Unit 2 (Week 7 Photosynthesis) Flashcards
1
Q
What is the process whereby light energy is captured by plant, algal, or photosynthetic bacterial cells and is used to synthesize organic molecules from CO2 and H2O (or H2S)?
A
Photosynthesis
2
Q
What is the first of two stages in the process of photosynthesis?
A
Light reactions.
During the light reactions, photosystem II and photosystem I absorb light energy and produce ATP, NADPH, and O2.
3
Q
What is the second stage in the process of photosynthesis?
A
Calvin cycle.
During this cycle, ATP is used as a source of energy and NADPH is used as a source of high-energy electrons, driving the synthesis of carbohydrates using CO2.
4
Q
What is a major contributor to the mass and size of plants?
A
CO2
5
Q
What do some photosynthetic bacteria use instead of water for photosynthesis?
A
Hydrogen sulfide (H2S). They release sulfur instead of oxygen.
6
Q
T/F The free-energy change required for the production of 1 mole of glucose from carbon dioxide is endergonic and requires sunlight to drive the synthesis of glucose by making the beginning process exergonic.
A
True.
7
Q
T/F The free-energy change required for the production of 1 mole of glucose from carbon dioxide is endergonic and requires sunlight to drive the synthesis of glucose by making the beginning process exergonic.
A
True.
8
Q
What is the regions on the surface of the Earth and in the atmosphere where living organisms exist?
A
Biosphere
9
Q
What are living organisms categorized as in respect to organic molecules and sustainment?
A
Heterotrophs and Autotrophs
10
Q
What is an organism that cannot produce their own organic molecules by using energy from inorganic sources or light; they must obtain one or more organic compounds from their environment?
A
Heterotroph
11
Q
What is an organism that has metabolic pathways that use energy from either inorganic molecules or light to make organic molecules?
A
Autotroph
12
Q
What is a photoautotroph?
A
An organism that uses the energy from light to make organic molecules from inorganic sources. This includes plants, algae, and some bacterial species such as cyanobacteria.
13
Q
What does life in the biosphere rely on?
A
The key energy cycle that involves the interplay between organic molecules (glucose) and inorganic molecules, namely, O2, CO2, and H2O.
Photosynthesis is a process in which light, CO2, and H2O are used to produce O2 and organic molecules (glucose). The organic molecules are broken down to CO2 and H2O via cellular respiration to supply energy in the form of ATP; O2 is reduced to H2O.
14
Q
What makes a large portion of the Earth’s organic molecules via photosynthesis by reusing CO2 produced by heterotrophs through cellular respiration to make O2?
A
Photoautotrophs.
15
Q
What are semiautonomous organelle found in plant and algal cells that carries out photosynthesis?
A
Chloroplasts
16
Q
What is a photosynthetic green pigment found in the chloroplasts of plants, algae, and some bacteria?
A
Chlorophyll
17
Q
Where does MOST of the photosynthesis in plants occur?
A
The leaves.
18
Q
What is the mesophyll? What is contained within this area located between the two epidermal cell layers of the leaf?
A
The internal tissue of a plant leaf; the site of photosynthesis. The mesophyll cells.
19
Q
Where is water taken up by the plant to allow photosynthesis to occur?
A
The roots.
20
Q
Where does carbon dioxide enter the plant and where oxygen leaves? Where are these pores located?
A
Pores in the plant called stomata (singular, stoma or stomate; from the Greek, meaning mouth)
These pores on located within the epidermal layers of the leaf and act as a “antiport” for oxygen and carbon dioxide.
21
Q
[Review] What parts does the chloroplast consist of within the Mesophyll cell? (8)
A
Outer membrane, intermembrane space, inner membrane, thylakoid and its membrane, thylakoid lumen, granum, and stroma.
22
Q
What is a membrane within the chloroplast that forms many flattened, fluid-filled tubules that enclose a single, convoluted compartment. It contains chlorophyll and is the site where the light-dependent reactions of photosynthesis occurs?
A
Thylakoid membrane
23
Q
What is a flattened, fluid-filled tubule found in cyanobacterial cells and the chloroplasts of photosynthetic protists and plants; the location of the light reactions of photosynthesis?
A
Thylakoid
24
Q
What is the fluid-filled compartment within a thylakoid?
A
Thylakoid lumen
25
What is a structure composed of stacked membrane-bound thylakoids within a chloroplast?
Granum
26
What is the fluid-filled region of the chloroplast between the thylakoid membrane and the inner membrane?
Stroma
27
How is the term photosynthesis derived?
Photo refers to the light reactions that capture the energy from sunlight.
Synthesis refers to the captured energy used to make carbohydrates that occurs in the Calvin cycle.
28
Where do the light reactions occur and Calvin occur specifically?
Light reactions occur at the thylakoid membrane while the Calvin cycle happens in the stroma of the chloroplast.
29
Can the Calvin cycle occur in the dark?
The Calvin cycle can occur in the dark as long as sufficient CO2, ATP, and NADPH are present in the stroma.
30
What does the light reaction create when storing the energy in the form of covalent bonds?
ATP, NADPH, and O2.
31
What provides the needed energy and electrons to drive the Calvin cycle?
The energy intermediates created in the light reaction cycle which are ATP and NADPH.
32
What is NADPH
Nicotinamide adenine dinucleotide phosphate; an energy intermediate that provides the energy and electrons to drive the Calvin cycle during photosynthesis.
33
How many electrons does the electron carrier, NADPH, accept?
2
34
What is the difference between NADH and NADPH?
