Question 1

Which molecule carries electrons to the luminal side of the positively charged PSI reaction center where they are transferred to pigment P700⁺,the positively charged reaction-center pigment of PSI?

Accepted Answer

Plastocyanin carries electrons from the cytochrome b6f complex to the PSI reaction center, where they are transferred to pigment P700⁺.

Question 2

What is the mechanism of action by which the herbicide paraquat kills plants?

Accepted Answer

Paraquat kills plants by generating highly reactive oxygen radicals when electrons attached to it are used to reduce oxygen. This process interferes with Photosystem I (PSI) function, as paraquat competes with ferredoxin for electrons from the PSI reaction center. The reactive oxygen species produced can damage chloroplasts and other cellular components, leading to the plant's death. Therefore, all the mechanisms listed contribute to the herbicidal action of paraquat.

Question 3

What is the mechanism by which the herbicides diuron,atrazine and terbutryn are able to kill plants?

Accepted Answer

The herbicides diuron, atrazine, and terbutryn block electron transport through photosystem II (PSII) in chloroplasts, leading to the accumulation of reactive oxygen species and ultimately the death of the plant. This occurs through binding to the D1 protein of PSII and inhibiting the transfer of electrons from water to plastoquinone, which is necessary for the synthesis of ATP and NADPH during photosynthesis.

Question 4

Why is the conversion of CO₂ to a 6-carbon sugar so energetically expensive?

Accepted Answer

CO₂ is the most highly oxidized and least energetic form in which carbon can occur. The conversion of CO₂ to a 6-carbon sugar requires energy input because it involves reduction, which is the opposite of oxidation. Therefore, converting a highly oxidized molecule like CO₂ to a less oxidized molecule like a 6-carbon sugar is energetically expensive.

Question 5

The reduction of ________ is accomplished with electrons passed through ferredoxin; this substance then reduces certain _______ in selected Calvin cycle enzymes.

Accepted Answer

The reduction of thioredoxin is accomplished with electrons passed through ferredoxin. This reduced thioredoxin then reduces certain disulfide bridges in selected Calvin cycle enzymes, thereby activating them.

Question 6

The production of ATP in chloroplasts and mitochondria differs in which of the following ways?

Accepted Answer

In mitochondria, the force that drives ATP production is primarily expressed as an electrochemical potential, which is generated by the movement of protons across the inner mitochondrial membrane. In contrast, in chloroplasts, the force that drives ATP production is largely due to a pH gradient, which is established across the thylakoid membrane. While there may be some electrochemical potential present as well, it is not the primary mechanism for generating the proton motive force in chloroplasts.

Question 7

Calvin originally thought that the acceptor molecule for carbon dioxide during carbon fixation contained how many carbons?

Accepted Answer

The answer of Calvin originally thought that the acceptor molecule...

Question 8

The initial product of carbon fixation contains ____ carbons,but it breaks down into two compounds containing _____ carbons.

Accepted Answer

The initial product of carbon fixation is typically a six-carbon compound called glucose, which then breaks down into two three-carbon compounds called pyruvate during the process of glycolysis. Therefore, option B (6,3) is the correct choice.

Question 9

In chloroplasts,a proton gradient is established with a higher concentration of protons found in the ______ and a lower concentration in the ______.

Accepted Answer

In chloroplasts, the proton gradient is established with a higher concentration of protons found in the thylakoid lumen and a lower concentration in the stroma. This gradient is important for ATP synthesis during photosynthesis. Choices A, B, D, and E are incorrect because they refer to other organelles (such as mitochondria) or incorrect compartments within chloroplasts.

Question 10

Algal cultures in sealed containers were exposed to radiolabeled [¹⁴C]O₂ for a brief incubation period.Soluble molecules were extracted from the algae and subjected to 2D-paper chromatography.How many carbons are found in the most predominant spot on the chromatogram?

Accepted Answer

The answer of Algal cultures in sealed containers were exposed...

Question 11

Why does an electrochemical potential build up in mitochondria,but not in chloroplasts?

Accepted Answer

In chloroplasts, proton movement into the thylakoid lumen is compensated for by the movement of other ions, such as magnesium and chloride. This prevents an electrochemical potential from building up. In contrast, in mitochondria, protons are pumped into the intermembrane space and there is no compensating movement of other ions. As a result, an electrochemical potential builds up across the inner mitochondrial membrane.

