Which of the following is the correct order of electron flow in the light reactions of photosynthesis?
answer
H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → NADPH
Electrons flow through the components of the linear electron pathway from water to NADPH.
question
When a pigment molecule in a light-harvesting complex absorbs a photon of light, what happens to its excited-state electron?
answer
The electron falls back to its ground state, while passing its excited-state energy to an electron in a nearby pigment molecule.
The electron itself does not move through the antenna complex pigments, just the energy that excites the next electron.
question
How many electrons at a time are passed between the pigment molecules in the light-harvesting complexes?
answer
0
The excited state energy of the electron passes between pigment molecules, not the electron itself.
question
For every molecule of O2 that is released by photosystem II, _____ H2O molecules are needed, which together pass ____ electrons to the PS II reaction-center complex.
answer
2, 4
Each water molecule donates one oxygen and two electrons. So two water molecules are needed for every molecule of O2 released by PS II, and four electrons are donated to the PS II reaction-center complex. Four protons (H+) are released during the process.
question
Why is it correct to say that the linear electron flow of the light reactions directly captures energy in NADPH but only indirectly captures energy in ATP?
answer
Electrons are directly transferred to NADP+ to form NADPH, but electron flow is used to generate a proton gradient for ATP synthesis. Electrons are not directly transferred to ATP.
NADPH is the product of a redox reaction and directly accepts electrons, but ATP is formed by a phosphorylation reaction that indirectly uses energy from the electron flow.
question
If the Calvin cycle slows down, what will happen to the rate of O2 production in PS II, and why?
answer
O2 production will slow down because less NADP+ will be regenerated in the Calvin cycle.
NADP+ is required as an electron acceptor during linear electron flow of the light reactions. Therefore, if less NADP+ is available because of a slowdown in the Calvin cycle, electron flow in the light reactions will slow down, and less O2 will be produced.
question
photosystem II only
answer
1. oxidation of water
2. reduction of the ETC between the 2 photosystems
question
photosystem I only
answer
1. reduction of NADP+
2. oxidation of ETC between the 2 photosystems
question
both ps II and ps I
answer
1. reduction of primary electron acceptor
2. light absorption
question
water--> P680+
answer
no energy input required
question
P680--> Pq (plastoquinone)
answer
energy input required
question
Pq--> P700+
answer
no energy input required
question
P700-> Fd (ferredoxin)
answer
energy input required
question
Fd--> NADP+
answer
no energy input required
question
in C3 plants the conservation of water promotes...
answer
photorespiration
conserving water simultaneously reduces the amount of CO2 available to the plant
question
in C4 and CAM plants CO2 is fixed in the ________ of mesophyll cells
answer
cytoplasm
question
C4 plants differ from C3 and CAM plants in that C4 plants _____
answer
transfer fixed carbon dioxide to cells in which the Calvin cycle occurs
question
Photosynthesis is a redox reaction. This means that H2O is _____ during the light reactions and CO2 is _____ during the Calvin cycle
answer
oxidized, reduced
(water is oxidized during light reaction) (carbon is reduced during the Calvin cycle)
question
The ultimate source of energy to support most life on Earth is _____
answer
sunlight
question
Which of these equations best summarizes photosynthesis?
answer
6 CO2 + 6 H2O → C6H12O6 + 6 O2
question
where does the Calvin cycle occur?
answer
in the stroma
question
The light reactions of photosynthesis use _____ and produce _____.
answer
water ... NADPH
(NADPH is a reactant in the Calvin cycle)
question
Plants are photoautotrophs. What does this mean?
answer
They use light energy to drive the synthesis of organic molecules from inorganic materials.
question
The photosynthetic membranes are found in the _____ in plant cells
answer
chloroplasts
question
In autotrophic bacteria, where is chlorophyll located?
answer
in infolded regions of the plasma membrane
question
Under what conditions do photosynthesis and cellular respiration occur in most plants?
answer
Photosynthesis occurs only in the light, and cellular respiration occurs in both the dark and the light.
question
The oxygen released by photosynthesis is produced by which of the following processes?
answer
splitting of water molecules
question
Which term describes ATP production resulting from the capture of light energy by chlorophyll?
answer
photophosphorylation
(The excitation of chlorophyll by light energy initiates a chain of events that leads to ATP production)
question
True or false? The chemiosmotic hypothesis states that the synthesis of ATP generates a proton gradient that leads to electron flow through an electron transport chain.
answer
false
(The chemiosmotic hypothesis states that the flow of electrons through an electron transport chain generates a proton gradient that leads to the synthesis of ATP.)
question
According to the chemiosmotic hypothesis, what provides the energy that directly drives ATP synthesis?
answer
proton gradient
question
Which of the following particles can pass through the ATP synthase channel?
