Biology Chapter 10

What is the basic role of CO2 in photosynthesis?

CO2 is fixed or incorporated into organic molecules.

Of the following, which occurs during the Calvin cycle?

CO2 is reduced.

What property of the pigment chlorophyll makes it appear green?

Chlorophyll absorbs all of the visible spectrum of light except green, which it reflects.

In C3 plants the conservation of water promotes _____.

Conserving water simultaneously reduces the amount of carbon dioxide available to the plant.

Following carbon atoms around the Calvin cycle

Counting carbons—keeping track of where the carbon atoms go in each reaction—is a simple way to help understand what is happening in the Calvin cycle. To produce 1 molecule of G3P (which contains 3 carbons), the Calvin cycle must take up 3 molecules of CO2 (1 carbon atom each). The 3 CO2 molecules are added to 3 RuBP molecules (which contain 15 total carbon atoms), next producing 6 molecules of 3-PGA (18 total carbon atoms). In reducing 3-PGA to G3P (Phase 2), there is no addition or removal of carbon atoms. At the end of Phase 2, 1 of the 6 G3P molecules is output from the cycle, removing 3 of the 18 carbons. The remaining 5 G3P molecules (15 total carbon atoms) enter Phase 3, where they are converted to 3 molecules of R5P. Finally, the R5P is converted to RuBP without the addition or loss of carbon atoms.

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

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

Select the correct molecule that is the main product of the Calvin cycle.

G3P Glucose is discussed as the product of photosynthesis primarily for convenience. In fact, very little free glucose is produced by or transported from photosynthetic cells. Read about the Calvin cycle.

Which of the following processes occurs during the second phase, the reduction phase, of the Calvin cycle?

G3P production

Which term describes ATP production resulting from the capture of light energy by chlorophyll?

Photophosphorylation The excitation of chlorophyll by light energy initiates a chain of events that leads to ATP production.

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

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

Why are plants classified as producers?

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

G3P is used in which of the following processes?

Production of glucose, cellulose, starch, sucrose

According to the chemiosmotic hypothesis, what provides the energy that directly drives ATP synthesis?

Proton gradient A proton gradient across chloroplast and mitochondrial membranes drives ATP synthesis by the enzyme ATP synthase.

_____ has a longer wavelength than _____.

Red ... green

Carbon fixation involves the addition of carbon dioxide to _____.

RuBP In the Calvin cycle, carbon dioxide is added to RuBP.

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

Six carbon dioxide molecules are required to produce two G3P molecules, which can be combined to make one glucose molecule.

Carbon dioxide and oxygen enter and exit a leaf by diffusion. Which structure(s) on a leaf allow(s) this process to happen?

Stomata

Where does the Calvin cycle of photosynthesis occur?

Stroma

the correct statement about the Calvin cycle.

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

During the Calvin cycle, what happens during the carbon fixation phase?

The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five-carbon sugar named ribulose bisphosphate.

The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night. Why?

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

the most accurate statement describing the basic function of the light reactions of photosynthesis.

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

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.

The chemiosmotic hypothesis states that the flow of electrons through an electron transport chain generates a proton gradient that leads to the synthesis of ATP.

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

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

Which of the following statements correctly describes the difference in carbon fixation between C3 and C4 plants?

The first product of carbon fixation in C4 plants is a four-carbon compound instead of a three-carbon compound.

During which process is molecular oxygen produced in photosynthesis?

The light reactions by linear electron flow

Why are most autotrophs referred to as the producers of the biosphere?

They are the ultimate sources of organic compounds for all nonautotrophic organisms.

Plants are photoautotrophs. What does this mean?

They use light energy to drive the synthesis of organic molecules from inorganic materials.

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.

How does carbon dioxide enter the leaf?

Through the stomata

The light reactions of photosynthesis use chemiosmosis to produce ATP that will be used in the Calvin cycle. The electrochemical gradient that drives this chemiosmosis is formed across which structure(s)?

Thylakoid membrane

Chlorophyll molecules are in which part of the chloroplast?

Thylakoid membranes

Where do the electrons entering photosystem II come from?

Water

Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?

Water is oxidized and carbon dioxide is reduced.

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?

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.

The most important role of pigments in photosynthesis is to __________.

capture light energy

The photosynthetic membranes are found in the _____ in plant cells.

chloroplasts An elaborate system of interconnected thylakoid membranes segregates the stroma from the thylakoid space in the chloroplast.

The overall function of the Calvin cycle is _____.

making sugar Using the ATP and NADPH made during the light reactions, carbon is reduced in the Calvin cycle and sugar is made.

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

oxidized...reduced During the light reactions of photosynthesis, water is oxidized, and during the Calvin cycle, carbon is reduced.

Which of the following is a product of the light reactions of photosynthesis?

oxygen, ATP, and NADPH

In the electromagnetic spectrum, the type of radiation that we call visible light occurs between _____.

radio waves and microwaves Visible light is a narrow band of the electromagnetic spectrum that lies between ultraviolet radiation and infrared radiation.

When light strikes chlorophyll molecules, they lose electrons, which are ultimately replaced by _____.

splitting water The electrons removed from water are transferred to P680.

The ultimate source of energy to support most life on Earth is _____.

sunlight For the most part, life on Earth is solar-powered. Plants are photoautotrophs, organisms that use light as a source of energy to synthesize organic substances.

When chloroplast pigments absorb light, __________.

their electrons become excited

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 To conserve water during hot, dry conditions, the stomata are fully or partially closed, preventing CO2 from reaching high concentrations.

The light reactions of photosynthesis occur in the __________.

thylakoids

C4 plants differ from C3 and CAM plants in that C4 plants _____.

transfer fixed carbon dioxide to cells in which the Calvin cycle occurs In C3 and CAM plants carbon dioxide fixation and the Calvin cycle occur in the same cells.

Both mitochondria and chloroplasts __________.

use chemiosmosis to produce ATP

The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from __________.

water

The light reactions of photosynthesis use _____ and produce _____.

water ... NADPH

the interrelatedness of sugar production and sugar breakdown in a plant cell.

A mutually dependent relationship exists between chloroplasts and mitochondria in the plant cell. Photosynthesis, which occurs in chloroplasts, generates the sugars and oxygen gas that are used in mitochondria for cellular respiration. Cellular respiration generates carbon dioxide, which in turn is used as a carbon source for the synthesis of sugars during photosynthesis. Cellular respiration also generates ATP and water, which are used in various chemical reactions in the plant cell.

Which of the following products of the light reactions of photosynthesis is consumed during the Calvin cycle?

NADPH During the Calvin cycle electrons stored in NADPH are used to reduce carbon.

After 3-PGA is phosphorylated, it is reduced by _____.

NADPH supplies the electrons that reduce the phosphorylated 3-PGA.

The light reactions of photosynthesis generate high-energy electrons, which end up in __________. The light reactions also produce __________ and __________.

NADPH; ATP; oxygen

In the light reactions of photosynthesis, ATP is produced by photophosphorylation. Which of the listed processes is most similar to photophosphorylation?

Oxidative phosphorylation in cellular respiration

In the Calvin cycle, how many ATP molecules are required to regenerate RuBP from five G3P molecules?

3

Which of these equations best summarizes photosynthesis?

6 CO2 + 6 H2O → C6H12O6 + 6 O2

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

H2O → NADPH → Calvin cycle

In C4 and CAM plants carbon dioxide is fixed in the _____ of mesophyll cells.

In C4 and CAM plants carbon dioxide fixation occurs in the cytoplasm.

How is photosynthesis similar in C4 plants and CAM plants?

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