CH.10: Photosynthesis
16) Plants photosynthesize ________.
C) only in the light but respire in light and dark
6) In photosynthetic cells, synthesis of ATP by the chemiosmotic mechanism occurs during ________.
C) photosynthesis and respiration
In what way are the structures of mitochondria and chloroplasts similar and different? What molecules or systems function in both types of organelles? WHich enzymes or processes are unique to each other?
Similarities: - Flattened Sacs (cristae vs thylakoids) - Both have 2 membranes - Both have their own ribosomes and DNA Differences: - Only chloroplasts carry out light-capturing reactions and the CC - Only chloroplasts can utilize sunlight bc they carry chlorophyll pigments - Chloroplasts carry rubisco and NADPH/NADP+ - Mitochondria carry NADH/NAD+/FADH2 Major Difference: - Mitochondria mainly breaks down large molecules into energy. - Chloroplasts functions mainly in building up molecules from things like H20 and light
8) Chlorophylls absorb most light in which colors of the visible range?
B) blue and red
4) When oxygen is released as a result of photosynthesis, it is a direct by-product of ________.
B) splitting water molecules
14) 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?
B) blue and violet
1) The process of photosynthesis probably originated ________.
B) in prokaryotes
24) Plastoquinone (PQ), an electron carrier of small molecular weight, is found in the electron transport chain associated with photosystem II. If PQ is not directly anchored to other membrane or cytoplasmic structures, it is probably ________.
D) both lipid soluble and a molecule that serves as a shuttle between the electron transport chain and ATP synthase
12) Energy from sunlight can excite electrons, kicking them out of their orbitals and creating free radicals. Free radicals are highly reactive atoms or molecules that have unpaired electrons and degrade and destroy other compounds in their vicinity. Carotenoids, one of the pigments present in most chloroplasts, can stabilize these free radicals. This suggests that ________.
B) carotenoids probably have a protective function in the cell
In the diagram of a chloroplast, which structure is best represented by the letter A?
Outer membrane
Oxygenic
oxygen producing
42) In plants, reduction of NADP+ occurs during ________
A) Photosynthesis
34) Suppose the interior of the thylakoids of isolated chloroplasts were made acidic and then transferred in the dark to a pH 8 solution. What would most likely happen?
A) The isolated chloroplasts would make ATP.
44) Which of the following statements best represents the relationships between the light reactions and the Calvin cycle?
A) The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns ADP, i, and NADP+ to the light reactions
39) The pH of the inner thylakoid space has been measured, as have the pH of the stroma and of the cytosol of a particular plant cell. Which, if any, relationship would you expect to find?
A) The pH within the thylakoid is less than that of the stroma.
The sequestering of carbon in CAM plants helps them to survive by __________.
allowing carbon dioxide to be gathered and used at different times of the day
10. 4: How is CO2 reduced to produce sugars:
- Carbon fixation is the addition of carbon dioxide to an organic compound. - The word "fix" is appropriate because the process converts—or fixes—CO2 gas to a biologically useful form. - Once carbon atoms are fixed, they can be used as sources of energy and as building blocks to construct the molecules found in cells. -Carbon fixation is a redox reaction—the carbon atom in CO2 is reduced by attaching it to another carbon
RuBP is the Initial Reactant with CO2
- five carbon compound ribulose bisphosphate (RuBP) is the initial reactant.
Converting Light Energy Into Chemical Energy
- In photosystem II, the action begins when the antenna complex transmits resonance energy to the reaction center, where the electron acceptor pheophytin comes into play (Figure 10.12) - pheophytin is identical to chlorophyll except that pheophytin lacks a magnesium atom in its head region. It accepts excited electrons from the reaction center chlorophylls. - The redox reaction between pheophytin and the reaction center chlorophyll pigment is a key step in transforming light energy into chemical energy. - Immediately after the excited electron is transferred to pheophytin, however, the reaction center pigment becomes an incredibly strong oxidizing agent. What prevents the electron from being pulled back to the oxidized pigment? The answer is that the electron is quickly shuttled away from the reaction center to an electron transport chain (ETC) in the thylakoid membrane. In both structure and function, the thylakoid ETC is similar to components in the mitochondrial ETC: 1. Structurally, the photosystem II and mitochondrial ETCs both contain quinones and cytochromes. 2. Functionally, the redox reactions that occur in both ETCs result in protons being actively transported from one side of an internal membrane to the other. The resulting protonmotive force drives ATP production via ATP synthase. plastoquinone (PQ)—a quinone similar to ubiquinone in the ETC of cellular respiration. - Ubiquinone is a small hydrophobic molecule that can transport electrons between molecules - Because plastoquinone is lipid soluble and not anchored to the thylakoid membrane, it is free to move within the thylakoid membrane. - When plastoquinone receives electrons from photosystem II, it carries them across the membrane to the lumen side of the thylakoid and delivers them to molecules with a higher redox potential in the cytochrome complex. - In this way, plastoquinone shuttles electrons from photosystem II to the cytochrome complex much like ubiquinone shuttled electrons between complexes I or II and complex III in mitochondria. - The potential energy released by these reactions allows plastiquinone to pick up protons from the chloroplast stroma and drop them off in the thylakoid lumen - The protons transported by plastoquinone result in a high concentration of protons in the thylakoid lumen - The pH in the thylakoid reaches 5 while the pH of the stroma hovers around 8. Because the pH scale is logarithmic (see BioSkills 5), the difference of 3 units means that the concentration of H+ is 10 : 10 : 10 = 1000 times higher in the lumen than in the stroma. - In addition, the stroma becomes negatively charged relative to the thylakoid lumen - The net effect of electron transport, then, is a large proton electrochemical gradient. This gradient results in a protonmotive force that, in turn, drives H+ out of the thylakoid lumen and into the stroma. - Proton flow down the electrochemical gradient is an exergonic process that is coupled to the endergonic synthesis of ATP from ADP and Pi. The stream of protons flows through ATP synthase, causing conformational changes in the enzyme that drive production of ATP. - Since the synthesis of ATP in chloroplasts is initiated by the energy from light, it is called photophosphorylation. Although photophosphorylation is similar to the oxidative phosphorylation that occurs in plant and animal mitochondria, there is a key difference in how this ATP is used. - In mitochondria, ATP is exported and fuels many different cellular processes. In chloroplasts, however, the ATP remains within the organelle and is used for the production of carbohydrate. - The photosystem II story is not yet complete, however. The electrons from PQ are passed through the cytochrome complex, but what about the oxidized photosystem II reaction center? To continue this ETC, the electrons removed from the reaction center pigments need to be replaced. Where do the electrons required by photosystem II come from?
Which of the following wavelengths represents the visible portion of the electromagnetic spectrum?
