CH 7 BIOL
Why is water required for the light reactions of photosynthesis?
To replace the electrons lost from P680
The ______ scheme describes the energy transitions of electrons as they move through the ______ reactions.
Z; light
The diagram pictured here shows a(n) ______ spectrum for ______.
absorption; individual pigments
The picture depicts a(n) _____ spectrum of photosynthesis.
action
A key difference between linear electron flow and cyclic electron flow is that in cyclic electron flow, electrons are ultimately transferred:
back to PSI
Carbohydrates are very important to plant cells because they:
can be used as an energy reserve form the building block for many organic macromolecules
Sequence the phases of the Calvin cycle from first (on top) to last:
carbon fixation, reduction and carbohydrate production, regeneration of ribulose bisphosphate
When the level of NADP+ is low, ____ electron flow is favored, while when NADP+ levels are high, ____electron flow is favored.
cyclic; linear
In CAM plants, the Calvin cycle occurs:
during the day
NADP+ reductase transfers two ____ and one ____ to NADP+ to generate NADPH.
electro9ns; H+
In the visible spectrum, light energy may be absorbed by boosting _____ to higher atomic energy levels, sometimes called energy shells.
electrons
In photosynthesis, glucose is synthesized from CO2. This reaction is:
endergonic
When an electron absorbs energy, it becomes ___
excited
During photosynthesis, CO2 is reduced to produce
glucose
Living organisms that are not plants depend on photosynthesis because photosynthesis produces: (1) organic molecules such as ____that can be used for nourishment; and (2) the ____gas that makes up a large portion of the Earth's atmosphere.
glucose; O2
In photosystem II, ____-energy electrons are transferred from P680* to pheophytin, and _____-energy electrons are transferred to P680+ to produce P680.
high; low
According to the Z-scheme, electrons:
increase and decrease their energy as they move through the light reactions
The thylakoid membrane is the location of the _____reactions of photosynthesis.
light
Roughly equal amounts of NADPH and ATP are generated in
linear electron flow
In photosynthesis, during ______ electron flow, electrons are ultimately accepted by NADP+. During ______ electron flow, electrons are instead transferred back to photosystem I.
linear; cyclic
Cyclic electron flow is favored when the level of NADP+ is ______, or when ATP levels are ______, while linear electron flow is favored when NADPH is ______.
low; low; low
In C4 plants, CO2 is combined with PEP to produce oxaloacetate. The oxaloacetate is then converted to:
malate
Where are chloroplasts found in a leaf?
mesophyll
Within a leaf, the cells that contain chloroplasts are found in the tissue known as
mesophyll
During photosynthesis, water is:
oxidized
A photon of light has properties of both
particle and a wave.
After leaving P680, a high-energy electron is transferred to _______, which diffuses away from the reaction center.
pheophytin, then to QA, and finally to QB
For an electron to absorb light energy, it must absorb a(n) _____ that contains enough energy to overcome the energy difference between the orbital the electron is in, and the one to which it will be boosted.
photon
The synthesis of ATP using light as the ultimate energy source is called:
photophosphorylation
P680 is located within the reaction center of:
photosystem II
In a chlorophyll molecule, an excited electron can follow a path around several atoms in the ____Blank 1 photonic , Incorrect Unavailable ring, meaning it is delocalized, and thus able to absorb light energy.
porphyrin
In a chlorophyll molecule, an excited electron can follow a path around several atoms in the ______ ring, meaning it is delocalized, and thus able to absorb light energy.
porphyrin
The reaction center quickly transfers an electron from P680 to the ____ ____ acceptor
primary electron acceptor
Leaves appear green because they ____ green light.
reflect
CO2 and H2O are produced during cellular ____ and consumed during the process of ____
respiration; photosynthesis
RuBP carboxylase/oxygenase, also known as ____, is the most abundant protein in chloroplasts.
rubisco
What is the most abundant protein found in chloroplasts?
rubisco
The pores in the surface of a leaf that can participate in gas exchange are called
stomata
The fluid-filled region of the chloroplast between the thylakoid membrane and the inner membrane is known as the
stroma
The reactions of the Calvin cycle occur in the:
stroma
The glucose that is made by plant cells can be converted to other carbohydrates, including:
sucrose starch
Following QB, excited electrons pass down an electron transport chain that is arranged according to:
the electronegativity of electron carriers
The splitting of water, the transfer of high energy electrons from PSII to PSI, and the generation of NADPH all contribute to
the generation of a H+ gradient.
Where do the light reactions occur?
thylakoid membrane
Where is the light-harvesting complex found?
thylakoid membrane
True or false: Photoautotrophs metabolize organic molecules via cellular respiration to supply their energy needs.
true
True or false: Photosystem II is the only known protein complex that can oxidize water resulting in the release of O2.
true
The energy level of electrons moving from photosystem II to NADP+ is represented by the Z scheme. Which of these molecules contains electrons with the lowest energy level?
water
Rank the following electrons that occur in photosystem II in order of potential energy levels. Begin at the TOP with the electron with the highest potential energy.
1. An electron excited and transferred to a primary electron acceptor 2. An electron transferred to QA 3. An electron transferred from water to P680 4. An electron waiting to be excited by sunlight
List the steps involved in electron flow in order. Start with the earliest at the top.
1. Excited electrons move from P680 2. Excited electrons transferred to QB 3. Excited electrons enter an electron transport chain 4. Excited electrons move into PSI
Place the steps in Calvin's isotope-labeling experiment in the correct order. Start with the earliest step at the top.
