Chapter 8 - Photosynthesis

Redox reactions of photosynthesis

*In the light reactions, light energy is used to remove electrons from (oxidize) water, producing O2 gas. These electrons are ultimately used to reduce NADP+ to NADPH. In the Calvin cycle, NADPH is oxidized back to NADP+ (which returns to the light reactions). The electrons released by the oxidation of NADPH are used to reduce three molecules of CO2 to sugar (G3P), which then exits the Calvin cycle.

Chloroplast structure and function

*The chloroplast is enclosed by a pair of envelope membranes (inner and outer) that separate the interior of the chloroplast from the surrounding cytosol of the cell. Inside the chloroplast, the chlorophyll-containing thylakoid membranes are the site of the light reactions. Between the inner envelope membrane and the thylakoid membranes is the aqueous stroma, which is the location of the reactions of the Calvin cycle. Inside the thylakoid membranes is the thylakoid space, where protons accumulate during ATP synthesis in the light reactions.

What wavelength of light in the figure is most effective in driving photosynthesis

420 mm

How many carbon dioxide molecules must be added to RuBP to make a single molecule of glucose?

6

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

6 CO2 + 6 H2O → C6H12O6 + 6 O2

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

A Photosystem II splits water into 1/2 O2, H+, and e- .

Chlorophyll can be found in _____.

A + C Photosystems I and II

Which of the following are products of the light reactions of photosynthesis that are utilized in the Calvin cycle? CO2 and glucose electrons and H+ ADP, i, and NADP+ ATP and NADPH H2O and O2

ATP and NADPH

Chloroplast membrane vesicles are equilibrated 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? ATP will not be produced because there is no ADP and inorganic phosphate in the solution. 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 vesicles and a higher concentration outside. ATP will be produced because the proton gradient favors proton movement through the ATP synthase channels. Protons will not diffuse toward the outside of the vesicles.

ATP will not be produced because there is no ADP and inorganic phosphate in the solution.

_____ releases energy that is used to pump hydrogen ions from the stroma into the thylakoid compartment.

B The energy released as electrons are passed along the electron transport chain is used to pump protons into the thylakoid compartment.

The alternative pathways of photosynthesis using the C4 or CAM systems are said to be compromises. Why? Each one minimizes both water loss and rate of photosynthesis. CAM plants allow more water loss, whereas C4 plants allow less CO2 into the plant. C4 plants allow less water loss but CAM plants allow more water loss. C4 compromises on water loss and CAM compromises on photorespiration. Both minimize photorespiration but expend more ATP during carbon fixation.

Both minimize photorespiration but expend more ATP during carbon fixation.

Energized electrons from ____ enter an electron transport chain and are then used to reduce NADP+

C Energized electrons from photosystem I are used to reduce NADP+.

What is the basic role of CO2 in photosynthesis?

CO2 is fixed or incorporated into organic molecules.

Identify a thylakoid

D (coin looking objects)

Which of these phosphorylates ADP to make ATP?

E ATP synthase Phosphorylates ADP

Identify the stroma

E (space between thylakoid and membrane)

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

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

False

The main product of the Calvin cycle is

G3P

P680+ is said to be the strongest biological oxidizing agent. Given its function, why is this necessary? It transfers its electrons to reduce NADP+ to NADPH. It is the molecule that transfers electrons to plastoquinone (Pq) of the electron transfer system. It has a positive charge. It obtains electrons from the oxygen atom in a water molecule, so it must have a stronger attraction for electrons than oxygen has. It is the receptor for the most excited electron in either photosystem.

It obtains electrons from the oxygen atom in a water molecule, so it must have a stronger attraction for electrons than oxygen has.

Which of the following events occurs in the light reactions of photosynthesis? Carbon dioxide is incorporated into PGA. ATP is phosphorylated to yield ADP. Light is absorbed and funneled to reaction-center chlorophyll a. NADP is produced. NADPH is reduced to NADP+.

Light is absorbed and funneled to reaction-center chlorophyll a.

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

NADPH

What compound provides the reducing power for the Calvin cycle reactions? NADPH ATP NAD+ NADH NADP+

NADPH

Which of the following molecules is the primary product of photosystem I? ATP Oxygen Carbon dioxide NADPH

NADPH

Which of the following products of the light reactions of photosynthesis is consumed during the Calvin cycle? water NADPH sugar ADP + Pi oxygen

NADPH

If photosynthesizing green algae are provided with CO2 containing heavy oxygen (18O), later analysis will show that all of the following molecules produced by the algae contain 18O except glucose. 3-phosphoglycerate. ribulose bisphosphate (RuBP). O2. glyceraldehyde 3-phosphate (G3P).

