Biology Quiz: Cell Transport Mechanisms
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Questions and Answers

What is the main function of the contractile vacuole in Paramecium?

  • To store nutrients
  • To assist in reproduction
  • To generate energy
  • To help in osmoregulation (correct)

    • A plant cell becomes turgid in a hypertonic solution.

    False (B)

    What process allows water to move through cell membranes via specialized proteins?

    Facilitated diffusion

    The _____ pump is a well-known example of active transport.

    <p>sodium-potassium</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Hypertonic = A solution with a higher concentration of solutes compared to another Isotonic = A solution with equal concentrations of solutes on both sides Hypotonic = A solution with a lower concentration of solutes compared to another Osmoregulation = The control of water balance in organisms</p> Signup and view all the answers

    Which of the following is a type of passive transport?

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

    Active transport requires energy to move substances against their concentration gradient.

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

    What happens to a plant cell in a hypertonic environment?

    <p>Plasmolysis occurs, causing the membrane to pull away from the cell wall.</p> Signup and view all the answers

    Channel proteins in facilitated diffusion allow specific _____ or ions to pass through the plasma membrane.

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

    Match the following types of transport with their characteristics:

    <p>Simple diffusion = Movement of molecules from high to low concentration without energy Facilitated diffusion = Passive movement aided by transport proteins Active transport = Movement of molecules against their concentration gradient with energy Plasmolysis = Separation of the cell membrane from the cell wall due to water loss</p> Signup and view all the answers

    What type of molecules is primarily moved by facilitated diffusion?

    <p>Water soluble molecules (B)</p> Signup and view all the answers

    Active transport requires channel proteins to function.

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

    Name the process by which a cell takes in macromolecules by forming vesicles from the plasma membrane.

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

    In __________, a cell engulfs a solid particle in a vacuole.

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

    Which of the following best describes symport?

    <p>Transport of two molecules in the same direction (A)</p> Signup and view all the answers

    Pinocytosis involves the uptake of solid particles.

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

    Describe the main function of exocytosis.

    <p>Transport vesicles fuse with the membrane to release contents.</p> Signup and view all the answers

    Receptor-mediated endocytosis is triggered by the binding of __________ to receptors.

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

    Match the transport type with its description:

    <p>Phagocytosis = Cellular eating Pinocytosis = Cellular drinking Symport = Transport in the same direction Antiport = Transport in opposite directions</p> Signup and view all the answers

    Which type of transport proteins are used in facilitated diffusion?

    <p>Carrier and channel proteins (B)</p> Signup and view all the answers

    What type of molecules are phospholipids?

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

    Integral proteins do not penetrate the hydrophobic core of the membrane.

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

    What is the fluid mosaic model?

    <p>A model describing the structure of the plasma membrane as a fluid layer with various proteins embedded.</p> Signup and view all the answers

    Membranes with shorter fatty acid chains are ______ than those with longer fatty acid chains.

    <p>more fluid</p> Signup and view all the answers

    Match the type of protein with its description:

    <p>Peripheral proteins = Bound to the surface of the membrane Integral proteins = Penetrate the hydrophobic core Transmembrane proteins = Span the entire membrane Cholesterol = Acts as a fluidity buffer</p> Signup and view all the answers

    How does cholesterol affect membrane fluidity at warm temperatures?

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

    Unsaturated fatty acids lead to tighter packing of phospholipids.

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

    What role do membrane proteins play?

    <p>They determine most of the membrane’s specific functions.</p> Signup and view all the answers

    The most abundant lipid in the plasma membrane is ______.

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

    Which of the following does NOT affect membrane fluidity?

    <p>Surface tension of the membrane (D)</p> Signup and view all the answers

    What connects carbohydrates to lipids in the plasma membrane?

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

    Polar molecules such as sugars can easily cross the lipid bilayer of the plasma membrane.

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

    What is the term for the net movement of water across a selectively permeable membrane?

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

    In a hypertonic solution, the solute concentration is _____ than that inside the cell.

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

    Which type of transport protein specifically facilitates the majority passage of water?

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

    Transport proteins can move substances against their concentration gradient without energy input.

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

    What is the term for the ability of a solution to cause a cell to gain or lose water?

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

    The _____ system provides the cell with a way to recognize other cells through carbohydrate molecules on the membrane.

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

    What is the proper scientific term for cell shriveling in hypertonic solutions?

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

    Study Notes

    Cell Membrane Structure & Function

    • Phospholipids are the most abundant lipids in the plasma membrane.
    • Phospholipids are amphipathic, meaning they have both hydrophobic (water-fearing) and hydrophilic (water-loving) regions.
    • The fluid mosaic model describes membranes as a fluid structure with various proteins embedded in the lipid bilayer.

    Fluidity of Membranes

    • Phospholipids can move within the bilayer.
    • Most lipids and some proteins drift laterally or rotate within the membrane.
    • Flip-flop (transverse movement) across the membrane is rare.
    • Lateral movement occurs at a rate of ~10⁷ times per second.
    • Flip-flop occurs approximately once per month.

