Chapter 10 & 11 (Questions) Flashcards Preview

Biology 1406 > Chapter 10 & 11 (Questions) > Flashcards

Flashcards in Chapter 10 & 11 (Questions) Deck (189):
1

In photosynthesis, plants use carbon from _____ to make sugar and other organic

carbon dioxide

2

Which of the following groups of organisms contains only heterotrophs?

Fungi

3

How does carbon dioxide enter the leaf?

through the stomata

4

In a rosebush, chlorophyll is located in _____.

thylakoids, which are in chloroplasts in the mesophyll cells of a leaf

5

Chlorophyll molecules are in which part of the chloroplast?

thylakoid membranes

6

The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from _____.

water

7

In photosynthesis, what is the fate of the oxygen atoms present in CO2? They end up _____.

in sugar molecules and in water

8

Molecular oxygen is produced during _____.

noncyclic electron flow during the light reactions

9

The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night. Why?

The Calvin cycle requires products only produced when the photosystems are illuminated.

10

The Calvin cycle occurs in the _____.

stroma

11

A photon of which of these colors would carry the most energy?

blue

12

The most important role of pigments in photosynthesis is to _____.

capture light energy

13

What is the range of wavelengths of light that are absorbed by the pigments in the thylakoid membranes?

blue-violet and red-orange

14

Based on the work of Engelmann, the wavelengths of light most effective in driving photosynthesis are referred to as _____.

an action spectrum

15

When chloroplast pigments absorb light, _____.

their electrons become excited

16

What structure is formed by the reaction center, light-harvesting complexes, and primary electron acceptors that cluster, and is located in the thylakoid membrane?

the photosystem

17

Where do the electrons entering photosystem II come from?

water

18

During photosynthesis in chloroplasts, O2 is produced from _____ via a series of reactions associated with _____.

H2O ... photosystem II

19

During photosynthesis, an electron transport chain is used to _____.

transport electrons from photosystem II to photosystem I

20

Which of the following is cycled in the cyclic variation of the light reactions?

electrons

21

Both mitochondria and chloroplasts _____.

use chemiosmosis to produce ATP

22

You could distinguish a granum from a crista because the granum, but not the crista, would _____.

have photosynthetic pigments

23

During photosynthesis in a eukaryotic cell, an electrochemical gradient is formed across the ______.

thylakoid membrane

24

The light reactions of photosynthesis generate high-energy electrons, which end up in _____. The light reactions also produce _____ and _____.

NADPH ... ATP ... oxygen

25

The energy used to produce ATP in the light reactions of photosynthesis comes from _____.

movement of H+ through a membrane

26

What is the role of NADP+ in photosynthesis?

It is reduced and then carries electrons to the Calvin cycle.

27

Of the following, which occurs during the Calvin cycle?

CO2 is reduced.

28

Of the following, which occurs during the Calvin cycle?

ATP is hydrolyzed and NADPH is oxidized.

29

Rubisco is _____.

the enzyme in plants that first captures CO2 to begin the Calvin cycle

30

In the Calvin cycle, CO2 is combined with _____.

a 5-carbon compound to form an unstable 6-carbon compound, which decomposes into two 3-carbon compounds

31

Glyceraldehyde-3-phosphate (G3P) is produced in the stroma of chloroplasts. Which of the following statements is most true about this compound?

-It is produced from glucose during glycolysis.
-It is a 3-carbon sugar.
-For every three molecules of CO2, six molecules of G3P are formed but only one molecule exits the cycle to be used by the plant cell.
-For every three molecules of CO2, six molecules of G3P are formed but five molecules must be recycled to regenerate three molecules of RuBP

32

Which of the following statements correctly describes the relationship between the light reactions and the Calvin cycle?

The light reactions produce ATP and NADPH, both of which are used in the Calvin cycle.

33

What is the role of NADP+ in photosynthesis?

