Chapter 10 Practice Questions

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The process of photosynthesis probably originated in


In autotrophic bacteria, where is chlorophyll located?

in the in-folded plasma membrane

Plants photosynthesize

only in light but respire in dark

Early investigators thought the oxygen produced by photosynthetic plants came from carbon dioxide, it come from


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

G3P, glucose, and RuBP

Every ecosystem must have


When oxygen is released as a result of photosynthesis, it is a direct-by-product of

splitting water molecules

Autotrophs vs Heterotrophs

autotrophs can nourish themselves beginning with CO2 and other nutrients that are inorganic

Why are the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis different?

Other pigments absorb light in addition to chlorophyll a.

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

420 mm

why are there several structurally different pigments in the reaction centers of photosystems?

This arrangement enables the plant to absorb light energy of a variety of wavelengths.

if pigments from a particular species of plant are extracted and subjected to paper chromatography, which of the following is most likely?

Paper chromatography would separate the pigments from a particular plant into several bands.

In autumn, the leaves of deciduous trees change colors. This is because chlorophyll is degraded and _____.

carotenoids and other pigments are still present in the leaves

What event accompanies energy absorption by chlorophyll (or other pigment molecules of the antenna complex)?

an electron is excited.

As electrons are passed through the system of electron carriers associated with photosystem II, they lose energy. What happens to this energy?

It is used to establish and maintain a proton gradient.

The final electron acceptor associated with photosystem I is _____.


The electrons of photosystem II are excited and transferred to electron carriers. From which molecule or structure do the photosystem II replacement electrons come?


In the thylakoid membranes, the pigment molecules in a light-harvesting complex _____.

absorb and transfer light energy to the reaction-center chlorophyll

Which of the following are directly associated with photosystem I?

receiving electrons from the thylakoid membrane electron transport chain

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 _____.

test for liberation of O2 in the light

What are the products of linear electron flow?


As a research scientist, you measure the amount of ATP and NADPH consumed by the Calvin cycle in 1 hour. You find that 30,000 molecules of ATP were consumed, but only 20,000 molecules of NADPH were consumed. Where did the extra ATP molecules come from?

cyclic electron flow

Assume a thylakoid is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will most directly affect the _____.

synthesis of ATP

In a plant cell, where are the ATP synthase complexes located?

thylakoid membrane and inner mitochondrial membrane

In mitochondria, chemiosmosis moves protons from the matrix into the intermembrane space, whereas in chloroplasts, chemiosmosis moves protons from the _____.

stroma to the thylakoid space

Which of the following statements best describes the relationship between photosynthesis and respiration?

Photosynthesis stores energy in complex organic molecules; respiration releases energy from complex organic molecules

In photosynthetic cells, synthesis of ATP by the chemiosmotic mechanism occurs during _____.

photosynthesis and respiration

Carbon dioxide is split to form oxygen gas and carbon compounds _____.

in neither photosynthesis nor respiration

What is the relationship between the wavelength of light and the quantity of energy per photon?

they are inversely related

P680+ is said to be the strongest biological oxidizing agent. Given its function, why is this necessary?

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

Carotenoids are often found in foods that are considered to have antioxidant properties in human nutrition. What related function do they have in plants?

They protect against oxidative damage from excessive light energy. / they dissipate excessive light energy.

In a plant, the reactions that produce molecular oxygen (O2) take place in _____.

the light reactions alone

The accumulation of free oxygen in Earth’s atmosphere began with the origin of _____.

cyanobacteria using photosystem II

In its mechanism, photophosphorylation is most similar to _____.

oxidative phosphorylation in cellular respiration

Which process is most directly driven by light energy?

removal of electrons from chlorophyll molecules

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?


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 _____.

be higher in the light, but lower in the dark

Which of the following are products of the light reactions of photosynthesis that are utilized in the Calvin cycle?


Where does the Calvin cycle take place?

stroma of the chloroplast

What is the primary function of the Calvin cycle?

synthesize simple sugars from carbon dioxide

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?

regeneration of RuBP

Which of the following does NOT occur during the Calvin cycle?

release of oxygen

What compound provides the reducing power for Calvin cycle reactions?


What would be the expected effect on plants if the atmospheric CO2 concentration was

3 plants would have faster growth; C4 plants would be minimally affected.

Why are C4 plants able to photosynthesize with no apparent photorespiration?

They use PEP carboxylase to initially fix CO2.

CAM plants keep stomata closed in the daytime, thus reducing loss of water. They can do this because they _____.

fix CO2 into organic acids during the night

The alternative pathways of photosynthesis using the C4 or CAM systems are said to be compromises. Why?

Both minimize photorespiration but expend more ATP during carbon fixation.

If plant gene alterations cause plants to be deficient in photorespiration, what would most probably occur?

here would be more light-induced damage to the cells.

