Photosynthesis Overview and Chemical Reactions
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Questions and Answers

What is the primary function of chlorophyll in photosynthesis?

  • To produce carbohydrates directly
  • To absorb solar energy (correct)
  • To regulate water loss in plants
  • To release oxygen into the atmosphere
  • Which of the following processes occurs during the light reactions of photosynthesis?

  • Production of glucose
  • Synthesis of ATP (correct)
  • Regeneration of RuBP
  • Carbon fixation
  • In cyclic electron flow, which Photosystem is utilized?

  • Only Photosystem I (correct)
  • Both Photosystem I and II
  • Photosystem II
  • Neither Photosystem I nor II
  • During the Calvin Cycle, which step involves the addition of CO2 to RuBP?

    <p>Carbon fixation (C)</p> Signup and view all the answers

    What is the end product of the Calvin Cycle after reduction?

    <p>Glyceraldehyde 3-phosphate (G3P) (A)</p> Signup and view all the answers

    What is produced as a result of cyclic electron flow?

    <p>ATP (C)</p> Signup and view all the answers

    Which component is regenerated during the Calvin Cycle to continue the process?

    <p>RuBP (A)</p> Signup and view all the answers

    What is the primary purpose of the light reactions in photosynthesis?

    <p>To transfer energy to ATP and NADPH (A)</p> Signup and view all the answers

    Which molecule is produced during the light reactions and is used in the Calvin Cycle?

    <p>ATP (A)</p> Signup and view all the answers

    Which of the following correctly describes cyclic electron flow?

    <p>Does not produce oxygen (C)</p> Signup and view all the answers

    Flashcards

    Photosynthesis

    The process by which autotrophic organisms use sunlight to convert carbon dioxide and water into energy-rich carbohydrates.

    Chlorophyll

    A pigment found in chloroplasts that absorbs sunlight for photosynthesis.

    Light reactions

    The first stage of photosynthesis, where light energy is converted into chemical energy in the form of ATP and NADPH.

    Calvin cycle

    The second stage of photosynthesis, where ATP and NADPH are used to convert carbon dioxide into sugar.

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    Cyclic electron flow

    An alternative electron flow pathway in photosynthesis using Photosystem I that produces ATP without NADPH.

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    Carbon fixation

    The initial step of the Calvin cycle, where carbon dioxide is incorporated into an organic molecule.

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    Reduction

    The step in the Calvin cycle where the organic molecule gains electrons, creating sugars.

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    Regeneration of RuBP

    The final step of the Calvin cycle, where the initial molecule RuBP (ribulose biphosphate) is regenerated, allowing the cycle to continue.

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    ATP

    Adenosine triphosphate, a molecule that stores and releases energy.

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    NADPH

    Nicotinamide adenine dinucleotide phosphate, a molecule that carries high-energy electrons in photosynthesis.

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    Thylakoid membranes

    Membranous sacs within chloroplasts where the light reactions of photosynthesis take place.

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    Study Notes

    Photosynthesis Introduction

    • Autotrophs use chlorophyll to harvest solar energy, storing it in ATP and carbohydrates.
    • In eukaryotes, chlorophyll is within chloroplast thylakoid membranes.
    • Photosynthesis involves three key processes:
      • Light-dependent reactions (energy absorption from sunlight)
      • Light-dependent reactions (reactivation of reaction center)
      • Dark reactions (carbohydrates production via carbon fixation)

    Photosynthesis Chemical Reaction

    • 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
    • Carbon dioxide + Water → Glucose + Oxygen
    • This is the overall chemical reaction for photosynthesis

    Photosynthesis During Photosynthesis

    • Energy from sunlight drives glucose synthesis from CO₂ and H₂O.
    • Sunlight's energy is converted into a usable form (potential)

    Stages of Photosynthesis - Light Reactions

    • Use sunlight to reduce NADP+ to NADPH and split water, releasing oxygen.
    • ATP is formed (phosphorylation) by the movement of hydrogen ions.
    • Happen in the thylakoids of the chloroplast

    Stages of Photosynthesis - Calvin Cycle

    • Also called dark reactions, doesn't require direct light energy.
    • CO₂ is incorporated into organic molecules (carbon fixation)
    • NADPH and ATP are used to produce carbohydrates from fixed carbon.
    • Occurs in the chloroplast stroma.
    • ADP, inorganic phosphate, and NADP+ are returned to the light reactions

    Light Reactions Events

    • Light energy excites chlorophyll electrons from Photosystem II to a higher energy level.
    • Electrons are passed through electron transport chains, releasing energy to pump H+ into the thylakoid space.
    • H+ ions flow through ATP synthase, producing ATP.
    • Electrons are passed to Photosystem I, then to NADP+ to produce NADPH.

    Cyclic Electron Flow

    • An alternative electron pathway, where electrons from Photosystem I return to the electron transport chain.
    • This route produces ATP but not NADPH.

    Calvin Cycle - Carbon Fixation

    • CO₂ is incorporated into RuBP (ribulose biphosphate), a 5-carbon sugar.
    • This reaction is catalyzed by RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase).
    • RuBisCO is one of the most common proteins on Earth.
    • The resulting product (6-carbon molecule) is unstable and immediately splits into 2 molecules of 3-phosphoglycerate (3-carbon molecule).

    Calvin Cycle - Reduction

    • A phosphate group from ATP is added to 3-phosphoglycerate, forming 1,3-biphosphoglycerate.
    • NADPH reduces 1,3-biphosphoglycerate to G3P (glyceraldehyde-3-phosphate).
    • G3P molecules are the building blocks for glucose (or other sugars).

    Calvin Cycle - Regeneration

    • Five out of six G3P molecules are used to regenerate RuBP, requiring ATP.
    • The regeneration of RuBP allows the Calvin cycle to continue.

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    Photosynthesis PDF

    Description

    Explore the fascinating process of photosynthesis through various stages and chemical reactions. This quiz covers the light-dependent and dark reactions, the role of chlorophyll, and the overall chemical equation involved. Test your knowledge on how plants convert sunlight into energy and produce oxygen.

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