Question 1

The hydrocarbon skeleton used to form fatty acids, glycerol, and amino acids (when N is added) is derived from

Accepted Answer

The hydrocarbon skeleton used to form fatty acids, glycerol, and amino acids is derived from G3P, which is produced during photosynthesis and is a precursor for the biosynthesis of many biomolecules. Starch, sucrose, and cellulose are carbohydrates and do not have hydrocarbon skeletons that can be used to form these biomolecules. Glucose phosphate is also a carbohydrate and is not a direct precursor for the biosynthesis of fatty acids, glycerol, and amino acids.

Question 2

The end product of the Calvin cycle is

Accepted Answer

The end product of the Calvin cycle is G3P (glyceraldehyde 3-phosphate), which is used to produce glucose and other organic compounds. It can also be used to regenerate RuBP (ribulose-1,5-bisphosphate), which is important for the continuation of the cycle. The other choices do not accurately reflect the end product of the Calvin cycle.

Question 3

Biologists are fairly certain that oxygen was built up in the atmosphere by the development of photosynthesis. The production of oxygen and, therefore, the beginning of extensive aerobic life was made possible by the evolution of

Accepted Answer

Biologists believe that oxygen was built up in the atmosphere by the development of photosynthesis. Specifically, oxygen-producing photosynthesis (known as oxygenic photosynthesis) arises from the evolution of photosystem II (PSII) in cyanobacteria and chloroplasts.

Question 4

The Calvin cycle reactions are dependent upon a supply of

Accepted Answer

The Calvin cycle reactions require carbon dioxide, NADPH, and ATP to fix carbon and produce glucose. Water is not directly involved in the Calvin cycle and oxygen is a product of photosynthesis, not a reactant. Glucose is a product of the Calvin cycle, not a reactant.

Question 5

In the Calvin cycle, the three-carbon molecule that will be immediately formed after carbon dioxide fixation occurs is

Accepted Answer

3PG (3-phosphoglycerate) is the first stable product formed in the Calvin cycle after the fixation of carbon dioxide.

Question 6

Which of the following is a CAM plant?

Accepted Answer

CAM (crassulacean acid metabolism) plants are those that open their stomata (small pores on the leaves) at night to take in carbon dioxide and fix it into a four-carbon compound. During the day, the stomata are closed to prevent water loss through transpiration. Cactus is a classic example of a CAM plant.

Question 7

Most major food plants such as wheat, oats, and rice are

Accepted Answer

Most major food plants such as wheat, oats, and rice are C₃ plants. C₃ plants are the most common type of plant, and they use a three-carbon molecule called ribulose 1,5-bisphosphate (RuBP) as the first step in photosynthesis.

Question 8

How much of the protein content in chloroplasts is made up of the enzyme RuBP carboxylase? Why?

Accepted Answer

RuBP carboxylase, also known as ribulose-1,5-bisphosphate carboxylase/oxygenase or RuBisCO, is the most abundant enzyme on Earth and makes up 20-50% of the protein content in chloroplasts. This high proportion is because the enzyme is very slow, necessitating a large amount of it to meet the photosynthetic demand of plants.

Question 9

During photosynthesis, CO₂ is reduced. This means that

Accepted Answer

Reduction is the gain of electrons, so when CO₂ is reduced during photosynthesis, it means it gains electrons.

Question 10

Which of the following would be a reasonable explanation of why the chloroplast would use the cyclic electron pathway as well as the noncyclic electron pathway?

Accepted Answer

The cyclic electron pathway is used to produce additional ATP without producing NADPH, balancing the ATP/NADPH consumption ratio required by the Calvin cycle, which consumes more ATP than NADPH.

Question 11

Plants need other molecules besides glucose. Where do these molecules, such as cellulose and fructose, come from?