400 nm to 710 nm
In the diagram, which molecule is best represented by the letter C?
ATP
What are the two main products of the light-capturing reaction of photosynthesis?
ATP and NADPH Other info: Electrons from photosystem I are used to produce NADPH, which is a reducing agent. Electrons from photosystem II are used to produce a proton-motive force that drives the synthesis of ATP. In combination, photosystems II and I produce chemical energy stored in ATP and NADPH. Sugars, such as glucose, are produced in the Calvin cycle, while oxygen is a product of the splitting of water, which occurs in the light-capturing reactions. Water is split in the light-capturing reactions to release oxygen. ATP is produced in the light-capturing reactions.
51) Reactions that require CO2 take place in ________.
B) the Calvin cycle alone
What color will a pigment appear to be if the pigments absorb all the wavelengths of the visible spectrum?
Black
Where (ie in which compartment of which organelle) do the reactions of the light-capturing part of photosynthesis take place? WHere do the reactions of the Calvin cycle reactions take place?
Both reactions take place in chloroplasts - Light-capturing reactions: thylakoids - Calvin cycle: Stroma
22) What is the difference between NAD+ and NADP?
C) Both function as electron carriers, but NADP has a phosphate group and NAD+ does not.
54) The alternative pathways of photosynthesis using the C4 or CAM systems are said to be compromises. Why?
C) Both minimize photorespiration but expend more ATP during carbon fixation.
23) As electrons are passed through the system of electron carriers associated with photosystem
C) It is used to establish and maintain a proton gradient
Refer to the figure. To identify the molecule that accepts CO2, Calvin and Benson manipulated the carbon-fixation cycle by either cutting off CO2 or cutting off light from cultures of photosynthetic algae. They then measured the concentrations of various metabolites immediately following the manipulation. How would these experiments help identify the CO2 acceptor?
C) The CO2 acceptor concentration would increase when the CO2 is cut off but decrease when the light is cut off.
19) Use the following information to answer the question below. 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?
C) a mixture of blue and red light
38) The accumulation of free oxygen in Earth's atmosphere began with the origin of ________
C) cyanobacteria using photosystem II
31) As a research scientist, you measure the amount of ATP and NADPH consumed by the Calvin cycle in 1 hour. You find that 30,000 molecules of ATP were consumed, but only 20,000 molecules of NADPH were consumed. Where did the extra ATP molecules come from?
C) cyclic electron flow
26) What is the main purpose of light-dependent reactions of photosynthesis?
C) to produce NADPH and ATP
How do CAM plants differ from C3 plants?
CAM plants open their stomata at night and store CO2 in the form of organic acids. Other Info: CAM plants differ from C3 plants in that CAM plants open their stomata at night and store CO2 in the form of organic acids. CAM plants are able to take in CO2 at night and reduce dehydration, compared to C3 plants, which open their stomata during the day. Neither serves to directly reduce the amount of oxygen found within plant cells. CAM plants are found in very hot and arid environments. CAM plants store fixed carbon in organic acids, providing CO2 to the Calvin cycle during the day. CAM and C4 plants use a PEP carboxylase to fix CO2 to produce four-carbon molecules for the Calvin cycle. The CAM and C4 pathways function as CO2 pumps. They minimize photorespiration when stomata are closed and CO2 cannot diffuse in directly from the atmosphere. ATP production does not change
Why are summer leaves green, even though carotenoids are present?
During summer, chlorophyll is more abundant than carotenoids in leaves.
3) Which of the following are products of the light reactions of photosynthesis that are utilized in the Calvin cycle?
E) ATP and NADPH
27) Which of the events listed below occurs in the light reactions of photosynthesis? A) NADP is produced
E) Light is absorbed and funneled to reaction-center chlorophyll a
In the diagram, which molecule is best represented by the letter A?
Ferredoxin
Which of the following best describes the process of fluorescence?
Fluorescence is the release of light when an excited electron falls back down to its ground state. Other Info: When an excited electron simply falls back to its ground state, the absorbed energy is released as heat or a combination of heat and electromagnetic radiation (light). When the electron energy produces light, it is called fluorescence. Reflected light is the light from the sun that is not absorbed or transmitted. The ability of one pigment molecule to transfer energy to another pigment molecule is known as resonance energy transfer. Excited electrons may simply fall back to their ground state, and the absorbed energy may be released as heat or a combination of heat and electromagnetic radiation (light). If only heat is released, no fluorescence would be observed.
The reduction of carbon dioxide to produce sugars demonstrated that 14C was incorporated into 3-phosphoglycerate by algae. To analyze the molecules produced after the addition of 14C-containing CO2, cells were homogenized and immersed in hot alcohol prior to chromatography. What was the purpose of immersing homogenates in hot alcohol?
Hot alcohol was used to denature the enzymes present in the cell homogenates to stop 14C fixation.
In the diagram of a chloroplast, which structure is best represented by the letter B?
Inner membrane
How does Photosystem 1 work?
NADPH function as electron carriers. Figure 10.14 explains how photosystem I works in chloroplasts—put your finger on the "2 Photons" arrows and trace the steps that follow. 1. Pigments in the antenna complex absorb photons and pass the energy to the photosystem I reaction center. 2. Electrons are excited in reaction center chlorophyll molecules. 3. The reaction center pigments are oxidized, and the excited electrons are passed through a series of carriers inside the photosystem, then to a molecule called ferredoxin, and then to the enzyme called NADP+ reductase. 4. NADP+ reductase transfers two electrons and a proton to reduce NADP+ and form NADPH. To summarize: Electrons from photosystem I are used to produce NADPH, which is a reducing agent similar in function to the NADH and FADH2 produced by the citric acid cycle (see Chapter 9). Electrons from photosystem II, in contrast, are used to produce a proton-motive force that drives the synthesis of ATP.
In the diagram, which molecule is best represented by the letter D?
Plastocyanin (PC) Other info: Cyclic electron flow is an alternative to the Z scheme. Instead of being donated to NADP+, electrons are returned to plastoquinone (PQ) from ferredoxin. These electrons are subsequently passed through the electron transport chain (ETC) and are accepted by PC and routed back to photosystem I. Thus, the cycle between photosystem I and the ETC, generating a proton gradient, results in the production of additional ATP via photophosphorylation. Ferredoxin donates the electrons to PQ. PQ accepts electrons from ferredoxin. ATP is generated by the additional energy contributed by the electrons passed from ferredoxin to PQ and ultimately passed through the ETC.
In the diagram, which molecule is best represented by the letter B?
Plastoquinone (PQ)
The primary biochemical outcome of the activity of photosystem I is to __________.
reduce NADP+
Give an example of two types of plant cells that lack chloroplasts. how do plant cells that lack chloroplasts produce the ATP they need? Do plant cells that contain chloroplasts also contain mitochondria?
