Ch. 8: Photosynthesis

In the first part of Phase 3, the G3P molecules left over from Phase 2 are converted to R5P with the release of Pi. For the net conversion of 3 molecules of CO2 into 1 molecule of G3P by the Calvin cycle, which of the following equations correctly accounts for the inputs and outputs of phosphate groups in Phase 3? 1. 5 P (in G3P) → 3 P (in R5P) + 2 Pi 2. 6 P (in G3P) → 3 P (in R5P) + 3 Pi 3. 15 P (in G3P) → 12 P (in R5P) + 3 Pi 4. 3 P (in G3P) → 2 P (in R5P) + 1 Pi

1. 5 P (in G3P) → 3 P (in R5P) + 2 Pi In the first part of Phase 3, 5 molecules of G3P (a total of 5 phosphate groups) are converted to 3 molecules of R5P (a total of 3 phosphate groups). Thus a net of two inorganic phosphate groups (Pi) are released.

Select the correct molecule that is the main product of the Calvin cycle. 1. G3P 2. NADPH 3. Glucose

1. G3P

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

The most important role of pigments in photosynthesis is to _____. 1. capture light energy 2. screen out harmful ultraviolet rays 3. store energy 4. catalyze the hydrolysis of water 5. catalyze the synthesis of ATP

1. capture light energy

Which process is most directly driven by light energy? 1. removal of electrons from chlorophyll molecules 2. carbon fixation in the stroma 3. creation of a pH gradient by pumping protons across the thylakoid membrane 4. reduction of NADP+ molecules 5. ATP synthesis

1. removal of electrons from chlorophyll molecules

Rubisco is _____. 1. the enzyme in plants that first captures CO2 to begin the Calvin cycle 2. the enzyme responsible for splitting H2O to produce O2 in photosynthesis 3. the enzyme that forms a 4-carbon compound in CAM photosynthesis 4. the first stable intermediate in C4 photosynthesis 5. the 5-carbon sugar molecule that reacts with CO2 to begin the Calvin cycle

1. the enzyme in plants that first captures CO2 to begin the Calvin cycle

Chlorophyll molecules are in which part of the chloroplast? 1. thylakoid membranes 2. stroma 3. stomata 4. plasma membrane 5. thylakoid lumen

1. thylakoid membranes

Both mitochondria and chloroplasts _____. 1. use chemiosmosis to produce ATP 2. obtain electrons from water 3. reduce NAD+, forming NADP 4. release oxygen as a by-product 5. are surrounded by a single membrane

1. use chemiosmosis to produce ATP

Phase 1 of the Calvin cycle (carbon fixation) consists of a reaction between a molecule of CO2 and a molecule of RuBP, catalyzed by the enzyme Rubisco. For each molecule of CO2 that enters the Calvin cycle, which equation correctly represents what happens to its carbon (C) as the next intermediate is produced? 1. 1 C + 2 C → 3 C 2. 1 C + 5 C → 3 C + 3 C 3. 3 C + 15 C → 18 C 4. 3 C + 3 C → 6 C 5. 1 C + 1 C → 2 C

2. 1 C + 5 C → 3 C + 3 C In Phase 1 of the Calvin cycle, the enzyme Rubisco catalyzes the addition of CO2 (1 carbon atom) to RuBP (5 carbon atoms). The result is a short-lived 6-carbon compound that immediately breaks down into 2 molecules of 3-phosphoglycerate (PGA), each containing 3 carbon atoms.

