Mastering Biology Homework: Photosynthesis

True or False? The chemiosmotic hypothesis states that the synthesis of ATP generates a proton gradient that leads to electron flow through an electron transport chain.

False (The chemiosmotic hypothesis states that the flow of electrons through an electron transport chain generates a proton gradient that leads to the synthesis of ATP)

After 3-PGA is phosphorylated, it is reduced by ______. - NADPH - ATP - CO2 - ADP - NADP+

NADPH (NADPH supplies the electrons that reduce the phosphorylated 3-PGA.

Which term describes ATP production resulting from the capture of light energy by chlorophyll? - Substrate-Level phosphorylation - Photophosphorylation - Dephosphorylation Oxidative phosphorylation

Photophosphorylation (The excitation of chlorophyll by light energy initiates a chain of events that leads to ATP production)

In C3 plants, the conservation of water promotes ______. - the light reactions - a shift to C4 photosynthesis - the opening of stomata - photosynthesis - photorespiration

Photorespiration (Conserving water simultaneously reduces the amount of carbon dioxide available to the plant)

_______ splits water into 1/2 O2, H+ and e-

Photosystem II

How many carbon dioxide molecules must be added to RuBP to make a single molecule of glucose? - 6 - 2 - 10 - 4 - 8

6 (Six carbon dioxide molecules are required to produce two G3P molecules, which can be combined to make one glucose molecule)

Which of these equations best summarizes photosynthesis? - 6 CO2 + 6 O2 → C6H12O6 + 6 H2O - C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy - 6 CO2 + 6 H2O → C6H12O6 + 6 O2 - C6H12O6 + 6 O2 → 6 CO2 + 12 H2O - H2O → 2 H+ + 1/2 O2 + 2e-

- 6 CO2 + 6 H2O → C6H12O6 + 6 O2

Engelmann counted the number of bacteria that were attracted to the algal filament associated with each color of light. As shown in the image below, most of the bacteria were attracted to the regions of the alga illuminated by red or violet-blue light. This distribution of bacteria shows that red and violet-blue wavelengths are most effective in driving photosynthesis. By measuring oxygen production with aerotactic bacteria, Engelmann described an action spectrum for photosynthesis. The action spectrum (indicated by the black line plot in the image above) shows the relative effectiveness of each color of light in driving photosynthesis. 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. - Every photon absorbed by the alga was used to drive oxygen production by the alga - The distribution of chloroplasts within each algal cell was approximately the same - The number of bacteria clusters at each wavelength (color) was approximately proportional to the amount of oxygen being produced by that portion of alga - The alga absorbed the same number of photons at each wavelength (color)

- The distribution of chloroplasts within each algal cell was approximately the same - The number of bacteria clusters at each wavelength (color) was approximately proportional to the amount of oxygen being produced by that portion of alga (Assumed: 1. The number of bacteria at any location on the slide was proportional to the amount of oxygen produced by the alga at that location 2. The distribution of chloroplasts among the cells in the algal filament was approximately equal Not assumed: 1. The alga absorbed the same number of photons at each wavelength 2. All absorbed photons drive photosynthesis, and thus oxygen production, by the alga

In photosynthesis, a redox compound that is produced in the light reactions is required to drive other redox reactions in the Calvin cycle, as shown in this figure along with other components of photosynthesis. Drag the terms to the appropriate blanks to complete the following sentences summarizing the redox reactions of photosynthesis. Terms may be used once, more than once, or not at all. 1. In the light reactions, light energy is used to oxidize _____ to ____. 2. The electrons derived from this oxidation reaction in the light reactions are used to reduce ____ to ____. 3. The Calvin cycle oxidizes the light-reactions product ____ to ____. 4. The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce ____ to ____.

1. In the light reactions, light energy is used to oxidize H2O to O2. 2. The electrons derived from this oxidation reaction in the light reactions are used to reduce NADP+ to NADPH. 3. The Calvin cycle oxidizes the light-reactions product NADPH to NADP+ 4. The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce CO2 to G3P.

