Chapter 11 Flashcards
1
Q
What are chloroplasts?
A
Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant.
2
Q
What is photosynthesis?
A
The process by which green plants and some other organisms use sunlight to synthesise nutrients from carbon dioxide and water.
3
Q
What are Autotrophs?
A
“Self-Feeders” They sustain themselves without eating anything derived from other living beings. They produce their organic molecules from CO2 and other inorganic raw materials.
4
Q
True or False? Plants are not autotrophs.
A
False, almost all plants are autotrophs.
5
Q
What are photoautotrophs?
A
Organisms that use light energy to drive the synthesis of organic molecules from carbon dioxide and water.
6
Q
What are Heterotrophs?
A
A heterotroph is an animal that can’t make its own food supply, so they have to eat other things, like plants or other animals, to survive
7
Q
What is the endosymbiont theory?
A
an evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms
8
Q
What are chloroplasts?
A
a plastid in green plant cells which contains chlorophyll and in which photosynthesis takes place.
9
Q
Where are chloroplasts usually found?
A
The cells of the mesophyll, the tissue in the interior of the leaf
10
Q
What is stroma?
A
The colorless fluid surrounding the grana within the chloroplast. Within the stroma are grana (stacks of thylakoid), and the sub-organelles or daughter cells, where photosynthesis is commenced before the chemical changes are completed in the stroma.
11
Q
What is the thylakoid?
A
Thylakoids are membrane-bound compartments or sacs inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis
12
Q
What is the thylakoid space?
A
The thylakoid space is the space inside of the thylakoid, which is defined by the a thylakoid’s individual membrane. In the thylakoid space is a substance called lumen, and this mostly serves to provide structure and to build up a concentration gradient of protons during photosynthesis.
13
Q
What is the granum?
A
A granum is a coin-shaped stack of thylakoids, which are the membrane-like structures found inside the chloroplasts of plant cells.
14
Q
What is chlorophyll?
A
A green pigment, present in all green plants and in cyanobacteria, which is responsible for the absorption of light to provide energy for photosynthesis
15
Q
What is the photosynthetic equation?
A
6CO2 + 6H2O + LIGHT ENERGY > C6H12O6 + 6O2
16
Q
What is the simplest form of the photosynthetic equation?
A
CO2 + H2O > [CH2O] + O2, the brackets indicate CH2O is not an actual sugar but represents the general formula for a carbohydrate.
17
Q
What is the O2 given of by plants derived from?
A
H2O not CO2
18
Q
Is photosynthesis an exothermic or endothermic reaction?
A
An endothermic reaction because the electrons increase in potential energy as they move from water to sugar. This required energy is provided by light.
19
Q
Is photosynthesis comprised of one process of two?
A
Two each with multiple steps
20
Q
What are the two stages of photosynthesis known as?
A
The light reactions and the calvin cycle.
21
Q
What occurs during the light reactions stage of photosynthesis?
A
This stage is the steps of photosynthesis in which converts solar energy to chemical energy. Water is split allowing a source of electrons and protons (Hydrogen ions) and giving of O2 as a by product. The light absorbed by the chlorophyll drives a transfer of the electrons and hydrogen ions from water to NADP+ where they are temporarily stored. This reduces NADP+ to NADPH. The light reactions also generate ATP to power the addition of a phosphate group to ADP
22
Q
What occurs during the calvin cycle stage of photosynthesis?
A
The cycle begins with incorporating CO2 from the air into organic molecules already present in the chloroplast (Carbon Fixation). The calvin cycle then reduces the fixed carbon to carbohydrate by the addition of electrons and chemical energy. The reducing power is provided by NADPH (acquired in light reactions). Chemical energy is also provided by the ATP produced in light reactions. This then produces the sugar
23
Q
What is photophosphorylation?
A
In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation
24
Q
What is Carbon fixation?
A
Carbon fixation or сarbon assimilation is the conversion process of inorganic carbon to organic compounds by living organisms. The most prominent example is photosynthesis.
