Chapter 8 Practice Questions

a. photosynthesis stores energy in organic molecule while respiration releases it

d. from breakdown of water

d. carboxylation, reduction, regeneration

c. oxidized

True

e. passed to a reaction center

d. cytochrome b6f

a. different electron acceptors and electron sources STUDY THIS

True

d. all three of these steps are hypothesized to have been important in the evolution of photosynthesis

c. carbon dioxide; sugar

False. Photosynthetic organisms can be in the photic zone which is from the surface of the ocean to about 100 meters deep because enough sunlight penetrates to enable photosynthesis. Photosynthesis can also occur in places that are moist and warm like grasslands and tropical rainforests. Photosynthesis can occur in dry regions as well with a combination of photosynthetic bacteria and unicellular algae that form an easily disturbed layer on the surface of the soil known as desert crust.

d. RuBP The carboxylation step of the Calvin cycle is where carbon dioxide is added to the five carbon molecule. Refer to page 157,158 in your book. The 5-carbon sugar is called ribulose 1,5-biphosphate (RuBP) and is catalyzed by the enzyme ribulose biphosphate carboxylase oxygenase (rubisco). RuBP and Co2 diffuse into the active site of rubisco and once the active site is occupied the addition of CO2 to RuBP proceeds spontaneously in the sense that NO ADDITION OF ENERGY IS REQUIRED. The product of caraboxylation is a 6-carbon compound that immediately breaks into two molecules of 3-phosphoglycerate (3-PGA).

b. donate a phosphate group to 3-PGA Nicotinamide adenine dinucleotide phosphate (NADPH) is the reducing agent used in the Calvin cycle and transfers the electrons that allow carbohydrates to be synthesized from CO2 so that rules out a and e. On page 158, "Regeneration of RuBP requires ATP". The reduction of 3-phosphoglyerate consists of two steps. The first step is that ATP donates a phosphate group to 3-PGA.

b. Electrons can be extracted from water and used to reduced NADP+ to NADPH.

b. NADP+

b. cyanobacteria

False. On page 170 of your book, it says, "Similarly, it is unlikely that these first photosynthetic organisms employed chlorophyll as a means of absorbing sunlight for the simple reason that the biosynthetic pathway for chlorophyll is complex, consisting of at least 17 enzymatic steps".

b. lumen

a. CO2 The Calvin cycle begins with carboxylation which is the addition of carbon dioxide to the five carbon structure.

a. The rate of ATP synthesis by ATP synthase will decrease. pH is determined by the negative log of the concentration of H+ ions The more H+ ions in a solution, the more acidic it is. On page 164, it says, "When the photosynthetic electron transport chain is operating at full capacity, the concentration of protons in the lumen can be more than 1000 times greater than their concentration in the stroma (equivalent to a difference of 3 pH units). This accumulation of proteins on one side of the thylakoid membrane can then be used to power the synthesis of ATP by oxidative phosphorylation". So when the electron transport chain is working at full capacity, the liquid inside the lumen is more acidic than basic since there is a lot more of a concentration of protons in the lumen than that of the stroma. As the solution gets more basic from a transition of a pH of 4 to 6, the concentration of H+ ions in the lumen is decreasing. When there was a higher concentration of H+ ions (more acidic) it was ideal and then the synthesis of ATP was high. When there is a lesser H+ concentration, it will slow it down.

c. thylakoid membrane The reaction center is where energy is transferred between chlorophyll molecules until it is finally transferred to a specifically configured pair of chlorophyll molecules called the reaction center In the reaction center, light is converted into chemical energy as a result. The reaction center is within the electron transport chain and the electron transport chain is within the thylakoid membrane.

c. the acquisition of two photosystems by cyanobacteria

False

c. CO2, O2, and RuBP Rubisco is in the carboxylation stage of the Calvin cycle and acts as a carboxylase because it adds carbon dioxide to the 5-carbon sugar called ribose 1,5-biphosphate (RuBP). Both RuBP and CO2 have to bind to the active site for the reaction to proceed. This reaction is spontaneous. According to section 8.4, rubisco can catalyze the addition of either carbon dioxide or oxygen to RuBP, but the addition of oxygen instead of carbon dioxide can substantially reduce the amount of carbohydrate produced.

a. light, electrons, and protons Accumulation of protons in the thykaloid lumen drives the synthesis of ATP. ATP synthase synthesizes ATP in the chloroplasts/mitochondria. Cell uses light energy to produce ATP. Movement of electrons through the photosynthetic electron train leads to the formation of ATP.