The presence of an additional phosphate group
35
In regards to the first law of thermodynamics, how does photosynthesis follow this law?
Well, energy cannot be created or destroyed but can be transformed into one form from another.
For photosynthesis, energy in the form of light is sent from the sun to the earth and is captured by a pigment molecule in a photosynthetic organism.
From there, a series of energy transformations occur in which light energy is changed into electrochemical energy and then into energy stored within chemical bonds.
36
What is a type of electromagnetic radiation, so named because it consists of energy in the form of electric and magnetic fields?
Light
37
What is the distance from one peak to the next in a sound wave or light wave?
Wavelength
38
What are all possible wavelengths of electromagnetic radiation, from relatively short wavelengths (gamma rays) to much longer wavelengths (radio waves)?
Electromagnetic spectrum
39
Since visible light is in the range of wavelengths detected by the human eye, what is the length of the wavelength (range)?
Commonly between 380 and 740 nm in length.
40
Which has higher energy, gamma rays or radio waves?
Gamma rays have higher energy than radio waves.
41
What is one of the discrete particles that make up light?
Photons.
A photon is massless and travels in a wavelike pattern. at the speed of light (about 300 million m/sec)
42
T/F Each photon does not contain a specific amount of energy.
False. They have specific amounts.
43
What protects organisms on Earth from some, if not most, of the harmful Sun's ultraviolet (UV) radiation?
The ozone layer.
Gamma rays, x-rays, and UV radiation have very high energy and when molecules absorb such energy, the results can be devastating. This can cause mutations in DNA and lead to cancer.
44
T/F Visible light is much less intense than gamma, x, and UV rays.
True
45
What are the three things that can happen when light comes into contact with something?
It may pass straight through.
It may refract or reflect.
It may be absorbed.
46
What is a molecule that can absorb light energy?
Pigment. Some light waves are absorbed while others are reflected.
Leaves look green to us because of the light energy they reflect back at us in the green region of the visible spectrum.
47
What reflects practically all visible light energy and what absorbs all visible light energy?
White and black objects, respectively.
48
In laymen speak, what does it mean for an atom or molecule to absorb light energy?
Light boosts an electron to a higher energy level.
49
What must an electron receive in order to change energy levels?
The difference of energy of its current orbital and the orbital in which it is going. This specificity of energy is received by a specific photon.
50
T/F Different pigment molecules have a variety of electrons that can be shifted to different energy levels.
True
51
What are the states that involve an electron being boosted by a photon?
The ground state to the excited state (a high energy electron photoexcited)
When this happens, an electron is further from its nucleus which makes is less retrained by the positive nucleus allowing it to become unstable.
52
Describe the four events that can enable a photoexcited electron to become more stable.
To become more stable by dropping down to a lower energy level, a photoexcited electron can release energy in the form of heat, release energy in the form of light, or transfer energy to another electron by resonance energy transfer.
Rather than releasing energy or transferring it to another molecule, an excited electron can be removed from the molecule in which it is unstable and transferred to another molecule where it is stable. When this occurs, the energy in the electron is said to be captured, because the electron does not readily drop down to a lower energy level and release heat or light.
Examples:
For example, on a sunny day, the sidewalk heats up because it absorbs light energy that is released as heat.
Certain organisms, such as jellyfish, possess molecules that make them glow. This glowing is due to the release of light when electrons drop down to lower energy levels, a phenomenon called fluorescence.
53
What is the process previously talked about by which energy (not an electron itself) can be transferred to adjacent pigment molecules during photosynthesis?
Resonance energy transfer.
54
What are the two types of chlorophyll pigments?
Chlorophyll a and chlorophyll b.
55
Where can chlorophyll a be found?
A type of chlorophyll pigment found in plants, algae, and cyanobacteria.
56
Where can chlorophyll b be found?
A type of chlorophyll pigment found in plants, green algae, and some other photosynthetic organisms.
57
What do the two chlorophylls consist of?
A porphyrin ring and a phytol tail.
58
Where is the magnesium ion (Mg2+) bound to?
The center of the porphyrin ring. The electron here is capable of accepting light energy which classifies it as a delocalized electron.
59
What is the function of the phytol tail?
Since it is a hydrocarbon which makes it hydrophobic, it is an anchor for the pigment to the surface of hydrophobic proteins within the thylakoid membrane of chloroplasts.
60
What is a type of photosynthetic or protective pigment found in plastids that imparts a color that ranges from yellow to orange to red?
Carotenoids. Found in many fruits, vegetables, and flowers. In leaves, the more abundant chlorophylls usually mask the colors of carotenoids.
In temperate climates where the leaves change colors, the quantity of chlorophyll in the leaf declines during autumn. The carotenoids become readily visible and produce the yellows, oranges, and reds of autumn foliage.
Car-rot-tin-oids
61
What is a diagram that depicts the wavelengths of electromagnetic radiation that are absorbed by a pigment?
Absorption spectrum.
62
What is the advantage of having different pigment molecules?
Having different pigment molecules allows plants to absorb a wider range of wavelengths of light.
63
What is the rate of photosynthesis plotted as a function of the wavelength of light?
Action spectrum
64
What do the thylakoid membranes of the chloroplast contain in two distinct complexes of proteins and pigment molecules?
Photosystem I (PSI) and photosystem II (PSII)
65
T/F Photosystem II was discovered first but Photosystem I is the initial step of photosynthesis.
False. PSI was the first step discovered but PSII is the initial step in photosynthesis.
66
What is a distinct complex of proteins and pigment molecules in chloroplasts that absorbs light and also generates oxygen from water during the light reactions of photosynthesis?