It forms NADPH to be used in the Calvin cycle

34

The use of non-C3 and non-CAM plants as crops may be limited in some regions because on hot, dry days, they close their stomata. What happens as a result of closing their stomata?

-It reduces water loss.
-It prevents carbon dioxide from entering the leaf.
-In a process called photorespiration, rubisco binds oxygen instead of carbon dioxide.
-It builds up oxygen from the light reactions in the leaf.

35

Why are C4 plants more suited to hot climates than C3 plants?

Unlike C3 plants, they keep fixing carbon dioxide even when the concentration of carbon dioxide in the leaf is low.

36

You have a large, healthy philodendron that you carelessly leave in total darkness while you are away on vacation. You are surprised to find that it is still alive when you return. What has the plant been using for an energy source while in the dark?

While it did have access to light, the plant stored energy in the form of sugars or starch, and it was able to derive energy from the stored molecules during your vacation.

37

Evidence that cell signaling evolved early in the history of life comes from _____.

the similarity of the mechanisms in organisms that have a very distant common ancestor

38

When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example thromboxane A2 is acting as a _____.

local regulator

39

Early work on signal transduction and glycogen metabolism by Sutherland indicated that _____.

the signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated

40

Certain yeast cells secrete a molecule called the α factor. The purpose of this molecule is to _____.

stimulate an a yeast cell to grow toward the α cell

41

Cells use different signaling strategies to achieve different goals. In hormonal signaling _____.

specialized cells release hormone molecules into the circulatory system, permitting distant cells to be affected

42

Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence?

Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus.

43

Different types of cells can respond differently to the same signaling molecule. Which of the following explains this apparent paradox?

Different types of cells possess different proteomes.

44

Steroid hormones can enter a cell by simple diffusion. Therefore steroids _____.

do not initiate cell signaling by interacting with a receptor in the plasma membrane

45

A small molecule that specifically binds to a larger molecule is called a(n) _____.

ligand

46

Receptors for signal molecules _____.

may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus

47

Testosterone does not affect all cells of the body because _____.

not all cells have cytoplasmic receptors for testosterone

48

G-protein-linked receptors _____, whereas receptor tyrosine kinases _____.

are not enzymes ... have enzymatic function

49

Which of the following is activated when the binding of single molecules causes it to form a dimer?

receptor tyrosine kinases

50

The binding of a signal molecule to a ligand-gated ion channel _____.

affects the membrane potential

51

Nitric oxide is unusual among animal signal molecules in that it _____.

is a gas

52

A G protein is active when _____.

GTP is bound to it

53

If a modified form of GTP that cannot be enzymatically converted to GDP were added to a culture of cells, the likely result would be _____.

that the activated G proteins would remain locked in the "on" position, transmitting signal even in the absence of a signaling molecule

54

What event would activate a G protein?

replacement of GDP with GTP

55

Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer. Ras normally signals to a cell that it should divide. Cancer cells divide uncontrollably. Which of the following changes to Ras would you expect to see in a cancer cell that has mutated Ras present?

a mutation that means Ras cannot hydrolyze GTP to GDP

56

The cellular response of a signal pathway that terminates at a transcription factor would be _____.

the synthesis of mRNA

57

Cholera develops when the bacterial toxin _____.

prevents G-protein inactivation, which leads to the continuous production of cAMP

58

What did Sutherland discover about glycogen metabolism in liver cells?

The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell.

59

The general name for an enzyme that transfers phosphate groups from ATP to a protein is _____.

protein kinase

60

ATPgammaS is a form of ATP that cannot be hydrolyzed by enzymes. If this compound was introduced to cells so that it replaced the normal ATP present in the cell, which of the following would you predict?

a decrease in phosphorylated proteins in the cell

61

Phosphorylation _____.

can either activate or inactivate a protein

62

The source of phosphate for a phosphorylation cascade is _____.

