8.1-8.5: photosynthesis and light reactions

What is the ultimate source of energy for almost all living cells on Earth?

the sun

In a leaf, the thick layer of cells that are rich in chloroplasts is called the ____

mesophyll

what part of the chloroplast is indicated by the arrow?

inner membrane

Which of the following is made during the light-dependent reactions of photosynthesis?

• NADPH

• Carbon monoxide

• Carbon dioxide

• Water

NADPH

The internal membrane of the chloroplast is also known as the Blank______.

• lamellar membrane

• stromal membrane

• thylakoid membrane

• primary membrane

thylakoid membrane

The energy used by most living cells comes ultimately from the ________ and is captured through the process of _______.

sun; photosynthesis

Which of the following describes van Helmont's experiment?

• He studied the photosynthesis of purple sulfur bacteria.

• He measured the effect of different light intensities, CO₂ concentrations and temperatures on the rate of photosynthesis.

• He grew a willow in a pot keeping an exact record of the weight of the soil and the tree over several years.

He grew a willow in a pot keeping an exact record of the weight of the soil and the tree over several years.

In a green plant, the majority of photosynthesis takes place in Blank______.

• the flowers

• the leaves

• the fruit

• the roots

• the stem/trunk

the leaves

according to the diagram, which of the following accelerate photosynthesis when light intensity is high?

• Decrease in temperature

• Increase in temperature

• Increase in CO₂

• Decrease in CO₂

• Increase in temperature

• Increase in CO₂

the arrow points to structures in the chloroplast known as ___

grana

The steps of photosynthesis that require light are commonly known as the light-_____ reactions

dependent

The inner (internal) membrane of the chloroplast is also called the ______ membrane.

thylakoid

Jan Baptista ______ _______ performed an experiment for which he grew a willow tree in a pot for several years, during which time he kept an exact record of changes in the weight of the soil.

van Helmont

In van Niel's generalized equation of photosynthesis, which of the following is the donor of electrons?

• 2A

• CO₂

• H₂A

• O₂

H₂A

The following diagram shows the change in the rate of photosynthesis as a function of the intensity of light under varying conditions. Which of the following statements can be concluded based on the graph?

• The rate of photosynthesis remains constant at all light intensities.

• The concentration of CO₂ does not play a role in determining the rate of photosynthesis.

• The rate of photosynthesis is limited by light at low light intensities.

• The rate of photosynthesis is limited by temperature at high light intensities.

• The rate of photosynthesis is limited by the concentration of CO₂ at high light intensities.

• The rate of photosynthesis is limited by light at low light intensities.

• The rate of photosynthesis is limited by temperature at high light intensities.

• The rate of photosynthesis is limited by the concentration of CO₂ at high light intensities.

If chloroplasts are isolated from a plant cell and exposed to light they release _____

oxygen

Which of the following is made during the light-dependent reactions of photosynthesis?

• Carbon dioxide

• Water

• NADPH

• Carbon monoxide

NADPH

A leaf that appears to be green to the human eye contains pigment molecules that are ______

reflecting green light

Light has properties of both ______ and _____

a particle and a wave

According to the generalized equation for photosynthesis proposed by van Niel, CO₂ + 2H₂A + light energy yields which of the following?

• 2CH₂O + ATP

• CH₂O + H₂O

• 2 CH₂O + O₂

• CH₂O + H₂O + 2A

CH₂O + H₂O + 2A

If chloroplasts are isolated from a plant and exposed to light in the absence of carbon dioxide, they accumulate _______

ATP

In the visible spectrum, light energy may be absorbed by boosting _____ to higher atomic energy levels, sometimes called energy shells.

electrons

A graph depicting the efficiency of photon absorption by a pigment molecule as a function of photon wavelength is known as the _____ spectrum of the pigment

absorption

Which are the two most important kinds of pigments in chloroplasts?