25
What are the thylakoids the site of, during photosynthesis?
The sites of the light reactions
26
What is the stroma the site of during photosynthesis?
The calvin cycle
27
What is the energy of light?
Electromagnetic energy, also called electromagnetic radiation
28
What is the electromagnetic spectrum?
The entire range of radiation is known as the electromagnetic spectrum.
29
What is visible light?
The segment most important to life is the narrow band from about 380 nm to 750 nm in wavelength. This radiation is known as visible light because it can be detected as various colors by the human eye.
30
What are photons?
a particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass. The shorter the wavelength, the greater the energy of each photon of that light. Thus, a photon of violet light packs nearly twice as much energy as a photon of red light
31
When light meets matter what 3 things can happen?
it may be reflected, transmitted, or absorbed.
32
What are pigments?
Substances that can absorb visible light. Different pigments absorb light of different wave- lengths, and the wavelengths that are absorbed disappear. the color we see is the color most reflected or transmitted by the pigment. (If a pigment absorbs all wavelengths, it appears black.)
33
Why do plants appear green?
We see green when we look at a leaf because chlorophyll absorbs violet-blue and red light while transmitting and reflecting green light
34
What does a spectrophotometer do?
It can measure the ability of a pigment to absorb various wavelengths of light. This machine directs beams of light of different wavelengths through a solution of the pigment and measures the fraction of the light transmit- ted at each wavelength. A graph plotting a pigment’s light absorption versus wavelength is called an absorption spectrum.
35
What is : chlorophyll a?
The key light-capturing pigment that participates directly in the light reactions; It absorbs most energy from wavelengths of violet-blue and orange-red light. It also reflects green-yellow light, and as such contributes to the observed green color of most plants.
36
What is : chlorophyll b?
Chlorophyll b is a form of chlorophyll. Chlorophyll b helps in photosynthesis by absorbing light energy. It is more soluble than chlorophyll a in polar solvents because of its carbonyl group. Its color is green, and it primarily absorbs blue light
37
What are carotenoids?
any of a class of mainly yellow, orange, or red fat-soluble pigments, including carotene, which give colour to plant parts such as ripe tomatoes and autumn leaves. they absorb violet and blue-green light
38
What is the action spectrum for photosynthesis?
This profiles the relative effectiveness of different wavelengths of radiation in driving the process. An action spectrum is prepared by illuminating chloroplasts with light of different colors and then plotting wavelength against some measure of photosynthetic rate, such as CO2 consumption or O2 release.
39
What is the difference between chlorophyll a and b?
A slight structural difference between them is enough to cause the two pigments to absorb at slightly different wavelengths in the red and blue parts of the spectrum. As a result, chlorophyll a appears blue green and chlorophyll b olive green under visible light.
40
What is an important function of some carotenoids?
Photoprotection: These compounds absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen, forming reactive oxidative molecules that are dangerous to the cell. Carrots, known for aiding night vision, due to being rich in carotenoids
41
What exactly happens when chlorophyll and other pigments absorb light?
When a molecule absorbs a photon of light, one of the molecule’s electrons is elevated to an orbital where it has more potential energy. When the electron is in its normal orbital, the pigment molecule is said to be in its ground state. Absorption of a photon boosts an electron to an orbital of higher energy, and the pigment molecule is then said to be in an excited state. The only photons absorbed are those whose energy is exactly equal to the energy difference between the ground state and an excited state, and this energy difference varies Thus, a particular compound absorbs only photons corresponding to specific wavelengths, which is why each pigment has a unique absorption spectrum.
42
Why are white cars the coolest on a hot sunny day?
White cars are coolest because their paint reflects all wave- lengths of visible light.
43
In isolation, some pigments, including chlorophyll, emit light as well as heat after absorbing photons. As excited electrons fall back to the ground state, photons are given off. What is the afterglow called?
Florescence.
44
What are photosystems?