ATP

63

Second messengers tend to be water-soluble and small. This accounts for their ability to _____.

rapidly move throughout the cell by diffusion

64

cAMP usually directly activates _____.

protein kinase A

65

A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to _____.

lower activity of protein kinase A

66

Domoic acid is a neurotoxin produced by some species of alga. Domoic acid binds to the kainate receptor on neurons in parts of the brain. The kainate receptor facilitates the movement of calcium into the cell. Excess domoic acid-induced stimulation of the neural kainate receptors causes neural damage and short-term memory loss. Based on this, which of the following is likely true?

The kainate receptor is a ligand-gated ion channel and domoic acid is a ligand.

67

In a typical cell, calcium ions _____.

are often concentrated within the endoplasmic reticulum

68

During the transduction of a signal, one molecule or ion may be closely associated with the activity of another. Select the pair that is correctly combined.

-calcium, IP3
-cAMP, adenylyl cyclase
-cAMP, protein kinase A
-DAG, IP3

69

A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that cAMP _____ and Ca2+ _____.

is synthesized by an enzyme in response to a signal ... is released from intracellular stores

70

IP3 (inositol trisphosphate) is produced as a result of _____.

the cleavage of a certain kind of phospholipid in the plasma membrane

71

IP3 (inositol trisphosphate) acts by _____.

opening Ca2+ channels

72

In eukaryotic cells, which of the following is a second messenger that is produced as a response to an external signal such as a hormone?

cyclic AMP

73

In the inherited disorder Wiskott-Aldrich syndrome, _____.

a multifunctional relay protein involved with the proliferation of immune cells is defective

74

In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, _____.

the signal is amplified

75

Cells of the gastrointestinal (GI) tract and cells of the heart respond differently to epinephrine because _____.

there are differences in the proteins found in the two types of cells

76

Apoptosis _____.

is essential for normal development of the nervous system

77

Which of the following statements is/are correct?

-Some apoptotic signals originate from outside a cell.
-Some apoptotic signals come from the nucleus, when DNA has suffered irreparable damage.
-Some apoptotic signals come from the endoplasmic reticulum when excessive protein misfolding occurs.
-Some apoptotic signals come from mitochondria.

78

The photosynthetic membranes are found in the _____ in plant cells.

chloroplasts

79

An elaborate system of interconnected thylakoid membranes segregates the

stroma from the thylakoid space in the chloroplast.

80

In the electromagnetic spectrum, the type of radiation that we call visible light occurs between _____.

ultraviolet radiation and infrared radiation

81

Which of the following is a product of the light reactions of photosynthesis?

oxygen, ATP, and NADPH

82

When light strikes chlorophyll molecules, they lose electrons, which are ultimately replaced by _____.

splitting water.

The electrons removed from water are transferred to P680.

83

Photosynthesis is a redox reaction. This means that H2O is _____ during the light reactions and CO2 is _____ during the Calvin cycle.

oxidized...reduced

84

Which of the following products of the light reactions of photosynthesis is consumed during the Calvin cycle?

NADPH

85

During the Calvin cycle electrons stored in NADPH are used to

reduce carbon

86

The overall function of the Calvin cycle is _____.

making sugar

87

Using the ATP and NADPH made during the light reactions, carbon is

reduced in the Calvin cycle and sugar is made.

88

C4 plants occur more commonly in desert conditions because _____.

they can fix carbon at the lower CO2 concentrations that develop when the stomata are closed.

To conserve water during hot, dry conditions, the stomata are fully or partially closed, preventing CO2 from reaching high concentrations.

89

Plants are photoautotrophs. What does this mean?

They use light energy to drive the synthesis of organic molecules from inorganic materials.

90

The ultimate source of energy to support most life on Earth is _____.

sunlight

91

Which of these equations best summarizes photosynthesis?

6 CO2 + 6 H2O → C6H12O6 + 6 O2

92

Where does the Calvin cycle occur?

In the stroma

93

The light reactions of photosynthesis use _____ and produce _____.

water ... NADPH

94

NADPH is a reactant in the

Calvin cycle

95

Photosynthesis, which occurs in chloroplasts, generates the sugars and oxygen gas that are used in

mitochondria for cellular respiration.