False

c. thylakoids; stroma The thylakoid membranes are structures that resemble flattened sacs that are grouped into structures called grana that are within a chloroplast. Page 156 says, "The photosynthetic electron transport chain is located in the thylakoid membrane". The stroma is the region surrounding the thylakoid membrane where carbohydrate synthesis takes place. Sunlight is captured and transformed into chemical energy by the photosynthetic electron transport chain in the thylakoid membrane.

c. Reduction Carboxylation is the first step within the Calvin cycle where a carbon dioxide is bonded to a 5-carbon sugar called RuPB. Reduction is the second step of the Calvin cycle where NADPH is needed. NADPH is a reducing agent that is used in the Calvin cycle that transfers electrons that allow carbohydrates to be synthesized from carbon dioxide. Reduction is the addition of an electron to something. In this step, NADPH transfers two electrons and one proton to the phosphorylated compound which releases one phosphate group to form the triose phosphates.

e. All of these choices are correct. Reactive oxygen species are highly reactive forms of oxygen that can be formed either by the transfer of absorbed light energy from antenna chlorophyll directly to O2 or by the transfer of an electron forming O2-. By the Calvin cycle's use of NADPH, NADP+ is returned to the photosynthetic electron transport chain which means any factor that causes the rate of NADPH use to fall behind the rate of light-driven electron transport can potentially lead to damage. Some chemicals can detoxify reactive oxygen species like ascorbate (vitamin C), beta carotene, and other antioxidants. Xanthophyll are yellow-orange pigments that slow the formation of reactive oxygen species by reducing excess light energy.

True.

b. NADPH Nicotinamide adenine dinucleotide phosphate is the reducing agent that is used to the Calvin cycle that transfers electrons that allow carbohydrates to be synthesized from carbon dioxide.

d. produce O2 Photosystems are protein-pigment complexes and functional and structural units that absorb light energy and use it to drive electron transport. O2 is the by-product of pulling electrons from water. Water is abundant within cells and is always available to serve as an electron donor in photosynthesis, but O2 diffuses away readily rather than accumulates. It takes a great deal of energy to pull electrons from water. The amount of energy that a single photosystem can capture from sunlight is not enough both to pull an electron from water and produce an electron donor capable of reducing NADP+. Photosystem II supplies electrons at the beginning of the electron transport chain and when Photosystem II loses an electron it is able to pull electrons from water. Photosystem I energizes electrons with a second input of light energy so they can be used to reduce NADP+.

d. decrease photorespiration rates Photorespiration is the process of consumption of O2 and release of CO2 in the presence of light. The reaction speed is affected because rubisco is an enzyme that is highly selective to favor the addition of carbon dioxide over oxygen. As temperatures get lower, the activity of rubisco is slow. Rubisco wants to be slow so that it will be highly selective and choose CO2 over O2 when binding with RuBP. Rubisco can have O2, but it is bad for the cell. Photorespiration is when O2 binds to the active site, but if the reaction is slow there is a lesser chance of that happening.

b. Glucose is stored as starch. - The Calvin cycle is capable of producing more carbohydrates than the cell needs or, in a multicellular organism, more than the cell is able to export. - If carbohydrates accumulated in the cell, they would cause water to enter the cell by osmosis which can damage the cell. Carbohydrates are formed in the reduction stage of the Calvin cycle. This can be studied on page 159 in figure 8.6. Melvin Calvin and Andrew Benson used 14CO2 to follow the incorporation of CO2 into carbohydrates. The first step in the first experiment was to inject 14CO2 into a flask containing Chlorella. (14 stands for the atomic mass, and in the 1940's radioactive 14CO2 became available in quantities that allowed experiments). The second step in the first experiment was that after a specified amount of time, drop cells of chlorella into boiling alcohol to halt the reactions. The third step in the first experiment was to identify radioactively labeled compounds using 2D paper chromatography. 2D paper chromatography separates molecules according to factors such as size and charge that affect their mobility. The results of the first experiment was that RuBP, triode phosphates, and 3-PGA all showed up. The first step of the second experiment was to shorten exposure to 14CO2 enough so that only one compound is labeled on the 2D paper chromatography. After only a short exposure to light, 3-PGA was the initial product of carboxylation. Experiment 3 was following exposure to 14CO2 as in experiment 1, it prevented carboxylation by withholding CO2 and seeing which labeled product increases and which decreases. When withholding CO2, RuBP increases while 3-PGA decreases relative to the amounts in Experiment 1, RuBP is the other substrate involved in the carboxylation step.