O2

Photorespiration occurs when rubisco reacts RuBP with 3-phosphoglycerate. NADPH. O2. glyceraldehyde 3-phosphate. CO2.

O2.

the figure shows the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis. Why are they different?

Other pigments absorb light in addition to chlorophyll a.

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

Photophosphorylation

Which process produces oxygen?

Photosynthesis

Which of the following statements best describes the relationship between photosynthesis and respiration? Respiration is anabolic and photosynthesis is catabolic. Respiration runs the biochemical pathways of photosynthesis in reverse. ATP molecules are produced in photosynthesis and used up in respiration. Photosynthesis occurs only in plants and respiration occurs only in animals. Photosynthesis stores energy in complex organic molecules, whereas respiration releases it.

Photosynthesis stores energy in complex organic molecules, whereas respiration releases it.

Why are plants classified as producers

Plants are classified as producers because they fix inorganic carbon into organic molecules.

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

Proton gradient

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

Protons

_____ has a longer wavelength than _____. Blue ... green Violet ... blue Yellow ... red Red ... green Green ... yellow

Red ... green

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

RuBP

Which molecule is regenerated in the regeneration phase of the Calvin cycle? Without regeneration of this molecule, the Calvin cycle would stop. 3-phosphoglycerate ATP RuBP G3P

RuBP

A flask containing photosynthetic green algae and a control flask containing water with no algae are both placed under a bank of lights, which are set to cycle between 12 hours of light and 12 hours of dark. The dissolved oxygen concentrations in both flasks are monitored. Predict what the relative dissolved oxygen concentrations will be in the flask with algae compared to the control flask. The dissolved oxygen in the flask with algae will always be higher. The dissolved oxygen in the flask with algae will not be different from the control flask at any time. The dissolved oxygen in the flask with algae will be higher in the light, but the same in the dark. The dissolved oxygen in the flask with algae will always be lower. The dissolved oxygen in the flask with algae will be higher in the light, but lower in the dark.

The dissolved oxygen in the flask with algae will be higher in the light, but lower in the dark.

Which of the following statements best represents the relationships between the light reactions and the Calvin cycle? The light reactions provide ATP and NADPH to the carbon fixation step of the Calvin cycle, and the cycle provides water and electrons to the light reactions. The light reactions provide ATP and NADPH to the Calvin cycle, and the cycle returns ADP, Pi, and NADP+ to the light reactions. There is no relationship between the light reactions and the Calvin cycle. The light reactions provide the Calvin cycle with oxygen for electron flow, and the Calvin cycle provides the light reactions with water to split. The light reactions supply the Calvin cycle with CO2 to produce sugars, and the Calvin cycle supplies the light reactions with sugars to produce ATP.

The light reactions provide ATP and NADPH to the Calvin cycle, and the cycle returns ADP, Pi, and NADP+ to the light reactions.

Which set of reactions uses H2O and produces O2

The light-dependent reactions

Which of the following statements best describes the relationship between the light-dependent and light-independent reactions of photosynthesis? The light-independent reactions release energy, and the light-dependent reactions require energy. The light-dependent reactions produce carbon dioxide, which is then used by the light-independent reactions. The light-dependent reactions produce ATP and NADPH, which are then used by the light-independent reactions. The light-dependent reactions pass electrons through an electron transport chain to the light-independent reactions.

The light-dependent reactions produce ATP and NADPH, which are then used by the light-independent reactions.

What is the importance of the light-independent reactions in terms of carbon flow in the biosphere? The light-independent reactions turn CO2, a gas, into usable carbon in the form of sugars. The light-independent reactions turn glucose, a sugar, into CO2 gas. The light-independent reactions use CO2 to make ATP. The light-independent reactions turn sugar into ATP for energy.

The light-independent reactions turn CO2, a gas, into usable carbon in the form of sugars.

The pH of the inner thylakoid space has been measured, as have the pH of the stroma and of the cytosol of a particular plant cell. Which, if any, relationship would you expect to find? The pH within the thylakoid is less than that of the stroma. The pH of the stroma is higher than that of the thylakoid space but lower than that of the cytosol. The pH of the stroma is lower than that of the other two measurements. There is no consistent relationship. The pH of the thylakoid space is higher than that anywhere else in the cell.