answer
protons
question
True or false? The region of ATP synthase that catalyzes the production of ATP from ADP and inorganic phosphate spans the chloroplast membrane.
answer
false
(The region of ATP synthase that catalyzes ATP production protrudes out of, but does not span, the chloroplast membrane; the region that spans the membrane is an ion channel through which protons can pass.)
question
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
ATP will not be produced because there is no ADP and inorganic phosphate in the solution.
question
In the electromagnetic spectrum, the type of radiation that we call visible light occurs between _____.
answer
ultraviolet radiation and infrared radiation
question
Which of the following is a product of the light reactions of photosynthesis?
answer
oxygen, ATP, and NADPH
question
When light strikes chlorophyll molecules, they lose electrons, which are ultimately replaced by _____
answer
splitting water
(the electrons removed from water are transferred to P680)
question
Theodor W. Engelmann illuminated a filament of algae with light that passed through a prism, thus exposing different segments of algae to different wavelengths of light. He added aerobic bacteria and then noted in which areas the bacteria congregated. He noted that the largest groups were found in the areas illuminated by the red and blue light. What did Engelmann conclude about the congregation of bacteria in the red and blue areas?
answer
Bacteria congregated in these areas because these areas had the most oxygen being released.
question
A spaceship is designed to support animal life for a multiyear voyage to the outer planets of the solar system. Plants will be grown to provide oxygen and to recycle carbon dioxide. Since the spaceship will be too far from the sun for photosynthesis, an artificial light source will be needed. What wavelengths of light should be used to maximize plant growth with a minimum of energy expenditure?
answer
a mixture of blue and red light
question
A spaceship is designed to support animal life for a multiyear voyage to the outer planets of the solar system. Plants will be grown to provide oxygen and to recycle carbon dioxide. Since the spaceship will be too far from the sun for photosynthesis, an artificial light source will be needed. Suppose a plant has a unique photosynthetic pigment and the leaves of this plant appear to be reddish yellow. What wavelengths of visible light are absorbed by this pigment?
answer
blue and violet
question
Why are C4 plants able to photosynthesize with no apparent photorespiration?
answer
they use PEP carboxylase to initially fix CO2
question
CAM plants keep stomata closed in the daytime, thus reducing loss of water. They can do this because they _____
answer
fix CO2 into organic acids during the night
question
Which of the following statements correctly describes a distinction between autotrophs and heterotrophs?
answer
Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic.
question
Why are the reaction centers of photosystems composed of several structurally different pigments?
answer
This arrangement enables the plant to absorb light energy of a variety of wavelengths.
question
What happens to the free energy released as electrons are passed from photosystem II to photosystem I through a series of electron carriers?
answer
It is used to establish and maintain a proton gradient.
question
Which molecule is the final electron acceptor for electrons from photosystem I?
answer
NADP+
question
what process produces oxygen? photosynthesis or cellular respiration?
answer
photosynthesis
question
Which set of reactions uses H2O and produces O2?
answer
the light reactions
question
What is the importance of the light-independent reactions in terms of carbon flow in the biosphere?
answer
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
True or false? The light-dependent reactions of photosynthesis use water and produce oxygen.
answer
true
(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
Which of the following molecules is the primary product of photosystem I?
answer
NADPH
question
What is the biological significance of the light-independent reactions of photosynthesis?
answer
They convert carbon dioxide to sugar.
question
Which of the following statements best describes the relationship between the light-dependent and light-independent reactions of photosynthesis?
answer
The light-dependent reactions produce ATP and NADPH, which are then used by the light-independent reactions.
question
Which molecule is regenerated in the regeneration phase of the Calvin cycle? Without regeneration of this molecule, the Calvin cycle would stop.
answer
RuBP
question
Which of the following products of the light reactions of photosynthesis is consumed during the Calvin cycle?
answer
NADPH
(NADPH are used to reduce carbon)
question
Which of the following molecules are products of the light reactions of photosynthesis that are utilized in the Calvin cycle?
answer
ATP and NADPH
question
Where in a plant cell does the Calvin cycle take place?
answer
stroma of the chloroplast
question
Which of the following processes occurs during the Calvin cycle?
answer
regeneration of the CO2 acceptor
question
The reducing power for Calvin cycle reactions is provided by which of the following molecules?
answer
NADPH
question
What is the basic role of CO2 in photosynthesis?
answer
CO2 is fixed or incorporated into organic molecules.
question
Select the most accurate statement describing the basic function of the light reactions of photosynthesis.
answer
The basic function of the light reactions of photosynthesis is the conversion of solar energy to chemical energy.
question
3 stages of the Calvin cycle
answer
carbon fixation, reduction, and regeneration of RuBP
question
Why are plants classified as producers?
answer
Plants are classified as producers because they fix inorganic carbon into organic molecules.
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