1. Injection of algae w 14C labeled CO2 2. Incubation of cells for various time periods 3. Paper chromatography 4. Autoradiography
Arrange the electron carriers in photosystem II in the correct order. Begin at the TOP with the molecule that accepts electrons from P680*.
1. Pp 2. QA 3. QB
Arrange the electron carriers in photosystem I in order of decreasing potential energy. Start at the TOP with the carrier with the highest potential energy.
1. primary electron acceptor 2. Fd 3. NADP+ reductase 4. NADP+
In the Calvin cycle, for every SIX carbon dioxide molecules that are incorporated into a carbohydrate such as glucose, ____molecules of ATP are hydrolyzed and ____molecules of NADPH are oxidized.
18; 12
According to the Z scheme, what is the number of photoactivation events that occur during photosynthesis?
2
The Calvin cycle can be very energy-expensive. How many molecules of ATP and NADPH respectively are required to incorporate one carbon dioxide molecule into the six-carbon sugar being formed?
3 ATP, 2 NADPH
The production of one molecule of glucose through photosynthesis requires _____ molecules of CO2 and ____ molecules of H2O as reactants.
6; 12
Which of the following best describes the structure of a phytol tail of a chlorophyll a or b?
A long hydrophobic hydrocarbon chain
Plant cells can produce additional amounts of _____ to fuel the Calvin cycle in a process known as cyclic photophosphorylation.
ATP
Plants can use cyclic photophosphorylation to increase production of:
ATP
Which of the following are products of the light reactions?
ATP O2 NADPH
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 ______.
ATP; NADPH
The Calvin cycle uses energy from ____ and high energy ____ supplied by NADPH.
ATP; electrons
How does the structure of chlorophyll enable its photosynthetic function?
An electron can be delocalized across the porphyrin ring, allowing it to absorb energy.
Why is it significant that energy from excited electrons in photosynthesis is "captured"?
Because the energy is not released but instead used productively
What type of organisms carry out cellular respiration?
Both heterotrophs and photoautotrophs
How might a plant increase its efficiency of light absorption?
By diversifying the pigments it has, such that it is able to absorb many wavelengths of light
What represents the balanced products of photosynthesis if we account for the production of glucose (C6H12O6)?
C6H12O6 + 6O2 + 6H2O
According to the general equation for photosynthesis, CO2+ 2H2O + light energy → ___+___+___
C6H12O6; O2; H2O
What molecule is reduced during the process of photosynthesis?
CO2
What molecule is reduced in the Calvin cycle?
CO2
Photosynthesis is a redox reaction where ______ is reduced and ______ is oxidized.
CO2; H2O
Plants take CO2 from the atmosphere via the ______ in order to synthesize carbohydrates.
Calvin Cycle
What is the origin of the carbons in a carbohydrate generated by photosynthesis?
Carbon dioxide in the atmosphere
In Calvin's isotope labeling experiment, some molecules appeared very quickly, but others appeared only after long incubations. Which two molecules appeared only after long incubations?
Glyceraldehyde-3-phosphate Ribulose bisphosphate
Which of the following organisms are photoautotrophs?
Green plants Algae Cyanobacteria
Most photosynthetic organisms use H2O for photosynthesis, although some bacteria use ___ instead of water.
H2S
What happens to a pair of electrons after it reaches QB?
It enters an electron transport chain in the thylakoid membrane
Which of the following happens to the molecule formed by the addition of carbon dioxide to ribulose bisphosphate?
It is immediately split into two more stable three carbon molecules.
What is the role of the reaction center in a photosystem?
It transfers a high-energy electron to another molecule.
What energy conversion occurs during photosynthesis?
Light energy is converted to electrochemical energy, which is converted to chemical energy
How is NADPH formed in PSI?
NADP+ reductase adds two electrons and a H+ to NADP+
During photosynthesis, ______ serves as an electron carrier that can accept two high-energy electrons.
NADPH
Which of the following are products of the light reactions that are used by the Calvin cycle?
NADPH and ATP
The process of photorespiration consumes ______ and produces ______.
O2; CO2
Cyclic electron flow is characteristic of what photosystem in plants?
Only photosystem I
Which of the following molecules is found in the reaction center of photosystem II?
P680
PSII electron carriers in terms of electronegativity
P680 Pp Qa Qb
What technique did Calvin and his colleagues use to separate the radiolabeled molecules synthesized by algae in their experiment?
Paper chromatography
How might you summarize what happens during photosynthesis?
Plants capture energy from sunlight and use it to synthesize organic molecules.
This diagram shows part of the Z scheme of photosynthesis. Which of the following molecules contains the highest-energy electrons?
QA
Excited electrons are moved out of photosystem II by a carrier called ____. These electrons enter a cytochrome complex, and then finally being transferred to a small protein called ____, which carries the electrons to photosystem I.
QB; Pc
Which of the following would be an appropriate radioactive tracer for studying the flow of carbon through the Calvin cycle?
Radioactive CO2
In the last phase of the Calvin cycle, what molecule is regenerated so that the next cycle can occur?
Ribulose bisphosphate
What part of a chlorophyll molecule anchors it to proteins within the thylakoid membrane?
The phytol tail
Which of the following accepts an electron from P680?
The primary electron acceptor
Which of the following will remove a high energy electron from P680 and transfer it to a more stable molecule?
The reaction center
Which of the following membranes contains pigments in a green plant?
The thylakoid membrane
In photosystem II, what happens to the low-energy electrons that are removed from water molecules?
They are used to restore P680+ to P680.
Why are carbohydrates critical for plant cells?
They provide a source of energy and form the precursors for most organic macromolecules