During photosynthesis in chloroplasts, O2 is produced from _____ via a series of reactions associated with _____. 1. CO2 ... photosystem II 2. H2O ... photosystem II 3. CO2 ... the Calvin cycle 4. H2O ... photosystem I 5. CO2 ... both photosystem I and the Calvin cycle

2. H2O ... photosystem II

The transport of protons across the thylakoid membrane contributes to the proton gradient that drives ATP synthesis. This proton transport is accomplished by one of the small electron carrier molecules that shuttles electrons between the major electron transport complexes. As the carrier transports protons across the thylakoid membrane, it also shuttles electrons across the membrane. Which component of the light reactions is involved in pumping protons across the thylakoid membrane? 1. Fd (ferredoxin) as it transfers electrons from PS I to NADP+ reductase 2. Pq (plastoquinone) as it transfers electrons from PS II to the cytochrome complex 3. the PS II complex as it transfers electrons from water to Pq 4. Pc (plastocyanin) as it transfers electrons from the cytochrome complex to PS I 5. the PS I complex as it transfers electrons from Pc to Fd

2. Pq (plastoquinone) as it transfers electrons from PS II to the cytochrome complex Plastoquinone (Pq) is found in the interior of the thylakoid membrane. When it is reduced by PS II, Pq picks up two protons from the stroma. When Pq is oxidized by the cytochrome complex, it releases the two protons in the thylakoid space. The net result is pumping of protons from the stroma to the thylakoid space as electrons flow from PS II to the cytochrome complex

Select the correct statement about the Calvin cycle. 1. The Calvin cycle takes place primarily in the dark. 2. The Calvin cycle has three phases: carbon fixation, reduction, and regeneration of RuBP. 3. The basic function of the Calvin cycle is the conversion of solar energy to chemical energy.

2. The Calvin cycle has three phases: carbon fixation, reduction, and regeneration of RuBP.

Which of the following statements correctly describes the relationship between the light reactions and the Calvin cycle? 1. The light reactions produce carbon dioxide, ATP, NADPH, all of which are used in the Calvin cycle. 2. The light reactions produce ATP and NADPH, both of which are used in the Calvin cycle. 3. The light reactions produce ADP and NADP+, both of which are used in the Calvin cycle. 4. The light reactions produce water, ATP, NADPH, all of which are used in the Calvin cycle. 5. The light reactions produce carbon dioxide and water, all of which are used in the Calvin cycle.

2. The light reactions produce ATP and NADPH, both of which are used in the Calvin cycle.

In Photosystem II (PS II), light energy is used to produce an electron acceptor that is strong enough to oxidize water. How does the oxidation of water contribute to the proton gradient across the thylakoid membrane? 1. Water molecules pick up protons from the stroma and transport them to the thylakoid space, where the water is oxidized. 2. The oxidation of water by PS II releases protons in the thylakoid space. 3. Electron transport through the PS II complex pumps protons across the thylakoid membrane. 4. Oxygen molecules produced by PS II react with water, releasing protons in the thylakoid space.

2. The oxidation of water by PS II releases protons in the thylakoid space. In PS II, the oxidation of water to O2 produces protons as a byproduct. Because this reaction occurs on the thylakoid space side of PS II, these protons are released into the thylakoid space.

Why are C4 plants more suited to hot climates than C3 plants? 1. They do not close their stomata in hot, dry weather. 2. Unlike C3 plants, they keep fixing carbon dioxide even when the concentration of carbon dioxide in the leaf is low. 3. They evolved in cold weather but migrated to the tropics, where they were more suitable. 4. They suspend photosynthesis in the heat. 5. The same cells that bind carbon dioxide perform the Calvin cycle.

2. Unlike C3 plants, they keep fixing carbon dioxide even when the concentration of carbon dioxide in the leaf is low.

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? 1. Even though it can't carry out the light reactions, the plant can still produce sugars because the Calvin cycle doesn't require light. 2. 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. 3. Even though the plant received no visible light, it was able to use the short-wave part of the electromagnetic spectrum (gamma rays and X-rays) to carry out photosynthesis. 4. When light energy is not available, plants can derive energy from inorganic molecules. 5. None of the listed responses is correct.

2. 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.

