BIO CH 10
The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night. Why?
The Calvin cycle requires products only produced when the photosystems are illuminated.
Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water). Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.)
The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease. A reaction or process is dependent on another if the output of the second is an input to the first. For example, the light reactions are dependent on the Calvin cycle because the NADP+ and ADP produced by the Calvin cycle are inputs to the light reactions. Thus, if the Calvin cycle slows (because of a decrease in the amount of available CO2), the light reactions will also slow because the supply of NADP+ and ADP from the Calvin cycle would be reduced.
In photosynthesis, plants use carbon from __________ to make sugar and other organic molecules.
carbon dioxide
The most important role of pigments in photosynthesis is to __________.
capture light energy
--
--
The Calvin cycle could not occur without the light reactions. Which of the following statements describes why this is the case?
ATP and NADPH produced in the light reactions provide the energy for the production of sugars in the Calvin cycle.
The light reactions of photosynthesis supply the Calvin cycle with __________.
ATP and NADPH.
Which of the following statements is a correct distinction between autotrophs and heterotrophs?
Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic.
Of the following, which occurs during the Calvin cycle?
CO2 is reduced.
What property of the pigment chlorophyll makes it appear green?
Chlorophyll absorbs all of the visible spectrum of light except green, which it reflects.
Which of the following processes occurs during the second phase, the reduction phase, of the Calvin cycle?
G3P production
In the light reactions of photosynthesis, ATP is produced by photophosphorylation. Which of the listed processes is most similar to photophosphorylation?
Oxidative phosphorylation in cellular respiration
A photosystem consists of which of the following structures?
Reaction-center complex Light-harvesting complexes Primary electron acceptor Chlorophyll molecules All of the listed structures are parts of a photosystem All of the listed structures are parts of a photosystem
Drag the labels to the appropriate locations on the diagram of the thylakoid membrane.
Photosynthetic electron transport contributes to the formation of a proton (H+) gradient across the thylakoid membrane in two places. In PS II, the oxidation of water releases protons into the thylakoid space. Electron transport between PS II and the cytochrome complex (through Pq) pumps protons from the stroma into the thylakoid space.
Drag each item into the appropriate bin depending on whether the process is associated with Photosystem II (PS II) only, Photosystem I (PS I) only, or both PS II and PS I. Note that "electron transport chain" here refers to the electron transport chain between the two photosystems, not the one that functions after PS I.
Photosystem II (PS II) only: reduction of electron transport chain between the two photosystems, and oxidation of water Photosystem I (PS I) only: oxidation of electron transport chain between two photosystems, and reduction of NADP+ both PS II and PS I: light absorption and reduction of primary electron acceptor The key function of each of the two photosystems is to absorb light and convert the energy of the absorbed light into redox energy, which drives electron transport. In PS II (the first photosystem in the sequence), P680 is oxidized (which in turn oxidizes water), and the PS II primary electron acceptor is reduced (which in turn reduces the electron transport chain between the photosystems). In PS I, the PS I primary electron acceptor is reduced (which in turn reduces other compounds that ultimately reduce NADP+ to NADPH), and P700 is oxidized (which in turn oxidizes the electron transport chain between the photosystems).
G3P is used in which of the following processes?
Production of glucose, starch, cellulose, sucrose, of cell walls in growing plants, or all of the listed processes can use G3P All of the listed processes can use G3P
Carbon dioxide and oxygen enter and exit a leaf by diffusion. Which structure(s) on a leaf allow(s) this process to happen?
Stomata
Where does the Calvin cycle of photosynthesis occur?
Stroma
Drag the labels onto the flowchart to show the relationship between the production of photons by the sun (Engelmann's light source) and the distribution of bacteria that Engelmann observed under his microscope. Not all labels will be used.
