Chapter 10 - Photosynthesis Flashcards
Label the indicated parts in this diagram of a chloroplast.
a. outer membrane
b. granum
c. inner membrane
d. thylakoid space
e. thylakoid
f. stroma
Fill in the blanks in this overview of photosynthesis in a chloroplast. Indicate the locations of the processes c and h.
a. light
b. H2O
c. light reactions in thylakoid membranes
d. O2
e. ATP
f. NADPH
g. CO2
h. Calvin cycle in stroma
i. CH2O (sugar)
An action spectrum shows the relative rates of photosynthesis under different wavelengths of light.
On the following graph, label the line that represents the absorption spectrum for chlorophyll a and the line for the action spectrum for photosynthesis.
Why are these lines different?
The solid line is the absorption spectrum; the dotted line is the action spectrum.
Some wavelengths of light, particularly in the blue and the yellow-orange range, result in a higher rate of photosynthesis than would be indicated by the absorption of those wavelengths by chlorophyll a.
These differences are partially accounted for by accessory pigments, such as chlorophyll b and the carotenoids, which absorb light energy from different wavelengths and make that energy available to drive photosynthesis.
Describe the components of a photosystem.
A photosystem contains light-harvesting complexes of pigment molecules (chlorophyll a, chlorophyll b, and carotenoids) bound to particular proteins and a reaction center, which includes two chlorophyll a molecules (P700 or P680) and a primary electron acceptor.
Fill in the steps of electron flow in the following diagram.
Circle the important products that will be used to provide chemical energy and reducing power to the Calvin cycle.
a. photosystem II
b. photosystem I
c. water (H2O)
d. oxygen (½ O2)
e. P680, reaction-center chlorophyll a
f. primary electron acceptor
g. electron transport chain
h. photophosphorylation by chemiosmosis
i. ATP
j. P700, reaction-center chlorophyll a
k. primary electron acceptor
l. NADP+ reductase
m. NADPH
a. on the diagram in Question 10.5, sketch the path that electrons from P700 take during cyclic electron flow.
b. Why is neither oxygen nor NADPH generated by cyclic electron flow?
c. How, then is ATP produced by cyclic electron flow?
a. Ferredoxin (Fd) passes the electrons to the cytochrome complex in the electron transport chain, from which they return to P700+.
b. Electrons from P680 are not passed to P700. Without the oxidizing agent P680+, water is not split. Fd does not pass electrons to NADP+ reductase to form NADPH.
c. Electrons do pass down the electron transport chain, and the energy released by their “fall” drives photophosphorylation.
a. In the light, the proton gradient across the thylakoid membrane is as great as 3 pH units. On which side is the pH lowest?
b. What three factors contribute to the formation of this large difference in H+ concentration between the thylakoid space and the stroma?
a. In the thylakoid space (pH of about 5)
b. (1) transport of protons into the thylakoid space as Pq transfers electrons to the cytochrome complex;
(2) protons from the splitting of water remain in the thylakoid space;
(3) removal of H+ in the stroma during the reduction of NADP+.
Label the three phases (a through c) and the key molecules (d through o) in this diagram of the Calvin cycle.
a. carbon fixation
b. reduction
c. regeneration of CO2 acceptor (RuBP)
d. 3 CO2
e. ribulose bisphosphate (RuBP)
f. rubisco
g. 3-phosphoglycerate
h. 6 ATP → 6 ADP
i. 1,3-bisphosphoglycerate
j. 6 NADPH → 6 NADP+
k. 6 ℗i
l. glyceraldehyde-3-phosphate (G3P)
m. G3P
n. glucose and other organic compounds
o. 3 ATP → 3 ADP
What are two possible explanations for photorespiration, a process that can result in the loss of as much as 50% of the carbon fixed in the Calvin cycle?
Photorespiration may be an evolutionary relic from the time when there was little O2 in the atmosphere and the ability to rubisco to distinguish between O2 and CO2 was not critical.
Photorespiration appears to protect plants from damaging products of the light reactions that build up when the Calvin cycle slows due to a lack of CO2.
a. Where does the Calvin cycle take place in C4 plants?
b. How can C4 plants successfully perform the Calvin cycle in hot, dry conditions when C3 plants would be undergoing photorespiration?
c. C4 photosynthesis requires more ATP than does C3 photosynthesis. Why?
a. in the bundle-sheath cells
b. Carbon is initially fixed into a four-carbon compound in the mesophyll cells by PEP carboxylas. When this compound is broken down in the bundle-sheath cells, CO2 is maintained at a high enough concentration that rubisco does not accept O2 and cause photorespiration.
c. ATP is used to convert pyruvate, returning from the bundle-sheath cells, to PEP in te mesophyll cells.
Create a diagram of the key events of photosynthesis.
Trace the flow of electrons through photosystems II and I, the production of ATP and NADPH by the light reactions and their transfer into the Calvin cycle, and the major steps in the production of G3P.
Note where these reactions occur in the chlorplast.
Create a concept map to confirm your understanding of the chemiosmotic synthesis of ATP in photophosphorylation.
Which of the following is mismatched with its location?
a. light reactions—grana
b. electron transport chain—thylakoid membrane
c. Calvin cycle—stroma
d. ATP synthase—double membrane surrounding chloroplast
e. splitting of water—thylakoid space
d. ATP synthase—double membrane surrounding chloroplast
Photosynthesis is a redox process in which
a. CO2 is reduced and water is oxidized.
b. NADP+ is reduced and RuBP is oxidized.
c. CO2, NADP+, and water are reduced.
d. O2 acts as an oxidizing agent and water acts as a reducing agent.
e. G3P is reduced and the electron transport chain is oxidized.
a. CO2 is reduced and water is oxidized.
Which of the following statements is false?
a. When isolated chlorophyll molecules absorb protons, their electrons fall back to ground state, giving off heat and light.
b. Accessory pigments, cyclic electron flow, and photorespiration may all contribute to photoprotection, protecting plants from the detrimental effects of intense light.
c. In the cyclic electron flow of purple sulfur bacteria, the electron transport chain would pump H+ across the plasma membrane from inside to outside the cell.
d. In both photosynthetic prokaryotes and eukaryotes, ATP synthases catalyze the production of ATP within the cytoplasm of the cell.
e. In sulfur bacteria, H2S provides the hydrogen (and thus electron) source for photosynthesis.
d. In both photosynthetic prokaryotes and eukaryotes, ATP synthases catalyze the production of ATP within the cytoplasm of the cell.
The following diagram is an absorption spectrum for an unknown pigment molecule. What color would this pigment appear to you?
a. violet
b. blue
c. green
d. yellow
e. red
b. blue