In the Calvin cycle, CO2 is combined with _____. 1. a 2-carbon compound to form a 3-carbon compound 2. a 5-carbon compound to form an unstable 6-carbon compound, which decomposes into two 3-carbon compounds 3. a 7-carbon compound to form two 4-carbon compounds 4. a 5-carbon compound to form a stable 6-carbon compound that can be converted directly to glucose 5. two 2-carbon compounds to form a 5-carbon compound

2. a 5-carbon compound to form an unstable 6-carbon compound, which decomposes into two 3-carbon compounds

What is the range of wavelengths of light that are absorbed by the pigments in the thylakoid membranes? 1. green, which is why plants are green 2. blue-violet and red-orange 3. the entire spectrum of white light 4. the infrared 5. the range absorbed by carotenoids

2. blue-violet and red-orange

In photosynthesis, plants use carbon from _____ to make sugar and other organic molecules. 1. water 2. carbon dioxide 3. chlorophyll 4. the sun 5. soil

2. carbon dioxide

What structure is formed by the reaction center, light-harvesting complexes, and primary electron acceptors that cluster, and is located in the thylakoid membrane? 1. the fluorescence center 2. the photosystem 3. the electron transport chain 4. NADP+ reductase 5. ATP synthase

2. the photosystem

During photosynthesis in a eukaryotic cell, an electrochemical gradient is formed across the ______. 1. chloroplast outer membrane 2. thylakoid membrane 3.chloroplast inner membrane 4. stomata 5. cristae

2. thylakoid membrane

Which of the following statements is a correct distinction between autotrophs and heterotrophs? 1. Only heterotrophs require chemical compounds from the environment. 2. Only heterotrophs have mitochondria. 3. Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic. 4. Cellular respiration is unique to heterotrophs. 5. Only heterotrophs require oxygen.

3. Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic.

What is the basic role of CO2 in photosynthesis? 1. CO2 is a source of electrons in the formation of organic molecules. 2. CO2 is taken in by plants as a form of inverse respiration, in which carbon dioxide is "breathed in" and oxygen is "breathed out." 3. CO2 is fixed or incorporated into organic molecules.

3. CO2 is fixed or incorporated into organic molecules.

Of the following, which occurs during the Calvin cycle? 1. Light energy is converted to chemical energy. 2. ATP and NADPH are synthesized. 3. CO2 is reduced. 4. Excited electrons are conveyed from chlorophyll to an electron acceptor. 5. Photons are absorbed.

3. CO2 is reduced.

The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night. Why? 1. It is often too cold at night for these reactions to take place. 2. Carbon dioxide concentrations decrease at night. 3. The Calvin cycle requires products only produced when the photosystems are illuminated. 4. Plants usually open their stomata at night. 5. At night, no water is available for the Calvin cycle.

3. The Calvin cycle requires products only produced when the photosystems are illuminated.

Only 1 of the G3P molecules produced in Phase 2 of the Calvin cycle is exported from the cycle. The remaining G3P molecules are used in Phase 3. What happens to the remainder of the G3P produced in Phase 2 of the Calvin cycle? 1. The G3Ps are needed to absorb the CO2 that was taken up in Phase 1. 2. The G3Ps are needed for reactions that use up the extra ATP and NADPH produced by the light reactions, keeping these molecules from accumulating in the cell. 3. The G3Ps are used in Phase 3 to regenerate the RuBP molecules used in Phase 1.

3. The G3Ps are used in Phase 3 to regenerate the RuBP molecules used in Phase 1.

Select the most accurate statement describing the basic function of the light reactions of photosynthesis. 1. The basic function of the light reactions of photosynthesis is the production of glucose. 2. The basic function of the light reactions of photosynthesis is the trapping of light energy. 3. The basic function of the light reactions of photosynthesis is the conversion of solar energy to chemical energy.

3. The basic function of the light reactions of photosynthesis is the conversion of solar energy to chemical energy.

A photon of which of these colors would carry the most energy? 1. green 2. yellow 3. blue 4. orange 5. red

3. blue

You could distinguish a granum from a crista because the granum, but not the crista, would _____. 1. be inside a mitochondrion 2. function in energy transformation 3. have photosynthetic pigments 4. contain protein but not lipids 5. Two of the listed responses are correct.

