Photosynthesis Overview and Mechanisms
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Questions and Answers

What is the primary purpose of photosynthesis in plants?

The primary purpose of photosynthesis in plants is to convert light energy into chemical energy and reducing power.

What role does NADP+ reductase play in photosynthesis?

NADP+ reductase is responsible for forming NADPH during photosynthesis.

How do chloroplasts manage to create a proton gradient during photosynthesis?

Chloroplasts generate a proton gradient through electron transport and chemiosmosis.

What is Förster resonant energy transfer and its significance in photosynthesis?

<p>Förster resonant energy transfer is a mechanism that facilitates the transfer of energy between chromophores, crucial for efficient light harvesting in photosystems.</p> Signup and view all the answers

How do herbicides target photosynthesis in plants?

<p>Herbicides typically target and disrupt the functions of photosystems, inhibiting the photosynthetic process.</p> Signup and view all the answers

What structural feature of chloroplasts is essential for their function in photosynthesis?

<p>The thylakoid membranes within chloroplasts are essential for the light-dependent reactions of photosynthesis.</p> Signup and view all the answers

What are the two main types of photosystems involved in photosynthesis?

<p>The two main types of photosystems involved in photosynthesis are Photosystem I and Photosystem II.</p> Signup and view all the answers

How does too much light affect the water-water cycle in photosynthesis?

<p>Excessive light can lead to the production of reactive oxygen species (ROS) from water, resulting in the formation of H2O2 and O2.</p> Signup and view all the answers

What is the primary role of the herbicide Atrazine in photosynthesis?

<p>Atrazine primarily disrupts Photosystem II, leading to the generation of reactive oxygen species (ROS).</p> Signup and view all the answers

Describe the importance of the cyclic electron flow in photosynthesis.

<p>Cyclic electron flow allows for the production of ATP without the need for NADPH, supporting the energy demands of the Calvin cycle.</p> Signup and view all the answers

What are the products of water photolysis in Photosystem II?

<p>The photolysis of water in Photosystem II produces oxygen, protons (4 H+), and electrons (4 e-).</p> Signup and view all the answers

What is the effect of low temperatures on the rate-limiting step of photosynthesis?

<p>Low temperatures can slow down the rate of photosynthesis due to the reduced activity of enzymes involved in the light-dependent reactions.</p> Signup and view all the answers

What is the primary role of photosynthetically active radiation in photosynthesis?

<p>It provides the light energy needed for the conversion to chemical energy.</p> Signup and view all the answers

Describe the function of NADP+ reductase in the light reactions of photosynthesis.

<p>NADP+ reductase facilitates the reduction of NADP+ to NADPH, which is crucial for the Calvin cycle.</p> Signup and view all the answers

Explain the significance of the light harvesting complex in photosystems.

<p>The light harvesting complex optimizes light absorption, enhancing energy transfer to the reaction center.</p> Signup and view all the answers

What event follows the primary charge separation in photosynthesis?

<p>The displacement of an electron occurs, initiating the electron transport chain.</p> Signup and view all the answers

How are chlorophyll a and chlorophyll b different in terms of their absorption maxima?

<p>Chlorophyll a has a maximum absorption near 680 nm, while chlorophyll b absorbs maximally around 650 nm.</p> Signup and view all the answers

What is the role of water in the process of photosynthesis?

<p>Water is oxidized to replenish electrons lost from the reaction center and produces oxygen as a byproduct.</p> Signup and view all the answers

Define the term 'action spectrum' in relation to photosynthesis.

<p>An action spectrum shows the effectiveness of different wavelengths in driving photosynthesis.</p> Signup and view all the answers

What is the main purpose of the Calvin cycle in photosynthesis?

<p>The Calvin cycle converts carbon dioxide into glucose using ATP and NADPH produced in the light reactions.</p> Signup and view all the answers

How does the electron transport chain contribute to ATP synthesis?

<p>The electron transport chain creates an electrochemical gradient that drives ATP synthesis via chemiosmosis.</p> Signup and view all the answers

What is Förster resonant energy transfer and its relevance in photosynthesis?

