Chapter 10 & 11 (Questions)

Question 1

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

Answer 1

carbon dioxide

Question 2

Which of the following groups of organisms contains only heterotrophs?

Answer 2

Fungi

Question 3

How does carbon dioxide enter the leaf?

Answer 3

through the stomata

Question 4

In a rosebush, chlorophyll is located in _____.

Answer 4

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

Question 5

Chlorophyll molecules are in which part of the chloroplast?

Answer 5

thylakoid membranes

Question 6

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

Answer 6

water

Question 7

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

Answer 7

in sugar molecules and in water

Question 8

Molecular oxygen is produced during _____.

Answer 8

noncyclic electron flow during the light reactions

Question 9

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

Answer 9

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

Question 10

The Calvin cycle occurs in the _____.

Answer 10

stroma

Question 11

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

Answer 11

blue

Question 12

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

Answer 12

capture light energy

Question 13

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

Answer 13

blue-violet and red-orange

Question 14

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

Answer 14

an action spectrum

Question 15

When chloroplast pigments absorb light, _____.

Answer 15

their electrons become excited

Question 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?

Answer 16

the photosystem

Question 17

Where do the electrons entering photosystem II come from?

Answer 17

water

Question 18

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

Answer 18

H2O … photosystem II

Question 19

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

Answer 19

transport electrons from photosystem II to photosystem I

Question 20

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

Answer 20

electrons

Question 21

Both mitochondria and chloroplasts _____.

Answer 21

use chemiosmosis to produce ATP

Question 22

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

Answer 22

have photosynthetic pigments

Question 23

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

Answer 23

thylakoid membrane

Question 24

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

Answer 24

NADPH … ATP … oxygen

Question 25

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

Answer 25

movement of H+ through a membrane

Question 26

What is the role of NADP+ in photosynthesis?

Answer 26

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

Question 27

Of the following, which occurs during the Calvin cycle?

Answer 27

CO2 is reduced.

Question 28

Of the following, which occurs during the Calvin cycle?

Answer 28

ATP is hydrolyzed and NADPH is oxidized.

Question 29

Rubisco is _____.

Answer 29

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

Question 30

In the Calvin cycle, CO2 is combined with _____.

Answer 30

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

Question 31

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

Answer 31

• 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

Question 32

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

Answer 32

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

Question 33

What is the role of NADP+ in photosynthesis?

Answer 33

It forms NADPH to be used in the Calvin cycle

Question 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?

Answer 34

• 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.

Question 35

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

Answer 35

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

Question 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?

Answer 36

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.

Question 37

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

Answer 37

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

Question 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 _____.

Answer 38

local regulator

Question 39

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

Answer 39

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

Question 40

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

Answer 40

stimulate an a yeast cell to grow toward the α cell

Question 41

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

Answer 41

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

Question 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?

Answer 42

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

Question 43

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

Answer 43

Different types of cells possess different proteomes.

Question 44

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

Answer 44

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

Question 45

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

Answer 45

ligand

Question 46

Receptors for signal molecules _____.

Answer 46

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

Question 47

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

Answer 47

not all cells have cytoplasmic receptors for testosterone

Question 48

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

Answer 48

are not enzymes … have enzymatic function

Question 49

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

Answer 49

receptor tyrosine kinases

Question 50

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

Answer 50

affects the membrane potential

Question 51

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

Answer 51

is a gas

Question 52

A G protein is active when _____.

Answer 52

GTP is bound to it

Question 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 _____.

Answer 53

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

Question 54

What event would activate a G protein?

Answer 54

replacement of GDP with GTP

Question 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?

Answer 55

a mutation that means Ras cannot hydrolyze GTP to GDP

Question 56

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

Answer 56

the synthesis of mRNA

Question 57

Cholera develops when the bacterial toxin _____.

Answer 57

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

Question 58

What did Sutherland discover about glycogen metabolism in liver cells?

Answer 58

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

Question 59

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

Answer 59

protein kinase

Question 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?

Answer 60

a decrease in phosphorylated proteins in the cell

Question 61

Phosphorylation _____.

Answer 61

can either activate or inactivate a protein

Question 62

The source of phosphate for a phosphorylation cascade is _____.

Answer 62

ATP

Question 63

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

Answer 63

rapidly move throughout the cell by diffusion

Question 64

cAMP usually directly activates _____.