96

Cellular respiration generates carbon dioxide, which in turn is used as a

carbon source for the synthesis of sugars during photosynthesis.

97

Which term describes ATP production resulting from the capture of light energy by chlorophyll?

Photophosphorylation

98

The excitation of chlorophyll by light energy initiates a chain of events that

leads to ATP production.

99

The chemiosmotic hypothesis states that the flow of electrons through an electron transport chain generates a

proton gradient that leads to the synthesis of ATP.

100

According to the chemiosmotic hypothesis, what provides the energy that directly drives ATP synthesis?

Proton gradient.

A proton gradient across chloroplast and mitochondrial membranes drives ATP synthesis by the enzyme ATP synthase.

101

Which of the following particles can pass through the ATP synthase channel?

Protons.

The channels formed by ATP synthase are specific for protons.

102

The region of ATP synthase that catalyzes ATP production protrudes out of, but does not span, the chloroplast membrane; the region that spans the membrane is an

ion channel through which protons can pass.

103

Chloroplast membrane vesicles are equilibrated in a simple solution of pH 5. The solution is then adjusted to pH 8. Which of the following conclusions can be drawn from these experimental conditions?

ATP will not be produced because there is no ADP and inorganic phosphate in the solution.

104

_____ has a longer wavelength than _____.

Red ... green

105

Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life?

The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

106

Which of the following is a substance that acts at a long distance from the site at which it is secreted?

hormone

107

Both animals and plants use

hormones for signaling at greater distances

108

To what does the term "ligand" refer in cell biology?

any small molecule that can bind in a specific manner to a larger one

109

Ligands are the small signaling molecules that

bind specifically to corresponding protein-receptor molecules.

110

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding to proteins in the cytoplasm, then altering the pattern of gene expression. Which of the following are likely to be the cytoplasmic proteins to which dioxin binds?

transcription factors

111

Steroid hormone receptors located in the cytoplasm could be bound by dioxin, just as they are bound by the steroids that diffuse into the cell. Once bound by the dioxins,

the cytoplasmic receptor/dioxin complexes could move into the nucleus, where they may act as transcription factors, instigating the synthesis of mRNA.

112

What is the function of tyrosine-kinase receptors?

enzymatic phosphorylation of tyrosine in the receptor protein

113

Which of the following are among the most common second messengers?

calcium ion and cAMP

114

Which of the following sequences is correct?

-binding of a signaling molecule to its receptor → G protein activation → phospholipase C activation → IP3 production → increase in cytoplasmic calcium concentration
-binding of a growth factor to its receptor → phosphorylation cascade → activation of transcription factor → transcription
-binding of a signaling molecule to its receptor → G protein activation → adenylyl cyclase activation → cAMP production → protein phosphorylation
-diffusion of a signaling molecule across the plasma membrane → binding of the signaling molecule to its receptor → movement of the signaling molecule-receptor complex into the nucleus → transcription

115

Why are there often so many steps between the original signal event and the cell's response?

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

-This amplification permits the signaling molecule to have a widespread effect throughout the cell.

116

Why can a signaling molecule cause different responses in different cells?

The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor.

-The signal simply initiates a process by activating a membrane receptor. How transduction proceeds can be quite different for different cells.

117

What is apoptosis?

controlled cell suicide

118

ATP synthase phosphorylates

ADP

119

The energy released as electrons are passed along the electron transport chain is used to

pump protons into the thylakoid compartment.

120

Photosystem II splits water into

1/2 O2, H+, and e- .

121

Energized electrons from ____ enter an electron transport chain and are then used to reduce NADP+.

photosystem 1.

(Energized electrons from photosystem I are used to reduce NADP+.)

122

The photosystems contain

chlorophyll

123

Approximately what wavelength of light is best absorbed by chlorophyll a, the pigment that participates directly in the light reactions?

435 nm

124

Which wavelength of light is best absorbed by chlorophyll b?