The pH within the thylakoid is less than that of the stroma.

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

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

What is the relationship between wavelength of light and the quantity of energy per photon? They are separate phenomena. They are inversely related. They are logarithmically related. They have a direct, linear relationship. They are only related in certain parts of the spectrum.

They are inversely related.

What is the biological significance of the light-independent reactions of photosynthesis? They convert carbon dioxide to sugar. They generate ATP and NADPH. They make oxygen. They convert ATP to sugar.

They convert carbon dioxide to sugar.

Why are C4 plants able to photosynthesize with no apparent photorespiration? They do not participate in the Calvin cycle. They are adapted to cold, wet climates. They use PEP carboxylase to initially fix CO2. They exclude oxygen from their tissues. They conserve water more efficiently.

They use PEP carboxylase to initially fix CO2.

True or false? The light-dependent reactions of photosynthesis use water and produce oxygen.

True

A gardener is concerned that her greenhouse is getting too hot from too much light, and seeks to shade her plants with colored translucent plastic sheets, the color of which allows passage of only that wavelength. What color should she use to reduce overall light energy, but still maximize plant growth?

blue

Generation of proton gradients across membranes occurs during respiration. photosynthesis. both photosynthesis and respiration. photorespiration. neither photosynthesis nor respiration.

both photosynthesis and respiration.

In photosynthetic cells, synthesis of ATP by the chemiosmotic mechanism occurs during neither photosynthesis nor respiration. both photosynthesis and respiration. photosynthesis only. photorespiration only. respiration only.

both photosynthesis and respiration.

Compared to C3 plants, C4 plants can continue to fix CO2 even at relatively low CO2 concentrations and high oxygen concentrations. make a four-carbon compound, oxaloacetate, which is then delivered to the citric acid cycle in mitochondria. do not use rubisco for carbon fixation. grow better under cool, moist conditions. have higher rates of photorespiration.

can continue to fix CO2 even at relatively low CO2 concentrations and high oxygen concentrations.

The photosynthetic membranes are found in the _____ in plant cells chloroplasts mitochondria Golgi apparatus nucleus endoplasmic reticulum

chloroplasts

In C4 and CAM plants carbon dioxide is fixed in the _____ of mesophyll cells. thylakoids cytoplasm stroma stomata grana

cytoplasm

When light strikes chlorophyll molecules of PS II, they lose electrons, which are ultimately replaced by _____. oxidizing glucose electrons released by splitting water breaking down ATP fixing carbon removing them from NADPH

electrons released by splitting water

What does the chemiosmotic process in chloroplasts involve? diffusion of electrons through the thylakoid membrane reduction of water to produce ATP energy formation of glucose, using carbon dioxide, NADPH, and ATP establishment of a proton gradient across the thylakoid membrane movement of water by osmosis into the thylakoid space from the stroma

establishment of a proton gradient across the thylakoid membrane

CAM plants keep stomata closed in daytime, thus reducing loss of water. They can do this because they fix CO2 into pyruvate in the mesophyll cells. fix CO2 into organic acids during the night. fix CO2 into sugars in the bundle-sheath cells. use photosystem I and photosystem II at night. use the enzyme phosphofructokinase, which outcompetes rubisco for CO2.

fix CO2 into organic acids during the night.

Halobacterium has a photosynthetic membrane that appears purple. Its photosynthetic action spectrum is the inverse of the action spectrum for green plants. (That is, the Halobacterium action spectrum has a peak where the green plant action spectrum has a trough.) What wavelengths of light do the Halobacterium photosynthetic pigments absorb?

green and yellow

Identify the chloroplast

green dots (a)

The overall function of the Calvin cycle is _____. oxidizing glucose producing carbon dioxide making sugar capturing sunlight splitting water

making sugar

The splitting of carbon dioxide to form oxygen gas and carbon compounds occurs during respiration. both photosynthesis and respiration. photorespiration. neither photosynthesis nor respiration. photosynthesis.

neither photosynthesis nor respiration.

Photosynthesis is a redox reaction. This means that H2O is _____ during the light reactions and CO2 is _____ during the Calvin cycle. consumed...reduced oxidized...reduced consumed...consumed reduced...oxidized reduced...reduced

oxidized...reduced

Which of the following is a product of the light reactions of photosynthesis? high-energy photons oxygen, ATP, and NADPH NADP+ and RuBP water and CO2 glyceraldehyde-3-phosphate

oxygen, ATP, and NADPH

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

photorespiration

Reduction of NADP+ occurs during both photosynthesis and respiration. neither photosynthesis nor respiration. photosynthesis. respiration.

photosynthesis.

