Photoreceptors and Plant Responses
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Questions and Answers

In photosynthesis, where does the reduction of NADP+ to NADPH primarily occur?

  • In the matrix
  • In the stroma (correct)
  • In the intermembrane space
  • In the thylakoid lumen

    • Cyclic photophosphorylation in PSI produces both ATP and NADPH.

    False (B)

    What enzyme catalyzes the first step of carbon fixation in the Calvin cycle?

    rubisco

    The electron transport chain pumps H+ ions into the __________ space in the chloroplasts.

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

    Match the following processes with their location:

    <p>ATP synthesis in chloroplasts = Thylakoid membrane NADH production in mitochondria = Matrix Carbon fixation = Stroma Electron transport in photosynthesis = Thylakoid membrane</p> Signup and view all the answers

    Which of these are products of the light reactions of photosynthesis? (Select all that apply)

    <p>Oxygen (A), NADPH (C), ATP (D)</p> Signup and view all the answers

    The primary cell wall is more rigid than the secondary cell wall.

    <p>False (B)</p> Signup and view all the answers

    What is the primary function of cellulose in the plant cell wall?

    <p>support and strength</p> Signup and view all the answers

    The Calvin cycle occurs in the ______ of the chloroplast.

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

    Match the following components of photosynthesis with their function/location:

    <p>Photosystem II = Produces oxygen and excited electrons Photosystem I = Produces NADPH Thylakoid membrane = Location of light reactions Stroma = Location of Calvin cycle</p> Signup and view all the answers

    Which of these is a key component of the secondary cell wall providing structural support and rigidity?

    <p>Hemicellulose (B)</p> Signup and view all the answers

    Cell elongation in plant cells occurs parallel to the encircling cellulose microfibrils.

    <p>False (B)</p> Signup and view all the answers

    The primary cell wall is ______ because of the large amounts of polar OH groups.

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

    Which of the following best describes the function of the middle lamella?

    <p>Connecting neighboring plant cells (D)</p> Signup and view all the answers

    Secondary growth is characterized by vertical growth, primarily facilitated by shoot apical meristems.

    <p>False (B)</p> Signup and view all the answers

    What are the two specialized tissues that make up vascular tissue?

    <p>phloem and xylem</p> Signup and view all the answers

    The _______ transports sugars, the products of photosynthesis, from where they are made to where they are needed or stored.

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

    Match the following transport pathways with their descriptions:

    <p>Transmembrane transport = Molecules move through plasma membranes and cell walls Symplastic transport = Molecules move through cytosols and plasmodesmata Apoplastic transport = Molecules move through cell walls</p> Signup and view all the answers

    Which of the following is NOT a primary function of ground tissue?

    <p>Water transport (D)</p> Signup and view all the answers

    When a plant cell is turgid, the plasma membrane does not press tightly against the cell wall.

    <p>False (B)</p> Signup and view all the answers

    What is the primary function of the shoot apical meristems in plants?

    <p>vertical growth</p> Signup and view all the answers

    What is the role of auxin in cell elongation?

    <p>It promotes H+ secretion, lowering the pH of the cell wall. (C)</p> Signup and view all the answers

    The Calvin cycle directly depends on light to convert CO2 to glucose.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the tissue within leaves that contains chloroplasts?

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

    Stacks of thylakoids are called ______.

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

    Where does the light reaction of photosynthesis take place?

    <p>Thylakoid membrane (B)</p> Signup and view all the answers

    During the electron transport chain in photosynthesis, H+ ions are pumped into the stroma.

    <p>False (B)</p> Signup and view all the answers

    Which molecule provides the electrons for PSII?

    <p>Water (D)</p> Signup and view all the answers

    Match the following locations in the chloroplast with the processes that take place there:

    <p>Thylakoid membrane = Light reactions Stroma = Calvin cycle Thylakoid space = H+ gradient formation for ATP synthesis</p> Signup and view all the answers

    What drives the movement of xylem sap according to the cohesion-tension theory?

    <p>A water potential difference between the leaf end and the root end of the xylem (D)</p> Signup and view all the answers

    Water moves from a region of low water potential to high water potential.

    <p>False (B)</p> Signup and view all the answers

    What are the two types of xylem cells?

    <p>Tracheids and Vessel elements</p> Signup and view all the answers

    The waxy substance in the root endodermis that blocks the apoplastic pathway is called the ______.

    <p>Casparian strips</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Osmosis = Movement of water from low to high solute concentrations Cohesion = Water molecules being attracted to each other Adhesion = Water molecules being attracted to other substances Bulk flow = Movement of liquid in response to a pressure gradient</p> Signup and view all the answers

    What is the primary function of phloem cells?

