Cell Membrane Permeability
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Questions and Answers

What is the primary reason for the establishment of a concentration gradient across the cell membrane?

  • To separate and store charge
  • To generate energy for the cell
  • To maintain the selective permeability of the membrane (correct)
  • To facilitate passive transport of molecules

    • Which of the following best describes the movement of ions across the cell membrane?

  • They are not affected by their concentration gradient
  • They are influenced solely by their concentration gradient
  • They are influenced by both their concentration gradient and the electrical gradient (correct)
  • They are not affected by the electrical gradient

    • What is the primary function of the selective permeability of the cell membrane?

  • To facilitate active transport of molecules
  • To maintain the concentration gradient across the membrane (correct)
  • To separate and store charge
  • To regulate the flow of water across the membrane

    • What is the net movement of water through a selectively permeable membrane?

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

    What percentage of resting energy is used to maintain concentration and electrical gradients?

    <p>30%</p> Signup and view all the answers

    What is the term for the difference in charged ions between the inside and outside of the membrane?

    <p>Membrane potential</p> Signup and view all the answers

    What is the term for the stored energy represented by the concentration and electrical gradients?

    <p>Potential energy</p> Signup and view all the answers

    What is the analogy used to describe the cell membrane in terms of storing and separating charge?

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

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

    <p>To mediate the transport of substances across the membrane</p> Signup and view all the answers

    Which of the following molecules can permeate the hydrophobic core of the lipid bilayer?

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

    What is the primary driving force behind diffusion?

    <p>Kinetic energy of particles</p> Signup and view all the answers

    What is the effect of increasing the surface area of a cell on diffusion?

    <p>It increases the rate of diffusion</p> Signup and view all the answers

    What is the maximum size of a cell that can rely solely on diffusion for transport?

    <p>20 µm</p> Signup and view all the answers

    What is the effect of membrane thickness on the rate of diffusion?

    <p>It slows down the rate of diffusion</p> Signup and view all the answers

    Which of the following molecules is impermeable to the lipid bilayer?

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

    What is the effect of increasing the temperature on the rate of diffusion?

    <p>It increases the rate of diffusion</p> Signup and view all the answers

    What is the condition for osmosis to occur across a biological membrane?

    <p>The membrane is permeable to water but not to certain solutes.</p> Signup and view all the answers

    What is the primary function of aquaporins in cell membranes?

    <p>To facilitate the transport of water across the membrane.</p> Signup and view all the answers

    What is the effect of mercury on the permeability of water through the cell membrane?

    <p>It specifically inhibits the permeability of water through water channels.</p> Signup and view all the answers

    What is the relationship between the permeability of water through the lipid bilayer (Pd) and the permeability of water through water channels (Pf)?

    <p>Pd is less than Pf.</p> Signup and view all the answers

    What determines the difference in osmolarity between two solutions?

    <p>The concentration of solutes in both solutions.</p> Signup and view all the answers

    What is the effect of temperature on the permeability of water through the lipid bilayer?

    <p>It increases the fluidity of the lipid bilayer, increasing the permeability of water.</p> Signup and view all the answers

    What is the definition of osmotic pressure?

    <p>The pressure required to prevent the inward flow of water across a semi-permeable membrane.</p> Signup and view all the answers

    What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?

    <p>Water will move from the solution with lower osmolarity to the solution with higher osmolarity.</p> Signup and view all the answers

    What is the primary function of proteins in the fluid mosaic model of membrane structure?

    <p>To act as gatekeepers and regulate traffic across the membrane</p> Signup and view all the answers

    What type of lipid molecules comprise 75% of the lipids in the cell membrane?

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

    What is the thickness of the cell membrane?

    <p>8 nm (8 x 10^-9 metre)</p> Signup and view all the answers

    What is the primary reason for the selective permeability of the cell membrane?

    <p>The lipid bilayer is impermeable to polar substances</p> Signup and view all the answers

    What is the primary mechanism of transport across cell membranes?

    <p>All of the above</p> Signup and view all the answers

    What is the primary function of the lipid bilayer in the cell membrane?

    <p>To act as a barrier to entry or exit of polar substances</p> Signup and view all the answers

    What is the term that describes the movement of substances from an area of higher concentration to an area of lower concentration?

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

    What is the structure of the phospholipid bilayer in the cell membrane?

