigments:

the light receptors

44

Pigments are substances that

absorb visible light

45

Different pigments absorb different

wavelengths

46

Wavelengths that are not absorbed are

reflected or transmitted

47

Leaves appear green because

chlorophyll reflects and transmits green light

48

Pigments absorb all of the colors but the

one color that is transmitted that makes the thing look that color.

49

The spectrophotometer measures a

pigment's ability to absorb various wavelengths

50

The spectrophotometer machine sends light through pigments and

measures the fraction of light transmitted at each wavelength

51

An absorption spectrum is a

graph plotting a pigment's light absorption versus wavelength

52

The absorption spectrum of chlorophyll a suggests that

violet-blue and red light work best for photosynthesis

53

Chlorophyll a is the

main photosynthetic pigment.

(the most important one)

54

Accessory pigments, such as chlorophyll b,

broaden the spectrum used for photosynthesis

55

Accessory pigments called carotenoids absorb

excessive light that would damage chlorophyll.

56

When a pigment absorbs light,

it goes from a ground state to an excited state, which is unstable

57

When excited electrons fall back to the ground state,

photons are given off, an afterglow called fluorescence

58

If illuminated, an isolated solution of chlorophyll will

fluoresce, giving off light and heat

59

A photosystem:

a reaction-center complex associated with light-harvesting complexes

60

Chloroplasts excited by light in a leaf behave

differently than isolated chloroplasts

61

A photosystem consists of a

reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes

62

The light-harvesting complexes

(pigment molecules bound to proteins) transfer the energy of photons to the reaction center

63

A primary electron acceptor in the reaction center accepts

excited electrons and is reduced as a result

64

Solar-powered transfer of an electron from a

chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions

65

There are two types of photosystems in the thylakoid membrane

Photosystem II (PSII)
Photosystem I (PSI)

66

Photosystem II (PSII) functions first

because the numbers reflect the order of discovery

67

Photosystem II (PSII) is best at absorbing a wavelength of

680nm

68

The reaction-center chlorophyll a of photosystem II (PSII) is called

P680

69

Photosystem I (PSI) is best at absorbing a wavelength of

700nm

70

The reaction-center chlorophyll a of photosystem I (PSI) is called

P700

71

The two photosystems work together to

use light energy to generate ATP and NADPH

72

During light reactions, there are two possible routes for electron flow:

linear and cyclic

73

Linear electron flow, the primary pathway, involves

both photosystems and produces ATP and NADPH using light energy

74

In linear electron flow,

a photon hits a pigment and its energy is passed among pigment molecules until it excites P680.

An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680^+)

75

(((linear electron flow)))

P680^+ is a

very strong oxidizing agent

76

(((linear electron flow)))

H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms

to P680^+, thus reducing it to P680

77

(((linear electron flow)))

O2 is released as a

by-product of this reaction

78

(((linear electron flow)))

Each electron "falls" down an electron transport chain from the

primary electron acceptor of PSII to PSI

79

(((linear electron flow)))

Energy released by the fall of the electrons down the electron transport chain drives the

creation of a proton gradient across the thylakoid membrane

80

(((linear electron flow)))

Diffusion of H+ (protons) across the membrane drives

ATP synthesis

81

(((linear electron flow)))

In photosystem I (like photosystem II), transferred light energy excites

P700, which loses an electron to an electron acceptor

82

(((linear electron flow)))

P700^+ (P700 that is missing an electron) accepts an electron passed down from

photosystem II via the electron transport chain

83

(((linear electron flow)))

Photosystem I draws the electrons down from

photosystem II

84

(((linear electron flow)))

Each electron "falls" down an electron transport chain from the

primary electron acceptor of Photosystem I to the protein ferredoxin (Fd)

85

(((linear electron flow)))

The electrons are then transferred to

NADP+ and reduce it to NADPH

86

(((linear electron flow)))

The electrons of NADPH are

available for the reactions of the Calvin Cycle.

This process also removes an H+ from the stroma

87

Cyclic Electron flow uses only

photosystem I and produces ATP, but not NADPH.

No oxygen is released.

88

Cyclic electron flow generates

surplus ATP, satisfying the higher demand in the calvin cycle.