Sun emits photons at all wavelengths --> prism disperses sunlight into individual wavelengths --> alga's photosynthetic pigments absorb photons at specific wavelengths --> absorbed photons drive photosynthesis in alga --> alga gives off oxygen as it photosynthesizes --> bacteria attracted to regions of highest oxygen concentration --> number of bacteria in different wavelength regions counted In this experiment, Engelmann was able to determine which wavelengths (colors) of light are most effective at driving photosynthesis. First, Engelmann used a prism to disperse white light from the sun into the colors (wavelengths) of the visible spectrum. Then, using a microscope, he illuminated a filament of green algae with the visible spectrum. The photosynthetic pigments in the alga absorbed some of the wavelengths of light, using the absorbed energy to drive the reactions of photosynthesis, including oxygen production. Engelmann used his recently discovered aerotactic bacteria to determine which wavelengths of light caused the alga to photosynthesize most. Because the aerotactic bacteria were attracted to areas of highest oxygen concentration, they congregated around the regions of the alga that photosynthesized the most. He then counted the bacteria associated with each region of the alga illuminated by the various colors of light. Engelmann found that some wavelengths of light attracted more bacteria, suggesting that these wavelengths drive more photosynthesis than others
During the Calvin cycle, what happens during the carbon fixation phase?
The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five-carbon sugar named ribulose bisphosphate.
Drag the labels to the appropriate targets to indicate the numbers of molecules of ATP/ADP, NADPH/NADP+, and Pi (inorganic phosphate groups) that are input to or output from the Calvin cycle.
The Calvin cycle requires a total of 9 ATP and 6 NADPH molecules per G3P output from the cycle (per 3 CO2 fixed). In Phase 2, six of the ATP and all of the NADPH are used in Phase 2 to convert 6 molecules of PGA to 6 molecules of G3P. Six phosphate groups are also released in Phase 2 (derived from the 6 ATP used). In the first part of Phase 3, 5 molecules of G3P (1 phosphate group each) are converted to 3 molecules of R5P (also 1 phosphate group each). Thus there is a net release of 2 Pi. In the second part of Phase 3, 3 ATP molecules are used to convert the 3 R5P into 3 RuBP. Note that in the entire cycle, 9 ATP are hydrolyzed to ADP; 8 of the 9 phosphate groups are released as Pi, and the ninth phosphate appears in the G3P output from the cycle.
Which of the following statements correctly describes the difference in carbon fixation between C3 and C4 plants?
The first product of carbon fixation in C4 plants is a four-carbon compound instead of a three-carbon compound.
During which process is molecular oxygen produced in photosynthesis?
The light reactions by linear electron flow
What assumptions did Engelmann make in order to conclude that red and violet-blue light were more effective than green light in driving photosynthesis? Select the two that apply.
The number of bacteria clustered at each wavelength (color) was approximately proportional to the amount of oxygen being produced by that portion of the alga. The distribution of chloroplasts within each algal cell was approximately the same. For Engelmann to be able to draw meaningful conclusions from his experiment, he had to assume that the number of bacteria at any location on the slide was proportional to the amount of oxygen produced by the alga at that location. If this were not the case, the distribution of the bacteria around the alga would be of no use in determining the amount of photosynthesis that occurs at each wavelength. Similarly, it was necessary for Engelmann to assume that the distribution of chloroplasts among the cells in the algal filament was approximately equal. Fewer chloroplasts in one cell compared to another would mean a lower potential for oxygen production at any color. Engelmann's microscope was sufficiently powerful to see that Cladophora cells contain many small chloroplasts that were nearly uniform in their distribution within and between cells. In contrast, Engelmann did not assume that the alga absorbed the same number of photons at each wavelength. In fact, most photosynthetic pigments absorb more strongly in the red and blue parts of the spectrum and less strongly in the yellow and green parts. He also did not assume that all absorbed photons drive photosynthesis, and thus oxygen production, by the alga. In fact, all photosynthetic organisms contain some pigments that absorb photons but do not contribute to photosynthesis or oxygen production.
Why are most autotrophs referred to as the producers of the biosphere?
They are the ultimate sources of organic compounds for all nonautotrophic organisms.
The light reactions of photosynthesis use chemiosmosis to produce ATP that will be used in the Calvin cycle. The electrochemical gradient that drives this chemiosmosis is formed across which structure(s)?
Thylakoid membrane
Chlorophyll molecules are in which part of the chloroplast?
Thylakoid membranes
Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?
