Cell Membrane Transport Mechanisms
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Questions and Answers

What is the primary function of channel proteins in a cell membrane?

  • To allow free movement of water (correct)
  • To interrupt lipid bilayer function
  • To bind with molecules or ions and then move them across the membrane
  • To provide energy for active transport

    • What is the movement of molecules or ions from low concentration to high concentration across the membrane with the help of a carrier protein called?

  • Facilitated diffusion
  • Simple diffusion
  • Active transport (correct)
  • Diffusion

    • What is the term for the random molecular movement of substances molecule by molecule through intermolecular space?

  • Absolute 0 temperature
  • Heat
  • Diffusion (correct)
  • Kinetic motion

    • What is the result of a moving molecule hitting a stationary molecule, transferring some kinetic energy and then moving on?

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

    What type of diffusion occurs when molecules or ions move through a membrane without the aid of carrier proteins?

    <p>Simple diffusion</p> Signup and view all the answers

    What is the primary difference between diffusion and active transport?

    <p>The requirement of energy</p> Signup and view all the answers

    What is the term for the kinetic motion of matter?

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

    What is the result of facilitated diffusion?

    <p>Movement of molecules or ions from high to low concentration</p> Signup and view all the answers

    What is the term for the movement of molecules or ions through a membrane with the aid of a carrier protein?

    <p>Facilitated diffusion</p> Signup and view all the answers

    What determines the rate of diffusion of lipid-soluble substances through the lipid bilayer?

    <p>Lipid solubility</p> Signup and view all the answers

    What type of proteins in the cell membrane permit water to diffuse through?

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

    Why does urea penetrate the cell membrane 1000 times more slowly than water?

    <p>Urea is 20% larger in size</p> Signup and view all the answers

    What is the primary means by which water and lipid-insoluble molecules diffuse through the cell membrane?

    <p>Protein channels</p> Signup and view all the answers

    Which of the following molecules is an example of a lipid-soluble substance that can diffuse through the lipid bilayer?

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

    What is the main function of vesicle transport in a cell?

    <p>To facilitate the movement of larger substances across the cell membrane</p> Signup and view all the answers

    Which process involves the cell taking in substances from outside the cell?

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

    What is the term for the process of cell eating, where the cell engulfs and breaks down particles?

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

    Which type of endocytosis involves the use of receptors to bind with molecules in the interstitial fluid?

    <p>Receptor-mediated endocytosis</p> Signup and view all the answers

    What is the result of the fusion of a vesicle with a lysosome?

    <p>The breakdown of particles into component molecules</p> Signup and view all the answers

    Where is cytosol located in a cell?

    <p>Inside the cell, separated from the interstitial fluid by the plasma membrane</p> Signup and view all the answers

    Which type of transport does not require energy?

    <p>Passive transport</p> Signup and view all the answers

    What is the direction of movement of molecules during osmosis?

    <p>From high concentration to low concentration</p> Signup and view all the answers

    What is the role of carrier proteins in facilitated diffusion?

    <p>To change shape and move molecules across the membrane</p> Signup and view all the answers

    What is the function of aquaporins in the plasma membrane?

    <p>To allow water to diffuse through the membrane</p> Signup and view all the answers

    What is the purpose of membrane transport in cells?

    <p>To maintain a constant internal environment</p> Signup and view all the answers

    What is the direction of movement of substances during diffusion?

    <p>From high concentration area to low concentration area</p> Signup and view all the answers

    What is the type of transport that moves substances against their concentration gradient?

    <p>Active transport</p> Signup and view all the answers

    What is the term for the movement of a second substance down its concentration gradient, providing energy for the movement of another substance against its concentration gradient?

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

    What is the term for the transport of substances in the same direction, using the energy from the movement of one substance down its concentration gradient?

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

    What is the term for the transport of substances in opposite directions, using the energy from the movement of one substance down its concentration gradient?

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

    What is the type of transport that uses a membrane-bound sac filled with materials?

    <p>Vestibular transport</p> Signup and view all the answers

    Study Notes

    Cell Membrane Structure and Function

    • The cell membrane is a lipid bilayer with cell membrane transport proteins.
    • Penetrating proteins interrupt lipid bilayer function as transport proteins.
    • Proteins that allow free movement of water are called channel proteins.
    • Carrier proteins bind with molecules or ions and then move them through interstices.

    Diffusion vs Active Transport

    • Diffusion is the random molecular movement of substances molecule by molecule through intermolecular space or with a carrier protein.
    • Active transport is the movement of ions or other substances across the membrane with a carrier protein, from low concentration to high concentration.