<p>Förster resonant energy transfer describes the energy transfer between closely spaced molecules, important in chlorophyll arrangements.</p> Signup and view all the answers

What primary role do cyanobacteria play in the context of Earth's atmosphere?

<p>Cyanobacteria were among the first organisms to perform photosynthesis, significantly increasing oxygen levels in the atmosphere.</p> Signup and view all the answers

What is the difference between the stroma and thylakoid in chloroplasts?

<p>The stroma is the fluid-filled space surrounding the thylakoids, while thylakoids are membrane-bound structures where photosynthesis reactions occur.</p> Signup and view all the answers

Why do leaves appear green?

<p>Leaves appear green because chlorophyll absorbs blue and red light while reflecting green light.</p> Signup and view all the answers

What are the main products of the light-dependent reactions of photosynthesis?

<p>The light-dependent reactions produce ATP and NADPH, along with oxygen as a byproduct.</p> Signup and view all the answers

What role does water play in photosynthesis?

<p>Water provides electrons and protons for the light reactions and produces oxygen when split during photosynthesis.</p> Signup and view all the answers

How does the structure of thylakoids facilitate photosynthesis?

<p>Thylakoids are organized in stacks to maximize surface area for light absorption and contain the proteins needed for the electron transport chain.</p> Signup and view all the answers

What is the function of NADP+ in the photosynthesis process?

<p>NADP+ acts as an electron carrier, accepting electrons to form NADPH in the light-dependent reactions.</p> Signup and view all the answers

What organisms are responsible for the first synthesis of organic compounds through photosynthesis?

<p>Cyanobacteria were the first organisms to perform photosynthesis, leading to the production of organic compounds.</p> Signup and view all the answers

Describe the overall equation for photosynthesis.

<p>The overall equation for photosynthesis can be summarized as: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.</p> Signup and view all the answers

What is the role of PSII in the photosynthetic process?

<p>Photosystem II (PSII) captures light energy to split water molecules, generating oxygen and electrons.</p> Signup and view all the answers

How does high light intensity affect the rate of photosynthesis?

<p>High light intensity can lead to rate-limiting reactions in PSII and cause non-photochemical quenching.</p> Signup and view all the answers

What are the end products of the reaction occurring in PSII involving water?

<p>The reaction produces oxygen gas (O2) and protons (H+).</p> Signup and view all the answers

Explain the significance of the electron transport chain in photosynthesis.

<p>The electron transport chain transfers electrons from PSII to PSI, helping to generate ATP and NADPH.</p> Signup and view all the answers

What role do zeaxanthin and violaxanthin play in photosynthesis?

<p>Zeaxanthin and violaxanthin are involved in photoprotection, helping to prevent damage from excess light.</p> Signup and view all the answers

Identify the relationship between pH and the function of VDE in chloroplasts.

<p>Low pH activates Violaxanthin De-Epoxidase (VDE), promoting the conversion of violaxanthin to zeaxanthin.</p> Signup and view all the answers

What is the consequence of generating too many protons (H+) in the thylakoid lumen?

<p>Too many protons in the thylakoid lumen can disrupt the proton gradient necessary for ATP synthesis.</p> Signup and view all the answers

How does the presence of NADP+ and NADPH vary throughout the light reaction stages?

<p>NADP+ accepts electrons leading to the formation of NADPH, which occurs mainly at the end of the light reactions.</p> Signup and view all the answers

What is the function of the Cyt b6f complex in the photosynthetic electron transport chain?

<p>Cyt b6f complex facilitates the transfer of electrons from plastoquinol (PQ) to plastocyanin (PC).</p> Signup and view all the answers

Describe the role of the stroma in photosynthesis.

<p>The stroma is the fluid-filled space where the light-independent reactions take place, utilizing NADPH and ATP.</p> Signup and view all the answers

Flashcards

Oxygenic Photosynthesis

A process where light energy is converted into chemical energy and reducing power, creating ATP and NADPH. It uses water as an electron donor, producing oxygen as a byproduct.