3. have photosynthetic pigments

The energy used to produce ATP in the light reactions of photosynthesis comes from _____. 1. the oxidation of sugar molecules 2. splitting water 3. movement of H+ through a membrane 4. carbon fixation 5. fluorescence

3. movement of H+ through a membrane

In Photosystem I (PS I), the excited state of P700 chlorophyll transfers an electron to the PS I primary electron acceptor. The resulting reduced primary electron acceptor in PS I is one of the strongest known biological reductants (electron donors). What is the role of the reduced PS I primary electron acceptor in the light reactions? 1. reduction of the electron transport chain between the photosystems 2. oxidation of the electron transport chain between the photosystems 3. reduction of NADP+ to NADPH 4. oxidation of water to O2

3. reduction of NADP+ to NADPH

Which process is most directly driven by light energy? 1. creation of a pH gradient by pumping protons across the thylakoid membrane 2. carbon fixation in the stroma 3. removal of electrons from chlorophyll molecules 4. reduction of NADP+ molecules 5. ATP synthesis

3. removal of electrons from chlorophyll molecules

The Calvin cycle occurs in the _____. 1. thylakoid membrane 2. thylakoid lumen 3. stroma 4. stomata 5. matrix

3. stroma

When chloroplast pigments absorb light, _____. 1. they become reduced 2. they lose potential energy 3. their electrons become excited 4. the Calvin cycle is triggered 5. their photons become excited

3. their electrons become excited

How is photosynthesis similar in C4 plants and CAM plants? 1. Both types of plants make sugar without the Calvin cycle. 2. In both cases, thylakoids are not involved in photosynthesis. 3. In both cases, electron transport is not used. 4. In both cases, rubisco is not used to fix carbon initially. 5. Both types of plants make most of their sugar in the dark

4. In both cases, rubisco is not used to fix carbon initially.

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.) 1. The rate of O2 production would decrease because the rate of G3P production by the Calvin cycle would decrease. 2. The rate of O2 production would remain the same because the light intensity did not change. 3. The rate of O2 production would remain the same because the light reactions are independent of the Calvin cycle. 4. The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease.

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

In Photosystem II (PS II), the excited state of P680 chlorophyll transfers an electron to the PS II primary electron acceptor. The resulting positively charged P680+ is the strongest known biological oxidant (electron acceptor). What is the role of P680+ in the light reactions? 1. reduction of the electron transport chain between the photosystems 2. reduction of NADP+ to NADPH 3. oxidation of the electron transport chain between the photosystems 4. oxidation of water to O2

4. oxidation of water to O2

Photons strike a photosystem. Which process occurs next? 1. reduction of NADP+ molecules 2. creation of a pH gradient by pumping protons across the thylakoid membrane 3. carbon fixation in the stroma 4. removal of electrons from chlorophyll molecules 5. ATP synthesis

4. removal of electrons from chlorophyll molecules

Phosphates are conserved in the Calvin cycle: For each turn of the Calvin cycle, the number of phosphate groups that enter the cycle from ATP is equal to the number of phosphate groups that are output from the cycle. Phosphate is output from the Calvin cycle in all of the following ways except 1. the output of Pi in Phase 2. 2. the output of Pi in Phase 3. 3. the output of 1 G3P per turn of the Calvin cycle. 4. the output of 5 G3P from Phase 2 to Phase 3 of the Calvin cycle.

4. the output of 5 G3P from Phase 2 to Phase 3 of the Calvin cycle.