Roots, bulb (underground so not exposed to light-no chloroplasts) - Plants that lack chloroplasts receive sugars but still need mitochondria to break up those sugars into ATP. Plant cells that contain chloroplast more than likely also contain mitochondria
How is photosynthesis regulated?
Rubisco is activated by regulatory molecules that are produced when light is available, but inhibited in conditions of low CO2 availability—when photorespiration is favored.
In the diagram of a chloroplast, which structure is best represented by the letter E?
Stroma
What is the evidence for the existence of two photosystems?
The combination of light at 680 nm and 700 nm is much more effective in stimulating photosynthesis than is either wavelength alone. Other info: Chloroplasts contain multiple pigments. The most abundant pigment is chlorophyll which reflects or transmits green light. Chloroplasts appear green when chlorophyll is present due to its overwhelming overabundance. Only when chlorophyll is degraded do the leaves appear red, yellow, and orange due to the remaining carotenoid pigments. However, this is not evidence that two photosystems exist. Chlorophylls, designated chlorophyll a and chlorophyll b, absorb strongly in the blue and red regions of the visible spectrum. However, this was not evidence that two photosystems existed. Two different high-energy molecules are produced during the light-dependent reactions of photosynthesis: ATP and NADPH. However, this was not evidence that two photosystems existed.
What is noncyclic electron flow?
The passage of electrons from water to NADP+ Other Info: Noncyclic electron flow is the passage of electrons from water to NADP+. The pumping of protons from the stroma into the thylakoid space is accomplished in photosystem II by the cytochrome complex. See following figure. The production of ATP by the ATP synthase results from chemiosmosis. During cyclic electron flow, photosystem I transfers electrons back to the electron transport chain associated with photosystem II, generating ATP through photophosphorylation instead of reducing NADP+.
Predict the color of a pigment that absorbs light of only green, yellow, and red wavelengths.
The pigment will appear blue.
How are the light-capturing reactions and CO2-reduction reactions of photosynthesis related?
The products of light-capturing reactions are used in CO2-reduction reactions. Other info: Specifically, the two reactions are linked by electrons that are released when water is split to form oxygen gas. During the light-capturing reactions, these electrons are promoted to a high-energy state by light and then transferred through a series of reduction-oxidation (redox) reactions to NADP+. These reactions form NADPH, which functions as a reducing agent. Some of the energy released from these redox reactions is also used to produce ATP. During the Calvin cycle, the electrons in NADPH and the potential energy in ATP are used to reduce CO2 to carbohydrate. The products of the light-capturing reactions are used in the CO2-reduction reaction. Light is needed for photosynthesis to occur. However, the link between the light-capturing reactions and CO2-reduction reactions of photosynthesis is that the products of the light reaction are used in the CO2-reduction reactions. next
The Calvin cycle uses six ATP molecules to produce one three-carbon sugar (glyceraldehyde-3-phosphate, G3P) from three molecules of RuBP and three molecules of carbon dioxide. Yet the Calvin cycle actually requires nine ATP molecules to function. Why?
Three additional ATP molecules are used to regenerate RuBP.
In the diagram of a chloroplast, which structure is best represented by the letter C?
Thylakoids
Cellular respiration is the process by which sugars are used to generate ATP and carbon dioxide, whereas photosynthesis uses ATP and carbon dioxide to make sugars. In photosynthesis, which of the following statements would be correct?
Water loses electrons and is oxidized.
Electromagnetic energy in the form of light is permanently converted to chemical energy when __________.
an electron acceptor accepts the energy and becomes reduced
If researchers could replicate the splitting of water in the laboratory, great amounts of O2 and H2 could be made. It is obvious what O2 can be used for. H2 can be used __________.
as a clean, inexpensive replacement for gasoline If researchers could replicate the splitting of water in the laboratory, great amounts of O2 and H2 could be made. It is obvious what O2 can be used for. H2 can be used as a clean, inexpensive replacement for gasoline. Hydrogen cannot replace oxygen for use in medicine. Hot-air balloons are not powered by hydrogen. Hydrogen is not used to sterilize medical equipment
In green plants, the primary function of the Calvin cycle is to _________________.
construct simple sugars from carbon dioxide Other Info: Water is split during the light-capturing reactions. Oxygen is released. RuBP is a five-carbon compound that joins with CO2 in the fixation phase of the Calvin cycle. This reaction occurs in the fluid portion of the chloroplast called the stroma. The conversion of stored energy in simple sugars to ATP occurs during cellular respiration.
Anoxygenic
does not produce O2
10. 1: Photosynthesis Harnesses Sunlight to Make Carbohydrate
energy in sunlight is transformed to chemical energy in the C-C and C-H bonds of carbohydrate. CO2 + H20 + light energy -----> (CH2O)n + O2 actual carbohydrate produced by photosynthesis is a phosphorylated three-carbon sugar Photosynthesis is an energy demanding series of redox reactions that produce sugar and O2 from CO2 and H2O CO2 and H2O participate in entirely different reactions and the oxygen atoms in O2 come from water
An organism that must obtain food, including sugars and other macromolecules, from other organisms is called a __________.
heterotroph An organism that must obtain food, including sugars and other macromolecules, from other organisms is called a heterotroph. Non-photosynthetic organisms are called heterotrophs ("different-feeders") because they have to obtain the sugars and many of the other macromolecules they need from other organisms. Eukaryotes can be either heterotrophs or autotrophs. Autotrophs ("self-feeders") make all their own food from ions and simple molecules. Archaebacteria can be either heterotrophs or autotrophs.
Fluorescence is always accompanied by the release of heat. Thus, the energy in the form of light that is released as fluorescence is always __________.
of lower energy than the photon of energy absorbed Fluorescence is always accompanied by the release of heat. Thus, the energy in the form of light that is released as fluorescence is always of lower energy than the photon of energy absorbed. When the electron energy produces light, it is called fluorescence. Because some of the original photon's energy is transformed to heat, the electromagnetic radiation that is given off during fluorescence has lower energy and a longer wavelength than the original photon did. The fluorescent light emitted cannot be higher in energy than the original photon. The fluorescent light emitted cannot have the same amount of energy as the original photon because heat is also emitted with fluorescence. When photons are absorbed by pigments in chloroplasts, only about 2 percent of the excited electrons produce fluorescence. The other 98 percent of the energized pigments use their excited electrons to drive photosynthesis.
Electrons excited by the absorption of light in photosystem I are transferred to iron-sulfur electron acceptors and, therefore, must be replaced. The replacement electrons come directly from __________.
plastocyanin Other info: - ATP is generated by ATP synthase, using the proton-motive force generated by the ETC. Electrons that have passed through the ETC are passed to plastocyanin. - NADP+ is the electron acceptor for ferredoxin. Water is the first electron donor used in photosystem II to convert the light energy captured in chlorophyll to chemical energy in ATP through the generation of a proton-motive force in the ETC.