    <p>Two parallel layers of phospholipid molecules</p> Signup and view all the answers

    What is the primary reason for the asymmetry of lipid composition in membrane leaflets?

    <p>Lipids rarely flip-flop between membrane leaflets</p> Signup and view all the answers

    What determines the fluidity of a membrane?

    <p>Lipid tail length and number of double bonds</p> Signup and view all the answers

    Which type of protein is attached to the surface of the cell membrane and is easily removed?

    <p>Peripheral protein</p> Signup and view all the answers

    What is the function of hydrophobic regions in integral membrane proteins?

    <p>To span the hydrophobic core of the lipid bilayer</p> Signup and view all the answers

    Which type of molecule is permeable through the lipid bilayer?

    <p>Nonpolar, uncharged molecules</p> Signup and view all the answers

    What is the primary function of receptor proteins in the cell membrane?

    <p>To act as cell identity markers</p> Signup and view all the answers

    What is the result of the molecular organization of the cell membrane?

    <p>Selective permeability and fluidity</p> Signup and view all the answers

    What is the characteristic of hydrophilic regions in integral membrane proteins?

    <p>They are polar and interact with the aqueous solution</p> Signup and view all the answers

    What is the primary reason for the limitation of cell size to approximately 20 μm in diameter?

    <p>The rate of diffusion sets a limit on the size of cells.</p> Signup and view all the answers

    What is the effect of increasing the surface area of a cell on diffusion?

    <p>The rate of diffusion increases.</p> Signup and view all the answers

    What is the effect of temperature on the rate of diffusion?

    <p>The rate of diffusion increases.</p> Signup and view all the answers

    What is the result of a difference in concentration between two sides of a membrane?

    <p>The solvent will move from the area of lower concentration to the area of higher concentration.</p> Signup and view all the answers

    What is the effect of membrane thickness on the rate of diffusion?

    <p>The thicker the membrane, the slower the rate of diffusion.</p> Signup and view all the answers

    Which of the following molecules can diffuse through the hydrophobic core of the lipid bilayer?

    <p>CO2</p> Signup and view all the answers

    What is the primary benefit of increasing the membrane area available for exchange?

    <p>It increases the rate of diffusion.</p> Signup and view all the answers

    What is the result of an increase in the surface area of a cell?

    <p>The rate of facilitated diffusion increases.</p> Signup and view all the answers

    Which of the following best describes the energy requirement for the maintenance of concentration and electrical gradients across the cell membrane?

    <p>It requires 30% of resting energy.</p> Signup and view all the answers

    What is the primary driving force behind the movement of ions across the cell membrane?

    <p>Electrochemical gradient</p> Signup and view all the answers

    What is the term for the difference in charged ions between the inside and outside of the cell membrane?

    <p>Membrane potential</p> Signup and view all the answers

    What is the primary consequence of osmosis across a biological membrane?

    <p>Net movement of water from low to high concentration</p> Signup and view all the answers

    What is the primary function of the selectively permeable cell membrane in terms of osmosis?

    <p>To regulate the movement of certain molecules</p> Signup and view all the answers

    What is the primary reason for the energy storage in concentration and electrical gradients across the cell membrane?

    <p>To store energy for cellular processes</p> Signup and view all the answers

    What is the term for the movement of substances from an area of higher concentration to an area of lower concentration?

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

    What is the primary analogy used to describe the cell membrane in terms of storing and separating charge?

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

    What is the primary reason for water movement across a biological membrane?

    <p>To eliminate an osmotic gradient</p> Signup and view all the answers

    Which of the following is a characteristic of Pf, the permeability of water through water channels?

    <p>It is mercury-insensitive</p> Signup and view all the answers

    What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?

    <p>Water will move from the higher to the lower osmolarity solution</p> Signup and view all the answers

    What is the term for the pressure applied to a solution to prevent the inward flow of water across a semi-permeable membrane?

    <p>Osmotic pressure</p> Signup and view all the answers

    Which of the following determines the difference in osmolarity between two solutions?

    <p>The concentration of solutes</p> Signup and view all the answers

    What is the effect of increasing the temperature on the permeability of water through the lipid bilayer?

    <p>It increases</p> Signup and view all the answers

    What is the relationship between Pf and Pd?

    <p>Pf is larger than Pd</p> Signup and view all the answers

    Which of the following is a characteristic of the movement of water across a biological membrane?