Photosystems are functional and structural units of protein complexes involved in photosynthesis that together carry out the primary photochemistry of photosynthesis: Photosystems are found in the thylakoid membranes. A photosystem is composed of a reaction-center complex surrounded by several light-harvesting complexes.
45
What is the reaction-center complex?
An organized association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor.
46
What does a light-harvesting complex consist of?
Consists of various pigment molecules (which may include chlorophyll a, chlorophyll b, and multiple carotenoids) bound to proteins. The number and variety of pigment molecules enable a photosystem to harvest light over a larger surface area and a larger portion of the spectrum than could any single pigment molecule alone.
47
How does the photosystem work?
When a pigment molecule absorbs a photon, the energy is transferred from pigment molecule to pigment molecule within a light-harvesting complex, like a human “wave” at a sports arena, until it is passed to the pair of chlorophyll a molecules in the reaction-center complex. The pair of chlorophyll a molecules in the reaction-center complex are special because their molecular environment—their location and the other molecules with which they are associated—enables them to use the energy from light not only to boost one of their electrons to a higher energy level, but also to transfer it to a different molecule—the primary electron acceptor, which is a molecule capable of accepting electrons and becoming reduced. The transfer of an electron from the reaction- center chlorophyll a pair to the primary electron acceptor is the first step of the light reactions.
48
The thylakoid membrane is populated by two types of photosystems called what?
photosystem II (PS II) and photosystem I (PS I)
49
Which type of photosystem in the thylakoid membrane functions first?
Photosystem ll
50
What is the reaction-center chlorophyll a
| of the photosystem II is known as?
P680 because this pigment is best at absorbing light having a wavelength of 680 nm (in the red part of the spectrum).
51
What is the reaction-center chlorophyll a
| of the photosystem I known as?
P700 because it most effectively absorbs light of wavelength 700 nm (in the far-red part of the spectrum)
52
What is the difference between photosystem II (PS II) and photosystem I (PS I)?
Their association with different proteins in the thylakoid membrane affects the electron distribution in the two pigments and accounts for the slight differences in their light-absorbing properties
53
How do photosystem II (PS II) and photosystem I (PS I) work together?
They work together in using light energy to generate ATP and NADPH, the two main products of the light reactions.
54
What are the two main products of the light reactions?
ATP and NADPH
55
Light drives the synthesis of ATP and NADPH by energizing what?
The two types of photosystems embedded in the thylakoid membranes of chloroplasts.The key to this energy transformation is a flow of electrons through the photosystems and other molecular components built into the thylakoid membrane. This is called linear electron flow, and it occurs during the light reactions of photosynthesis.
56
What is the first step for how linear electron flow during the light reactions generates ATP and NADPH?
(Mexican wave to PSII) A photon of light strikes one of the pigment molecules in a light-harvesting complex of PS II, boosting one of its electrons to a higher energy level. As this electron falls back to its ground state, an electron in a nearby pigment molecule is simultaneously raised to an excited state. The process continues, with the energy being relayed to other pigment molecules until it reaches the P680 pair of chlorophyll a molecules in the PS II reaction-center complex. And it excites an electron in this pair of chlorophylls to a higher energy state.
57
What is the second step for how linear electron flow during the light reactions generates ATP and NADPH?
The excited electron is transferred from the excited P680 to the primary electron acceptor. We can refer to the resulting form of P680, missing the negative charge of an electron, as P680+.
58
What is the third step for how linear electron flow during the light reactions generates ATP and NADPH?
(Splitting of H2O to make H+ ions and O2) An enzyme catalyses the splitting of a water molecule into two electrons, two hydrogen ions (H+), and an oxygen atom. The electrons are supplied one by one to the P680+ pair, each electron replacing one transferred to the primary electron acceptor. (P680+ is the strongest biological oxidising agent known; its electron “hole” must be filled. This greatly facilitates the transfer of electrons from the split water molecule.) The H+ are released into the thylakoid space (interior of the thylakoid). The oxygen atom immediately combines with an oxygen atom generated by the splitting of another water molecule, forming O2.