The enzyme needed to begin the Calvin cycle in C3 plants is ____________.
rubisco
Rubisco differs from PEP carboxylase in that __________.
rubisco can use oxygen gas as a substrate Other info: PEP carboxylase fixes only carbon into a four-carbon organic acid that is transported to cells where rubisco activity is high. There, CO2 is released for rubisco to use, and the three-carbon compounds are transported back to mesophyll cells to regenerate PEP. Rubisco is found in both C3 and C4 plants. Both rubisco and PEP can "fix" CO2, catalyzing its attachment to an organic compound. Both rubisco and PEP are found in the leaves of plants. Rubisco is found in bundle-sheath cells that surround vascular tissue, whereas PEP is found in mesophyll cells near the surface of the cell.
The Z scheme is ______________.
the characteristic path of electrons from photosystem II to photosystem I.
Photosynthesis:
the use of sunlight to manufacture carbohydrate.
Heterotrophs (different feeders)
they have to obtain the sugars and many of the other macromolecules they need from other organisms
Autotrophs (self-feeders)
they make their own food from ions and simple molecules (ex: maples, mosses, and other photosynthetic organism)
Between 1945 and 1955, a team led by Melvin Calvin began introducing radioactively labeled carbon dioxide (14CO2) to algae performing photosynthesis and identified the molecules that subsequently became labeled with the radioisotope. Calvin found that the molecules labeled with 14C __________.
were 3-phosphoglycerate and many other intermediates in the formation of glucose
Use the accompanying figure to answer the question(s) below. 20) What wavelength of light in the figure is most effective in driving photosynthesis?
A) 420 mm
15) Carotenoids are often found in foods that are considered to have antioxidant properties in human nutrition. What related function do they have in plants?
B) They protect against oxidative damage from excessive light energy.
10) Why are there several structurally different pigments in the reaction centers of photosystems?
B) This arrangement enables the plant to absorb light energy of a variety of wavelengths
In the diagram of a chloroplast, which structure is best represented by the letter D?
Granum - are interconnected stacks of thylakoids.
Use the following information to answer the question(s) below. 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. 56) If the power fails and the lights go dark, CO2 levels will ________.
A) rise as a result of both animal and plant respiration
49) Where do the enzymatic reactions of the Calvin cycle take place?
A) stroma of the chloroplast
52) The phylogenetic distribution of the enzyme rubisco is limited to ________.
D) bacterial and eukaryotic photoautotrophs
50) What is the primary function of the Calvin cycle?
E) synthesizing simple sugars from carbon dioxide
21) The proteins of the electron transport chain active in the light-dependent reactions ________.
A) are membrane proteins present in the thylakoid
11) In autumn, the leaves of deciduous trees change colors. This is because chlorophyll is degraded and ________.
A) carotenoids and other pigments are still present in the leaves
33) The chemiosmotic process in chloroplasts involves the ________.
A) establishment of a proton gradient across the thylakoid membrane
53) CAM plants keep stomata closed in the daytime, thus reducing loss of water. They can do this because they ________.
A) fix CO2 into organic acids during the night
47) Photorespiration ________.
A) generates carbon dioxide and consumes ATP and oxygen
29) Which of the following are directly associated with photosystem I?
B) receiving electrons from the thylakoid membrane electron transport chain
30) 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 ________.
B) test for liberation of O2 in the light
The Calvin Cycle Is a Three-Step Process The complete Calvin cycle, as it came to be called, has three phases (Figure 10.19):
1. Fixation phase The Calvin cycle begins when CO2 reacts with RuBP. This phase fixes carbon and produces two molecules of 3PGA, which is a three-carbon organic acid. 2. Reduction phase The 3PGA is phosphorylated by ATP and then reduced by electrons from NADPH. The product is the phosphorylated three-carbon sugar glyceraldehyde3-phosphate (G3P). Some of the G3P that is synthesized is drawn off to produce other organic molecules, like the six carbon sugar glucose. 3. Regeneration phase The rest of the G3P keeps the cycle going by serving as the substrate for the third phase in the cycle: reactions that use additional ATP in the regeneration of RuBP. **All three phases take place in the stroma of chloroplasts. One turn of the Calvin cycle fixes one molecule of CO2. Three turns of the cycle fix three molecules of CO2, yielding one molecule of G3P and three fully regenerated RuBP
Refer to the figure. If the carbon atom of each of the incoming CO2 molecules is labeled with a radioactive isotope of carbon, which organic molecules will be radioactively labeled after one cycle?
B) B, C, D, and E
57) What would be the expected effect on plants if the atmospheric CO2 concentration was doubled?
B) C3 plants would have faster growth; C4 plants would be minimally affected.
7) Which of the following sequences correctly represents the flow of electrons during photosynthesis?
B) H2O → NADPH → Calvin cycle
45) The light-independent reactions of plants function to make organic molecules using carbon dioxide as a carbon source. What is the electron source that helps reduce carbon dioxide to sugars and other organic molecules?
B) NADPH
5) Which of the following statements best describes the relationship between photosynthesis and respiration?
B) Photosynthesis stores energy in complex organic molecules; respiration releases energy from complex organic molecules
18) Use the following information to answer the question below. 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. If you ran the same experiment as Engelmann without passing light through a prism, what would you predict?
B) The bacteria would be relatively evenly distributed along the algal filaments
43) How are the light-dependent and light-independent reactions of photosynthesis related?
B) The products of light-dependent reactions are used in light-independent reactions.
40) In its mechanism, photophosphorylation is most similar to ________.
B) oxidative phosphorylation in cellular respiration
46) Which of the following procedures would identify the enzyme that catalyzes the carboxylation of ribulose-1,5-bisphosphate?
C) purifying a variety of proteins from plant extracts and testing each protein individually to see if it can carboxylate ribulose-1,5-bisphosphate
36) In mitochondria, chemiosmosis moves protons from the matrix into the intermembrane space, whereas in chloroplasts, chemiosmosis moves protons from the ________.
C) stroma to the thylakoid space
25) The electrons of photosystem II are excited and transferred to electron carriers. From which molecule or structure do the photosystem II replacement electrons come?