Chlorophylls and carotenoids

For an electron to absorb light energy, it must absorb a(n) ______ that contains enough energy to overcome the energy difference between the orbital the electron is in, and the one to which it will be boosted.

photon

The range and efficiency of photons that a pigment molecule is capable of absorbing constitute its characteristic absorption ________

spectrum

The two most important classes of pigments in chloroplasts are chlorophylls and ________

carotenoids

Which of the following are used by green plants to absorb light energy?

• Chlorophyll a

• Chloroplast c

• Xanthophyll b

• Chlorophyll b

• Chlorophyll c

• Chlorophyll a

• Chlorophyll b

If chloroplasts are isolated from a plant and exposed to light in the absence of carbon dioxide, they accumulate ________

ATP

In the visible spectrum, light energy may be absorbed by boosting ______ to higher atomic energy levels, sometimes called energy shells.

electrons

In photosynthesis, _____ molecules preferentially absorb violet-blue and red light.

chlorophyll

A graph depicting the efficiency of photon absorption by a pigment molecule as a function of photon wavelength is known as the ________

absorption spectrum of the pigment

On an absorption spectrum for chlorophyll, which color of light would have a low rate of of absorption?

green

On the following diagram of the absorption spectra of various pigments, the dotted line shows the absorption spectrum of _______

chlorophyll b

Which of the following accurately describes pigments in the chloroplast?

• Carotenoids are primary light-absorbing pigments

• Chlorophyll a is the main photosynthetic pigment in plants.

• Chlorophyll b is the only pigment that can act directly to convert light energy into chemical energy.

Chlorophyll a is the main photosynthetic pigment in plants.

Which of the following wavelengths of light are preferentially absorbed by chlorophyll molecules?

• Red

• Green

• Yellow

• Violet-blue

• Red

• Violet-blue

Which of the following are parts of a chlorophyll molecule?

• A hydrocarbon tail

• A porphyrin ring

• A manganese atom

• An anchoring protein

• A hydrocarbon tail

• A porphyrin ring

The following diagram represents light absorption as a function of wavelength of various pigments. Which of the three pigments might reflect an orange or red color?

The pigment represented by the gray line

According to the generalized equation for photosynthesis proposed by van Niel, CO₂ + 2H₂A + light energy yields which of the following?

• CH₂O + H₂O

• CH₂O + H₂O + 2A

• 2 CH₂O + O₂

• 2CH₂O + ATP

CH₂O + H₂O + 2A

Which of the following is an accurate description of carotenoids?

• They are made of a porphyrin ring connected to a long hydrophobic chain.

• They are made a long carbon chain with multiple double bonds at one end and several hydroxyl groups at the other end.

• They are made of carbon rings connected to carbon chains with alternating single and double bonds.

They are made of carbon rings connected to carbon chains with alternating single and double bonds.

Chlorophyll _____ is the main photosynthetic pigment in plants as it converts light energy into chemical energy; chlorophyll _____ acts as an accessory pigment.

a; b

How do carotenoids assist in the photosynthetic process?

By capturing light wavelengths that are not efficiently absorbed by chlorophylls.

A chlorophyll molecule is made of a _____ ring and a ______ tail

porphyrin; hydrophobic

How is the output of photosynthesis related to the amount of light available at different light intensities?

Linear increase at low light intensities and saturation at high light intensities

______ are accessory photosynthetic pigments that consist of carbon rings linked to chains with alternating single and double bonds.

carotenoids

When photosynthesis in the alga Chlorella was studied, scientists determined that the production of one molecule of ______ from water requires several thousand chlorophyll molecules.

oxygen

Similar to other pigments, carotenoids assist photosynthesis by capturing energy from _______, however, they absorb wavelengths that are not efficiently absorbed by ______. In addition, they scavenge ______ radicals.

light/photons; chlorophylls; free

Almost all photosynthetic organisms capture light using ______

photosystems

A photosystem consists of two components, a(n) _____ complex and a(n) ______ center.

antenna; reaction

In a photosystem, the ______ complex captures light energy and passes it to the _____ center where electrons are transferred out of the photosystem.

antenna; reaction

At low light intensities, how is the output of photosynthesis related to the intensity of illumination?