59
What is the forth step for how linear electron flow during the light reactions generates ATP and NADPH?
(Electron transport chain) Each photoexcited electron passes from the primary electron acceptor of PS II to PS I via an electron transport chain. The electron transport chain between PS II and PS I is made up of the electron carrier plastoquinone (Pq), a cytochrome complex, and a protein called plastocyanin (Pc). Each component carries out redox reactions as electrons flow down the electron transport chain, releasing free energy that is used to pump protons (H+) into the thylakoid space, contributing to a proton gradient across the thylakoid membrane.
60
What is the fifth step for how linear electron flow during the light reactions generates ATP and NADPH?
(Synthesising ATP) The potential energy stored in the proton gradient is used to make ATP in a process called chemiosmosis, to be discussed shortly
61
What is the sixth step for how linear electron flow during the light reactions generates ATP and NADPH?
(Formation of electron acceptor) Meanwhile, light energy has been transferred via light- harvesting complex pigments to the PS I reaction-center complex, exciting an electron of the P700 pair of chlorophyll a molecules located there. The photoexcited electron is then transferred to PS I’s primary electron acceptor, creating an electron “hole” in the P700—which we now can call P700+. In other words, P700+ can now act as an electron acceptor, accepting an electron that reaches the bottom of the electron transport chain from PS II.
62
What is the seventh step for how linear electron flow during the light reactions generates ATP and NADPH?
Photoexcited electrons are passed in a series of redox reactions from the primary electron acceptor of PS I down a second electron transport chain through the protein ferredoxin (Fd). (This chain does not create a proton gradient and thus does not produce ATP.)
63
What is the eighth step for how linear electron flow during the light reactions generates ATP and NADPH?
The enzyme NADP+ catalyzes the transfer of electrons from Fd to NADP+. Two electrons are required for its reduction to NADPH. Electrons in NADPH are at a higher energy level than they are in water (where they started), so they are more readily available for the reactions of the Calvin cycle. This process also removes an H+ from the stroma.
64
What is the big picture explanation of light reactions?
The light reactions use solar power to generate ATP and NADPH, which provide chemical energy and reducing power, respectively, to the carbohydrate-synthesizing reactions of the Calvin cycle.
65
What is the cyclic electron flow?
An alternative path for photo-excited electrons which uses photo- system I but not photosystem II. The electrons cycle back from ferredoxin (Fd) to the cytochrome complex then via a plastocyanin molecule (Pc) to a P700 chlorophyll in the PS I reaction-center complex. There is no production of NADPH and no release of oxygen that results from this pro- cess. On the other hand, cyclic flow does generate ATP
66
What does the cyclic electron flow produce?
ATP but not NADPH
67
What happens if you only have photosystem l and not photosystem ll?
You will only produce ATP and not NADPH
68
True or False? Cyclic electron flow can also occur in photosynthetic species that possess both photosystems
True, this includes some prokaryotes, such as the cyanobacteria. as well as the eukaryotic photosynthetic species that have been tested thus far.
69
Plants with mutations that render them unable to carry out cyclic electron flow are capable of growing well in low light, but do not grow well when?
When light is intense. This is evidence for the idea that cyclic electron flow may be photoprotective.
70
True or False? Chloroplasts and mitochondria generate ATP by the same basic mechanism.
True, this is via chemiosmosis
71
What is chemiosmosis?
An electron transport chain pumps protons (H+) across a membrane as electrons are passed through a series of carriers that are progressively more electronegative. An ATP synthase complex in the same membrane couples the diffusion of hydrogen ions down their gradient to the phosphorylation of ADP, forming ATP.
72
What are the differences between photophosphorylation in chloroplasts and oxidative phosphorylation in mitochondria?