C) water
Photosynthesis: 2 Linked sets of Reactions
CO2 + 2H2S + Light energy -------> (CH2O)n +H20 + 2S Van Niels work was crucial for 2 reasons: 1. Showed that in these bacteria, H2S and CO2 do not combine directly during photosynthesis 2. It showed that the O atoms in CO2 are not released as O2 Biologist hypothesized that O atoms released during plant photosynthesis must come form H2O There were 2 distinct sets of reactions: one that uses light to produce O2 from H2O and one that converts CO2 into sugars Melvin Calvin created Calvin Cycle: the reactions that reduce carbon dioxide and produce sugars To summarize: Early research showed that photosynthesis consists of 2 linked sets of reactions. One set is triggered by light; the other set-the CC-requires the products of the light capturing reactions. These produce O from H2O; the CC produces sugar from CO2 The two reactions r linked by a series of redox reactions that starts when water is split or oxidized to form O2 During light-capturing reactions electron r promoted to a high energy state by light and then transferred through a series of reactions to reduce a phosphorylated version of NAD+, called NADP∙ (nicotinamide adenine dinucleotide phosphate). This reaction forms NADPH, which functions as a reducing agent similar to the NADH produced in cellular respiration. Some of the energy released from these redox reactions is also used to produce ATP (Figure 10.2)
Carotenoids are thought to protect leaves from damage. Which of the following accounts for that protection?
Carotenoids absorb the high-energy, short-wavelength light that can generate free radicals in plant cells. Other info: Carotenoids are thought to protect leaves from damage. To do this, carotenoids absorb the high-energy, short-wavelength light that can generate free radicals in plant cells. The high-energy, short-wavelength photons in the ultraviolet part of the electromagnetic spectrum contain enough energy to knock electrons out of atoms and create free radicals. Free radicals, in turn, trigger reactions that can disrupt and degrade molecules. Carotenoids "quench" free radicals by accepting or stabilizing unpaired electrons. As a result, they protect chlorophyll molecules from harm. In autumn, when the leaves of deciduous trees die, their chlorophyll degrades first. The wavelengths reflected by the carotenoids and other pigments that remain turn forests into spectacular displays of yellow, orange, and red. Carotenoids absorb wavelengths of light that are not absorbed by chlorophylls. As a result, they extend the range of wavelengths that can drive photosynthesis.
Which of the following organisms would be considered an autotroph?
Corn Other Info: Corn would be considered an autotroph. Photosynthetic organisms are termed autotrophs ("self-feeders") because they make all their own food from ions and simple molecules. Corn uses photosynthesis to make its own food. Chimpanzees do not use photosynthesis as a means to make their own food and are heterotrophs ("different-feeders") because they have to obtain the sugars and many of the other macromolecules they need from other organisms. Seahorses do not use photosynthesis as a means to make their own food and are heterotrophs because they have to obtain the sugars and many of the other macromolecules they need from other organisms. Fruit flies do not use photosynthesis as a means to make their own food and are heterotrophs because they have to obtain the sugars and many of the other macromolecules they need from other organisms.
13) What event accompanies energy absorption by chlorophyll (or other pigment molecules of the antenna complex)?
D) An electron is excited.
9) Which of the following is a difference between chlorophyll a and chlorophyll b?
D) Chlorophyll a and b absorb light energy at slightly different wavelengths.
37) P680+ is said to be the strongest biological oxidizing agent. Given its function, why is this necessary?
D) It obtains electrons from the oxygen atom in a water molecule, so it must have a stronger attraction for electrons than oxygen has.
17) Use the accompanying figure to answer the question below. The figure shows the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis. Why are they different?
D) Other pigments absorb light in addition to chlorophyll a
28) Which statement describes the functioning of photosystem II?
D) The electron vacancies in P680+ are filled by electrons derived from water
48) A flask containing photosynthetic green algae and a control flask containing water with no algae are both placed under a bank of lights, which are set to cycle between 12 hours of light and 12 hours of dark. The dissolved oxygen concentrations in both flasks are monitored. Predict what the relative dissolved oxygen concentrations will be in the flask with algae compared to the control flask. The dissolved oxygen in the flask with algae will ________.
D) be higher in the light but lower in the dark
41) Which process is most directly driven by light energy?
D) removal of electrons from chlorophyll molecules
32) Assume a thylakoid is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will most directly affect the ________.
D) synthesis of ATP
35) In a plant cell, where are the ATP synthase complexes located?
D) thylakoid membrane and inner mitochondrial membrane
C. B. Van Niel's experiments with purple sulfur bacteria led to which of the following hypotheses?
During plant photosynthesis, the oxygen gas that is released comes from water. Other Info: Hydrogen sulfide is only required in some cases of photosynthesis. Most plants use water instead of hydrogen sulfide to donate electrons, releasing oxygen as a by-product of splitting water molecules. Van Niel's experiments showed that the oxygen atoms in CO2 are not released as oxygen gas (O2). The purple sulfur bacteria produced no oxygen, even though carbon dioxide participated in the reaction—just as it did in plants. The photosystem II of cyanobacteria and eukaryotic chloroplasts perform oxygenic ("oxygen-producing") photosynthesis because they generate oxygen as a by-product of the process. Other organisms that have only a single photosystem do not oxidize water, and thus do not produce O2 gas. Instead, these organisms use different electron donors, such as H2S used by the purple sulfur bacteria, to perform anoxygenic ("no oxygen-producing") photosynthesis. Purple sulfur bacteria are capable of photosynthesis. To obtain electrons, purple sulfur bacteria split hydrogen sulfide, releasing sulfur into the medium instead of oxygen (from water).
2) If photosynthesizing green algae are provided with CO2 containing heavy oxygen (18O), later analysis will show that all of the following molecules produced by the algae contain 18O EXCEPT ________.
E) O2
Sunlight is a form of energy. Which of the following terms best describes the type of energy that sunlight represents?
Electromagnetic energy Other Info: Light is a type of electromagnetic radiation, a form of energy. Photosynthesis converts electromagnetic energy in the form of sunlight into chemical energy in the C-C and C-H bonds of sugar. Physicists describe light's behavior as both wavelike and particlelike. Like water waves or airwaves, electromagnetic radiation is characterized by its wavelength—the distance between two successive wave crests (or wave troughs). The wavelength determines the type of electromagnetic radiation. Potential energy is stored energy, such as that found in the separation of charge across the thylakoid membrane due to the pumping of protons into the thylakoid space. The energy used to pump the protons into the thylakoid (against their concentration gradient) is stored and used to drive the synthesis of ATP using the ATP synthase. Chemical energy is the energy stored in chemical bonds. Energy is required to make chemical compounds, as the state of matter goes from more disordered to less disordered (thus, entropy decreases). The input of energy required for this process is stored in the chemical bonds and can be liberated through glycolysis or aerobic respiration. Wave energy, such as that found in air or water or light, has energy characterized by the wavelength. Light, and hence electromagnetic radiation, has both wavelike properties and as particlelike properties. A packet of light, called a photon, contains a particular wavelength of light as well as a particular amount of energy.
