Question 1

Which of the following sequences accurately represents the flow of electrons through living organisms?

Accepted Answer

The answer of Which of the following sequences accurately represents...

Question 2

In a thylakoid membrane, absorbed light energy is passed from one chlorophyll molecule to another until it is:

Accepted Answer

The absorbed light energy is ultimately passed to a reaction center in the thylakoid membrane where it can be used for photosynthesis, making choice C the correct answer. Choices A and B are incorrect because they describe alternative pathways for the dissipation of energy rather than its use. Choice D is also incorrect because only one of the options is correct.

Question 3

After several weeks of no rain during the summer, you observe that leaves of some plants are wilted. Which of the following would you expect to observe at the cellular level with respect to photosynthesis?

Accepted Answer

During water stress, the rate of photosynthesis decreases. The limited water supply may lead to a decrease in electron flow through the thylakoid electron transport chain, which may cause an increase in the reduction of chlorophyll molecules, leading to photodamage. This would eventually result in damage to the photosynthetic machinery, which leads to the production of reactive oxygen species and ultimately, the wilting of leaves. Therefore, the best choice is E, which states that the rate of the reduction of chlorophyll molecules will be decreased.

Question 4

Which of the following could be TRUE if a plant cell is exposed to a toxin that somehow causes the outer chloroplast membrane to be less permeable to water?

Accepted Answer

The answer of Which of the following could be TRUE...

Question 5

Some bacteria carry out a type of photosynthesis that uses H₂S in place of H₂O. Assuming that the process is otherwise similar to green plant photosynthesis, which of the following could represent the overall reaction?

Accepted Answer

In photosynthesis, carbon dioxide and water are converted into glucose and oxygen. The given question suggests a similar process but with hydrogen sulfide (HS) replacing water (H2O). The correct equation (B) reflects this substitution, producing glucose, elemental sulfur, and water as products, aligning with the principles of photosynthesis where an inorganic carbon source (CO2) is converted into an organic molecule (glucose) using an electron donor (in this case, HS instead of H2O).

Question 6

As electrons flow from one photosystem to another, the amount of energy present in the electrons decreases. How does the plant cell use the energy lost by the electrons?

Accepted Answer

The energy lost by the electrons is used to create and maintain a proton gradient. This gradient is established by pumping protons from the stroma to the lumen of the thylakoid. The difference in proton concentration and charge between the lumen and stroma generates an electrochemical gradient that is useable to power ATP synthesis via ATP synthase. Thus, the energy of the electrons is converted into a form that can be used by the plant cell.

Question 7

Which of the following could be TRUE if a plant cell is exposed to a toxin that makes the thylakoid membrane freely permeable to protons?

Accepted Answer

If the thylakoid membrane is freely permeable to protons, then the proton gradient that is normally used to drive ATP synthesis will be dissipated. This means that there will be no ATP available to drive carbohydrate synthesis in the Calvin cycle (A). However, the splitting of water molecules early in the light-dependent pathway does not require ATP (B). In the absence of light energy, there will be no ATP produced in the chloroplasts to power photosynthesis (C). The mitochondria will not be able to generate enough ATP to power photosynthesis and supply the many other processes that require it (D). The amount of NADPH in the chloroplast will increase because the electrons that are normally used to reduce NADP+ will not be able to be used to generate ATP (E).

Question 8

In the chloroplast, cytochrome b₆f is an important complex in the photosynthetic electron transport chain because it accepts electrons from photosystem II and donates them to photosystem I. Another vital function of cytochrome b₆f is that, during its reduction-oxidation cycle, it moves _____ from the _____.

Accepted Answer

Cytochrome b6f complex functions in the photosynthetic electron transport chain by pumping protons from the stroma into the thylakoid lumen, contributing to the proton gradient used for ATP synthesis.

Question 9

Suppose a mutation caused photosystem I to function at only 10 percent of its normal capacity. Which of the following would you predict would happen?