Question 12

A mechanism that is known to regulate basic cell processes,like protein folding,transcription,translation and chloroplast metabolism,by controlling the activity of proteins is known as ________.

Accepted Answer

The mechanism that is known to regulate basic cell processes by controlling the activity of proteins is called redox control. This mechanism involves the transfer of electrons between molecules to regulate cellular processes, such as protein folding, transcription, translation, and chloroplast metabolism. Redox control can manipulate the activity of proteins by oxidizing or reducing them, which affects their structure and function.

Question 13

______is a small,water-soluble,iron-sulfur protein that transfers electrons to NADP⁺ to form NADPH.

Accepted Answer

Ferredoxin is a small, water-soluble, iron-sulfur protein that transfers electrons to NADP+ to form NADPH. Ferritin is a protein that stores iron, sulfate is a salt, and sulfotriene and sulferritin are not relevant to electron transfer.

Question 14

What waste product of photolysis is released to the environment?

Accepted Answer

Oxygen is released as a waste product of photolysis, which is the process of splitting water molecules into oxygen, electrons, and hydrogen ions using energy from sunlight.

Question 15

How does paraquat destroy human tissue?

Accepted Answer

Paraquat generates oxygen radicals by diverting electrons from complex I of the respiratory chain. These oxygen radicals then cause damage to the tissue.

Question 16

A cluster of what kind of ions is responsible for passing electrons one-at-a-time to the nearby P680+ in the reaction center?

Accepted Answer

The cluster of 4 manganese ions and one calcium ion (Mn4CaO5) is known as the oxygen-evolving complex, and it is responsible for water oxidation and the transfer of electrons one-at-a-time to the nearby P680+ in the reaction center of Photosystem II during the light-dependent reactions of photosynthesis. This process ultimately results in the production of oxygen, ATP, and NADPH.

Question 17

Mercaptoethanol is a reagent that breaks disulfide linkages.If you were to treat Calvin cycle enzymes with this reagent,what effect might it conceivably have on them?

Accepted Answer

The answer of Mercaptoethanol is a reagent that breaks disulfide...

Question 18

Starch stored as granules in the chloroplasts serves what purpose?

Accepted Answer

Starch stored as granules in the chloroplasts serves the purpose of providing plants with sugars at night when light-dependent reactions are not possible. This allows plants to continue their metabolic processes even in the absence of sunlight.

Question 19

Why are plants unlikely to produce many carbohydrates at night?

Accepted Answer

Selected Calvin cycle enzymes require the reducing power of thioredoxin to maintain their active state by reducing their disulfide linkages. However, in the dark, thioredoxin is oxidized and unable to reduce these linkages, resulting in the inactivation of these enzymes. Therefore, plants are unlikely to produce many carbohydrates at night due to the inactivation of these enzymes.

Question 20

Which molecule conveys protons from the chloroplast stroma into the thylakoid lumen?

Accepted Answer

Cytochrome b6f is the protein complex responsible for transporting electrons between Photosystem II and Photosystem I in the thylakoid membrane. As it transports electrons, it also translocates protons across the thylakoid membrane, creating a proton gradient that is utilized by ATP synthase to produce ATP.

Quiz 6: Photosynthesis and the Chloroplast

Which molecule carries electrons to the luminal side of the positively charged PSI reaction center where they are transferred to pigment P700⁺,the positively charged reaction-center pigment of PSI?

What is the mechanism of action by which the herbicide paraquat kills plants?

What is the mechanism by which the herbicides diuron,atrazine and terbutryn are able to kill plants?

Why is the conversion of CO₂ to a 6-carbon sugar so energetically expensive?

The reduction of __ is accomplished with electrons passed through ferredoxin; this substance then reduces certain _ in selected Calvin cycle enzymes.

The production of ATP in chloroplasts and mitochondria differs in which of the following ways?

Calvin originally thought that the acceptor molecule for carbon dioxide during carbon fixation contained how many carbons?

The initial product of carbon fixation contains carbons,but it breaks down into two compounds containing _ carbons.

In chloroplasts,a proton gradient is established with a higher concentration of protons found in the and a lower concentration in the .