    Diffusion

    • Molecules and ions are constantly moving due to heat, which is a form of kinetic energy.
    • Greater motion is associated with higher temperatures.
    • Motion ceases at absolute 0 temperature.
    • In diffusion, a moving molecule hits a stationary molecule, transferring some kinetic energy and continuing movement.

    Diffusion Through the Cell Membrane

    • There are two types of diffusion through the cell membrane: simple diffusion and facilitated diffusion.
    • Simple diffusion is the kinetic movement of molecules or ions through a membrane without carrier proteins.
    • The rate of simple diffusion depends on the amount, velocity, and number of molecules.
    • Simple diffusion occurs in two ways: through interstices of the lipid bilayer and through water channels penetrating the membrane.
    • Facilitated diffusion is the interaction with a carrier protein.

    Diffusion Through the Lipid Bilayer

    • Lipid solubility determines the rate of diffusion through the lipid bilayer
    • Oxygen (O2), nitrogen (N2), and carbon dioxide (CO2) are examples of lipid-soluble substances that can diffuse rapidly through the lipid bilayer

    Diffusion Through Protein Channels

    • Cell membranes contain protein "pores" called aquaporins that permit the passage of water and other lipid-insoluble molecules
    • Aquaporins act as channels for water molecules to pass through the membrane
    • Urea, a molecule 20% larger than water, has a 1000 times slower penetration rate due to its size

    Vesicle Transport

    • Vesicle transport requires the use of energy
    • It involves the transport of larger substances by membranous sacs

    Exocytosis

    • Exocytosis is the process of secreting materials from the cell to the interstitial fluid outside the cell
    • Vesicles fuse with the cell membrane, releasing their contents outside the cell

    Endocytosis

    • Endocytosis is the process of taking in contents from outside the cell
    • The plasma membrane traps substances by folding inward, forming vesicles
    • There are several types of endocytosis:

    Types of Endocytosis

    • Phagocytosis: vesicles fuse with lysosomes, which break down particles into component molecules, also known as "cell eating"
    • Pinocytosis: the plasma membrane folds inward and engulfs interstitial fluids containing solutes, also known as "cell drinking"
    • Receptor-mediated endocytosis: receptors bind to molecules in interstitial fluids, folding and enclosing to form new vesicles

    Cellular Fluids

    • Interstitial fluid is the fluid outside of the cell.
    • Cytosol is the inner part of the cell.
    • The plasma membrane (or cell membrane) separates interstitial fluid and cytosol.

    Membrane Transport

    • Passive transport does not require energy.
    • Active transport requires energy.

    Types of Passive Transport

    • Simple diffusion: small non-polar solutes move between lipid bilayer.
    • Facilitated diffusion: small charged or polar solutes pass through plasma membrane.

    Channel-Mediated Transport

    • Ions move through a water-filled channel.
    • There are three types of channels: leak channels, gated channels, and stimulus channels.

    Carrier-Mediated Transport

    • Small polar molecules move across the membrane with carrier proteins.
    • Glucose binds to a carrier protein, causing a shape change that moves the glucose molecule to the other side.

    Osmosis

    • Osmosis is the passive movement of water through a selectively permeable membrane.
    • It occurs when there is a difference in water concentration.
    • Water can move through the membrane in two ways:
      • Between phospholipid molecules that make up the plasma membrane.
      • Through integral protein water channels called aquaporins.
    • Molecules move from high concentration to low concentration to achieve equilibrium.

    Diffusion

    • Movement of substances from high concentration area to low concentration area

    Active Transport

    • Movement of solute against concentration gradient (from low to high)
    • Two types: primary transport and secondary active transport

    Primary Transport

    • Cellular protein pump called ion pump moves ions across the membrane against their concentration gradient
    • ATP binds to sodium ions, breaks down to ADP and Pi, releasing energy
    • Energy is used to change the shape of the pump, moving ions to the other side
    • Potassium ions move back, reverting the shape of the pump

    Secondary Active Transport

    • Substance is moved against its concentration gradient by the movement of a second substance down its concentration gradient
    • Energy is provided by the movement of the second substance from high to low concentration

    Types of Secondary Active Transport

    • Symport: two substances moved in the same direction
    • Antiport: two substances moved in opposite directions

    Vesicular Transport

    • Transport by vesicle, a membrane-bound sac filled with material

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    Description

    Understand the structure and function of cell membranes, including lipid bilayer, transport proteins, and types of protein-mediated transport such as diffusion and active transport.

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