Both work by way of chemiosmosis, but in chloroplasts, the high-energy electrons dropped down the transport chain come from water, while in mitochondria, they are extracted from organic molecules (which are thus oxidized). Chloroplasts do not need molecules from food to make ATP; their photosystems capture light energy and use it to drive the electrons from water to the top of the transport chain. In other words, mitochondria use chemiosmosis to transfer chemical energy from food molecules to ATP, whereas chloroplasts use it to transform light energy into chemical energy in ATP.
The spatial organisation of chemiosmosis also differs slightly between chloroplasts and mitochondria.
73
How does the electron transport proteins work for the pumping of H+ ions in the mitochondria?
Proteins in the inner membrane of the mitochondrion pump protons from the mitochondrial matrix out to the intermembrane space, which then serves as a reservoir of hydrogen ions.
74
How does the electron transport proteins work for the pumping of H+ ions in the chloroplasts?
Electron transport chain proteins in the thylakoid membrane of the chloroplast pump protons from the stroma into the thylakoid space (interior of the thylakoid), which func- tions as the H+ reservoir.
75
What is the difference between the mitochondrion and the chloroplasts in terms of the diffusion to the ATP synthase?
In the mitochondrion, protons diffuse down their conc gradient from the intermembrane space through ATP synthase to the matrix, driving ATP synthesis. In the chloroplast, ATP is synthesized as the hydrogen ions diffuse from the thylakoid space back to the stroma through ATP synthase complexes. Thus, ATP forms in the stroma, where it is used to help drive sugar synthesis during the Calvin cycle.
76
When chloroplasts in an experimental setting are illuminated, the pH in the thylakoid space drops to about what and why?
About 5 (the H+ concentration increases), and the pH in the stroma increases to about 8 (the H+ concentration decreases).
77
What is the complete summary of light reactions?
Electron flow pushes electrons from water, where they are at a state of low potential energy, ultimately to NADPH, where they are stored at a state of high potential energy. The light-driven electron flow also generates ATP. Thus, the equipment of the thylakoid membrane converts light energy to chemical energy stored in ATP and NADPH. Oxygen is produced as a by-product. (ATP, NADPH and O2 are produced)
78
True or False? The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
True
79
Is the calvin cycle catabolic or anabolic?
Anabolic
80
What are the differences between the calvin cycle and the citric cycle?
However, the citric acid cycle is catabolic, oxidizing acetyl CoA and using the energy to synthesize ATP, while the Calvin cycle is anabolic, building carbohydrates from smaller molecules and consuming energy.
81
True or False? Carbon enters the Calvin cycle in the form of CO2 and leaves in the form of sugar.
True
82
What does the calvin cycle spend as an energy source and consumes as a reducing power?
The calvin cycle spends ATP as an energy source, and consumes NADH and a reducing power to make a sugar.
83
What is the sugar produced directly from the calvin cycle?
A three-carbon sugar called glyceraldehyde 3-phosphate (G3P). For the net synthesis of one molecule of G3P, the cycle must take place three times, fixing three molecules of CO2—one per turn of the cycle.
84
What are the 3 phases of the calvin cycle?
Carbon fixation, reduction, and regeneration of the CO2 acceptor.
85
What is phase 1 of the calvin cycle?
Carbon Fixation: The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five- carbon sugar. The enzyme that catalyzes this first step is rubisco. (This is the most abundant protein in chloroplasts and is also thought to be the most abundant protein on Earth.) The product of the reaction is a six-carbon intermediate that is short-lived because it is so energetically unstable that it immediately splits in half, forming two molecules of 3-phosphoglycerate (for each CO2 fixed).
86
What is phase 2 of the calvin cycle?
Reduction: Each molecule of 3-phosphoglycerate receives an additional phosphate group from ATP becoming 1,3-bisphosphoglycerate Next, a pair of electrons donated from NADPH reduces 1,3-bisphosphoglycerate, which also loses a phosphate group in the process, becoming glyceraldehyde 3-phosphate (G3P). Specifically, the electrons from NADPH reduce a carboyxl group to the aldehyde group of G3P, which stores more potential energy. G3P is a sugar—the same three-carbon sugar formed in glycolysis by the splitting of glucose. Notice that for every three molecules of CO2 that enter the cycle, there are six molecules of G3P formed, but only one molecule of this three-carbon sugar can be counted as a net gain of carbohydrate because the rest are required to complete the cycle. One molecule exits the cycle to be used by the plant cell, but the other five molecules must be recycled to regenerate the three molecules of RuBP.