455 nm

125

You obtain the pigments called carotenoids in your diet when you eat carrots. Why do carotenoids appear yellow and orange?

They absorb blue/green light and reflect yellow and red wavelengths of light.

126

Can you tell from these absorption spectra whether red light is effective in driving photosynthesis?

One cannot tell from this graph, but because chlorophyll a does absorb red light, we can predict that it would be effective in driving photosynthesis.

127

If only chlorophyll a were involved in the light reactions, would blue light (wavelength about 490 nm) be effective in driving photosynthesis?

The graph indicates that chlorophyll a absorbs very little blue light, so we can predict that blue light would not be effective.

128

An action spectrum plots the rate of photosynthesis at various wavelengths of visible light, and it shows that blue light with a wavelength of about 490 nm is effective in driving photosynthesis. Based on this information and the absorption spectra shown at left, what role may chlorophyll b and carotenoids play in photosynthesis?

These pigments are able to absorb more wavelengths of light (and thus more energy) than chlorophyll a alone can absorb. As part of light-harvesting complexes in photosystems, they broaden the range of light that can be used in the light reactions.

129

Which process produces oxygen?

photosynthesis

130

Oxygen is a by-product of the

photosynthetic process

131

Which set of reactions uses H2O and produces O2?

The light-dependent reactions

132

What is the importance of the light-independent reactions in terms of carbon flow in the biosphere?

The light-independent reactions turn CO2, a gas, into usable carbon in the form of sugars.

-CO2 is unusable until plants have "fixed" this carbon into sugar.

133

The light-dependent reactions of photosynthesis use

water and produce oxygen.

-The water molecules are split to replenish electrons in photosystem II, leaving behind protons, which are used to generate a proton gradient for the formation of ATP, and oxygen, which is released as a by-product.

134

Which of the following molecules is the primary product of photosystem I?

NADPH

135

The NADPH produced by photosystem I is used to supply energy for the

production of sugars during photosynthesis.

136

What is the biological significance of the light-independent reactions of photosynthesis?

They convert carbon dioxide to sugar.

137

All organisms use the sugars produced by photosynthesis to

generate energy

138

Which of the following statements best describes the relationship between the light-dependent and light-independent reactions of photosynthesis?

The light-dependent reactions produce ATP and NADPH, which are then used by the light-independent reactions.

139

Light energy drives the formation of ATP and NADPH during the light-dependent reactions; these energy molecules are then used during

the light-independent reactions to form sugars.

140

Which of the following reactions ensures that the Calvin cycle can make a continuous supply of glucose?

Regneration of RuBP

141

The regeneration of RuBP ensures that the Calvin cycle can proceed indefinitely, since

RuBP fixes carbon dioxide into an organic molecule that is used to produce sugar.

142

Carbon fixation involves the addition of carbon dioxide to _____.

RuBP

-In the Calvin cycle, carbon dioxide is added to RuBP

143

After 3-PGA is phosphorylated, it is reduced by _____.

NADPH

-NADPH supplies the electrons that reduce the phosphorylated 3-PGA.

144

How many carbon dioxide molecules must be added to RuBP to make a single molecule of glucose?

6

-Six carbon dioxide molecules are required to produce two G3P molecules, which can be combined to make one glucose molecule.

145

In the Calvin cycle, how many ATP molecules are required to regenerate RuBP from five G3P molecules?

3

146

The chloroplast is enclosed by a pair of envelope membranes (inner and outer) that separate the interior of the chloroplast from the surrounding cytosol of the cell. Inside the chloroplast, the chlorophyll-containing thylakoid membranes are the site of the light reactions.

Between the inner envelope membrane and the thylakoid membranes is the aqueous stroma, which is the location of the reactions of the Calvin cycle. Inside the thylakoid membranes is the thylakoid space, where protons accumulate during ATP synthesis in the light reactions.

