Chapter 10

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

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 others: The stroma is the fluid inside the chloroplast in which the Calvin cycle occurs. Cristae are the inner membrane folds found in a mitochondrion. None of the reactions of photosynthesis occurs on the outer membrane of the chloroplast. Stomata are microscopic pores through which oxygen and carbon dioxide diffuse. Photosystem II absorbs light energy, which drives the first steps in the light reactions, but it is not involved in chemiosmosis.

Chlorophyll molecules are in which part of the chloroplast?

Thylakoid membranes

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 light reactions of photosynthesis supply the Calvin cycle with __________.

ATP and NADPH The light reactions of photosynthesis capture solar energy and use it to make ATP and transfer electrons from water to NADP+, forming NADPH. The Calvin cycle uses the ATP and NADPH to produce sugar from carbon dioxide. The energy that enters the chloroplasts as sunlight becomes stored as chemical energy in organic compounds.

The Calvin cycle could not occur without the light reactions. Which of the following statements describes why this is the case?

ATP and NADPH produced in the light reactions provide the energy for the production of sugars in the Calvin cycle.

Which of the following statements is a correct distinction between autotrophs and heterotrophs?

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

Of the following, which occurs during the Calvin cycle?

CO2 is reduced.

In photosynthesis, plants use carbon from __________ to make sugar and other organic molecules.

Carbon Dioxide

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

G3P production

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

G3P is used in which of the following processes? Production of glucose All of the listed processes can use G3P. Production of starch Production of sucrose Production of cellulose Production of cell walls in growing plants

Production of glucose Production of starch Production of sucrose Production of cellulose Production of cell walls in growing plants

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

Stomata

stroma

Stroma is the fluid found inside a chloroplast.

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.

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 Light drives the synthesis of ATP and NADPH by energizing the two photosystems embedded in the thylakoid membranes of chloroplasts. The key to this energy transformation is a flow of electrons through the photosystems and other molecular components built into the thylakoid membrane. This is called linear electron flow, and it occurs during the light reactions of photosynthesis. There are multiple steps in this process. In the step that produces oxygen, an enzyme catalyzes the splitting of a water molecule into two electrons, two hydrogen ions (H+), and an oxygen atom. The H+ are released into the thylakoid space. The oxygen atom immediately combines with an oxygen atom generated by the splitting of another water molecule, forming O2.

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

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

The energy used to produce ATP in the light reactions of photosynthesis comes from __________.

movement of H+ through a membrane Termed chemiosmosis, the diffusion of hydrogen ions through ATP synthase provides the energy to produce ATP. Chloroplasts generate ATP by chemiosmosis. An electron transport chain assembled in a membrane pumps protons across the membrane as electrons are passed through a series of carriers that are progressively more electronegative. In this way, electron transport chains transform redox energy to a proton-motive force, potential energy stored in the form of an H+ gradient across a membrane. Built into the same membrane is an ATP synthase complex that couples the diffusion of hydrogen ions down their gradient to the phosphorylation of ADP. In chloroplasts, the high-energy electrons dropped down the transport chain are extracted from water.

Where does the Calvin cycle of photosynthesis occur?

stroma

When chloroplast pigments absorb light, __________.

their electrons become excited

How does carbon dioxide enter the leaf?

through the stomata

The light reactions of photosynthesis occur in the __________.

thylakoids

Both mitochondria and chloroplasts __________.

use chemiosmosis to produce ATP In other words, mitochondria use chemiosmosis to transfer chemical energy from food molecules to ATP, whereas chloroplasts transform light energy into chemical energy in ATP.

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

water

Where do the electrons entering photosystem II come from?

water