PSII (photosystem 2)
67
What is a distinct complex of proteins and pigment molecules in chloroplasts that absorbs light during the light reactions of photosynthesis?
PSI (photosystem 1)
68
Are ATP, NADPH, and O2 produced in the stroma or in the thylakoid lumen?
ATP and NADPH are produced in the stroma of the thylakoid while O2 is produced in the thylakoid lumen.
69
When the photon excites an electron causing it to excite from PSII, what is used to replenish the lost electron in the reaction center?
Two molecules of water bind to the water-splitting enzyme in the thylakoid lumen that is attached to PSII.
The splitting of the water molecules creates O2 and 4 H+ ions. The electrons released from oxidized water molecules replenish the electrons that are removed from P680.
70
What is the acceptor of the electron once it leaves PSII?
Plastoquinone (plastic-wi-non). Remember: Ubiquinone (You-Bick-Wi-Noun) is used in animal cells as a electron acceptor in the ETC of ATP creation.
The plastoquinone is reduced and sends the electron to the next membrane complex.
71
[Bonus] What plays a vital role in electron transport chains?
Quinones
72
What happens to the b6-f complex when it receives an electron from the plastoquinone?
It causes the complex to pump protons (H+ ions) into the thylakoid lumen from the stroma of chloroplast.
73
How is ADP and inorganic phosphate phosphorylated into ATP?
The protons must pass through the ATP-synthase channel and released into the stroma. This is known as photophosphorylation.
74
When light is absorbed by PSI, what happens to the electron when it leaves the system?
The reaction center passes the high energy electron to ferredoxin and then through this reduction, the electron is passed to NADP-reductase where it is attached to NADP+ to create NADPH
75
How does the reaction center for PSI replace the loss of an electron it used in NADP-reductase in the creation of NADPH?
PSII sends an electron through the b6-f complex to a small protein called Plastocyanin where it is then transported to PSI.
76
What is another name for the reaction centers in PSII and PSI?
Light-harvesting complex.
77
What are some of the pigment molecules within in PSII that are electron carriers?
P680, Pheophytin (Pp), Qa, and Qb.
78
What is the pigment molecule within PSI where a high-energy electron is removed and then transported to an electron acceptor?
P700
79
How many electrons can the protein called Ferredoxin accept?
2. One electron at a time.
80
What is in the light reactions of photosynthesis, the movement of electrons from PSII to PSI and ultimately to NADP+ to form NADPH?
Linear electron flow
The electrons move linearly from PSII to PSI and ultimately reduce NADP+ to NADPH.
81
What is the key differences between how PSII and PSI source their electrons received by their respective pigment molecules?
An oxidized pigment in PSII called P680 receives an electron from water. By comparison, an oxidized pigment in PSI called P700 receives an electron from the protein Pc. Therefore, PSI does not need to split water to reduce this pigment and does not generate oxygen.
82
What is the process via chemiosmosis by which the light reactions of photosynthesis produce ATP?
Photophosphorylation
83
What are the three ways the gradient in the thylakoid lumen is generated?
The splitting of water places H+ in the thylakoid lumen.
The movement of high-energy electrons along the ETC from photosystem II to photosystem I pumps H+ into the thylakoid lumen.
The formation of NADPH consumes H+ in the stroma.
84
Now, how are the steps of the light reactions of photosynthesis producing products: O2, NADPH, and ATP?
O2 is produced in the thylakoid lumen by the oxidation of water by photosystem II. Two electrons are removed from water, producing 2 H+ and 1/2 O2. The two electrons are transferred to P680 molecules.
NADPH is produced in the stroma using high-energy electrons that are first boosted to a higher energy level in photosystem II and then are boosted a second time in photosystem I. Two high-energy electrons and one H+ are transferred to NADP+ to produce NADPH.
ATP is produced in the stroma via ATP synthase that uses an H+ electrochemical gradient.
85
T/F The electron flow within photosynthesis produces roughly the same amount of NADPH and ATP.
True.
However, as we will see later, the Calvin cycle uses more ATP than NADPH.
86
During photosynthesis, what is a pattern of electron flow in the thylakoid membrane that is cyclic and generates only ATP? Otherwise known as, cyclic electron flow.
Cyclic photophosphorylation.
(1) the path of electrons is cyclic, (2) light energizes the electrons, and (3) ATP is made via the phosphorylation of ADP.
87
Why does cyclic photophosphorylation provide an advantage to a plant over using only linear electron flow?
How does cyclic photophosphorylation help create more ATP than NADPH?
Linear electron flow produces equal amounts of ATP and NADPH. However, plants usually need more ATP than NADPH. Cyclic photophosphorylation allows plants to make just ATP, thereby increasing the relative amount of ATP.
As electrons travel in this cyclic route, they release energy, and some of this energy is used to transport H+ into the thylakoid lumen. This resulting H+ gradient drives the synthesis of ATP via ATP synthase. When there is low NADP+ and high NADPH, this cycle is favored since there is enough NADPH to power the Calvin cycle later. Linear electron flow is favored when NADPH is low and NADP+ is high. Cyclic is also favored when ATP is low.
88
What are genes derived from the same ancestral gene that have accumulated random mutations that make their sequences slightly different?
Homologous genes
89
Explain why the three-dimensional structures of cytochrome b and cytochrome b6 are very similar.
Because these two proteins are homologous, this means that the genes that encode them were derived from the same ancestral gene. Therefore, the amino acid sequences of these two proteins are expected to be very similar, though not identical. Because the amino acid sequence of a protein determines its structure, two proteins with similar amino acid sequences would be expected to have similar structures.