147

-To produce 1 molecule of G3P (which contains 3 carbons), the Calvin cycle must take up 3 molecules of CO2 (1 carbon atom each).
-The 3 CO2 molecules are added to 3 RuBP molecules (which contain 15 total carbon atoms), next producing 6 molecules of 3-PGA (18 total carbon atoms).
-In reducing 3-PGA to G3P (Phase 2), there is no addition or removal of carbon atoms.

-At the end of Phase 2, 1 of the 6 G3P molecules is output from the cycle, removing 3 of the 18 carbons.
-The remaining 5 G3P molecules (15 total carbon atoms) enter Phase 3, where they are converted to 3 molecules of R5P.
-Finally, the R5P is converted to RuBP without the addition or loss of carbon atoms.

148

The Calvin cycle requires a total of 9 ATP and 6 NADPH molecules

per G3P output from the cycle (per 3 CO2 fixed).

-In Phase 2, six of the ATP and all of the NADPH are used in Phase 2 to convert 6 molecules of PGA to 6 molecules of G3P. Six phosphate groups are also released in Phase 2 (derived from the 6 ATP used).
-In the first part of Phase 3, 5 molecules of G3P (1 phosphate group each) are converted to 3 molecules of R5P (also 1 phosphate group each). Thus there is a net release of 2 Pi.
-In the second part of Phase 3, 3 ATP molecules are used to convert the 3 R5P into 3 RuBP.
-Note that in the entire cycle, 9 ATP are hydrolyzed to ADP; 8 of the 9 phosphate groups are released as Pi, and the ninth phosphate appears in the G3P output from the cycle.

149

The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. Thus, lower light levels generally mean a lower rate of O2 production.
In addition, lower light levels also affect the rate of CO2 uptake by the Calvin cycle. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. In this way, the Calvin cycle depends on the light reactions.
But is the inverse true as well? Do the light reactions depend on the Calvin cycle?
Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water).
Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.)

The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease.

150

A reaction or process is dependent on another if the output of the second is an input to the first.

For example, the light reactions are dependent on the Calvin cycle because the NADP+ and ADP produced by the Calvin cycle are inputs to the light reactions.
-Thus, if the Calvin cycle slows (because of a decrease in the amount of available CO2), the light reactions will also slow because the supply of NADP+ and ADP from the Calvin cycle would be reduced.

151

In C3 plants the conservation of water promotes _____.

photorespiration

-Conserving water simultaneously reduces the amount of carbon dioxide available to the plant.

152

In C4 and CAM plants carbon dioxide is fixed in the _____ of mesophyll cells.

cytoplasm

153

C4 plants differ from C3 and CAM plants in that C4 plants _____.

transfer fixed carbon dioxide to cells in which the Calvin cycle occurs

-In C3 and CAM plants carbon dioxide fixation and the Calvin cycle occur in the same cells.

154

Which of the following is generally true about the stratosphere?

It is very dry.

155

Based on current findings, which of the following is true?

As climate change speeds up, there will be an increase in the number of strong storms, in turn causing an increased amount of ozone depletion.

156

Where was the thinning of ozone initially discovered?

Over the Antarctic

157

You are the CEO of a major manufacturing company that decides to use CFCs in production of your products. What are you failing to abide by?

Montreal Protocol

158

Which of the following two things worked in conjunction to make CFCs harmful to the ozone?

chlorine and sunlight

159

The light reactions require the cooperation of two photosystems to power

linear electron flow from water to NADP+.

160

The key function of each of the two photosystems is to

absorb light and convert the energy of the absorbed light into redox energy, which drives electron transport.

161

In PS II (the first photosystem in the sequence), P680 is oxidized (which in turn oxidizes water), and the

PS II primary electron acceptor is reduced (which in turn reduces the electron transport chain between the photosystems).

162

In PS I, the PS I primary electron acceptor is reduced (which in turn reduces other compounds that ultimately reduce NADP+ to NADPH), and

P700 is oxidized (which in turn oxidizes the electron transport chain between the photosystems).