The Z Scheme: Photosystem 1 and 2 work together (Might not even need to know this)
Figure 10.15 illustrates the Z-scheme model for how photosystems II and I interact. - The process starts when photons excite electrons in the chlorophyll molecules of photosystem II's antenna complex. - When the energy in the excited electrons is transferred to the reaction center, a specialized pair of chlorophyll molecules, each called P680, passes excited electrons to pheophytin. - These are the same reaction center pigments described previously, and the name represents the optimal wavelength absorbed by the pigments (680 nm). - When pheophytin is reduced, it transfers an electron from the high-energy bond to an electron transport chain. There the electron is gradually stepped down in potential energy through redox reactions among a series of quinones and cytochromes. - Using the energy released by the redox reactions, plastoquinone (PQ) carries protons across the thylakoid membrane, from the stroma to the lumen. ATP synthase uses the resulting protonmotive force to phosphorylate ADP, creating ATP. - When electrons reach the end of the cytochrome complex, they are passed to a small diffusible protein called plastocyanin (PC). The reduced plastocyanin diffuses through the lumen of the thylakoid, and donates the electron to an oxidized reaction center pigment in photosystem I.
The localization of photosystem I, photosystem II, the cytochrome complex, and the ATP synthase in chloroplasts is strategically determined based on the substrates required for each of their reactions. What feature of grana might cause problems with respect to the placement of photosystem I or the ATP synthase deep in these structures?
Grana are densely packed stacks of thylakoid membranes that may not have significant amounts of stroma for ATP synthesis. Other Info: The localization of photosystem I, photosystem II, the cytochrome complex, and the ATP synthase in chloroplasts is strategically determined based on the substrates required for each of their reactions. Grana are densely packed stacks of thylakoid membranes that may not have significant amounts of stroma for ATP synthesis. This might cause problems to the placement of photosystem I or the ATP synthase deep in these structures. Photosystem II and the cytochrome complex are much more abundant in the interior stacked membranes of grana, whereas photosystem I and ATP synthase are much more common in the exterior unstacked membranes. This organization seems appropriate for ATP synthase as this enzyme complex is oriented with its bulky head toward the stroma. Thus, avoiding the tightly stacked grana makes sense. The surface area of grana does not determine where the photosystems or enzymes are located. Instead, the availability of substrates such as ADP, Pi, and NADP+, which would not be as readily available if the enzymes were buried in the membrane folds of the grana, appears to determine the localization of these complexes. Pigments are localized in both grana and non-grana-associated thylakoid membranes. The ability of isoprenoid tails to localize pigments in thylakoid membranes is not affected by the tight stacking of thylakoids in grana. The membranes remain the same size.
The transport of CO2 into plant cells is regulated by stomata. What additional cells help regulate this transport?
Guard cells Other Info: The transport of CO2 into plant cells is regulated by stomata and guard cells. The surface of a leaf is dotted with openings bordered by two distinctively shaped cells called guard cells. The opening between these paired cells is called a pore, and the entire structure is a stoma (plural: stomata). Mesophyll cells are found near the surface of leaves and contain the enzyme PEP carboxylase, which is important in the C4 pathway.Vascular cells are used in transport of water, sugars, and/or nutrients. Photosynthetic cells are located beneath the leaf's surface.
!0.3: The Discovery of Photosystems 1 and 11
If cells were exposed to a combination of both wavelengths, the rate of photosynthesis increased more than the sum of the rates produced by each wavelength independently. This phenomenon was called the enhancement effect, and is not limited to algal cells. According to the two-photosystem hypothesis, the enhancement effect occurs because photosynthesis is much more efficient when both photosystems operate together.
What determines whether a pigment can absorb a wavelength of light or not?
In order for a pigment to absorb a particular wavelength of light, that photon must contain the amount of energy needed to excite an electron from its ground state of 0 to a higher energy state of 1 or 2. Other Info: When a photon strikes a pigment molecule, the photon's energy can be transferred to an electron in the chlorophyll molecule's head region. The excited electron states that are possible in a particular pigment are discrete—meaning incremental rather than continuous—and can be represented as lines on an energy scale. These discrete energy levels are a property of the electron configurations in a particular pigment. If the difference between the possible energy states (1 and 2) is the same as the energy in the photon, the photon can be absorbed and an electron excited to a higher energy state. Wavelengths that do not contain these amounts of energy cannot be absorbed. The determination of whether or not a pigment can absorb a particular wavelength of light is dependent on the electron configuration and not the number of electrons in that pigment. The number of chloroplasts and chlorophyll molecules determines how much energy can be absorbed but does not determine whether a pigment can absorb a particular wavelength of light. The atoms in a pigment molecule will have characteristic protons and neutrons for those atoms. The ability of the pigment to absorb light, however, rests in the configuration of electrons.
Why is the chemical reduction of an electron acceptor in the photosynthetic reaction center important to plant function?
It allows the energy of absorbed light to be trapped and converted to chemical energy. Other info: The photosynthetic reaction's function in plants is focused on transforming electromagnetic energy in the form of sunlight into chemical energy in the phosphate bonds of ATP and the electrons of NADPH. The reduction of the electron acceptor pheophytin in photosystem II leads to the passage of electrons through additional carriers and an electron transport chain that generates a proton gradient used to drive ATP synthesis. When a chlorophyll molecule is excited in the reaction center, its excited electron is transferred to an electron acceptor. When the acceptor becomes reduced, the energy transformation event that started with the absorption of light becomes permanent: Electromagnetic energy is transformed to chemical energy. The reduction-oxidation (redox) reaction that occurs in the reaction center results in the production of chemical energy from sunlight. The chemical reduction of an electron acceptor does not result in matching the energy of light illuminating the leaf. The energy from the photon excites an electron that fluoresces and/or emits heat, and once the energy reaches the reaction center, the energy collected and not lost as heat is given to an electron acceptor. Fluorescence occurs if the excited electron simply falls back to its ground state, releasing the absorbed energy as electromagnetic radiation (light) as well as heat. The reduction of an electron acceptor does change the wavelength of chlorophyll fluorescence. The electron acceptor does not provide electrons to be excited by the absorbed light, but instead it accepts electrons from an electron donor (water) that have been excited by the energy absorbed and passed via pigments to the reaction center.
Why is it critical for plants to maintain a high concentration of carbon dioxide in the leaves?
It helps prevent photorespiration. Other info: Oxygen and carbon dioxide compete at the RuBP's active sites, which slows the rate of CO2 reduction. One of the molecules produced from the addition of oxygen to RuBP is processed in reactions that consume ATP and release CO2 in order to regenerate 3PGA. Part of this pathway occurs in chloroplasts, and part occurs in peroxisomes and mitochondria. The reaction sequence resembles respiration because it consumes oxygen and produces carbon dioxide. As a result, it is called photorespiration. In low CO2 conditions, the plant will undergo photorespiration, using energy and releasing fixed CO2. Oxygen and carbon dioxide are both substrates for RuBP. Oxygen and carbon dioxide compete at the enzyme's active sites, which slows the rate of CO2 reduction. Photorespiration consumes energy and releases fixed CO2. When photorespiration occurs, the overall rate of photosynthesis declines, but does not stop. Oxygen will still be produced but at a lower rate. CO2 is not required for the regeneration of RuBP from G3P. This regeneration requires ATP and G3P.