87
What is phase 3 of the calvin cycle?
In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle into three molecules of RuBP. To accomplish this, the cycle spends three more molecules of ATP. The RuBP is now prepared to receive CO2 again, and the cycle continues.
88
For the net synthesis of one G3P molecule, the Calvin cycle consumes a total of how many ATP molecules?
9 ATP molecules and 6 molecules of NADPH
89
The G3P spun off from the Calvin cycle becomes the starting material for what?
metabolic pathways that synthesize other organic compounds, including glucose (from two molecules of G3P), the disaccharide sucrose, and other carbohydrates.
90
Can the light reactions or the Calvin cycle alone can make sugar from CO2?
No
91
What is photorespiration?
A respiratory process in many higher plants by which they take up oxygen in the light and give out some carbon dioxide, opposite to the general pattern of photosynthesis.
92
In most plants, initial fixation of carbon occurs via what?
Rubisco the Calvin cycle enzyme that adds CO2 to ribulose bisphosphate.
93
What are C3 plants?
C3 plants are plants in which the initial product of the assimilation of carbon dioxide through photosynthesis is 3-phosphoglycerate, which contains 3 carbon atoms. Rice, wheat, and soy- beans are C3 plants that are important in agriculture.
94
On hot and dry days what is the response from C3 plants?
Their stomata partially closes on hot, dry days, and C3 plants produce less sugar because the declining level of CO2. Rubisco is capable of binding O2 in place of CO2 so as CO2 becomes scarce within the air spaces of the leaf and O2 builds up, rubisco adds O2 to the Calvin cycle instead of CO2. The product splits, and a two-carbon compound leaves the chloroplast. Peroxisomes and mitochondria within the plant cell rearrange and split this compound, releasing CO2. (Photorespiration; opposite to photosynthesis)
95
What is the difference between photorespiration and cellular respiration?
Unlike normal cellular respiration, photorespiration uses ATP rather than generating it
96
What is the difference between photorespiration and photosynthesis?
Unlike photosynthesis, photorespiration produces no sugar. In fact, photorespiration decreases photosynthetic output by siphoning organic material from the Calvin cycle and releasing CO2 that would otherwise be fixed.
97
How can we explain the existence of a metabolic process that seems to be counterproductive for the plant?
According to one hypothesis, photorespiration is evolutionary baggage— a metabolic relic from a much earlier time when the atmosphere had less O2 and more CO2 than it does today. There is also some evidence that photorespiration may provide protection against the damaging products of the light reactions, which build up when the Calvin cycle slows due to low CO2.
98
What are C4 plants?
They preface the Calvin cycle with an alternate mode of carbon fixation that forms a four-carbon compound as its first product. Among the C4 plants important to agriculture are sugarcane and corn, members of the grass family. In C4 plants, there are two distinct types of photosynthetic cells: bundle-sheath cells and mesophyll cells.
99
What are bundle-sheath cells?
Bundle-sheath cells are arranged into tightly packed sheaths around the veins of the leaf
100
What are mesophyll cells?
Between the bundle sheath and the leaf surface are the more loosely arranged mesophyll cells, which, in C4 leaves, are closely associated and never more than two to three cells away from the bundle-sheath cells.
101
In C4 plants the Calvin cycle is preceded by incorporation of what? into organic compounds in the mesophyll cells.
CO2
102
What is the first step of the C4 plant pathway?