    Temperature and Membrane Fluidity

    • As temperature increases, membranes transition from a solid (gel) state to a more fluid state.
    • Membranes with shorter fatty acid chains are more fluid than those with longer chains.
    • Shorter chains have less surface area, reducing hydrophobic/van der Waals interactions between neighboring phospholipid molecules.

    Saturated vs. Unsaturated Fatty Acids and Membrane Fluidity

    • Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids.
    • Kinks (or bends) in unsaturated fatty acid tails prevent tight packing of phospholipids.

    Cholesterol and Membrane Fluidity

    • In animal cells, cholesterol acts as a fluidity buffer against temperature extremes.
    • At warm temperatures, cholesterol restrains phospholipid movement, decreasing membrane fluidity.
    • At cool temperatures, cholesterol prevents tight packing, increasing membrane fluidity.

    Membrane Proteins and Their Functions

    • Membranes are composed of various proteins embedded in the lipid bilayer.
    • Proteins determine most of the membrane's specific functions.
    • Peripheral proteins are bound to the membrane surface.
    • Integral proteins penetrate the hydrophobic core.
    • Transmembrane proteins span the entire membrane.
    • Hydrophobic regions of integral proteins consist of one or more stretches of non-polar amino acids, often coiled into alpha helices.

    Six major functions of membrane proteins

    • Transport
    • Enzymatic activity
    • Signal transduction
    • Cell-cell recognition
    • Intercellular joining
    • Attachment to the cytoskeleton and extracellular matrix

    Role of Membrane Carbohydrates

    • Cells recognize each other by binding to surface molecules, often carbohydrates, on the plasma membrane.
    • Membrane carbohydrates are covalently bonded to lipids (forming glycolipids) or to proteins (forming glycoproteins).
    • Carbohydrate chains on the external side of the plasma membrane vary among species, individuals, and even cell types within an individual.

    Selective Permeability

    • Cells exchange materials with their surroundings via the plasma membrane.
    • Plasma membranes are selectively permeable, regulating the cell's molecular traffic.
    • Hydrophobic (non-polar) molecules readily dissolve in the lipid bilayer and pass through the membrane quickly. Water, a polar molecule, also crosses easily.
    • Polar molecules (e.g., sugars) do not cross the membrane easily.
    • Charged substances (ions) are virtually unable to pass through the lipid bilayer.

    Transport Proteins

    • Transport proteins allow passage of hydrophilic substances across the membrane.
    • Channel proteins form hydrophilic channels that certain molecules or ions can use as a tunnel, spanning the entire membrane.
    • Aquaporins facilitate the majority of water passage.
    • Carrier proteins bind to molecules and change shape to shuttle them across the membrane.
    • Transport proteins are specific to the substance they transport.

    Passive Transport

    • Diffusion is the tendency for molecules to spread out evenly into the available space.
    • Molecules diffuse down their concentration gradient (from high concentration to low).
    • Diffusion across a biological membrane is passive transport, requiring no energy investment from the cell.

    Osmosis

    • Osmosis is the diffusion of water across a selectively permeable membrane.
    • Water diffuses from a region of lower solute concentration to a region of higher solute concentration.

    Water balance in Cells Without Cell Walls

    • Tonicity describes a solution's ability to cause a cell to gain or lose water.
    • Isotonic solution: solute concentration is the same as inside the cell; no net water movement.
    • Hypertonic solution: solute concentration is greater than inside the cell; the cell loses water.
    • Hypotonic solution: solute concentration is less than inside the cell; the cell gains water.

    Water balance in Cells with Cell Walls

    • Cell walls help maintain water balance. A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid (firm)
    • If a plant cell and its surroundings are isotonic, there is no net water movement, and the cell is flaccid (limp).
    • In a hypertonic environment, plant cells lose water; the membrane pulls away from the wall, a usually lethal effect called plasmolysis.

    Facilitated Diffusion

    • Transport proteins speed the passive movement of molecules across the plasma membrane.
    • Channel proteins provide facilitated diffusion corridors.
    • Aquaporins facilitate water diffusion through ion channels.
    • Carrier proteins change shape, translocating the solute-binding site across the membrane

    Active Transport

    • Active transport moves substances against their concentration gradient (from low to high).
    • Active transport requires energy, usually in the form of ATP. The sodium-potassium pump is an example.

    Co-transport

    • Co-transport is the simultaneous Movement of two distinct molecules across a biological membrane by one membrane transport protein.
    • Symport: two molecules transported in the same direction.
    • Antiport: two molecules transported in opposite directions.

    Bulk Transport

    • Exocytosis: transport vesicles fuse with the membrane and release their contents.
    • Endocytosis: the cell takes in macromolecules by forming vesicles from the plasma membrane.
    • Types of endocytosis: Phagocytosis, Pinocytosis, Receptor-mediated endocytosis.

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    Test your understanding of various cell transport mechanisms in this quiz, which covers topics such as active and passive transport, osmosis, and the role of cell organelles like the contractile vacuole. Explore how cells manage ion movement and the effects of hypertonic environments on plant cells.

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