What is the source of atmospheric oxygen released during photosynthesis?
It is produced via splitting of the water molecules during the light-capturing reactions. Other info: Researchers used heavy isotopes of oxygen and observed the 18O in oxygen gas only when algae or plants were exposed to 18O-labeled H2O, not to 18O-labeled CO2. In addition, the reactions responsible for producing oxygen gas occurred only in the presence of sunlight and did not require the presence of CO2. The light-capturing reactions produce oxygen from water; the Calvin cycle produces sugar from CO2. The soil contributes needed water and nutrients, such as nitrogen, phosphorus, and potassium. Other secondary macronutrients and trace elements are also provided by the soil.
Why is pheophytin an important component of photosystem II?
It transforms light energy by acting as the initial electron acceptor. Other info: In photosystem II, the action begins when the antenna complex transmits resonance energy to the reaction center, where the electron acceptor pheophytin accepts high-energy electrons from the excited reaction center chlorophylls. The reduction of pheophytin (and the accompanying oxidation of the reaction center chlorophyll pigment) is a key step in the transformation of light energy into chemical energy. Instead of acting as a pigment that energizes an electron when it absorbs a photon, pheophytin instead accepts high-energy electrons from the excited reaction center chlorophylls. Pheophytin plays a role in photosystem II, not photosystem I. Pheophytin accepts energy passed from chlorophylls to the reaction center to a pair of chlorophylls called P680 in photosystem II. These chlorophylls absorb photons of wavelength 680 nm. The importance of pheophytin is its ability to convert the light energy collected in the antenna complex and passed to the P680 reaction center into chemical energy by accepting high-energy electrons and participating in this important reduction-oxidation (redox) reaction.
During photosynthesis, which of the following reactions occur?
Light energy is used to raise the potential energy of electrons. Other info: When a photon strikes a chlorophyll molecule, the photon's energy can be transferred to an electron in the chlorophyll molecule's head region. In response, the electron is "excited," or raised to a higher energy state. Energy in the form of electromagnetic radiation is transferred to an electron, raising the potential energy of the electron. ATP is used for the chemical reactions that reduce carbon dioxide (CO2) to produce sugars. Water acts as an electron donor during photosynthesis. ATP is produced in the stroma of chloroplasts.
Light can be transmitted, absorbed, or reflected. The light that reaches chloroplasts and the pigments in the chloroplasts does which of those?
Light that hits pigments in chloroplasts can be transmitted, absorbed, and reflected. Light that hits pigments in chloroplasts can be transmitted, absorbed, and reflected. Pigments are molecules that absorb only certain wavelengths of light—other wavelengths are either reflected or transmitted (pass through). Pigments have colors because people see the wavelengths that they do not absorb. Some of the light that hits chloroplasts will be transmitted, or pass through, because the pigment does not absorb or reflect that particular wavelength of light. Pigments in chloroplasts can both absorb and reflect light, but they can also have light be transmitted, or pass through. The reflected light of chloroplasts does give leaves their color, because the remainder of the light is either absorbed or transmitted. Only the reflected light is seen as the color.
How are the light-capturing and Calvin cycle parts of photosynthesis coupled? How would poisoning the electron transport system associated with the light-capturing reactions of photosynthesis affect the Calvin cycle reactions?
Light-capturing reactions use H20 and light energy to produce oxygen and sugar. Light energy is captured and uses ATP from ADP and NADPH reduced from NADP+. The Calvin Cycle uses NADPH and ATP produced form the light capturing reactions to reduce carbon dioxide to carbohydrates. Poisoning the electron transport system would prevent the production of NADPH and ATP, which are necessary for Calvin cycle
Isolated thylakoids were incubated in an acidic solution at pH 4 until the pH was equilibrated across the thylakoid membrane. The thylakoids were then transferred to a buffer at pH 8 with ADP and inorganic phosphate. ATP was synthesized. Did this experiment require light to generate the ATP?
No, because ATP synthesis depends only on the presence of a hydrogen ion gradient and does not require light directly. Other info: - Light is required to generate the proton motive force necessary to drive the ATP synthesis. If a hydrogen ion gradient is established by other means, then no light would be necessary to drive the ATP synthesis. - High-energy electrons from photosystem II are required to establish a proton gradient across the thylakoid membrane and not to drive the ATP synthesis. - The transfer of electrons in photosystem II from chlorophylls, to pheophytin and ultimately to photosystem I, results in the movement of protons into the thylakoid space. This movement results in the proton gradient that holds the potential energy necessary to activate the ATP synthesis. - ATP synthesis does result from the light-dependent reactions of photosynthesis; however, using artificial conditions to generate a proton gradient across a thylakoid membrane would result in ATP synthesis in the laboratory. -
The reduction of which of the following molecules is responsible for the transformation of light energy into chemical energy?
Pheophytin *The reduction of pheophytin (and the accompanying oxidation of the reaction center chlorophyll pigment) is a key step in the transformation of light energy into chemical energy. Instead of acting as a pigment that energizes an electron when it absorbs a photon, pheophytin accepts high-energy electrons from the excited reaction center chlorophylls. Plastoquinone is an electron carrier that shuttles electrons from pheophytin to the cytochrome complex. Cytochromes in the cytochrome complex accept electrons from plastoquinone and pass electrons on to ferredoxin. Ferredoxin is an electron acceptor that accepts electrons from the cytochrome complex and passes them to NADP+.
The equation 6 CO2 + 6 H2O + light energy → C6 H12 O6 (glucose) + 6 O2 represents which of the following processes?
Photosynthesis Other info: The equation 6 CO2 + 6 H2O + light energy → C6 H12 O6 (glucose) + 6 O2 represents photosynthesis. Photosynthesis allows plants to convert the electromagnetic energy of sunlight into chemical energy in the C-C and C-H bonds of carbohydrates. When glucose is the carbohydrate that is eventually produced, the overall reaction utilizes light energy, six molecules of carbon dioxide, and six water molecules to generate glucose and six molecules of oxygen. See figure below. Glycolysis is the process by which glucose is converted to two molecules of pyruvate. Glycolysis may qualify as the most ancient set of energy-related chemical reactions from an evolutionary viewpoint because both autotrophs and heterotrophs perform glycolysis. The citric acid cycle converts acetyl-CoA into two molecules of carbon dioxide, GTP, and NADH and FADH2. The citric acid cycle occurs in mitochondria, and the electron carriers NADH and FADH2 shuttle the energy in electrons to the electron transport chain to ultimately generate ATP. The Calvin cycle, or dark cycle, is part of the overall photosynthetic equation. In the Calvin cycle, carbon dioxide is fixed into glucose 3-phosphate using the energy of ATP and NADPH, which is generated in the light cycle of photosynthesis.
