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Chapter 8: Problem 28

Describe the electron transfer pathway from photosystem II to photosystem I in the light-dependent reactions. a. After splitting water in PS-II, high energy electrons are delivered through the chloroplast electron transport chain to PS-I. b. After splitting water in PS-I, high energy electrons are delivered through the chloroplast electron transport chain to PS-II. c. After the photosynthesis reaction, the released products like glucose help in the transfer of electrons from PS-II to PS-I. d. After the completion of the light dependent reactions, the electrons are transferred from PSII to PS-I.

Short Answer

Expert verified
Option a: Electrons are transferred from PS-II to PS-I through an electron transport chain after splitting water in PS-II.

Step by step solution

01

Identify the Electron Source

Understand that photosystem II (PS-II) is responsible for the splitting of water molecules to release electrons, protons, and oxygen.
02

Examine Electron Pathway from PS-II

Determine that after the splitting of water by PS-II, the high-energy electrons are initially delivered to the chloroplast electron transport chain.
03

Identify Final Electron Destination

Conclude that these high-energy electrons from PS-II are ultimately transferred to photosystem I (PS-I) through the electron transport chain.
04

Eliminate Incorrect Options

Review the provided options to eliminate choices that do not correctly describe the pathway: option b and c describe incorrect pathways, and option d does not accurately reflect the detailed process.
05

Select Correct Answer

Choose the correct answer, which accurately describes the electron pathway from PS-II to PS-I: Option a.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

photosystem II
Photosystem II (PS-II) is the first protein complex involved in the light-dependent reactions of photosynthesis. It is located in the thylakoid membrane of chloroplasts. One of its key functions is to harness light energy to split water molecules, a process also known as photolysis. This process generates:
  • Electrons
  • Protons (H+)
  • Oxygen (O2)
The electrons released play a crucial role in the photosynthesis electron transfer pathway.
PS-II is vital for the continuation of the light-dependent reactions as it provides the initial supply of electrons that are then transported through the electron transport chain (ETC).
photosystem I
Photosystem I (PS-I) is another essential component in the light-dependent reactions, located in the thylakoid membrane. Unlike PS-II, PS-I primarily works towards the end of the electron transport chain. It receives electrons that have traveled through a series of proteins embedded in the thylakoid membrane.
One of the key roles of PS-I is to absorb light and use that energy to boost the electrons to an even higher energy level. These high-energy electrons are then used to reduce NADP+ to NADPH.
NADPH is another crucial molecule used in the Calvin cycle, which is the light-independent phase of photosynthesis.
light-dependent reactions
The light-dependent reactions are the initial steps in the process of photosynthesis and occur in the thylakoid membranes of chloroplasts. Their main goal is to capture light energy and convert it into chemical energy in the form of ATP and NADPH. These reactions require sunlight to function. The core processes include:
  • Absorption of light by chlorophyll
  • Electron transport through PS-II and PS-I
  • Production of ATP via ATP synthase
  • Formation of NADPH
Both ATP and NADPH are then utilized in the light-independent reactions (Calvin cycle) to synthesize glucose from carbon dioxide.
chloroplast electron transport chain
The chloroplast electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from PS-II to PS-I. This chain is embedded in the thylakoid membrane. Here鈥檚 how the ETC functions step-by-step:
  • Electrons are first released from water molecules by PS-II.
  • These high-energy electrons move through the ETC via several carriers including plastoquinone (PQ) and cytochrome b6f.
  • As electrons travel through the chain, they lose energy, which is used to pump protons into the thylakoid lumen, creating a proton gradient.
  • This gradient powers ATP synthase to produce ATP.
  • Finally, electrons reach PS-I where they are re-energized by light absorption and then used to form NADPH.
The ETC is crucial for maintaining the flow of electrons that drives the synthesis of ATP and NADPH, essential molecules for the Calvin cycle.
water splitting in photosynthesis
Water splitting, also known as photolysis, occurs within PS-II during photosynthesis. This process is essential because it provides the necessary electrons for the electron transport chain.
Here鈥檚 what happens during water splitting:
  • Light energy absorbed by PS-II excites its electrons to a higher energy level.
  • PS-II then breaks down water molecules into oxygen, protons, and electrons. The simplified equation is: 2H2O 鈫� 4H+ + 4e- + O2.
  • The released electrons are then transferred to the primary electron acceptor in PS-II.
  • Oxygen is released as a byproduct, which is expelled into the atmosphere.
The protons contribute to the creation of a proton gradient used by ATP synthase to generate ATP. This breakdown process is fundamental for sustaining the flow of electrons, which drive the entire process of photosynthesis.

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Most popular questions from this chapter

Why are chemoautotrophs not considered the same as photoautotrophs if they both extract energy and make sugars? a. Chemoautotrophs use wavelengths of light not available to photoautotrophs. b. Chemoautotrophs extract energy from inorganic chemical compounds. c. Photoautotrophs prefer the blue side of the d. Photoautotrophs make glucose, while chemoautophs make galactose.

What is the primary energy source for cells? a. glucose b. starch c. sucrose d. triglycerides

Carbon, in the form of \(\mathrm{CO}_{2},\) must be taken from the atmosphere and attached to an existing organic molecule in the Calvin cycle. Therefore, the carbon is bound to the molecule. The products of the cycle only occur because of the added carbon. What are the products of the Calvin cycle and what is regenerated? a. The product of the Calvin cycle is glyceraldehyde-3 phosphate and RuBP is regenerated. b. The product of the Calvin cycle is glyceraldehyde-3 phosphate and RuBisCO is regenerated. c. The product of the Calvin cycle is a 3-PGA molecule and glyceraldehyde-3 phosphate is regenerated. d. The product of the Calvin cycle is glyceraldehyde-3 phosphate and oxygen is regenerated.

Explain why X-rays and ultraviolet light wavelengths are dangerous to living tissues. a. UV and X-rays are high energy waves that penetrate the tissues and damage cells. b. UV and X-rays are low energy waves that penetrate the tissues and damage cells. c. UV and X-rays cannot penetrate tissues and thus damage the cells. d. UV and X-rays can penetrate tissues and thus do not damage the cells.

The classical theory of evolution is based on a gradual transformation, the accumulation of many random mutations that are selected. The biological evidence for evolution is overwhelming, particularly when one considers what has not changed: core conserved characteristics. A. Describe three conserved characteristics common to both chloroplasts and mitochondria Some hypotheses that have been proposed to account for biological diversity are saltatory, involving sudden changes, rather than gradualist. In defense of the classical gradualist theory of evolution, nearly all biologists in the late 1960s rejected the theory of endosymbiosis as presented by Lynn Margulis in 1967. B. Suppose that you want to disprove the theory of endosymbiosis. Explain how the following evidence could disprove the theory: i. a 鈥渢ransitional species鈥� with cellular features that are intermediate cells with and without mitochondria ii. a 鈥渢ransitional organelle鈥� with some features, such as compartmentalized metabolic processes, but not other features, such as DNA Explain how the following evidence supports the theory of endosymbiosis: iii. bacteria live within your intestines, but you still have a separate identity iv. no one has directly observed the fusion of two organisms in which a single organism results.
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