Answer 64

protein kinase A

Question 65

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

Answer 65

lower activity of protein kinase A

Question 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?

Answer 66

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

Question 67

In a typical cell, calcium ions _____.

Answer 67

are often concentrated within the endoplasmic reticulum

Question 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.

Answer 68

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

Question 69

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

Answer 69

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

Question 70

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

Answer 70

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

Question 71

IP3 (inositol trisphosphate) acts by _____.

Answer 71

opening Ca2+ channels

Question 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?

Answer 72

cyclic AMP

Question 73

In the inherited disorder Wiskott-Aldrich syndrome, _____.

Answer 73

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

Question 74

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

Answer 74

the signal is amplified

Question 75

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

Answer 75

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

Question 76

Apoptosis _____.

Answer 76

is essential for normal development of the nervous system

Question 77

Which of the following statements is/are correct?

Answer 77

• 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.

Question 78

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

Answer 78

chloroplasts

Question 79

An elaborate system of interconnected thylakoid membranes segregates the

Answer 79

stroma from the thylakoid space in the chloroplast.

Question 80

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

Answer 80

ultraviolet radiation and infrared radiation

Question 81

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

Answer 81

oxygen, ATP, and NADPH

Question 82

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

Answer 82

splitting water.

The electrons removed from water are transferred to P680.

Question 83

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

Answer 83

oxidized…reduced

Question 84

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

Answer 84

NADPH

Question 85

During the Calvin cycle electrons stored in NADPH are used to

Answer 85

reduce carbon

Question 86

The overall function of the Calvin cycle is _____.

Answer 86

making sugar

Question 87

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

Answer 87

reduced in the Calvin cycle and sugar is made.

Question 88

C4 plants occur more commonly in desert conditions because _____.

Answer 88

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.

Question 89

Plants are photoautotrophs. What does this mean?

Answer 89

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

Question 90

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

Answer 90

sunlight

Question 91

Which of these equations best summarizes photosynthesis?

Answer 91

6 CO2 + 6 H2O → C6H12O6 + 6 O2

Question 92

Where does the Calvin cycle occur?

Answer 92

In the stroma

Question 93

The light reactions of photosynthesis use _____ and produce _____.

Answer 93

water … NADPH

Question 94

NADPH is a reactant in the

Answer 94

Calvin cycle

Question 95

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

Answer 95

mitochondria for cellular respiration.

Question 96

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

Answer 96

carbon source for the synthesis of sugars during photosynthesis.

Question 97

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

Answer 97

Photophosphorylation

Question 98

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

Answer 98

leads to ATP production.

Question 99

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

Answer 99

proton gradient that leads to the synthesis of ATP.

Question 100

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

Answer 100

Proton gradient.

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

Question 101

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

Answer 101

Protons.

The channels formed by ATP synthase are specific for protons.

Question 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

Answer 102

ion channel through which protons can pass.

Question 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?

Answer 103

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

Question 104

_____ has a longer wavelength than _____.

Answer 104

Red … green

Question 105

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

Answer 105

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

Question 106

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

Answer 106

hormone

Question 107

Both animals and plants use

Answer 107

hormones for signaling at greater distances

Question 108

To what does the term “ligand” refer in cell biology?

Answer 108

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

Question 109

Ligands are the small signaling molecules that

Answer 109

bind specifically to corresponding protein-receptor molecules.

Question 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?

Answer 110

transcription factors

Question 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,

Answer 111

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

Question 112

What is the function of tyrosine-kinase receptors?

Answer 112

enzymatic phosphorylation of tyrosine in the receptor protein

Question 113

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

Answer 113

calcium ion and cAMP

Question 114

Which of the following sequences is correct?

Answer 114

• 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

Question 115

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

Answer 115

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.

Question 116

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

Answer 116

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.

Question 117

What is apoptosis?

Answer 117

controlled cell suicide

Question 118

ATP synthase phosphorylates

Answer 118

ADP

Question 119

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

Answer 119

pump protons into the thylakoid compartment.

Question 120

Photosystem II splits water into

Answer 120

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

Question 121

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

Answer 121

photosystem 1.

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

Question 122

The photosystems contain

Answer 122

chlorophyll

Question 123

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

Answer 123

435 nm

Question 124

Which wavelength of light is best absorbed by chlorophyll b?