Accepted Answer

Photosystem I is responsible for the reduction of NADP+ to NADPH. If its capacity is reduced, NADP+ reductase activity would decrease due to less availability of electrons from photosystem I.

Question 10

Which of the following CORRECTLY lists the path taken by electrons through the light dependent reactions of photosynthesis?

Accepted Answer

The correct path taken by electrons through the light dependent reactions of photosynthesis is from water to photosystem II to cytochrome b6f to photosystem I to NADPH. Choice C correctly lists this path.

Question 11

Suppose you discovered a mutant strain of spinach in which the thylakoid membranes were slightly permeable to protons, thus allowing a slow leakage. (Remember that normal membranes are not permeable to protons at all.) How might this defect affect the yield of ATP and/or NADPH from the light reactions?

Accepted Answer

The proton gradient across the thylakoid membrane is crucial for ATP synthesis in chloroplasts. If the membrane is permeable to protons, the gradient would dissipate, reducing the efficiency of ATP synthesis.

Question 12

The electrochemical gradient in a chloroplast can have a concentration of protons 1000 times greater on one side of a thylakoid membrane than the other.

Accepted Answer

This is true. During photosynthesis, protons are pumped from the stroma into the thylakoid lumen, creating a gradient of protons that can be used to generate ATP via ATP synthase. The concentration of protons in the lumen can become 1000 times greater than in the stroma.

Question 13

Leaves absorb the LEAST amount of light in the _____ range of the visible spectrum.

Accepted Answer

Leaves appear green because they reflect green light and absorb the least amount of light in the green range of the visible spectrum.

Question 14

In the chloroplast, cytochrome b₆f is an important complex in the photosynthetic electron transport chain because it accepts electrons from photosystem II and donates them to photosystem I. Explain why the repeated reduction and oxidation of cytochrome b₆f is a vital step in the light dependent reactions and why it is critical to the overall process of photosynthesis.

Accepted Answer

The answer of In the chloroplast, cytochrome b₆f is an...

Question 15

Which of the following outcomes would you expect if the pH of the thylakoid lumen increases from 4 to 6?

Accepted Answer

The decrease in proton concentration in the thylakoid lumen will lead to a decrease in the proton motive force, which is the force that drives ATP synthesis by ATP synthase. Therefore, the rate of ATP synthesis by ATP synthase will decrease. The other options are not affected by a change in thylakoid lumen pH.

Question 16

Why is the photosynthetic electron transport chain sometimes referred to as the "Z scheme"?

Accepted Answer

The "Z scheme" refers to the pattern of energy changes of electrons as they move through the photosynthetic electron transport chain, where their energy level increases, decreases, and then increases again, resembling the shape of the letter "Z".

Question 17

Which of the following is the primary advantage to eukaryotic photosynthetic organisms of having two photosystems?

Accepted Answer

The primary advantage of having two photosystems in eukaryotic photosynthetic organisms is that it allows for the use of water as a source of electrons. This process splits water molecules, releasing oxygen as a byproduct, which is a fundamental aspect of the oxygenic photosynthesis found in plants, algae, and cyanobacteria.

Question 18

If a plant is exposed to a toxin that makes the thylakoid membranes permeable to protons, predict the impact of the toxin on each of the following the: 1. proton gradient across the thylakoid membrane. 2. oxidation of NADPH to NADP⁺. 3. pH in the thylakoid lumen. 4. production of carbohydrate in the Calvin cycle.

Accepted Answer

The answer of If a plant is exposed to a...

Question 19

As electrons flow through the light-dependent reactions, they become associated with several molecules and molecular complexes. When do the electrons have the GREATEST amount of energy?

Accepted Answer

The answer of As electrons flow through the light-dependent reactions,...

Question 20

As light levels increase, some electrons from photosystem I are redirected from _____ back into the electron-transport chain.

Accepted Answer

The answer of As light levels increase, some electrons from...

Quiz 8: Photosynthesis: Using Sunlight to Build Carbohydrates