a. An excited-state antenna chlorophyll Most of the chlorophyll molecules in the thylakoid membrane act as an antennae. Energy is transferred between chlorophyll molecules until it is finally transferred to a specially configured pair of chlorophyll molecules known as the reaction center. The reaction energy is where light energy is converted into chemical energy and a result of the excited electron's transfer to an adjacent molecule. Antennae gather light energy.

b. No, because the light absorbed by chlorophyll would be released as heat and thus not used to make ATP or NADPH. Xanthophylls slow the forming of reactive oxygen species by reducing excess light energy. They convert light energy into heat.

b. a plasma membrane REVIEW

c. donate a phosphate group to 3-PGA

d. energy transfer

a. produce ATP; reduce CO2 The Calvin cycle requires two molecules of NADH and three molecules of ATP per CO2 incorporated in to carbohydrates. The transport of four electrons through the photosynthetic electron transport chain needed to reduce NADP molecules does not transfer enough protons into the lumen to produce the required 3 ATPs. In addition to the electron transport chain, another electron transport is needed to increase the production of ATP. Cyclic electron transport causes electrons from photosystem 1 to be redirected from ferrodoxin back into the electron transport chain. These electrons reenter the photosynthetic electron transfer chain.

e. None of the other answer options is correct.

e. absorb light energy Photosystem II supplies electrons to the beginning of the electron transport chain. When photosystem II loses an electron and is oxidized, it is able to pull electrons from water.

a. ATP and NADPH The process of the photosynthetic electron transport chain is as follows: 1. begins with the absorption of sunlight by protein-pigment complexes 2. absorbed sunlight provides energy that drives electrons through the photosynthetic electron transport chain - movement of electrons through the transport chain is used to produce ATP and NADPH which are the energy sources needed to synthesize carbohydrates using CO2 in the calvin cycle

b. they take place in different compartments of the same organelle. Light dependent reactions take place in the thylakoid membrane within the chloroplast. The Calvin cycle takes place in the stroma of the chloroplast.

a. The protein likely travels through a common lumen shared by thylakoid membranes and grana, and cannot easily diffuse through the thylakoid membrane.

a. 2 The first step of the Calvin cycle is carboxylation where carbon dioxide is combined with RuBP which produces a 6-carbon compound that immediately breaks into two molecules of 3-phosphoglycerate which is the first stable product of the Calvin cycle. Rubisco is responsible for the addition of the carbon atoms needed for the formation of carbohydrates. For energy increase to take place, carbon compounds must be reduced. NADPH (nicotinamide adenine dinucleotide phosphate) is the reducing agent that is used to transfer electrons that allow carbohydrates to be synthesized from CO2. The next step of the Calvin cycle is the reduction of the 3-phosphoglycerate that was produced when the CO2 was added to the RuBP. ATP donates a phosphate group to 3-phosphoglycerate and NADPH transfers two electrons and one proton to the phosphorylated compound which releases one phosphate group. A triose phosphate is the result of the formation of the 3-carbon carbohydrate molecule formed by the previous energy transfer. Triose phosphates are the true products of the Calvin cycle. Triose phosphates are the form that carbohydrates are exported from the chloroplast during photosynthesis.

b. slow catalysis and the ability to use two substrates

b. none of the other answer options is correct the six carbon compound that is produced when carbon dioxide and RuBP immediately breaks into two molecules of 3-phosphoglycerate which is the first stable product of the calvin cycle.

e. narrower range of wavelength reflection

e. electrons are transferred from ferredoxin to plastoquinone