    <p>It is a passive process</p> Signup and view all the answers

    What is the primary mechanism by which cholesterol and glycolipids are scattered among the phospholipid molecules in the cell membrane?

    <p>Hydrophobic interactions</p> Signup and view all the answers

    What is the primary consequence of the amphipathic nature of phospholipid molecules in the cell membrane?

    <p>Selective permeability of the membrane</p> Signup and view all the answers

    What is the primary role of membrane proteins in the fluid mosaic model of membrane structure?

    <p>To regulate traffic across the membrane</p> Signup and view all the answers

    What is the primary driving force behind the movement of substances from an area of higher concentration to an area of lower concentration?

    <p>Concentration gradient</p> Signup and view all the answers

    What is the primary consequence of the difference in osmolarity between two solutions separated by a semi-permeable membrane?

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

    What is the primary function of the lipid bilayer in the cell membrane?

    <p>To act as a barrier to the entry or exit of polar substances</p> Signup and view all the answers

    What is the primary characteristic of facilitated diffusion?

    <p>Requires the presence of membrane proteins</p> Signup and view all the answers

    What is the primary consequence of increasing the surface area of a cell?

    <p>Increased rate of diffusion</p> Signup and view all the answers

    What is the primary mechanism by which nonpolar, uncharged molecules cross the cell membrane?

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

    Which type of molecules are permeable through the lipid bilayer due to their lipid solubility?

    <p>Steroids, fatty acids, and some vitamins</p> Signup and view all the answers

    What is the primary function of hydrophilic regions in integral membrane proteins?

    <p>To interact with the aqueous solution</p> Signup and view all the answers

    What determines the fluidity of a membrane?

    <p>Lipid tail length, number of double bonds, and amount of cholesterol</p> Signup and view all the answers

    What is the result of the molecular organization of the cell membrane?

    <p>The membrane allows some substances to cross but excludes others</p> Signup and view all the answers

    Which type of protein is attached to the surface of the cell membrane and is easily removed?

    <p>Peripheral membrane protein</p> Signup and view all the answers

    What is the primary function of transporter proteins in the cell membrane?

    <p>To facilitate the transport of specific molecules</p> Signup and view all the answers

    What is the primary reason for the asymmetry of lipid composition in membrane leaflets?

    <p>Lipids rarely flip flop between membrane leaflets</p> Signup and view all the answers

    What is the primary reason for the difference in permeability of water through the lipid bilayer (Pd) and through water channels (Pf)?

    <p>Aquaporin isoforms</p> Signup and view all the answers

    What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?

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

    What determines the permeability of water through the lipid bilayer (Pd)?

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

    What is the primary function of aquaporin isoforms in cell membranes?

    <p>To mediate water permeability</p> Signup and view all the answers

    What is the primary driving force behind the movement of water across a semi-permeable membrane?

    <p>Concentration gradient</p> Signup and view all the answers

    What determines the rate of diffusion across a cell membrane?

    <p>Concentration gradient</p> Signup and view all the answers

    What is the result of an increase in the surface area of a cell?

    <p>Increased diffusion rate</p> Signup and view all the answers

    What is the term that describes the movement of substances from an area of higher concentration to an area of lower concentration?

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

    What is the primary factor that determines the rate of diffusion?

    <p>Concentration gradient</p> Signup and view all the answers

    Which of the following factors increases the rate of diffusion?

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

    What is the result of a large concentration gradient across a membrane?

    <p>Faster rate of diffusion</p> Signup and view all the answers

    What is the effect of increasing the size of the diffusing substance?

    <p>Decrease in rate of diffusion</p> Signup and view all the answers

    What is the primary reason for the limitation of cell size?

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

    What is the effect of increasing the temperature on the rate of diffusion?

    <p>Increase in rate of diffusion</p> Signup and view all the answers

    What is the effect of increasing the membrane thickness on the rate of diffusion?

    <p>Decrease in rate of diffusion</p> Signup and view all the answers

    What is the primary benefit of increasing the membrane area available for exchange?

    <p>Increase in diffusion rate</p> Signup and view all the answers

    What is the primary factor that determines the rate of diffusion across a cell membrane?

    <p>Concentration gradient</p> Signup and view all the answers

    What is the effect of increasing the surface area of a cell on the rate of diffusion?