Homologous proteins cytochrome b6 in chloroplasts and cytochrome b in mitochondria both donate electrons to another protein within their complexes, cytochrome f or cytochrome c1 respectively.
90
Explain why the three-dimensional structures of cytochrome b and cytochrome b6 are very similar.
Because these two proteins are homologous, this means that the genes that encode them were derived from the same ancestral gene. Therefore, the amino acid sequences of these two proteins are expected to be very similar, though not identical. Because the amino acid sequence of a protein determines its structure, two proteins with similar amino acid sequences would be expected to have similar structures.
Homologous proteins cytochrome b6 in chloroplasts and cytochrome b in mitochondria both donate electrons to another protein within their complexes, cytochrome f or cytochrome c1 respectively.
91
[8.3 Molecular Features of Photosystems]
| What are the two main components of PSII and PSI?
Light-harvesting complex and a reaction center.
92
What is a component of PSII and PSI composed of several dozen pigment molecules that are anchored to proteins in the thylakoid membrane of a chloroplast?
Light-harvesting complex.
93
What is the role of the light-harvesting complexes?
To capture light which is done by boosting an electron to a higher energy level.
94
What is important about resonance energy transfer when a pigment within the light-harvesting complex has an electron boosted to another energy level?
The energy (not the electron itself) is transferred to adjacent pigment molecules and may be transferred many times until it is eventually transferred to a special pigment.
95
What is the special pigment molecule in PSII where the energy is transferred to in the beginning stages of linear electron flow? What about the special pigment in PSI?
Why are these pigments named the way they are?
P680. P700.
P = pigment; 680 and 700 are the wavelengths of light they can directly absorb in nanometers.
96
Where are the special pigments in PSII and PSI located?
In the reaction center.
97
What is used to denote when P680 has an electron excited?
How is P680 more commonly excited?
An asterisk *
By resonance energy transfer.
98
What is another name for the light-harvesting complex?
The antenna complex because it acts like an antenna that absorbs energy from light and funnels that energy to P680 in the reaction center.
99
T/F High-energy (photoexcited) electrons in pigment molecule are very stable.
False. They are very unstable.
100
What is the chemical formula for P680 that allows it to release its high energy electron and change its chemical bond?
P680* ---> P680+ + e-
101
What is the molecule to which a high-energy electron from an excited pigment molecule such as P680* or P700* is transferred during photosynthesis?
The primary electron acceptor. This acceptor becomes reduced and stable.
102
What prevents the electron from losing energy in the form of light or heat when it is transferred from the a pigment molecule such as P680 to the primary electron acceptor?
The speed. It happens in less than a few picoseconds which is equal to one-trillionth of a second, or 10 ^-12.
103
What is the name of the primary electron acceptor in PSII?
Pheophytin. This energy is then used to produce energy intermediates such as ATP and NADPH.
104
After the high energy electron is transferred to pheophytin, what needs to happen with P680+?
The electron must be replaced so P680 can function again.
105
What is the chemical reaction for the oxidation of water to donate electrons to P680?
H2O --> 2 H+ + 1/2 O2 + 2 e-
2 P680+ + 2 e- --> 2 P680
106
What results in the oxidation of water which is used by many organisms for cellular respiration where PSII is the only known protein complex capable of completing?
The creation and release of O2 into the atomosphere.
107
T/F Electrons Vary in Energy as They Move from Photosystem II to Photosystem I to NADP+
True
108
What is a model depicting the series of energy changes of an electron during the light reactions of photosynthesis. The electron absorbs light energy twice, resulting in an energy curve with a zigzag shape?
Z scheme
109
During its journey from photosystem II to NADP+, at what point does an electron have the highest amount of energy?
An electron has the highest amount of energy just after its energy has been boosted by light in photosystem I.
110
What has the lowest energy in the z scheme of the linear electron flow?
An electron on a nonexcited pigment molecule in PSII.
111
[8.4 Calvin Cycle Begins]
| What is the second phase of photosynthesis?
The Calvin cycle
112
Where does the Calvin cycle occur in plants and algae and where does it occur in photosynthetic bacteria?
For plants and algae, this cycle occurs in the stroma. In photosynthetic bacteria, it occurs in the cytoplasm of the cell.
113
What does the Calvin cycle take from the atmosphere and incorporate the carbon into organic molecules, namely, carbohydrates?
CO2
114
Why are carbohydrates so critical? (2)
- They provide the precursors to make organic molecules and macromolecules of nearly all living things.
- The storage of energy.
115
What is used as energy when it is dark outside in plants?
The carbohydrates that have been created and stored through photosynthesis are used as a source of energy.
116
What is another name for the Calvin cycle?
The Calvin-Benson cycle
117
T/F The Calvin cycle requires a massive amount of energy.
True. For every 6 carbon dioxide molecules that are incorporated into a carbohydrate such as glucose (C6H12O6), 18 ATP molecules are hydrolyzed and 12 NADPH molecules are oxidized.
118
What is the reaction formula for the Calvin cycle energy use?
6 CO2 + 12 H2O --> C6H12O6 + 6 O2 + 6 H2O
119
What is a common misconception about the Calvin cycle and glucose?
Glucose isn't really a product of photosynthesis because it does not directly create it.
Rather, it creates glyceraldehyde-3-phosphate, which are starting materials for the synthesis of glucose and other molecules, including sucrose.
120
When glucose is converted to either starch or sucrose, where do they go?
Starches are created and stored in the chloroplast for later use while sucrose can be transported to other parts of the plant.
