Biology 251 Week 4

How many electrons at a time are passed between the pigment molecules in the light-harvesting complexes? A) 0 B) 1 C) 2 D) 3 E) 4

A) 0

For every molecule of O2 that is released by photosystem II, ______ H2O molecules are needed, which together pass ________ electrons to the PS II reaction-center complex. A) 2 B) 3 C) 4 D) 6

A) 2 and C) 4

In eukaryotes, all the reactions of photosynthesis occur in various membranes and compartments of the chloroplast. -Identify the membranes or compartments of the chloroplast by dragging the blue labels to the blue targets. -Then, identify where the light reactions and Calvin cycle occur by dragging the pink labels to the pink targets.

A) Stroma B) Thylakoid membrane C) Cytosol D) Location of Calvin cycle E) Thylakoid Space F) Location of light reactions G)Envelope membranes

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

D) transfer fixed carbon dioxide to cells in which the Calvin cycle occurs

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.

See photo for answers

This diagram shows the basic pattern of electron transport through the four major protein complexes in the thylakoid membrane of a chloroplast. 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. 1.) Water --> P680+ 2.) P680 --> Pq (plastoquinone) 3.) Pq --> P700+ 4.) P700 --> Fd (ferredoxin) 5.) Fd --> MADP+

1.) Water --> P680+ no energy input required 2.) P680 --> Pq (plastoquinone) energy input required 3.) Pq --> P700 no energy input required 4.) P700 --> Fd (ferredoxin) energy input required 5.) Fd --> NADP+ no energy input required

In C4 and CAM plants carbon dioxide is fixed in the _____ of mesophyll cells. A) Cytoplasm B) Stomata C) Stroma D) Grana E) Thylakoids

A) Cytoplasm

If the Calvin cycle slows down, what will happen to the rate of O2 production in PS II, and why? A) O2 production will slow down because less NADP+ will be regenerated in the Calvin cycle. B) O2 production will slow down because the chloroplast will need less light energy to send to the Calvin cycle. C) O2 production will not change because light energy will still be absorbed by the pigment molecules and excite the PS II chlorophyll a pair. D) O2 production will not change because the Calvin cycle is a separate process from the light reactions. E)O2 production will speed up because not as much NADPH will be used in the Calvin cycle and so it will accumulate in the chloroplast.

A) O2 production will slow down because less NADP+ will be regenerated in the Calvin cycle.

When a pigment molecule in a light-harvesting complex absorbs a photon of light, what happens to its excited-state electron? A) The electron falls back to its ground state, while passing its excited-state energy to an electron in a nearby pigment molecule. B) The excited-state electron excites electrons in other pigments around it, so that multiple pigments can send electrons to P680 or P700. C) The excited-state electron is passed to electron acceptors P680 or P700. D) The excited-state electron is removed and transferred to a nearby pigment molecule, causing the next pigment to enter an excited state.

A) The electron falls back to its ground state, while passing its excited-state energy to an electron in a nearby pigment molecule.

In C3 plants the conservation of water promotes _____. A) The light reactions B) Photorespiration C) The opening of stomata D) A shift to C4 photosynthesis E) Photosynthesis

B) Photorespiration

Why is it correct to say that the linear electron flow of the light reactions directly captures energy in NADPH but only indirectly captures energy in ATP? A) Electrons are directly transferred to NADP+ to form NADPH in the electron transport chain after PS I, but ATP synthesis requires electrons that have flowed through both photosystems. B) Electrons used to generate ATP are extracted from water, but electrons used to generate NADPH come directly from PS I. C) Electrons are directly transferred to NADP+ to form NADPH, but electron flow is used to generate a proton gradient for ATP synthesis. Electrons are not directly transferred to ATP. D) NADPH is generated directly in the chloroplast, but ATP is synthesized in the mitochondrion. E) Light energy is used to excite electrons used to generate NADPH, but the energy used to make ATP comes from the cytochrome complex.

C) Electrons are directly transferred to NADP+ to form NADPH, but electron flow is used to generate a proton gradient for ATP synthesis. Electrons are not directly transferred to ATP.

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). A) The rate of O2 production would remain the same because the light reactions are independent of the Calvin cycle. B) The rate of O2 production would decrease because the rate of G3P production by the Calvin cycle would decrease C) The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease. D) The rate of O2 production would remain the same because the light intensity did not change.

C) The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease.

Which of the following is the correct order of electron flow in the light reactions of photosynthesis? A) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → ATP → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → NADPH B) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → ATP C) O2 → P680 chlorophyll a pair → PS I primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS II primary electron acceptor → Fd → NADPH D) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → NADPH E) H2O → P700 chlorophyll a pair → PS I primary electron acceptor → Pc → cytochrome complex → Pq → P680 chlorophyll a pair → PS II primary electron acceptor → Fd → NADPH Submit

D) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → NADPH

The light reactions require the cooperation of two photosystems to power linear electron flow from water to NADP+. 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 ll (PS ll) only-- oxidation of water and reduction of electron transport chain between the two photosystems Photosystem l (PS l) only-- oxidation of electron transport chain between the two photosystems and reduction of NADP+ Both PS ll and PS l-- reduction of primary electron acceptor and light absorption

ATP synthesis in chloroplasts is very similar to that in mitochondria: Electron transport is coupled to the formation of a proton (H+) gradient across a membrane. The energy in this proton gradient is then used to power ATP synthesis. Two types of processes that contribute to the formation of the proton gradient are: --processes that release H+ from compounds that contain hydrogen, and --processes that transport H+ across the thylakoid membrane.

See photo for answers

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.

See photo for answers

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. Labels may be used once, more than once, or not at all.

See photo for answers

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.

See photos for answers

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-reaction produce _____ to ______. 4. The electrons derived from this oxidation in the Calvin cycle are used to reduce _____ to _____.

1. H2O to O2 2. NADP+ to NADPH 3. NADPH to NADP+ 4. CO2 to G3P