Water is oxidized and carbon dioxide is reduced.
You have a large, healthy philodendron that you carelessly leave in total darkness while you are away on vacation. You are surprised to find that it is still alive when you return. What has the plant been using for an energy source while in the dark?
While it did have access to light, the plant stored energy in the form of sugars or starch, and it was able to derive energy from the stored molecules during your vacation.
The energy used to produce ATP in the light reactions of photosynthesis comes from __________.
movement of H+ through a membrane
When chloroplast pigments absorb light, __________.
their electrons become excited
How does carbon dioxide enter the leaf?
through the stomata
The light reactions of photosynthesis occur in the __________.
thylakoids
Both mitochondria and chloroplasts __________.
use chemiosmosis to produce ATP
The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from __________.
water
Where do the electrons entering photosystem II come from?
water
Which red line shows the same action spectrum corrected for the unequal number of photons emitted across the visible spectrum?
Graph with black and red line not touching until around 550 nm, red line above the black An action spectrum is typically plotted so that the "action" shown on the y-axis is measured with an equal number of photons at each wavelength of the visible spectrum. But our sun does not emit equal numbers of photons at each wavelength. Instead, the sun emits the most photons in the yellow part of the spectrum, with relatively fewer photons emitted in the red and violet-blue parts of the spectrum. Thus, the red and violet-blue regions of Engelmann's action spectrum were measured with fewer photons than in the yellow part of the spectrum. To correct for this, you have to consider how increasing the number of photons in the red and violet-blue parts of the spectrum--to match the emission level in the yellow part--would change the amount of oxygen produced, and thus the number of bacteria that accumulated, in the red and violet-blue spectral regions. The corrected action spectrum would show higher peaks in the red and violet-blue parts of the spectrum, but the plot in the yellow part of the spectrum would be approximately the same as Engelmann's.
The light reactions of photosynthesis generate high-energy electrons, which end up in __________. The light reactions also produce __________ and __________.
NADPH; ATP; oxygen
For each step of photosynthetic electron flow from water to NADP+, drag the appropriate label to indicate whether or not that step requires an input of energy.
Water --> P680+ - no energy input required P680 --> Pq (plastoquinone) - energy input required Pq --> P700+ - no energy input required P700 --> Fd (ferredoxin) - energy input required Fd --> NADP+ - no energy input required In both PS II and PS I, light energy is used to drive a redox reaction that would not otherwise occur. In each photosystem, this redox reaction moves an electron from the special chlorophyll pair (P680 in PS II and P700 in PS I) to that photosystem's primary electron acceptor. The result in each case is a reductant (the reduced primary electron acceptor) and an oxidant (P680+ in PS II and P700+ in PS I) that are able to power the rest of the electron transfer reactions without further energy input.
For each intermediate compound in the Calvin cycle, identify the number of molecules of that intermediate and the total number of carbon atoms contained in those molecules. As an example, the output G3P is labeled for you: 1 molecule with a total of 3 carbon atoms. Labels may be used once, more than once, or not at all.
a. 3 molecules, 3 carbons b. 6 molecules, 18 carbons c. 6 molecules, 18 carbons d. 5 molecules, 15 carbons e. 3 molecules, 15 carbons, f. 3 molecules, 15 carbons Counting carbons—keeping track of where the carbon atoms go in each reaction—is a simple way to help understand what is happening in the Calvin cycle. To produce 1 molecule of G3P (which contains 3 carbons), the Calvin cycle must take up 3 molecules of CO2 (1 carbon atom each). The 3 CO2 molecules are added to 3 RuBP molecules (which contain 15 total carbon atoms), next producing 6 molecules of 3-PGA (18 total carbon atoms). In reducing 3-PGA to G3P (Phase 2), there is no addition or removal of carbon atoms. At the end of Phase 2, 1 of the 6 G3P molecules is output from the cycle, removing 3 of the 18 carbons. The remaining 5 G3P molecules (15 total carbon atoms) enter Phase 3, where they are converted to 3 molecules of R5P. Finally, the R5P is converted to RuBP without the addition or loss of carbon atoms.