121
What are the three phases of the Calvin cycle?
1. Carbon fixation
2. Reduction and carbohydrate production
3. Regeneration of ribulose bisphosphate (RuBP)
122
Why is NADPH needed during this cycle?
NADPH reduces organic molecules and makes them more able to form C─C and C─H bonds.
123
[Phase 1] What is the process in which carbon from inorganic CO2 is incorporated into an organic molecule such as a carbohydrate?
Carbon fixation.
The fixation is to the 5-carbon sugar, RuBP.
6 RuBP and 6 CO2 molecules.
124
Why is the term fixation used?
The carbon has been removed from the atmosphere and incorporated into an organic molecule that is not a gas.
125
What is the product of carbon fixation?
Two molecules of 3-phosphoglycerate or 3PG.
126
What enzyme catalyzes the 6-carbon molecule into the two separate 3PG?
RuBP carboxylase/oxygenase, or rubisco.
Rubisco = The enzyme that catalyzes the first step in the Calvin cycle, in which CO2 is incorporated into an organic molecule.
127
What is the most abundant protein in chloroplasts and perhaps the most abundant protein on Earth which underscores the massive amount of carbon fixation that happens in the biosphere?
Rubisco.
128
[Phase 2] What is used to convert 3PG to 1,3-BPG (1,3-bisphosphoglycerate)?
12 molecules of ATP
129
What is used to reduce 1,3-BPG to G3P (glyceraldehyde-3-phosphate) that has three carbon atoms that has a C-H bond versus a C-O bond in BPG?
12 molecules of NADPH
130
Why does the C-H bond result?
Because, two electrons are used to reduce 3PG from a NADPH molecule which results in NADP+, Pi, and H+.
The C-H bonds stores more energy and enables the G3P to be ready to form larger organic molecules such as glucose.
131
How many G3P molecules are made at the end of phase 2 and how many are actually used in carbohydrate synthesis?
12 molecules of G3P are created.
2 molecules of G3P are used in carbohydrate production while the other 10 G3P molecules are needed in the next phase of the Calvin cycle to regenerate RuBP.
132
[Phase 3 - Regeration for RuBP] How many molecules of ATP are used to convert 10 G3P molecules into 6 RuBP (Ribulose bisphosphate) 5-carbon molecules?
6 molecules of ATP
133
Since 6 molecules of RuBP have been regenerated, what has this allowed the Calvin cycle to do?
It allows the 5-carbon molecules to become acceptors of CO2 again.
134
Why can you not directly link CO2 molecules to form the larger molecules like carbohydrates?
The number of electrons that are around the carbon atoms. They are considered electron poor and oxygen is very electronegative which monopolizes the electrons it shares with other atoms.
By comparison, in an organic molecule, the carbon atom is electron-rich. This is done by reducing the carbon atom with energy from ATP and the donation of high-energy electrons from NADPH.
135
What really allows the C-H and C-C bonds to form?
The calvin cycle combines less electronegative atoms with carbon atoms which allows this bonds to form and further allowing the Carbon atom to be the more electronegative atom in the molecule.
136
What was the purpose of the study conducted by Calvin and his colleagues?
The researchers were attempting to determine the biochemical pathway of the process of carbohydrate synthesis via photosynthesis. The researchers wanted to identify different molecules produced over time to determine the steps of the biochemical pathway.
137
In Calvin’s experiment shown in Figure 8.14, why did the researchers use 14C-labeled CO2? Why did they examine samples taken after several different time periods? How were the different molecules in the samples identified?
The purpose for using 14C-labeled CO2 was to label the different carbon molecules produced during the biochemical pathway. The researchers could “follow” the carbon molecules from the radiolabeled CO2 that were incorporated into the organic molecules during photosynthesis. The radioactive isotope provided the researchers with a method of labeling the different molecules. The purpose of the experiment was to determine the steps in the biochemical pathway of photosynthesis. By examining samples from different times after the introduction of the labeled carbon source, the researchers were able to determine which molecules were produced first and, thus, distinguish products of the earlier steps of the pathway from products of later steps of the pathway. The researchers used two-dimensional paper chromatography to separate the different molecules from each other. After being separated, the different molecules were identified by various chemical methods.
138
Interpret the results of Calvin’s study.
Calvin and his colleagues were able to determine the biochemical process that incorporates CO2 into organic molecules during photosynthesis. The researchers were able to identify the biochemical steps and the molecules produced at these steps of what is now called the Calvin cycle.
139
[8.5 Variations in Photosynthesis]
| What envrironmental conditions alter the way in which the Calvin cycle operates?
Conditions such as temperature, water availability, and light intensity.
140
What is a plant that adds CO2 to RuBP to produce 3PG, a three-carbon molecule?
C3 plants
141
[Bonus] Approximately how many plants on Earth are C3 plants?
About 90%.
142
What have researchers discovered about the active site of rubisco in reference to its affinity.
It can accept O2 but its affinity for CO2 is 10-fold higher.
143
When a plant uses O2 to attach to RuBP, what is created instead of 2 molecules of 3PG?
One molecule of 3PG is created and a two-carbon molecule called phosphoglycolate.
144
What happens to this two-carbon molecule?
It is dephosphorylated to glycolate and released from the chloroplast and then eventually oxidized in peroxisomes and mitochondria to produce an organic molecule plus a molecule of CO2.
RuBP + O2 --> 3PG + phosphoglycolate
Phosphoglycolate --> Glycolate --> --> Organic molecule + CO2
145
What is the metabolic process occurring in C3 plants when the enzyme rubisco combines with O2 instead of CO2 and produces only one molecule of 3PG instead of two, thereby reducing photosynthetic efficiency?