    <p>Transport sugars from source to sink (D)</p> Signup and view all the answers

    Guard cells become turgid when stomata close.

    <p>False (B)</p> Signup and view all the answers

    What is the role of root hairs in water absorption?

    <p>Increase surface area for absorption</p> Signup and view all the answers

    Which of the following is NOT a type of photoreceptor?

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

    The active form of phytochrome, Pfr, absorbs red light.

    <p>False (B)</p> Signup and view all the answers

    What is the role of electrochemical gradients in plant cells?

    <p>They drive action potentials.</p> Signup and view all the answers

    When a plant absorbs red light, the phytochrome Pr is converted to the ______ form, Pfr.

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

    What happens to a plant’s morphology that is grown in shade?

    <p>It will have less branches and leaves and it will be taller. (B)</p> Signup and view all the answers

    In order to get an action potential, the difference in charge inside and outside a neuron must be above -75 mV.

    <p>False (B)</p> Signup and view all the answers

    During an action potential, the opening of voltage-gated sodium channels causes the membrane to ______.

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

    Match the following photoreceptors with the type of light they primarily respond to:

    <p>Phytochromes = Red and far-red light Phototropins = Blue light Cryptochromes = Blue light Zeaxanthin = Blue light</p> Signup and view all the answers

    Study Notes

    Photoreceptors in Plants

    • Photoreceptors are receptors that respond to light
    • Two main groups: blue-light and red/far-red light
    • Blue-light receptors: phototropins, zeaxanthin, cryptochromes
    • Red/far-red receptors: phytochromes
    • Phytochromes are a molecular switch
      • Inactive Pr absorbs red light
      • Active Pfr absorbs far-red light
      • Red light → Pfr → cellular response (germination)
    • Insufficient red light or darkness → Pfr → Pr
      • Plants with high sunlight have more Pfr → Pr, shorter, more branches
      • Plants in shade have more Pr → Pfr, taller, less branches

    Plant Response to Mechanical Stimuli

    • Plants respond to gravity and touch via action potentials
    • Action potentials are rapid changes in electrical potential across the cell membrane
    • Membrane potential is the difference in electrical charge between the inside and outside of the plasma membrane.
    • To generate an action potential, the cell reaches a threshold of -55mV.
    • This opens voltage-gated sodium channels, sodium diffuses in.
    • Ions (e.g. calcium, potassium) move in & out to depolarize and repolarize the membrane
    • Electrochemical gradients drive these changes in membrane potential.

    Cell Signaling in Plants

    • Signal reception: receptors in the plasma membrane detect signals (hormones, etc.)
    • Signal transduction: signal passes through the cell via secondary messengers and proteins.
    • Cellular response: the cell responds to the signal.
    • Auxin is a hormone that affects phototropism and cell elongation.
    • Auxin promotes stem elongation. It moves to the shaded side of shoots promoting growth
    • Auxin causes roots to grow downward (positive gravitropism).
    • Auxin's role in regulating cell elongation involves making the cell wall more acidic and activating expansins. Expansins break up the hydrogen bonds in the cell.

    Photosynthesis: Light Reactions and Calvin Cycle

    • Photosynthesis occurs in the mesophyll cells on the inside of leaves
    • Chloroplasts contain thylakoid membranes (containing chlorophyll) where light-dependent reactions occur
    • Stroma is the area between the thylakoid and inner membrane where the light-independent reactions occur (the Calvin cycle).
    • Light reactions:
      • Use light energy to generate ATP and NADPH
      • Use water as a source of electrons that produce oxygen as a by-product
      • Electrons move along the electron transport chain (ETC).
      • Electrons use the electrochemical energy gradient to produce ATP from ADP+Pi
      • Photosystem I makes NADPH
    • Calvin cycle:
      • Converts CO2 into sugars
      • Needs ATP and NADPH from the light reactions
      • Rubisco catalyzes the initial carbon fixation step
    • The Calvin cycle uses the energy from ATP and NADPH to reduce CO2 to sugars

    Electron Transport Chain (ETC) and Chemiosmosis

    • Both ETC in mitochondria and chloroplasts use a membrane-bound ETC system and chemiosmosis to make ATP.
    • The ETC pumps H+ ions across a membrane creating an electrochemical gradient.
    • ATP synthase utilizes the diffusion of H+ ions back across the membrane to produce ATP.

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    Description

    Explore the fascinating world of plant photoreceptors and their responses to light. This quiz covers the main types of photoreceptors, their functions, and how plants react to mechanical stimuli. Test your knowledge on the intricate signaling involved in plant growth and development.

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