The NADPH required for the Calvin cycle comes from glycolysis. reactions initiated in photosystem I. oxidative phosphorylation. the citric acid cycle. reactions initiated in photosystem II.

reactions initiated in photosystem I.

Which of the following are directly associated with photosystem I? generation of molecular oxygen receiving electrons from the thylakoid membrane electron transport chain passing electrons to the thylakoid membrane electron transport chain extraction of hydrogen electrons from the splitting of water harvesting of light energy by ATP

receiving electrons from the thylakoid membrane electron transport chain

In the process of carbon fixation, RuBP attaches a CO2 to produce a six-carbon molecule, which is then split to produce two molecules of 3-phosphoglycerate. After phosphorylation and reduction produces glyceraldehyde 3-phosphate (G3P), what more needs to happen to complete the Calvin cycle? inactivation of RuBP carboxylase enzyme addition of a pair of electrons from NADPH regeneration of RuBP regeneration of ATP from ADP regeneration of NADP+

regeneration of RuBP

When oxygen is released as a result of photosynthesis, it is a direct by-product of splitting water molecules. the electron transfer system of photosystem I. the electron transfer system of photosystem II. chemiosmosis. reducing NADP+.

splitting water molecules.

where does the calvin cycle occur

stroma (e)

Where do the enzymatic reactions of the Calvin cycle take place? thylakoid membranes thylakoid space cytosol around the chloroplast stroma of the chloroplast matrix of the mitochondria

stroma of the chloroplast

Where does the Calvin cycle take place? cytoplasm surrounding the chloroplast thylakoid membrane outer membrane of the chloroplast interior of the thylakoid (thylakoid space) stroma of the chloroplast

stroma of the chloroplast

The ultimate source of energy to support most life on Earth is _____ the carbon cycle photosynthetic plants chemosynthetic microbes geothermal heat sunlight

sunlight

What is the primary function of the Calvin cycle? split water and release oxygen use ATP to release carbon dioxide transport RuBP out of the chloroplast use NADPH to release carbon dioxide synthesize simple sugars from carbon dioxide

synthesize simple sugars from carbon dioxide

In C3 photosynthesis, the reactions that require ATP take place in the chloroplast, but are not part of photosynthesis. the Calvin cycle alone. both the light reactions and the Calvin cycle. the light reactions alone. neither the light reactions nor the Calvin cycle.

the Calvin cycle alone.

Reactions that require CO2 take place in neither the light reactions nor the Calvin cycle. the Calvin cycle alone. both the light reactions and the Calvin cycle. the light reactions alone. the chloroplast, but are not part of photosynthesis.

the Calvin cycle alone.

The reactions that produce molecular oxygen (O2) take place in the light reactions alone. the chloroplast, but are not part of photosynthesis. the Calvin cycle alone. both the light reactions and the Calvin cycle. neither the light reactions nor the Calvin cycle.

the light reactions alone.

C4 plants occur more commonly in desert conditions because _____. they can fix carbon at the lower CO2 concentrations that develop when the stomata are closed they store carbon by incorporating CO2 into organic acids that are later catabolized they produce water as a product of their photosynthetic pathways they produce carbon dioxide internally via photorespiration the stomata open at night and close in the day

they can fix carbon at the lower CO2 concentrations that develop when the stomata are closed

In a plant cell, where are the ATP synthase complexes located? inner mitochondrial membrane only thylakoid membrane and plasma membrane plasma membrane only thylakoid membrane and inner mitochondrial membrane thylakoid membrane only

thylakoid membrane and inner mitochondrial membrane

Some photosynthetic organisms contain chloroplasts that lack photosystem II, yet are able to survive. The best way to detect the lack of photosystem II in these organisms would be to do experiments to generate an action spectrum. to test for CO2 fixation in the dark. to test for production of either sucrose or starch. to test for liberation of O2 in the light. to determine if they have thylakoids in the chloroplasts.

to test for liberation of O2 in the light.

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

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

In the thylakoid membranes, what is the main role of the pigment molecules in a light-harvesting complex? split water and release oxygen to the reaction-center chlorophyll concentrate photons within the stroma transfer light energy to the reaction-center chlorophyll transfer electrons to ferredoxin and then NADPH synthesize ATP from ADP and i

transfer light energy to the reaction-center chlorophyll

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

water ... NADPH