Answer 124

455 nm

Question 125

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

Answer 125

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

Question 126

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

Answer 126

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.

Question 127

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

Answer 127

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

Question 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?

Answer 128

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.

Question 129

Which process produces oxygen?

Answer 129

photosynthesis

Question 130

Oxygen is a by-product of the

Answer 130

photosynthetic process

Question 131

Which set of reactions uses H2O and produces O2?

Answer 131

The light-dependent reactions

Question 132

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

Answer 132

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.

Question 133

The light-dependent reactions of photosynthesis use

Answer 133

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.

Question 134

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

Answer 134

NADPH

Question 135

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

Answer 135

production of sugars during photosynthesis.

Question 136

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

Answer 136

They convert carbon dioxide to sugar.

Question 137

All organisms use the sugars produced by photosynthesis to

Answer 137

generate energy

Question 138

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

Answer 138

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

Question 139

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

Answer 139

the light-independent reactions to form sugars.

Question 140

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

Answer 140

Regneration of RuBP

Question 141

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

Answer 141

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

Question 142

Carbon fixation involves the addition of carbon dioxide to _____.

Answer 142

RuBP

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

Question 143

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

Answer 143

NADPH

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

Question 144

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

Answer 144

6

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

Question 145

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

Answer 145

3

Question 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.

Answer 146

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.

Question 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.

Answer 147

• 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.

Question 148

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

Answer 148

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.

Question 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.)

Answer 149

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

Question 150

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

Answer 150

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.

Question 151

In C3 plants the conservation of water promotes _____.

Answer 151

photorespiration

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

Question 152

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

Answer 152

cytoplasm

Question 153

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

Answer 153

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.

Question 154

Which of the following is generally true about the stratosphere?

Answer 154

It is very dry.

Question 155

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

Answer 155

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.

Question 156

Where was the thinning of ozone initially discovered?

Answer 156

Over the Antarctic

Question 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?

Answer 157

Montreal Protocol

Question 158

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

Answer 158

chlorine and sunlight

Question 159

The light reactions require the cooperation of two photosystems to power

Answer 159

linear electron flow from water to NADP+.

Question 160

The key function of each of the two photosystems is to

Answer 160

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

Question 161

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

Answer 161

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

Question 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

Answer 162

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

Question 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.

Answer 163

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.

Question 164

Photosynthetic electron transport contributes to the

Answer 164

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

Question 165

In PS II, the oxidation of water releases

Answer 165

protons into the thylakoid space

Question 166

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

Answer 166

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

Question 167

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

Answer 167

signal molecule

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

Question 168

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

Answer 168

ligand

Question 169

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

Answer 169

transduction

Question 170

The binding of signal molecules to tyrosine-kinase receptors activates

Answer 170

tyrosine-kinase enzymes, which phosphorylate tyrosines.

Question 171

An ion-channel receptor would

Answer 171

allow Na+ to flow into the cell

Question 172

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

Answer 172

estrogen

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

Question 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.

Answer 173

steroid

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

Question 174

Steroids are nonpolar and

Answer 174

can diffuse through the plasma membrane.

Question 175

Thyroid hormones bind to _____ receptors.

Answer 175

tyrosine-kinase

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

Question 176

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

Answer 176

signal transduction pathway.

Question 177

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

Answer 177

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

Question 178

Activated transcription factors

Answer 178

trigger transcription.

Question 179

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

Answer 179

signal molecule

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

Question 180

Which of these acts as a second messenger?

Answer 180

cyclic AMP

Question 181

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

Answer 181

endoplasmic reticula

Question 182

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

Answer 182

Phospholipase C … IP3 …. Ca2+

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

Question 183

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

Answer 183

amplification

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

Question 184

Which of these is a logical signal transduction pathway?

Answer 184

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.

Question 185

The cleavage of glycogen by glycogen phosphorylase releases _____.

Answer 185

glucose-1-phosphate

-Glycogen is a polysaccharide composed of glucose monomers.

Question 186

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

Answer 186

G-protein-linked receptor

Question 187

Which of these is a receptor for calcium ions?

Answer 187

calmodulin

Question 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.

Answer 188

G-protein-linked

-GTP activates G proteins.

Question 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.

Answer 189

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.