How does carbon dioxide enter the leaf? 1. through the chloroplasts 2. through the roots 3. through the thylakoids 4. through the stomata 5. through the vascular system

4. through the stomata

During photosynthesis, an electron transport chain is used to _____. 1. transport NADPH from the light reactions to the Calvin cycle 2. transport excited electrons from P700 to an electron acceptor 3. transport excited electrons from P680 to an electron acceptor 4. transport electrons from photosystem II to photosystem I 5. transport excited electrons from P700 to an electron acceptor and transport excited electrons from P680 to an electron acceptor

4. transport electrons from photosystem II to photosystem I

The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from _____. 1. carbon dioxide 2. glucose 3. radioisotopes 4. water 5. light

4. water

Glyceraldehyde-3-phosphate (G3P) is produced in the stroma of chloroplasts. Which of the following statements is most true about this compound? 1. It is produced from glucose during glycolysis. 2. It is a 3-carbon sugar. 3. For every three molecules of CO2, six molecules of G3P are formed but only one molecule exits the cycle to be used by the plant cell. 4. For every three molecules of CO2, six molecules of G3P are formed but five molecules must be recycled to regenerate three molecules of RuBP 5. All of the listed responses are correct.

5. All of the listed responses are correct.

The use of non-C3 and non-CAM plants as crops may be limited in some regions because on hot, dry days, they close their stomata. What happens as a result of closing their stomata? 1. It reduces water loss. 2. It prevents carbon dioxide from entering the leaf. 3. In a process called photorespiration, rubisco binds oxygen instead of carbon dioxide. 4. It builds up oxygen from the light reactions in the leaf. 5. All of the listed responses are correct.

5. All of the listed responses are correct.

What is the role of NADP+ in photosynthesis? 1. It helps produce ATP from the light reactions. 2. It absorbs light energy. 3. It forms part of photosystem II. 4. It is the primary electron acceptor. 5. It forms NADPH to be used in the Calvin cycle.

5. It forms NADPH to be used in the Calvin cycle.

What is the role of NADP+ in photosynthesis? 1. It assists chlorophyll in capturing light. 2. It acts as the primary electron acceptor for the photosystems. 3. As part of the electron transport chain, it manufactures ATP. 4. As a component of photosystem II, it catalyzes the hydrolysis of water. 5. It is reduced and then carries electrons to the Calvin cycle.

5. It is reduced and then carries electrons to the Calvin cycle.

The light reactions of photosynthesis generate high-energy electrons, which end up in _____. The light reactions also produce _____ and _____. 1. ATP ... NADPH ... oxygen 2. oxygen ... sugar ... ATP 3. chlorophyll ... ATP ... NADPH 4. water ... sugar ... oxygen 5. NADPH ... ATP ... oxygen

5. NADPH ... ATP ... oxygen

Based on the work of Engelmann, the wavelengths of light most effective in driving photosynthesis are referred to as _____. 1. an effective spectrum 2. an absorption spectrum 3. an electromagnetic spectrum 4. a visible light spectrum 5. an action spectrum

5. an action spectrum

In photosynthesis, what is the fate of the oxygen atoms present in CO2? They end up _____. 1. as molecular oxygen 2. in sugar molecules 3. in water 4. as molecular oxygen and in sugar molecules 5. in sugar molecules and in water

5. in sugar molecules and in water

When light strikes chlorophyll molecules, they lose electrons, which are ultimately replaced by _____. 1. oxidizing glucose 2. removing them from NADPH 3. breaking down ATP 4. fixing carbon 5. splitting water

5. splitting water

In a rosebush, chlorophyll is located in _____. 1. chloroplasts, which are in mesophyll cells in the thylakoids of a leaf 2. mesophyll cells, found within the thylakoids of a leaf's chloroplasts 3. thylakoids, which are in mesophyll cells in the chloroplasts of a leaf 4. chloroplasts, which are in thylakoids in the mesophyll cells of a leaf 5. thylakoids, which are in chloroplasts in the mesophyll cells of a leaf

5. thylakoids, which are in chloroplasts in the mesophyll cells of a leaf

Where do the electrons entering photosystem II come from? 1. chlorophyll molecules in the antenna complex 2. ATP 3. the electron transport chain 4. light 5. water

5. water