Photorespiration. It releases the CO2 which inhibits plant growth.
146
Where does photorespiration most likely to occur?
When plants are exposed to hot and dry environments.
147
What closes instead of remaining open in plants when photorespiration happens?
The stomata. This prevents CO2 from entering the leaf and prevents O2 from being released into the atmosphere.
148
What percentage of photosynthetic work is reversed by the process of photorespiration because of hot or dry environmental conditions?
25-50%. This process may be a protective mechanism to prevent damage to the plant via highly toxic oxygen-containing molecules such as free radicals.
149
What is a plant that uses PEP carboxylase to initially fix CO2 into a four-carbon molecule and later uses rubisco to fix CO2 into simple sugars; this mechanism is an adaptation to hot, dry environments?
C4 plant. The first product in fixation is not 3PG, a 3 carbon molecule, but rather 4 carbon molecule called oxaloacetate! This has occurred in sugarcane.
Remember: this process of created oxaloacetate is what happens in the citric acid cycle.
150
What is the pathway sometimes called in respect to the molecule being produced by C4 plants as oxaloacetate?
The Hatch-Slack pathway.
151
What makes the leaf structure in C4 plants different that C3 plants?
The interior of leaves have two cell organization that is composed of mesophyll and bundle-sheath cells.
152
What happens when CO2 enters the stomata on the leaves of a C4 plant?
The enzyme PEP carboxylase attaches CO2 to phosphenolpyruvate (PEP), a three carbon molecules, to produce oxaloacetate, a four carbon molecule.
153
What does PEP carboxylase not recognize which then does not promote photorespiration when CO2 is low and O2 is high but continues to fix CO2?
It does not recognize oxygen.
154
How does the cellular arrangement in C4 plants minimize photorespiration?
The arrangement of cells in C4 plants makes the level of CO2 high and the level of O2 low in the bundle-sheath cells.
155
After oxaloacetate is created, what is it convertated to?
Malate. It is then broken down into pyruvate and CO2.
The pyruvate is then sent back to the mesophyll cell from the bundle-sheath cell where it is converted to PEP via ATP. This helps rejuvenate the cycle in the mesophyll cell.
156
Why does the CO2 concentration remain high in the bundle-sheath cell?
Because the mesophyll cell continues to pump pyruvate into the cell which then continues to create CO2.
Additionally, the mesophyll cell shields the bundle-sheath cell from high concentrations of O2 which further increase the concentration of CO2 in the bundle-sheath cell.
157
What are the primary difference between C3 and C4 plants?
C4 plants have an advantage by conserving water because of partially closed stomata and they minimize photorespiration but require ATP to regenerate PEP from pyruvate.
C3 plants have the edge in cooler climates because they can fix CO2 with less energy.
158
What are C4 plants that open their stomata at night to take up CO2?
CAM plants. Stands for Crassulacean Acid Metabolism.
159
What are CAM plants where this discovery was found?
Water-storing plants such as succulents like cacti, bromeliads (include pineapple), and sedums.
To avoid water loss, CAM plants keep their stomata closed during the day and open them at night, when it is cooler and the relative humidity is higher.
160
Where does photosynthesis occur in CAM plants and how is it temporally active?
Photosynthesis occurs completely in the mesophyll cells but the synthesis of the C4 molecule and Calvin cycle occur at different times.
161
What are the advantages for C3, C4, and CAM plants?
When there is plenty of moisture and it is not too hot, C3 plants are more efficient. However, under hot and dry conditions, C4 and CAM plants have the advantage because they lose less water and avoid photorespiration.
162
What are the advantages for C3, C4, and CAM plants?
When there is plenty of moisture and it is not too hot, C3 plants are more efficient. However, under hot and dry conditions, C4 and CAM plants have the advantage because they lose less water and avoid photorespiration.
163
The water necessary for photosynthesis
is split into H2 and O2.
is directly involved in the synthesis of carbohydrates.
provides the electrons to replace those lost in photosystem II.
provides the H+ needed to synthesize G3P.
does none of the above.
C
164
In PSII, P680 differs from the pigment molecules of the light-harvesting complex in that it
is a carotenoid.
absorbs light energy and transfers that energy to other molecules via resonance energy transfer.
transfers an excited electron to the primary electron acceptor.
transfer an excited electron to O2.
acts like ATP synthase to produce ATP.
C
165
The cyclic electron flow that occurs via photosystem I produces
NADPH.
oxygen.
ATP.
all of the above.
a and c only.
C
166
During linear electron flow, the high-energy electron from P680*
eventually moves to NADP+.
becomes incorporated in water molecules.
is pumped into the thylakoid space to drive ATP production.
provides the energy necessary to split water molecules.
falls back to the low-energy state in photosystem II.
A
167
During the first phase of the Calvin cycle, carbon dioxide is incorporated into ribulose bisphosphate (RuBP) by
oxaloacetate.
rubisco.
RuBP.
quinone.
G3P.
B
168
The NADPH produced during the light reactions is necessary for
the carbon fixation phase, which incorporates carbon dioxide into an organic molecule during the Calvin cycle.
the reduction phase, which produces carbohydrates in the Calvin cycle.
the regeneration of RuBP of the Calvin cycle.
all of the above.
a and b only.
B
169
The majority of the G3P produced during the reduction and carbohydrate production phase is used in making
glucose.
ATP.
RuBP to continue the cycle.
rubisco.
all of the above.