Why is there so much ribulose bisphosphate carboxylase (RuBP) on Earth?
RuBP is absolutely required to fix carbon into glyceraldehyde 3-phosphate and ultimately into glucose, and it is an extremely inefficient enzyme. Other info: The CO2-fixing enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (commonly referred to as rubisco), is found in all photosynthetic organisms that use the Calvin cycle to fix carbon and is thought to be the most abundant enzyme on Earth. The rubisco enzyme is cube-shaped and consists of 16 polypeptides that form eight active sites where CO2 is fixed. Despite its large number of active sites, rubisco is a slow enzyme. Each active site catalyzes just three reactions per second; other enzymes typically catalyze thousands of reactions per second. Plants synthesize huge amounts of rubisco, possibly as an adaptation compensating for its lack of speed. Besides being slow, rubisco is inefficient because it will catalyze the addition of either O2 or CO2 to RuBP. This is a key point: Oxygen and carbon dioxide compete at the enzyme's active sites, which slows the rate of CO2 reduction. RuBP only catalyzes the fixation of carbon from CO2 to ribulose bisphosphate. RuBP is an incredibly slow enzyme; therefore, plants make it in abundance to make up for its slow speed. The rubisco enzyme is cube-shaped and consists of 16 polypeptides that form eight active sites where CO2 is fixed.
Both chlorophylls and carotenoids contain ring structures and isoprenoid tails. Which of these structures allows pigments to absorb light?
The ring structures of chlorophylls and carotenoids allow these pigments to absorb light.
Chlorophyll consists of a magnesium-containing head and a long, hydrophobic hydrocarbon tail. Why is the tail region important to the molecule's function?
The tail region anchors chlorophyll in the thylakoid membrane. Other info: Chlorophyll molecules have two fundamental parts: a long isoprenoid "tail" and a "head" consisting of a large ring structure with a magnesium atom in the middle. The tail interacts with proteins embedded in the thylakoid membrane; the head is where light is absorbed. The electrons donated during photosynthesis come from the splitting of water, releasing electrons that replace those that became excited in the reaction center by the energy absorbed by pigments. The pigments in the chloroplasts capture the energy in sunlight and pass that energy by resonance energy transfer to the reaction center. The tail of the chlorophyll molecule anchors the pigment in the chloroplast membrane.
Photosynthesis Occurs in Chloroplasts
photosynthesis takes place only in the green portions of plants called chloroplasts ("green-formed elements") Figure 10.3: a chloroplast is enclosed by an outer membrane and an inner membrane The interior is dominated by flattened, sac-like structures called thylakoids which often occur in interconnected stacks called grana (singular: granum). The space inside a thylakoid is its lumen. (Lumen is a general term for the interior of any sac-like structure. Your stomach and intestines have a lumen.) fluid-filled space between the thylakoids and the inner membrane is the stroma Pigments are molecules that absorb only certain wavelengths of light—other wavelengths are either reflected or transmitted (pass through) Plants oxidize sugars in their mitochondria and consume O2 in the process of producing ATP, just as animals and other eukaryotes do
When photosynthesis is happening rapidly, the sugars produced are stored as the polymer __________. When photosynthesis slows, the polymer can be converted into the disaccharide __________ and, finally, __________ is liberated to undergo glycolysis to provide ATP.
starch; sucrose; glucose Other Info: When photosynthesis is happening rapidly, the sugars produced are stored as the polymer starch. When photosynthesis slows, the polymer can be converted into the disaccharide sucrose and, finally, glucose is liberated to undergo glycolysis to provide ATP. When photosynthesis is proceeding rapidly and sucrose is abundant, glucose molecules are polymerized to form starch in the leaves and in storage cells in the roots. Starch production occurs inside the chloroplast; sucrose synthesis takes place in the cytosol. In photosynthesizing cells, starch acts as a temporary sugar storage product. When photosynthesis is taking place slowly, almost all the glucose that is produced is used to make sucrose. Sucrose is water-soluble and readily transported to other parts of the plant. If sucrose is delivered to rapidly growing parts of the plant, it is broken down to fuel cellular respiration and growth. The products of the Calvin cycle enter one of several reaction pathways. The most important of these reaction sequences produces the monosaccharides glucose and fructose from G3P via gluconeogenesis. This glucose is often combined with fructose to form the disaccharide ("two-sugar") sucrose. Glucose is a monosaccharide, and sucrose is a disaccharide of glucose and fructose.
The enhancement effect observed in which more oxygen is produced in the presence of two different wavelengths of light at the same time than when the discrete amounts of oxygen produced separately by each wavelength of light are combined suggests __________.
that the rate of photosynthesis for red and far-red light is more efficient when they are present together than when they are separate The enhancement effect observed in which more oxygen is produced in the presence of two different wavelengths of light at the same time than when the discrete amounts of oxygen produced separately by each wavelength of light are combined suggests that the rate of photosynthesis for red and far-red light is more efficient when they are present together than when they are separate. The enhancement effect results from two distinct types of reaction centers, each absorbing different wavelengths of light. According to the two-photosystem hypothesis, the enhancement effect occurs because photosynthesis is much more efficient when both photosystems operate together. If each photosystem acts completely independently of the other, one would expect that the amount of oxygen produced would be additive and not enhanced. The enhancement effect demonstrates that more oxygen is produced when two different wavelengths of light are present at the same time. This argues against the answer that only one pigment can absorb light at any given time. The enhancement effect does suggest that the amount of oxygen produced by photosynthesis is not simply additive for each wavelength of light; however, it does not determine how much of an enhancement is present.
Electrons excited by absorption of light in photosystem II are transferred to plastoquinone via pheophytin, and, therefore, must be replaced. The replacement electrons come from __________.
water Other info: Electrons excited by absorption of light in photosystem II are transferred to plastoquinone via pheophytin, and, therefore, must be replaced. The replacement electrons come from water. Electrons are stripped away from water, producing oxygen gas as a by-product to replace the electrons that initially leave photosystem II by passage from pheophytin to plastoquinone. Photosystem I accepts electrons from plastocyanin following their use to drive proton transport into the thylakoid space. Oxygen is a by-product of the reduction of water. The electrons from water are used to replace the electrons that leave photosystem II. The cytochrome complex is used to shuttle electrons from plastoquinone to plastocyanin and to generate the proton gradient.
