Photosynthesis: Light Reactions Overview
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Questions and Answers

What is the primary purpose of the Calvin Cycle?

  • To absorb light energy
  • To split water molecules
  • To produce glucose (correct)
  • To return ADP to the light reactions

    • Which molecule provides the energy required for the Calvin Cycle?

  • Glucose
  • Adenosine Triphosphate (ATP) (correct)
  • NADP+
  • Oxygen

    • Where does the Calvin Cycle occur within a plant cell?

  • In the cytoplasm
  • In the thylakoid
  • In the reaction center
  • In the stroma (correct)

    • What happens to P680 after it loses an electron?

    <p>It becomes positively charged (P680+)</p> Signup and view all the answers

    What is produced when water is split by P680?

    <p>Oxygen and hydrogen ions</p> Signup and view all the answers

    Which process helps to pump hydrogen ions across the membrane during light reactions?

    <p>Chemiosmosis</p> Signup and view all the answers

    What happens to NADP+ after the Calvin Cycle?

    <p>It returns to the light reactions</p> Signup and view all the answers

    Which statement about the light reactions is true?

    <p>They generate ATP and NADPH</p> Signup and view all the answers

    What molecule is produced from ADP through the action of ATP synthase?

    <p>ATP</p> Signup and view all the answers

    What causes the P700 chlorophyll in Photosystem I to become positively charged?

    <p>Loss of electrons to the primary electron acceptor</p> Signup and view all the answers

    Which enzyme transfers an electron to NADP+ in the light reactions?

    <p>NADP+ reductase</p> Signup and view all the answers

    What is produced from the process of cyclic electron flow?

    <p>ATP</p> Signup and view all the answers

    Which component is involved in the transfer of photo-excited electrons after Photosystem I?

    <p>Ferredoxin</p> Signup and view all the answers

    From which molecule does the carbon in your body originate?

    <p>Carbon dioxide</p> Signup and view all the answers

    What happens during a short-circuited path of cyclic electron flow?

    <p>Electrons are transferred to the cytochrome complex</p> Signup and view all the answers

    What characterizes the high-energy phosphate bonds in ATP?

    <p>They store energy</p> Signup and view all the answers

    What are the primary products of the light reactions in photosynthesis?

    <p>ATP and NADPH</p> Signup and view all the answers

    Where do the light reactions of photosynthesis occur?

    <p>Thylakoids</p> Signup and view all the answers

    What role does sunlight play in the light reactions of photosynthesis?

    <p>It provides the energy needed for electron transfer.</p> Signup and view all the answers

    What happens to water during the light reactions?

    <p>It is split, producing oxygen as a byproduct.</p> Signup and view all the answers

    Why is photosynthesis deemed essential for life on Earth?

    <p>It provides food and oxygen for living organisms.</p> Signup and view all the answers

    What is formed through phosphorylation during the light reactions?

    <p>ATP</p> Signup and view all the answers

    Which molecule is reduced to form NADPH during the light reactions?

    <p>NADP+</p> Signup and view all the answers

    What gas is primarily released as a byproduct of the light reactions?

    <p>Oxygen</p> Signup and view all the answers

    What is the main product of the Calvin Cycle as described?

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

    How many molecules of ATP are required to make one molecule of G3P?

    <p>9</p> Signup and view all the answers

    Which of the following molecules is not needed to produce G3P in the Calvin Cycle?

    <p>Sucrose</p> Signup and view all the answers

    What happens to Glyceraldehyde-3-Phosphate (G3P) after its release from the Calvin Cycle?

    <p>It combines to form sucrose.</p> Signup and view all the answers

    How many times does the Calvin Cycle need to 'spin' to make one molecule of G3P?

    <p>3</p> Signup and view all the answers

    What is the primary product formed in the Calvin cycle?

    <p>Glucose</p> Signup and view all the answers

    Which enzyme is crucial for the carbon fixation phase of the Calvin cycle?

    <p>Rubisco</p> Signup and view all the answers

    In which part of the chloroplast does the Calvin cycle occur?

    <p>Stroma</p> Signup and view all the answers

    How many molecules of G3P are produced in one turn of the Calvin cycle?

    <p>Six</p> Signup and view all the answers

    What happens to five out of the six produced G3P molecules in the Calvin cycle?

    <p>Used to regenerate RuBP</p> Signup and view all the answers

    What is the initial carbon molecule that enters the Calvin cycle?

    <p>Carbon dioxide (CO2)</p> Signup and view all the answers

    What is produced at the end of the reduction phase of the Calvin cycle?

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

    Why is the Calvin cycle important to all living organisms?

    <p>It provides food and energy for plants and indirectly for herbivores and carnivores.</p> Signup and view all the answers

    Study Notes

    Photosynthesis: Light Reactions

    • Photosynthesis is a vital process for life on Earth
    • Plants (autotrophs) use water, carbon dioxide, and sunlight to make food
    • Humans and other organisms depend on plants for survival
    • If photosynthesis stops, organic matter and oxygen levels will decrease significantly
    • Chemosynthetic bacteria are independent of light energy

    Stages of Photosynthesis

    • Photosynthesis is a two-stage process: light reactions and the Calvin cycle
    • Light reactions take place in the thylakoids of chloroplasts
    • Light reactions use sunlight to produce ATP and NADPH

    Light Reactions Events

    • Light energy excites electrons in Photosystem II (P680)
    • Water molecules are split, releasing oxygen as a byproduct, and providing electrons
    • Electrons move through an electron transport chain, generating ATP
    • Electrons are transferred to Photosystem I (P700), which generates NADPH
    • ATP and NADPH are used in the Calvin cycle
    • The process happens in thylakoids

    Cyclic Electron Flow (Alternative Pathway)

    • Electrons can take a short-circuited path via Photosystem I, bypassing Photosystem II
    • This route produces ATP but not NADPH

    Photosynthesis: Calvin Cycle

    • Calvin cycle occurs in the stroma of chloroplasts
    • The Calvin cycle fixes carbon dioxide from the air into organic molecules
    • The Calvin cycle occurs in three phases: carbon fixation, reduction, and regeneration.
    • Rubisco is the key enzyme in carbon fixation
    • The Calvin cycle produces G3P, a three-carbon sugar
    • G3P is used to make glucose, sucrose, starch, and other molecules
    • The cycle uses ATP and NADPH, produced in the light reactions.

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    Description

    This quiz explores the light reactions of photosynthesis, a crucial process that allows plants to convert sunlight into chemical energy. Key stages include the excitation of electrons, water splitting, and the generation of ATP and NADPH. Understanding these processes is essential for recognizing how plants support life on Earth.

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