Match items for energy use during photosynthetic electron flow from water to NADP+ 1. Water --> P680+ 2. P680 --> Pq (plastoquinone) 3. Pq --> P700+ 4. P700 --> Fd (ferredoxin) 5. Fd --> NADP+

1. No energy input required 2. Energy input required 3. No energy input required 4. Energy input required 5. No energy input required

In Engelmann's experiment, he used aerotactic (oxygen-seeking) bacteria to determine which wavelengths of visible light were most effective in driving the reactions of photosynthesis in green algae. A diagram of his apparatus is shown below. Can you deduce the logical link between light of different wavelengths and the distribution of bacteria that Engelmann observed? 1. Sun emits photons at all wavelengths .... 7. Number of bacteria in different wavelength regions counted.

2. Prism disperses sunlight into individual wavelengths 3. Alga's photosynthetic pigments absorb photons at specific wavelengths 4. Absorbed photons drive photosynthesis in alga 5. Alga gives off oxygen as it photosynthesizes 6. Bacteria attracted to regions of highest oxygen concentration (Engelmann was able to determine which wavelengths (colors) of lights are most effective at driving photosynthesis - he found that some wavelengths of light attracted more bacteria than others)

In the Calvin cycle, how many ATP molecules are required to generate RuBP from five G3P molecules? - 2 - 1 - 5 - 4 - 3

3

What phosphorylates ADP to make ATP?

ATP synthase

Chloroplast membrane vesicles are equilibrates in a simple solution of pH 5. The solution is then adjusted to pH 8. Which of the following conclusions can be drawn from these experimental conditions? - The change in the solution's pH results in a gradient across the chloroplast membranes such that there is a lower concentration of protons inside the vesicle and a higher concentration outside - Protons will not diffuse toward the outside of the vessicles. - ATP will not be produced because there is no ADP and inorganic phosphate in the solution - ATP will be produced because the protein gradient favors proton movement through the ATP synthase channels.

ATP will not be produced because there is no ADP and inorganic phosphate in the solution (Although the proton gradient is present, ADP and inorganic phosphate are required to make ATP and were not added to the reaction)

In C4 and CAM plants, carbon dioxide is fixed in the ______ of mesophyll cells. - Thylakoids - Cytoplasm - Grana - Stomata - Stroma

Cytoplasm

_______ releases energy that is used to pump hydrogen ions from the storm into the thylakoid membrane..

Electrons (The energy released as electrons are passed along the transport chain and is used to pump protons into the thylakoid compartment)

True or false? The region of ATP synthase that catalyzes the production of ATP from ADP and inorganic phosphate spans the entire chloroplast membrane

False (The region of ATP synthase that catalyzes ATP production protrudes out of, but does not span, the chloroplast membrane; the region that spans the membrane is an ion channel through which proteins can pass)

Inputs and Outputs of the Light Reactions: From the following choices, identify those that are the inputs and outputs of the light reactions. (Recall that inputs to chemical reactions are modified over the course of the reaction as they are converted into products. In other words, if something is required for a reaction to occur, and it does not remain in its original form when the reaction is complete, it is an input.) Drag each item to the appropriate bin. If the item is not an input to or an output from the light reactions, drag it to the "not input or output" bin.

Inputs: - light - NADP+ - water - ADP Outputs: - NADPH - ATP - O2 Neither input or output: - glucose - CO2 - G3P

Inputs and Outputs of the Calvin Cycle: From the following choices, identify those that are the inputs and outputs of the Calvin cycle. Drag each item to the appropriate bin. If the item is not an input to or an output from the Calvin cycle, drag it to the "not input or output" bin.

Inputs: - NADPH - ATP - CO2 Outputs - ADP - NADPH - G3P Neither inputs or outputs - O2 - glucose - light

Energized electrons from ______ enter an electron transport chain and are then reduce NADP+.

Photosystem I

What processes are associated with Photosystem II (PS II) only, Photosystem I (PS I) only, or both PS II and PS I?