Photosynthesis Summary

The conversion of light energy into chemical energy and reducing power, using chemiosmosis to create ATP and NADP+ reductase forming NADPH.

Chemiosmosis

The process in photosynthesis that uses a proton gradient to generate ATP.

NADP+ reductase

An enzyme that catalyzes the reduction of NADP+ to NADPH, which is used in energy transfer.

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Photosystems I and II

Protein complexes that capture light energy and initiate electron transfer during photosynthesis.

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Förster Resonance Energy Transfer

The movement of energy between chlorophyll molecules in a plant.

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Chloroplast structure

The organelle within plant cells where photosynthesis occurs, including thylakoid membranes and the stroma.

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Photosynthesis

The process used by plants and other organisms to convert light energy into chemical energy in the form of sugars.

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Thylakoid function

The thylakoid membrane is where light-dependent reactions of photosynthesis occur. It contains chlorophyll and electron transport chains.

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Chlorophyll

A green pigment in chloroplasts that absorbs light energy for photosynthesis.

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Cyanobacteria and chloroplasts

Ancient bacteria (cyanobacteria) likely played a role in the development of chloroplasts in plant cells. They were instrumental for early oxygen production.

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Photosystem II

A protein complex in the thylakoid membrane that captures light energy and splits water to produce oxygen, electrons and protons.

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Photosystem I

A protein complex in the thylakoid membrane that uses light energy to transfer electrons and create energy carrying molecules (ATP and NADPH).

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Chlorophyll's color

Chlorophyll absorbs most colors of light except green which reflects and appears as a green color when light comes to leaves.

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Earth formation timeline

A timeline of events in earth's history that illustrate when life and photosynthesis started.

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Photosynthetically Active Radiation (PAR)

The specific range of light wavelengths (400-700 nm) that plants use for photosynthesis.

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Action Spectrum

A graph showing the relative effectiveness of different wavelengths of light in driving a specific process, like photosynthesis.

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Relative Absorbance

The measurement of how much light is absorbed by a substance at different wavelengths.

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Light Harvesting Complex

A group of pigment molecules (chlorophyll and carotenoids) that absorb light energy and transfer it to the reaction center.

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Reaction Center (RC)

The core of a photosystem containing a specialized chlorophyll molecule that initiates the electron transfer chain.

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Förster Resonance Energy Transfer (FRET)

The process of non-radiative energy transfer between pigment molecules, transferring energy without emitting light.

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Primary Charge Separation

The initial step in photosynthesis where an excited electron is transferred from chlorophyll to an electron acceptor.

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Electron Transport Chain (ETC)

A series of protein complexes that pass electrons along, releasing energy used to generate a proton gradient for ATP synthesis.

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PSI (Photosystem I)

A protein complex involved in photosynthesis that captures light energy and transfers excited electrons to reduce NADP+ to NADPH. It does not produce oxygen.

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Rate-limiting step in photosynthesis

The slowest step in the process of photosynthesis, which limits the overall rate of the reaction. In high light and low temperatures, the rate-limiting step is often electron transport in the stroma.

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Herbicide action: Effects on Photosynthesis

Herbicides like Atrazine can disrupt Photosystem II, resulting in increased production of reactive oxygen species (ROS) causing oxidative stress.

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Cyclic Photosynthesis

A type of photosynthesis that uses only photosystem I and cyclic electron flow, producing ATP but not NADPH. It's important in purple and green bacteria, and some plants under stress.

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External electron donor

A substance that provides electrons to the electron transport chain in cyclic photosynthesis. It can be required for cyclic photosynthesis in organisms like bacteria.

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Photosystem II (PSII)

A protein complex within the thylakoid membrane that captures light energy and uses it to split water, releasing oxygen, electrons, and protons.

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Rate Limiting Step in PSII

The slowest step in the electron transport chain, particularly under high light and low temperature conditions, which limits the overall rate of photosynthesis.