C
170
Photorespiration
is the process in which plants use sunlight to make ATP.
is an inefficient way that plants can produce organic molecules by using O2 and releasing CO2.
is a process that plants use to convert light energy to NADPH.
occurs in the thylakoid lumen.
is the normal process of carbohydrate production in cool, moist environments.
B
171
Photorespiration is avoided by C4 plants because
these plants separate the formation of a four-carbon molecule from the rest of the Calvin cycle in different cells.
these plants carry out only anaerobic respiration.
the enzyme PEP carboxylase functions to maintain high CO2 concentrations in the bundle-sheath cells.
all of the above.
a and c only.
E
172
Plants commonly found in hot and dry environments that carry out carbon fixation at night are
oak trees.
C3 plants.
CAM plants.
all of the above.
a and b only.
C
173
What are the two stages of photosynthesis? What are the key products of each stage?
The two stages of photosynthesis are the light reactions and the Calvin cycle. The key products of the light reactions are ATP, NADPH, and O2. The key product of the Calvin cycle is carbohydrates. The initial product is G3P, which is used to make sugars and other organic molecules.
174
What is the function of NADPH in the Calvin cycle?
NADPH is used during the reduction phase of the Calvin cycle. It donates its electrons to 1,3-BPG.
175
At the level of the biosphere, what is the role of photosynthesis in the utilization of energy by living organisms?
At the level of the biosphere, the role of photosynthesis is to incorporate carbon dioxide into organic molecules. These organic molecules can then be broken down, by autotrophs and by heterotrophs, to make ATP. The organic molecules made during photosynthesis are also used as starting materials to synthesize a wide variety of organic molecules and macromolecules that are made by cells.
176
The process by which plants capture light energy and use it to synthesize glucose and other organic molecules is called
Photosynthesis
177
Photosynthesis is divided into two stages: the ______
| reactions and the ________cycle.
light; calvin
178
The energy required for the synthesis of glucose from carbon dioxide ultimately comes from _________
sunlight
179
Which of the following organisms can carry out photosynthesis?
Algae
Bacteria
Plants
180
What is the general equation for photosynthesis?
Multiple choice question.
CO2 + 2H2A + light energy → 2 CH2O + A2
CO2 + 2H2A + light energy → CH2O + A2 + H2O
CO2 + 2H2A →2CH2O + ATP
CO2 + 2H2A + light energy → CH2O + H2O
CO2 + 2H2A + light energy → CH2O + A2 + H2O
181
What happens during photosynthesis?
Multiple choice question.
Plants capture energy from sunlight and convert the energy into glucose.
Plants convert glucose into oxygen.
Plants use energy from the sun to synthesize chlorophyll.
Plants capture energy from sunlight and use it to synthesize organic molecules.
Plants capture energy from sunlight and use it to synthesize organic molecules.
182
In the generalized equation for photosynthesis, the transfer of electrons occurs such that CO2 is ________ and H2A is ________.
.
reduced; oxidized
183
What are the two stages of photosynthesis?
Multiple select question.
Cellular respiration
Calvin cycle
Light reactions
Krebs cycle
Oxygen reactions
Calvin cycle
Light reactions
184
In photosynthesis, glucose is synthesized from CO2. This reaction is ______.
Multiple choice question.
spontaneous
an oxidation reaction
endergonic
exergonic
Endergonic
185
Sunlight enables the synthesis of glucose from carbon dioxide by providing the _____________
that is necessary for the process.
Energy
186
True or false: Photosynthesis occurs only in plants.
True false question.
True
False
False. Algae and bacteria too.
187
According to the general equation for photosynthesis, CO2+ 2H2O+ light energy → ________ + _________ + _____________
CH2O, O2, H2O
188
During photosynthesis, CO2 is reduced to produce ______.
Multiple choice question.
ATP
glucose
water
O2
Glucose.
Not oxygen because oxygen is from the oxidation of H2O
189
What molecule is reduced during the process of photosynthesis?
Multiple choice question.
Oxygen
ATP
CO2
Water
CO2
190
Organism that can synthesize organic molecules from inorganic molecules are called __________
, while those that must consume food to obtain organic molecules are termed ___________.
Autotrophs and Heterotrophs
191
True or false: The synthesis of glucose from carbon dioxide is an exergonic reaction.
True false question.
True
False
False
192
Plants appear green because they contain:
Multiple choice question.
rubisco
chlorophyll
carotenoids
chlorophyll
193
The reactions of the Calvin cycle occur in the ______.
Multiple choice question.
thylakoid membrane
plasma membrane
thylakoid lumen
stroma
cytoplasm
stroma
194
What is the product of the oxidation of water during photosynthesis?
Multiple choice question.
H2O2
ATP
Glucose
O2
CO2
O2
195
Which of the following are products of the light reactions?
Multiple select question.
Carbohydrates
NADPH
CO2
O2
ATP
NADP+
NADPH
O2
ATP
196
The green color of plants is due primarily to the absorptive properties of the pigment _________ found in the chloroplasts.
chlorophyll
197
In photosynthesis, the light reactions convert ___________ energy into __________
energy stored in covalent bonds.
light; chemical
198
What energy conversion occurs during photosynthesis?
Multiple choice question.
Chemical energy is converted to electrochemical energy, which is converted to chemical energy.
Light energy is converted to electrochemical energy, which is converted to chemical energy.
Light energy is converted to chemical energy, which is converted to carbohydrate energy.
Electron transport energy is converted into a biological battery.
Light energy is converted to electrochemical energy, which is converted to chemical energy.
199
Where do the light reactions occur?