89

Some organisms such as purple sulfur bacteria have

photosystem I but not photosystem II

90

Cyclic electron flow is thought to have evolved before

linear electron flow

91

Cyclic electron flow may protect cells from

light-induced damage

92

Chloroplasts and mitochondria generate ATP by

chemiosmosis, but use different sources of energy

93

Mitochondria transfer

chemical energy from food to ATP

94

chloroplasts transfer

light energy into the chemical energy of ATP

95

Spatial organization of chemiosmosis differs between

chloroplasts and mitochondria but also shows similarities

96

In mitochondria, protons are pumped to the

intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix

97

In chloroplasts, protons are pumped into the

thylakoid space and drive ATP synthesis as they diffuse back into the Stroma

98

In chloroplasts, ATP and NADPH are produced on the side facing

the stroma where the calvin cycle takes place.

99

In summary, the light reactions generate ATP and

increase the potential energy of electrons by moving them from H2O to NADPH

100

The calvin cycle uses the

chemical energy of ATP and NADPH to reduce CO2 to sugar

101

The calvin cycle, like the citric acid cycle, regenerates its starting material after

molecules enter and leave the cycle

102

The calvin cycle builds sugar from smaller molecules by using

ATP and the reducing power of electrons carried by NADPH

103

Carbon enters the calvin cycle as CO2 and leaves as

a sugar named glyceraldehyde 3-phosphate (G3P)

104

For net synthesis of 1 G3P, the calvin cycle must take place

three times, fixing 3 molecules of CO2

105

The calvin cycle has three phases

1. Carbon Fixation (catalyzed by rubisco)
2. Reduction
3. Regeneration of the CO2 acceptor (RuBP)

106

Alternative mechanisms of carbon fixation have evolved in

hot, arid climates

107

Dehydration is a problem for

plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis

108

On hot, dry days, plants close stomata, which

conserves H2O but also limits photosynthesis

109

The closing of stomata reduces access to

CO2 and causes O2 to build up

110

These conditions (closing the stomata) favor an apparently wasteful proces called

photorespiration

111

In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a

three-carbon compound (3-phosphoglycerate)
-rice, wheat, soybeans

112

In photorespiration, rubisco adds O2 instead of

CO2 in the calvin cycle, producing a two-carbon compound

113

Photorespiration consumes O2 and organic fuel and releases

CO2 without producing ATP or sugar.

114

Plants do not want to do

photorespiration that much.

115

Photorespiration may be an evolutionary relic because

rubisco first evolved at a time when the atmosphere had far less O2 and more CO2

116

Photorespiration limits damaging products of

light reactions that build up in the absence of the Calvin cycle

117

In many plants, photorespiration is a problem because

on a hot, dry day it can drain as much as 50% of the carbon fixed by the calvin cycle

118

C4 plants minimize the cost of photorespiration by

incorporating CO2 into four-carbon compounds in msophyll cells
-sugarcane, corn, grasses

This step requires the enzyme PEP carboxylase

119

PEP carboxylase has a higher affinity for CO2 than rubisco does; it can

fix CO2 even when CO2 concentrations are low

120

In C4 plants, these four-carbon compounds are exported to

bundle-sheath cells, where they release CO2 that is then used in the calvin cycle

121

C4 plants store CO2 in case

the stomata closes.

They store carbon in one cell, then can use carbon in another cell for the calvin cycle

122

The mesophyll cells of a C4 plant pump CO2 into the bundle sheath, keeping the CO2 concentration

high enough in the bundle sheath cells for rubisco to work

123

In the last 150 years since the industrial revolution,

CO2 levels have risen greatly


(X)

124

Increasing levels of CO2 may affect

C3 and C4 plants differently, perhaps changing the relative abundance of these species.

The effects of such changes are unpredictable and a cause for concern.

(X)

125

Some plants, including succulents, use

crassulacean acid metabolism (CAM) to fix carbon

126

CAM plants open their stomata at night (when it is cooler), incorporating

CO2 into organic acids

127

In CAM plants, stomata close during the day, and CO2 is released from

organic acids and used in the calvin cycle

128

C4 and CAM are plants solutions to

photorespiration

(?)

129

The energy entering chloroplasts as sunlight gets stored as

chemical energy in organic compounds

130

Sugar made in the chloroplasts supplies chemical energy and

carbon skeletons to synthesize the organic molecules of cells.

(what everything else needs to be alive)

131

Plants store excess sugar as starch in structures such as

roots, tubers, seeds, and fruits

132

In addition to food production, photosynthesis produces

the O2 in our atmosphere