In mesophyll cells, the enzyme PEP carboxylase adds CO2 to PEP, forming a four- carbon compound. PEP has
a much higher affinity (attraction) for CO2 than does rubisco and no affinity (attraction) for O2. Therefore, PEP carboxylase can fix carbon efficiently when rubisco cannot—that is, when it is hot and dry and stomata are partially closed, causing CO2 concentration in the leaf to be lower and O2 concentration to be relatively higher.
103
What is the second step of the C4 plant pathway?
The four-carbon compound (such as malate) moves into a bundle-sheath cell via plasmodesmata
104
What is the third step of the C4 plant pathway?
In bundle-sheath cells, CO2 is released and enters the Calvin cycle. The same reaction regenerates pyruvate, which is transported to mesophyll cells. There, ATP is used to convert pyruvate to PEP, which can accept addition of another CO2, allowing the reaction cycle to continue. To generate this extra ATP, bundle-sheath cells carry out cyclic electron flow, In fact, these cells contain PS I but no PS II, so cyclic electron flow is their only photosynthetic mode of generating ATP.
105
What is an advantageous feature of the C4 plants?
They are advantageous in hot regions with intense sunlight, where stomata partially close during the day, and it is in such environments that C4 plants evolved and thrive today
106
Scientists are concerned that increasing CO2 concentration (due to industrial revolution) and temperature may affect what?
C3 and C4 plants differently, thus changing the relative abundance of these species in a given plant community
107
Which type of plant would stand to gain more from increasing CO2 levels?
Rising CO2 levels should benefit C3 plants by lowering the amount of photorespiration that occurs. At the same time, rising temperatures have the opposite effect, increasing photo- respiration.
108
Is C3 or C4 more efficient?
C4 photosynthesis is considered more efficient than C3 photosynthesis because it uses less water and resources.
109
What are CAM plants?
These plants open their stomata during the night and close them during the day, just the reverse of how other plants behave. Closing stomata during the day helps desert plants conserve water, but it also prevents CO2 from entering the leaves. During the night, when their stomata are open, these plants take up CO2 and incorporate it into a variety of organic acids.
110
What is the mode of carbon fixation: crassulacean acid metabolism (CAM)?
is a CO2 fixation pathway that maximizes water‐use efficiency (WUE), compared with the C3/C4 CO2 pathway, which permits CAM plants to adapt to arid environments
111
How do CAM cells work?
The mesophyll cells of CAM plants store the organic acids they make during the night in their vacuoles until morning, when the stomata close. During the day, when the light reactions can supply ATP and NADPH for the Calvin cycle, CO2 is released from the organic acids made the night before to become incorporated into sugar in the chloroplasts.
112
What is the difference between C4 plants and CAM plants?
In C4 plants, the initial steps of carbon fixation are separated structurally from the Calvin cycle, whereas in CAM plants, the two steps occur within the same cell but at separate times.
113
What is the major similarity between C3, C4, and CAM plants?
CAM, C4, and C3 plants all eventually use the Calvin cycle to make sugar from carbon dioxide.
114
What percentage of the organic material made by photosynthesis is consumed as fuel for cellular respiration in plant cell mitochondria?
50%
115
In most plants, carbohydrate is transported out of the leaves to the rest of the plant in the form of what?
Sucrose a disaccharide, the sucrose provides raw material for cellular respiration and a multitude of anabolic pathways that synthesise proteins, lipids, and other products.
116
Plants stockpile the extra sugar by what?
Synthesizing starch, storing some in the chloroplasts themselves and some in storage cells of roots, tubers, seeds, and fruits.
117
True or False? photosynthesis is the process responsible for the presence of oxygen in our atmosphere.
True
118
What happens to the free energy released as electrons are passed from photosystem II to photosystem I through a series of electron carriers?
It excites electrons of the reaction center in photosystem I.
119
How is photosynthesis similar in C4 plants and CAM plants?
In both cases, rubisco is not used to fix carbon initially.
120
Some photosynthetic organisms contain chloroplasts that lack photosystem II, yet are able to survive. The best way to detect the lack of photosystem II in these organisms would be
To test for liberation of O2 in the light.