Multiple choice question.
In the cell wall
In the stroma
In the inner membrane of a chloroplast
In the thylakoid membrane
In the thylakoid membrane
200
Why is light considered a form of electromagnetic radiation?
Multiple choice question.
Because it responds to magnetic stimuli.
Because it is polarized.
Because it consists of both electric and magnetic energy.
Because light and magnetic waves can bend.
Because it consists of both electric and magnetic energy.
201
During photosynthesis, CO2 is reduced to produce ______.
Multiple choice question.
ATP
O2
glucose
water
glucose
202
The wavelength of visible light is ______.
Multiple choice question.
a single wavelength
between 1-100 nm
between 545-833 nm
between 380-740 nm
between 380-740 nm
203
The light reactions of photosynthesis produce three chemical products: _______, ________________, and ____________
O2, ATP, NADPH
204
Question Mode
True or False Question
True or false: All photons contain the same amount of energy.
True false question.
True
False
False
205
What is the purpose of the light reactions of photosynthesis?
Multiple choice question.
The synthesis of glucose and other carbohydrates
The conversion of light energy to chemical energy
The fixation of carbon
The conversion of light energy to chemical energy
206
A molecule that can absorb light energy is called a(n) ______.
Multiple choice question.
photon
pigment
electromagnet
spectrum
pigment
207
In photosynthesis, light energy is converted to _________ energy, which in turn is converted to ________ energy in a sugar molecule.
Electrochemical; chemical
208
Light is a type of ______ radiation because it consists of energy in the form of electric and magnetic fields.
electromagnetic
209
Why are leaves green?
Multiple choice question.
They transform other colors of light to green.
They absorb green light.
They reflect green light.
They reflect green light.
210
The human eye can detect light wavelengths in the range of the visible spectrum, which is between ___________ and ________ nm.
380-740
211
Green plants utilize ________ a and b to absorb light energy in photosynthesis.
Chlorophylls
212
Every photon contains a specific amount of ____
energy
213
The ___________ membrane of the chloroplast contains two independent, light capturing complexes of proteins and pigments called photosystems I and II.
Thylakoid
214
A pigment is a molecule that can ______.
Multiple choice question.
inhibit light
absorb light
create light
absorb light
215
As water is oxidized during photosynthesis, the pH of the thylakoid lumen ______.
Multiple choice question.
decreases
does not change
increases
Decreases
216
In the light reactions, both photosystems absorb and capture light energy in the form of excited electrons; however PSII is able to oxidize ___________
, which results in the production of oxygen.
Water
217
Homologous genes have similarity to one another because they are ______.
Multiple choice question.
expressed at the same time
found in similar tissues
derived from a similar organism
derived from the same ancestral gene
derived from the same ancestral gene
218
Which of the following are components of both PSI and PSII?
Multiple select question.
A reaction center
NADP+ reductase
An ATP synthase
A light harvesting complex
A reaction center
A light harvesting complex
219
The electron transport chain directly associated with PSII is used to generate ______, while the electron transport chain directly associated with PSI is used to generate ______.
oxygen; water
ATP; NADPH
water; NADPH
ATP; oxygen
NADPH; ATP
ATP; NADPH
220
The splitting of water in photosystem II results in the production of ____________ gas.
O2
221
In plants and algae, the Calvin cycle occurs in the ______ of chloroplasts.
Multiple choice question.
membrane
grana
stroma
matrix
stroma
222
In the light reactions, both photosystems absorb and capture light energy in the form of excited electrons; however PSII is able to oxidize __________
, which results in the production of oxygen.
Water
223
What is the origin of the carbons in a carbohydrate generated by photosynthesis?
Multiple choice question.
Nutrients taken up from the soil
Water in the cells
Water taken up through xylem elements
Carbon dioxide in the atmosphere
Carbon dioxide in the atmosphere
224
The photosynthetic light reactions are composed of a series of ______.
Multiple choice question.
energy transfers
photosystems
pigment molecules
energy transfers
225
Which of the following is the primary output of the Calvin cycle?
Multiple choice question.
Starch
Glucose
Glyceraldehyde-3-phosphate
Ribulose biphosphate
Glyceraldehyde-3-phosphate
226
The Calvin cycle is affected by certain environmental conditions, including light intensity, ____ availability, and ______________
Water; temperature
227
What happens during photorespiration?
Multiple choice question.
Light stimulates mitochondria to consume O2 and produce CO2.
Rubisco attaches O2 to RuBP, and CO2 is produced.
Light energy is used to oxidize glucose, resulting in the production of CO2.
Rubisco attaches O2 to RuBP, and CO2 is produced.
228
Which of the following are products of the light reactions of photosynthesis that are used as reactants in the Calvin cycle?
Multiple select question.
ATP
Carbohydrates
CO2
NADPH
O2
ATP
NADPH
229
In some plants, carbon fixation yields a four-carbon molecule instead of 3GP as the first product. Such plants are known as __________
plants.
C4 Plants
230
How do CAM plants avoid water loss?
Multiple choice question.
CAM plants live only in moist, cool areas.
CAM plants are succulents, so they contain such a high percentage of water that the sheer amount of water in the system prevents evaporation.
CAM plants close their stomata during the day and open them at night.
CAM plants have a tap root, which replaces water as quickly as it is lost.
CAM plants close their stomata during the day and open them at night.
231
Which of the following conditions affect the way the Calvin cycle operates in photosynthetic organisms?
Multiple select question.
Light intensity
Temperature
The presence of herbivores
Water availability
Light intensity
Temperature
Water availability
