Cellular Respiration

Question 1

What drives the synthesis of ATP and NADPH in photosynthesis?

Answer 1

Light energizing the two photosystems embedded in the thylakoid membranes of chloroplasts.

Question 2

What is linear electron flow?

Answer 2

The flow of electrons through photosystems and other molecular components in the thylakoid membrane during the light reactions of photosynthesis.

Question 3

What is the role of the primary electron acceptor in PS II?

Answer 3

It receives an electron from the excited P680 pair of chlorophyll a molecules.

Question 4

What happens to water molecules during the light reactions?

Answer 4

Water is split into two electrons, two hydrogen ions (H+), and an oxygen atom.

Question 5

Which electron carrier is involved between PS II and PS I?

Answer 5

Plastoquinone (Pq).

Question 6

What is the role of the cytochrome complex?

Answer 6

It pumps H+ into the thylakoid space, contributing to the proton gradient used in ATP synthesis.

Question 7

What is produced when photoexcited electrons from PS I are transferred to NADP+?

Answer 7

NADPH.

Question 8

What is the difference between linear electron flow and cyclic electron flow?

Answer 8

Linear electron flow produces both ATP and NADPH, while cyclic electron flow produces only ATP.

Question 9

True or False: Cyclic electron flow occurs in both photosynthetic bacteria with a single photosystem and in species with both photosystems.

Answer 9

True.

Question 10

What is chemiosmosis?

Answer 10

The process that uses membranes to couple redox reactions to ATP production.

Question 11

How do chloroplasts and mitochondria generate ATP?

Answer 11

By the same basic mechanism of chemiosmosis.

Question 12

What is the function of ATP synthase?

Answer 12

It couples the diffusion of hydrogen ions down their gradient to the phosphorylation of ADP, forming ATP.

Question 13

Fill in the blank: In chloroplasts, the high-energy electrons used in the electron transport chain come from _______.

Answer 13

water.

Question 14

What is the significance of the proton gradient in chloroplasts?

Answer 14

It drives ATP synthesis during the light reactions.

Question 15

What are the final products of the light reactions of photosynthesis?

Answer 15

ATP, NADPH, and O2.

Question 16

How does the pH in the thylakoid space change during the light reactions?

Answer 16

It drops as H+ concentration increases.

Question 17

What is the role of ferredoxin (Fd) in cyclic electron flow?

Answer 17

It shuttles electrons back to the cytochrome complex.

Question 18

What is the role of NADP+ reductase?

Answer 18

It catalyzes the transfer of electrons from Fd to NADP+.

Question 19

What does the light-driven electron flow ultimately generate?

Answer 19

Chemical energy stored in ATP and NADPH.

Question 20

Fill in the blank: The light reactions convert light energy to _______ stored in ATP and NADPH.

Answer 20

chemical energy.

Question 21

What molecule is produced as a by-product of the light reactions?

Answer 21

O2.

Question 22

What is potential energy in the context of photosynthesis?

Answer 22

Potential energy refers to the energy stored in the thylakoid membrane as light energy is converted to chemical energy in ATP and NADPH.

Oxygen is a by-product of this process.

Question 23

What color of light is least effective in driving photosynthesis?

Answer 23

Green light is least effective in driving photosynthesis.

This is because chlorophyll reflects green light.

Question 24

What is the initial electron donor in the light reactions of photosynthesis?

Answer 24

Water (H2O) is the initial electron donor.

The electrons from water ultimately end up in NADPH.

Question 25

What happens to the rate of ATP synthesis if a compound is added that makes membranes freely permeable to hydrogen ions?

Answer 25

The rate of ATP synthesis would decrease. ## Footnote This is because the proton gradient necessary for ATP synthesis would be disrupted.

Question 26

What is the primary function of the Calvin cycle?

Answer 26

The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar. ## Footnote It is an anabolic process that builds carbohydrates.

Question 27

How does the Calvin cycle differ from the citric acid cycle?

Answer 27

The Calvin cycle is anabolic, while the citric acid cycle is catabolic. ## Footnote The citric acid cycle oxidizes acetyl CoA to synthesize ATP.

Question 28

What is the product of the Calvin cycle?

Answer 28

The product is glyceraldehyde 3-phosphate (G3P), a three-carbon sugar. ## Footnote G3P is the direct product of the Calvin cycle.

Question 29

What is carbon fixation in the Calvin cycle?

Answer 29

Carbon fixation is the initial incorporation of CO2 into organic material. ## Footnote It involves attaching CO2 to ribulose bisphosphate (RuBP).

Question 30

What enzyme catalyzes the first step of the Calvin cycle?

Answer 30

The enzyme is RuBP carboxylase-oxygenase, or rubisco. ## Footnote Rubisco is the most abundant protein in chloroplasts.

Question 31

What happens to the six-carbon intermediate formed during carbon fixation?

Answer 31

The six-carbon intermediate immediately splits into two molecules of 3-phosphoglycerate. ## Footnote This occurs because the six-carbon compound is energetically unstable.

Question 32

What is the role of ATP in the Calvin cycle?

Answer 32

ATP provides the energy necessary for the conversion of 3-phosphoglycerate to glyceraldehyde 3-phosphate (G3P). ## Footnote ATP is consumed during the reduction phase.

Question 33

How many molecules of CO2 are fixed for the net synthesis of one G3P molecule?

Answer 33

Three molecules of CO2 are fixed. ## Footnote This occurs as part of three turns of the Calvin cycle.

Question 34

What is the net output of the Calvin cycle for every three molecules of CO2 that enter?

Answer 34

The net output is one molecule of glyceraldehyde 3-phosphate (G3P).

Question 35

What must happen to the five molecules of G3P after one exits the cycle?

Answer 35

The five molecules must be recycled to regenerate three molecules of RuBP.

Question 36

What is the total consumption of ATP and NADPH in the Calvin cycle for the net synthesis of one G3P molecule?

Answer 36

The Calvin cycle consumes a total of nine molecules of ATP and six molecules of NADPH.

Question 37

What organic compounds can G3P be used to synthesize?

Answer 37

G3P can be used to synthesize glucose, sucrose, and other carbohydrates.

Question 38

True or False: Photosynthesis can occur independently in the light reactions or the Calvin cycle.

Answer 38

False. ## Footnote Photosynthesis is an emergent property of the intact chloroplast that integrates both stages.