Accepted Answer

G3P, which is produced through photosynthesis, can be used as a precursor molecule for the synthesis of a variety of organic molecules such as cellulose, fructose, and other carbohydrates, lipids, and amino acids. Therefore, plants do not need to produce glucose first and then convert it to other molecules, but they can directly produce a variety of molecules from G3P.

Question 12

NADPH and ATP are used in the

Accepted Answer

NADPH and ATP are used in the Calvin cycle reactions, which are responsible for converting carbon dioxide into glucose during photosynthesis.

Question 13

What are the stages of the Calvin cycle?

Accepted Answer

The Calvin cycle involves three main stages: carbon dioxide fixation, carbon dioxide reduction, and regeneration of RuBP (ribulose-1,5-bisphosphate). These processes are essential for the synthesis of glucose in plants during photosynthesis.

Question 14

The reservoir for H⁺ during photosynthesis is the

Accepted Answer

During photosynthesis, the thylakoid space (also known as the lumen) acts as the reservoir for H+ ions (protons) as they accumulate during the light-dependent reactions, creating a proton gradient used for ATP synthesis.

Question 15

What is the function of ribulose bisphosphate (RuBP) during photosynthesis?

Accepted Answer

Ribulose bisphosphate (RuBP) is a 5-carbon sugar that plays a crucial role in the process of carbon fixation, which is the first step in photosynthesis. RuBP combines with carbon dioxide (CO2) to produce two molecules of a 3-carbon compound called 3-phosphoglycerate (3PG). This reaction is catalyzed by the enzyme RuBisCO (ribulose bisphosphate carboxylase/oxygenase), and it is the starting point for the Calvin cycle, which ultimately leads to the production of glucose.

Question 16

How many total carbons are involved in carbon dioxide fixation when there are 3 molecules of carbon dioxide and 3 molecules of RuBP?

Accepted Answer

Each molecule of RuBP has 5 carbons, so 3 molecules of RuBP have a total of 15 carbons. 3 molecules of carbon dioxide each have 1 carbon, so a total of 3 carbons. Therefore, the total carbons involved in carbon dioxide fixation is 15 + 3 = 18. So, the answer is C, 18.

Question 17

Some herbicides inhibit the electron transport chain in the thylakoid membrane. Without the movement of electrons, hydrogen ions would not be pumped from the stroma to the thylakoid space and the hydrogen ion gradient would not be established. How would this affect the Calvin cycle reactions?

Accepted Answer

The establishment of the hydrogen ion gradient is necessary for ATP production via chemiosmosis. Without ATP, the Calvin cycle reactions cannot occur.

Question 18

The formation of carbohydrate molecules occurs within the

Accepted Answer

The stroma is the site of the Calvin Cycle, where the formation of carbohydrate molecules from carbon dioxide occurs during photosynthesis. The other options are not directly involved in this process.

Question 19

The ATP synthase complex in cellular respiration and photosynthesis

Accepted Answer

Both the ATP synthase complex in cellular respiration and photosynthesis produce ATP by working via chemiosmosis, requiring a proton gradient across a membrane. Additionally, they are both located in a membrane. Therefore, all of the answers are correct.

Question 20

The H⁺ (protons) accumulate in the thylakoid space during electron transport between photosystems I and II. The excess of protons in the thylakoid space

Accepted Answer

The excess of protons in the thylakoid space moves from the thylakoid space to the stroma through the ATP synthase complex, generating ATP in the process. This process is known as chemiosmosis and is a key mechanism for the production of ATP in photosynthesis. Option A is incorrect because the photorespiration pathway is not related to the excess of protons in the thylakoid space. Option B is incorrect because the excess of protons does not raise the pH indefinitely, as this would ultimately result in the cessation of photosynthesis. Option C is incorrect because the excess of protons is not small enough to diffuse back out through the lipid bilayer. Option D is incorrect because the conversion of NADP+ to NADPH is part of the light-independent reactions of photosynthesis and is not directly related to the excess of protons in the thylakoid space.

Quiz 8: Photosynthesis