Compared to C3 plants, C4 plants _____.

can continue to fix CO2 even at lower CO2 concentrations and higher oxygen concentrations

In autotrophic bacteria, where are the enzymes located that can carry on organic synthesis?

along the inner surface of the plasma membrane

A plant has a unique photosynthetic pigment. The leaves of this plant appear to be reddish yellow. What wavelengths of visible light are being absorbed by this pigment?

blue and violet

What did Engelmann conclude about the congregation of bacteria in the red and blue areas?

Bacteria congregated in these areas because these areas had the most oxygen being released.

An outcome of this experiment was to help determine

the relationship between wavelengths of light and the oxygen released during photosynthesis.

If you ran the same experiment without passing light through a prism, what would you predict?

The bacteria would be relatively evenly distributed along the algal filaments.

Compared with the lines for chlorophyll a in the figure, where would you expect to find the lines to differ for chlorophyll b?

the absorption spectrum line would be lowest for chlorophyll b somewhat to the right of that for chlorophyll a (500—600).

he reaction-center chlorophyll of photosystem I is known as P700 because

this pigment is best at absorbing light with a wavelength of 700 nm.

Which of the events listed below occur in the light reactions of photosynthesis?

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

Which statement describes the functioning of photosystem II?

The electron vacancies in P680 are filled by electrons derived from water.

Suppose the interior of the thylakoids of isolated chloroplasts were made acidic and then transferred in the dark to a pH-8 solution. What would be likely to happen?

The isolated chloroplasts will make ATP.

Reduction of oxygen which forms water occurs during


Reduction of NADP+ occurs during


Generation of proton gradients across membranes occurs during

both photosynthesis and respiration

In a protein complex for the light reaction (a reaction center), energy is transferred from pigment molecule to pigment molecule, to a special chlorophyll a molecule, and eventually to the primary electron acceptor. Why does this occur?

The molecular environment lets it boost an electron to a higher energy level and also to transfer the electron to another molecule.

P680+ is said to be the strongest biological oxidizing agent. Why?

is molecule results from the transfer of an electron to the primary electron acceptor of photosystem II and strongly attracts another electron.

Some photosynthetic bacteria (e.g., purple sulfur bacteria) have photosystem I but not II, while others (e.g. cyanobacteria) have both PSI and PSII. Which of the following might this observation imply?

photosystem I must be more ancestral.

Cyclic electron flow may be photoprotective (protective to light-induced damage). Which of the following experiments could provide information on this phenomenon?

using mutated organisms that can grow but that cannot carry out cyclic flow of electrons and compare their abilities to photosynthesize in different light intensities

n thylakoids, protons travel through ATP synthase from the stroma to the thylakoid space. Therefore the catalytic ʺknobsʺ of ATP synthase would be located

on the stroma side of the membrane

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 Calvin cycle, and the cycle returns ADP, Pi, and NADP+ to the light reactions.

Where do the enzymatic reactions of the Calvin cycle take place?

stroma of the chloroplast

Produces molecular oxygen (O2)

light reactions

Requires ATP

the calvin cycle

Produces NADH

neither the light reactions nor the calvin cycle

Produces NADPH

light reactions

Produces three carbon sugars

calvin cycle

requires CO2

the calvin cycle

requires glucose


The sugar that results from three ʺturnsʺ of the Calvin cycle is glyceraldehyde-3-phosphate (G3P). Which of the following is a consequence of this?

The formation of starch in plants involves assembling many G3P molecules, with or without further rearrangements.

In the process of carbon fixation, RuBP attaches a CO2 to produce a 6 carbon molecule,
which is then split in two. After phosphorylation and reduction, what more needs to happen in the Calvin cycle?

regeneration of rubisco

In metabolic processes of cell respiration and photosynthesis, prosthetic groups such as heme and iron-sulfur complexes are encountered. What do they do?

both oxidize and reduce during electron transport

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.

In an experiment studying photosynthesis performed during the day, you provide a plant
with radioactive carbon (14C) dioxide as a metabolic tracer. The 14C is incorporated first into oxaloacetate. The plant is best characterized as a

C4 Plants

CAM plants keep stomata closed in daytime, thus reducing loss of water. They can do this because they

fix CO2 into organic acids during the night.

Photorespiration lowers the efficiency of photosynthesis by preventing the formation of

3-phosphoglycerate molecules

If plant gene alterations cause the plants to be deficient in photorespiration, what would most probably occur?

Less ATP would be generated.

The light reactions of photosynthesis supply the Calvin cycle with


Which of the following sequences correctly represents the flow of electrons during photosynthesis?

H2O->NADPH->Calvin Cycle

In mechanism, photophosphorylation is most similar to

oxidative phosphorylation in cellular respiration.

How is photosynthesis similar in C4 and CAM plants?

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

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