Algal cultures in sealed containers were exposed to radiolabeled [¹⁴C]O₂ for a brief incubation period.Soluble molecules were extracted from the algae and subjected to 2D-paper chromatography.How many carbons are found in the most predominant spot on the chromatogram?

Why does an electrochemical potential build up in mitochondria,but not in chloroplasts?

A mechanism that is known to regulate basic cell processes,like protein folding,transcription,translation and chloroplast metabolism,by controlling the activity of proteins is known as ________.

______is a small,water-soluble,iron-sulfur protein that transfers electrons to NADP⁺ to form NADPH.

What waste product of photolysis is released to the environment?

How does paraquat destroy human tissue?

A cluster of what kind of ions is responsible for passing electrons one-at-a-time to the nearby P680+ in the reaction center?

Mercaptoethanol is a reagent that breaks disulfide linkages.If you were to treat Calvin cycle enzymes with this reagent,what effect might it conceivably have on them?

Starch stored as granules in the chloroplasts serves what purpose?

Why are plants unlikely to produce many carbohydrates at night?

Which molecule conveys protons from the chloroplast stroma into the thylakoid lumen?

Quiz 6: Photosynthesis and the Chloroplast

Which molecule carries electrons to the luminal side of the positively charged PSI reaction center where they are transferred to pigment P700+,the positively charged reaction-center pigment of PSI?

What is the mechanism of action by which the herbicide paraquat kills plants?

What is the mechanism by which the herbicides diuron,atrazine and terbutryn are able to kill plants?

Why is the conversion of CO2 to a 6-carbon sugar so energetically expensive?

The reduction of ________ is accomplished with electrons passed through ferredoxin; this substance then reduces certain _______ in selected Calvin cycle enzymes.

The production of ATP in chloroplasts and mitochondria differs in which of the following ways?

Calvin originally thought that the acceptor molecule for carbon dioxide during carbon fixation contained how many carbons?

The initial product of carbon fixation contains ____ carbons,but it breaks down into two compounds containing _____ carbons.

In chloroplasts,a proton gradient is established with a higher concentration of protons found in the ______ and a lower concentration in the ______.

Algal cultures in sealed containers were exposed to radiolabeled [14C]O2 for a brief incubation period.Soluble molecules were extracted from the algae and subjected to 2D-paper chromatography.How many carbons are found in the most predominant spot on the chromatogram?

Why does an electrochemical potential build up in mitochondria,but not in chloroplasts?

A mechanism that is known to regulate basic cell processes,like protein folding,transcription,translation and chloroplast metabolism,by controlling the activity of proteins is known as ________.

______is a small,water-soluble,iron-sulfur protein that transfers electrons to NADP+ to form NADPH.

What waste product of photolysis is released to the environment?

How does paraquat destroy human tissue?

A cluster of what kind of ions is responsible for passing electrons one-at-a-time to the nearby P680+ in the reaction center?

Mercaptoethanol is a reagent that breaks disulfide linkages.If you were to treat Calvin cycle enzymes with this reagent,what effect might it conceivably have on them?

Starch stored as granules in the chloroplasts serves what purpose?

Why are plants unlikely to produce many carbohydrates at night?

Which molecule conveys protons from the chloroplast stroma into the thylakoid lumen?

Which molecule carries electrons to the luminal side of the positively charged PSI reaction center where they are transferred to pigment P700⁺,the positively charged reaction-center pigment of PSI?

Why is the conversion of CO₂ to a 6-carbon sugar so energetically expensive?

The reduction of __ is accomplished with electrons passed through ferredoxin; this substance then reduces certain _ in selected Calvin cycle enzymes.

The initial product of carbon fixation contains carbons,but it breaks down into two compounds containing _ carbons.

In chloroplasts,a proton gradient is established with a higher concentration of protons found in the and a lower concentration in the .

Algal cultures in sealed containers were exposed to radiolabeled [¹⁴C]O₂ for a brief incubation period.Soluble molecules were extracted from the algae and subjected to 2D-paper chromatography.How many carbons are found in the most predominant spot on the chromatogram?

______is a small,water-soluble,iron-sulfur protein that transfers electrons to NADP⁺ to form NADPH.