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Non-Photochemical Quenching (NPQ)

A protective mechanism in plants that dissipates excess light energy as heat, preventing damage from high light intensity.

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Zeaxanthin

A carotenoid pigment involved in NPQ, helping to dissipate excessive light energy as heat.

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Violaxanthin

A precursor to zeaxanthin, important for NPQ, converted to zeaxanthin under high light conditions.

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Proton Gradient

The difference in proton (H+) concentration between the thylakoid lumen and the stroma, creating a potential energy source for ATP production.

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ATP Synthase

An enzyme embedded in the thylakoid membrane that harnesses the proton gradient to produce ATP, the energy currency of the cell.

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Stroma

The fluid-filled space within the chloroplast that surrounds the thylakoids, where the Calvin cycle reactions occur.

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Calvin Cycle

A series of reactions in the stroma that uses ATP and NADPH from the light-dependent reactions to convert carbon dioxide into sugar.

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Study Notes

Oxygenic Photosynthesis

  • Oxygenic photosynthesis is the process where light energy is converted into chemical energy and reducing power.
  • Chemiosmosis is used to produce ATP.
  • NADP+ reductase is used to form NADPH.

Photosynthesis Summary

  • Photosynthesis converts light energy into chemical energy and reducing power.
  • ATP is created through chemiosmosis.
  • NADPH is formed by NADP+ reductase.
  • Smith, & Smith, A. M. (Alison M. 2010). Plant biology, Garland Science.
  • ISBN: 9780815340256
  • 3 copies available in the Main Library, General Shelving 580, P713.

Photosynthesis Learning Objectives

  • Understanding the photosynthetic use of different wavelengths of light.
  • Knowledge of chloroplast structure.
  • Detailed knowledge of photosystems I and II, including their structure, function and molecular mechanism.
  • Förster resonant energy transfer.
  • Light conversion to chemical energy through charge separation.
  • Production of H+ gradient.
  • Electron transport.
  • How herbicides target photosynthesis.
  • How chloroplasts adapt to environmental changes.

What has Photosynthesis Ever Done for Us?

  • Graph showing the increase in atmospheric oxygen over billions of years, directly correlated with the development of life, photosynthesis, and oxygenic photosynthesis.

Cyanobacteria and Chloroplasts

  • Images comparing the structure of cyanobacteria and chloroplasts.

Cyanobacteria and Chloroplasts (Detailed)

  • TEM image of a chloroplast with labeled components: stroma, thylakoid, inner bilayer membrane, outer bilayer membrane, and granum.

The Structure of a Chloroplast

  • Diagram showing the different components of a chloroplast, including the stroma, stromal thylakoid, granal thylakoid, lumen, outer envelope (bilayer), and inner envelope (bilayer).

The Structure of a Thylakoid

  • Illustration depicting the electron transport chain within the thylakoid lumen, involving Photosystem II, Cytochrome bf, Photosystem I, and the components P680, P700, PQ (plastoquinone), PC (plastocyanin), FD (ferredoxin), and various molecules that mediate electron transfer.

Why are Chloroplasts Green?

  • Chloroplasts appear green due to the presence of chlorophyll.

Photosynthetically Active Radiation

  • Graph showing the absorption spectrum of chlorophyll a and chlorophyll b across different wavelengths of light.

Further Reading

  • Additional topics include: why there's only one electron path in PSII, cyclic photosynthesis, organization and regulation of PSI and PSII, absorbed blue light, and plant compensation points.
  • Several recommended textbooks are listed as resources for further research.

Gatsby Summer Studentships

  • 10-week funding, £4700 stipend, and expenses.
  • Practical project anywhere in the UK.
  • Highly prestigious.
  • Closing date around February 20th, 2025.

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Photosynthesis - Hemsley - 2024 PDF

Description

This quiz covers essential concepts of oxygenic photosynthesis, including the role of chemiosmosis, ATP production, and the function of NADP+ reductase. It aims to enhance understanding of chloroplast structure and the function of photosystems in light energy conversion. Ideal for students studying plant biology.

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