163

In both PS II and PS I, light energy is used to drive a redox reaction that would not otherwise occur. In each photosystem, this redox reaction moves an electron from the special chlorophyll pair (P680 in PS II and P700 in PS I) to that photosystem’s primary electron acceptor.

The result in each case is a reductant (the reduced primary electron acceptor) and an oxidant (P680+ in PS II and P700+ in PS I) that are able to power the rest of the electron transfer reactions without further energy input.

164

Photosynthetic electron transport contributes to the

formation of a proton (H+) gradient across the thylakoid membrane in two places.

165

In PS II, the oxidation of water releases

protons into the thylakoid space

166

Electron transport between PS II and the cytochrome complex (through Pq) pumps protons from the stroma into the thylakoid space.

The resulting proton gradient is used by the ATP synthase complex to convert ADP to ATP in the stroma.

167

A signal transduction pathway is initiated when a _____ binds to a receptor.

signal molecule

-The binding of a signal molecule to a receptor initiates a signal transduction pathway

168

A signal molecule is also known as a(n) _____.

ligand

169

Which of these is the second of the three stages of cell signaling?

transduction

170

The binding of signal molecules to tyrosine-kinase receptors activates

tyrosine-kinase enzymes, which phosphorylate tyrosines.

171

An ion-channel receptor would

allow Na+ to flow into the cell

172

Which of these extracellular signal molecules could diffuse through a plasma membrane and bind to an intracellular receptor?

estrogen

-Nonpolar molecules can diffuse through the plasma membrane and bind to intracellular receptors.

173

A(n) _____ is an example of a signal molecule that can bind to an intracellular receptor and thereby cause a gene to be turned on or off.

steroid

-Steroids bind to intracellular receptors, which can then bind to, and regulate, the expression of genes.

174

Steroids are nonpolar and

can diffuse through the plasma membrane.

175

Thyroid hormones bind to _____ receptors.

tyrosine-kinase

-Thyroid hormones are able to pass through the plasma membrane.

176

The attachment of a signal molecule to a plasma membrane receptor initiates a

signal transduction pathway.

177

What role does a transcription factor play in a signal transduction pathway?

By binding to DNA it triggers the transcription of a specific gene.

178

Activated transcription factors

trigger transcription.

179

A signal transduction pathway is initiated when a _____ binds to a receptor.

signal molecule

-The binding of a signal molecule to a receptor initiates a signal transduction pathway.

180

Which of these acts as a second messenger?

cyclic AMP

181

Calcium ions that act as second messengers are stored in _____.

endoplasmic reticula

182

_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell's cytoplasm.

Phospholipase C ... IP3 .... Ca2+

-Phospholipase C cleaves IP3 from a membrane protein, and IP3 then binds to a calcium channel on the ER.

183

A protein kinase activating many other protein kinases is an example of _____.

amplification

-By activating many other molecules the initial signal is amplified.

184

Which of these is a logical signal transduction pathway?

A G-protein-linked receptor activates G protein, which activates phospholipase C, which cleaves a membrane lipid to form IP3, which binds to a calcium channel on the ER, which opens to release calcium ions into the cytoplasm, which bind to an intracellular enzyme that carries out a response.

185

The cleavage of glycogen by glycogen phosphorylase releases _____.

glucose-1-phosphate

-Glycogen is a polysaccharide composed of glucose monomers.

186

Epinephrine acts as a signal molecule that attaches to _____ proteins.

G-protein-linked receptor

187

Which of these is a receptor for calcium ions?

calmodulin

188

A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors.

G-protein-linked

-GTP activates G proteins.

189

Receptor proteins (located in the plasma membrane or inside the cell) bind signaling molecules. The reception of the signal causes a shape change in the receptor molecule, to which other molecules inside the cell respond.

The message is then relayed through signal transduction, which may involve a phosphorylation cascade or second messengers such as cAMP, Ca2+, or IP3. Possible responses to the signal may include synthesis of a particular protein or regulation of a particular enzyme.