Photosystem II (PS II) only: - Oxidation of water - Reduction of electron transport chain between the two photosystem Photosystem I (PS I) only: - Oxidation of electron transport chain between the two photosystems - Reduction of NADP+ Both PS II and PS I - Light absorption - Reduction of primary electron acceptor

Chlorophyll can be found in ______.

Photosystem II and Photosystem I

According to the chemiosmotic hypothesis, what provides the energy that directly drives ATP synthesis? - Electrons - Proton gradient _ Temperature gradient _ Osmotic gradient

Proton gradient (A proton gradient across the chloroplast and mitochondrial membranes drives ATP synthesis by the enzyme ATP synthase)

Which of the following particles can pass through the ATP synthase channel? - ATP - Protons - Inorganic phosphate - ADP

Protons (The channels formed by ATP synthase are specific for protons)

Carbon fixation involves the addition of carbon dioxide to ______. - G3P - 3 -PGA - RuBP - Rubisco - NADPH

RuBP (Carbon dioxide is added to RuBP in the Calvin cycle)

Where does the Calvin cycle occur?

Stroma (the fluid between the inner membrane of the chloroplast and thylakoid)

Do the light reactions of photosynthesis depend on the Calvin cycle? The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. Thus, lower light levels generally mean a lower rate of O2 production. In addition, lower light levels also affect the rate of CO2 uptake by the Calvin cycle. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. In this way, the Calvin cycle depends on the light reactions. But is the inverse true as well? Do the light reactions depend on the Calvin cycle? 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 ad 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.)

How is Engelmann's action spectrum deduced from the distribution of aerotatic bacteria around the alga?

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

C4 plants differ from C3 and CAM plants in that C4 plants _____. - open their stomata only at night - are better adapted to wet conditions - transfer fixed carbon dioxide to cells in which the Calvin cycle occurs - use PEP carboxylase to fix carbon dioxide - use magic acid to transfer carbon dioxide to the Calvin cycle

Transfer fixed carbon dioxide to cells in which the Calvin cycle occurs (In C3 and CAM plants, carbon dioxide fixation and the Calvin cycle occur in the same cells)

The light reactions of photosynthesis use ______ and produce ______. - water ... NADPH - carbon dioxide ... oxygen - carbon dioxide ... sugar - NADPH ... oxygen - NADPH ... NADP+

Water ... NADPH (NADPH is a reactant in the Calvin cycle)

Following carbon atoms around the Calvin cycle: The net reaction of the Calvin cycle is the conversion of CO2 into the three-carbon sugar G3P. Along the way, reactions rearrange carbon atoms among intermediate compounds and use the ATP and NADPH produced by the light reactions. In this exercise, you will track carbon atoms through the Calvin cycle as required for the net production of one molecule of G3P. 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.

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 (-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.

Quantifying the inputs of ATP and NADPH and output of Pi The Calvin cycle depends on inputs of chemical energy (ATP) and reductant (NADPH) from the light reactions to power the conversion of CO2 into G3P. In this exercise, consider the net conversion of 3 molecules of CO2 into 1 molecule of G3P. 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.

a. 6 ATP 6 ADP b. 6 NADPH 6 NADP+ c. 6 Pi d. 2 Pi e. 3 ADP 3 ATP 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.

Photosynthesis and respiration in plants... ___a____ provides energy for ___b___ which occurs in ___c____ which contains the pigment ______. ___b____ produces oxygen and ___d___ which are inputs for ___e___ which occurs in ___f___ that produces ATP and ___g___ and which provides carbon for ___b___.

a. sunlight b. photosynthesis c. chloroplasts d. sugar e. chlorophyll f. cellular respiration g. mitochondria h. carbon dioxide (A mutually dependent relationship exists between chloroplasts and mitochondria in the plant cell. Photosynthesis, which occurs in chloroplasts, generates the sugars and oxygen gas that are used in mitochondria for cellular respiration. Cellular respiration generates carbon dioxide, which in turn is used as a carbon source for the synthesis of sugars during photosynthesis. Cellular respiration also generates ATP and water, which are used in various chemical reactions in the plant cell)