The output of photosynthesis increases linearly with increases in the intensity of illumination.

The role of the _____ -harvesting complex in a photosystem is to directly absorb photons of light.

light

The production of one molecule of O₂ during photosynthesis requires how many chlorophyll molecules?

thousands

In chloroplasts, the light-harvesting complex is composed of a web of ______ molecules linked together and held tightly in the thylakoid membrane by a matrix of proteins.

pigment

In all photosynthetic organisms studied to date, except one class of photosynthetic bacteria, light is captured by clusters of chlorophyll and accessory pigment molecules, which together are called _____

photosystems

Once a photon is captured by the light harvesting complex, the pigments in it transfer _______

the energy of excited electrons but not electrons themselves

What are the two components of a photosystem?

• A reaction center

• An antenna complex

How is the reaction center positioned in the membrane?

It is a transmembrane complex.

In the reaction center of a photosystem, which of the following excited subatomic particles are transferred to an acceptor?

Electrons

Where do the light-dependent reactions of photosynthesis occur in the chloroplast?

• In the stroma

• In the outer chloroplast membrane

• In the thylakoid membrane.

• In the thylakoid lumen

In the thylakoid membrane.

The role of the light-harvesting complex is to _____

directly absorb photons of light

Anoxygenic bacteria have how many photosystems?

one

The light-harvesting complex of a photosystem in a green plant contains a large number of _______

pigments

In the light-harvesting complex of the chloroplast, it is excitation ______, not the electrons themselves, that pass from one pigment molecule to the next.

energy

The reaction center in chloroplasts is a transmembrane ______-pigment complex.

protein

the light-______ reactions of photosynthesis occur in the membranes.

dependent

chloroplasts have _____ type(s) of photosystem(s)

two

In chloroplasts, when the two photosystems work in series, electrons ejected from the photosystems do not return to them, which is known as _____

noncyclic photophosphorylation

A Z diagram illustrates how many electron-energizing steps?

two

he electron transport chain directly associated with photosystem II is used to generate ______, while the electron transport chain directly associated with photosystem I is used to generate ______.

ATP; NADPH

The process in which electrons from water move through PSII and PSI and ultimately to NADPH is also known as _______ photophosphorylation

non-cyclic

The ______ diagram describes the energy transitions of electrons as they move through the ______ reactions.

Z; light-dependent

The primary electron acceptor for the excited electron leaving photosystem II is a ______ molecule

plastoquinone

What is the function of the b₆-f complex?

To pump protons in the thylakoid space

Which photosystem's main function is to generate high-energy electrons for the synthesis of ATP?

Photosystem II

Review the diagram of photosynthesis in the chloroplast. What does the thick arrow labeled with the letter A point to?

b₆-f complex

The reaction center of photosystem I consists of a core transmembrane complex made of ___ protein subunits and ___ bound P₇₀₀ chlorophyll molecules

12-14; 2

Photosystem I passes electrons to

ferredoxin

Reduced plastoquinone is a strong electron donor that passes a pair of electrons to ______

the b₆-f complex

On the following diagram of photosynthesis in the chloroplast, the thick arrow labeled with the letter A points to

photosystem I

On the stromal side of the thylakoid membrane, two molecules of reduced ____ donate two electrons for the synthesis of one molecule of NADPH.

ferredoxin

The iron-sulfur protein _____ accepts electrons from photosystem I.

ferredoxin

The primary electron acceptor for the excited electron leaving photosystem II is a ______ molecule.

plastoquinone

The ATP synthases of chloroplasts and mitochondria are evolutionarily _____

related

Recent studies with the atomic force microscope have shown that PSI and the ATP synthase are not randomly distributed in thylakoid membranes, rather, they seem concentrated primarily in the _______

primarily in the connections between grana (the stroma lamellae)

Which molecule donates electrons for the synthesis of NADPH in chloroplasts?

Reduced ferredoxin