    <p>Increases the rate of diffusion</p> Signup and view all the answers

    What is the primary mechanism of transport across cell membranes?

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

    What is the primary driving force behind the movement of ions across the cell membrane?

    <p>Electrochemical gradient</p> Signup and view all the answers

    What is the primary benefit of increasing the membrane area available for exchange?

    <p>Increases the rate of diffusion</p> Signup and view all the answers

    What is the result of a difference in concentration between two sides of a membrane?

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

    What is the primary reason for the limitation of cell size to approximately 20 μm in diameter?

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

    What is the effect of temperature on the rate of diffusion?

    <p>Increases the rate of diffusion</p> Signup and view all the answers

    What determines the direction of diffusion of non-charged molecules across a cell membrane?

    <p>The concentration gradient of the molecule</p> Signup and view all the answers

    What is the primary reason for the establishment of an electrical gradient across a cell membrane?

    <p>The difference in concentration of charged ions between the inside and outside of the membrane</p> Signup and view all the answers

    Which of the following is a characteristic of the movement of ions across a cell membrane?

    <p>Ions are influenced by the electrical gradient</p> Signup and view all the answers

    What is the primary function of the selective permeability of the cell membrane?

    <p>To establish a concentration gradient across the membrane</p> Signup and view all the answers

    What determines the rate of diffusion of non-charged molecules across a cell membrane?

    <p>The concentration gradient of the molecule</p> Signup and view all the answers

    What is the result of the difference in concentration of charged ions between the inside and outside of a cell membrane?

    <p>An electrical gradient is established</p> Signup and view all the answers

    What is the primary driving force behind the movement of non-charged molecules across a cell membrane?

    <p>The concentration gradient of the molecule</p> Signup and view all the answers

    What is the result of the movement of ions down their concentration gradient across a cell membrane?

    <p>An electrical gradient is established</p> Signup and view all the answers

    What is the primary factor that determines the rate of diffusion across a cell membrane?

    <p>The concentration gradient of the substance</p> Signup and view all the answers

    What is the effect of increasing the concentration of a substance on one side of a cell membrane?

    <p>It increases the rate of diffusion</p> Signup and view all the answers

    What is the relationship between the concentration gradient and the rate of diffusion across a cell membrane?

    <p>Directly proportional</p> Signup and view all the answers

    What is the effect of decreasing the temperature on the rate of diffusion across a cell membrane?

    <p>It decreases the rate of diffusion</p> Signup and view all the answers

    What is the primary mechanism by which cells maintain concentration gradients across their cell membranes?

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

    What is the effect of increasing the surface area of a cell membrane on the rate of diffusion?

    <p>It increases the rate of diffusion</p> Signup and view all the answers

    What is the relationship between the concentration gradient and the direction of diffusion across a cell membrane?

    <p>The concentration gradient determines the direction of diffusion</p> Signup and view all the answers

    What is the primary benefit of maintaining a concentration gradient across a cell membrane?

    <p>It allows for the regulation of intracellular ion concentrations</p> Signup and view all the answers

    Study Notes

    Selective Permeability and Diffusion

    • The cell membrane is selectively permeable, allowing certain substances to cross while excluding others
    • The lipid bilayer is permeable to nonpolar, uncharged molecules (e.g. O2, N2, benzene) and lipid-soluble molecules (e.g. steroids, fatty acids, some vitamins)
    • The lipid bilayer is impermeable to large uncharged polar molecules (e.g. glucose, amino acids) and ions (e.g. Na+, K+, Cl-, Ca2+)

    Diffusion

    • Diffusion is the random mixing of particles in a solution due to kinetic energy
    • Diffusion occurs from an area of high concentration to an area of low concentration
    • Factors affecting the rate of diffusion:
      • Concentration gradient: the greater the difference in concentration, the faster the rate of diffusion
      • Temperature: higher temperatures increase the rate of diffusion
      • Particle size: larger particles diffuse slower
      • Surface area: increasing surface area increases the rate of diffusion
      • Distance: increasing diffusion distance slows down the rate of diffusion

    Osmosis

    • Osmosis is the diffusion of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration
    • Osmosis occurs to eliminate osmotic gradients
    • Cell membranes are permeable to water but not to certain solutes, allowing osmosis to occur

    Membrane Permeability to Water

    • The cell membrane has a permeability coefficient (Pw) that is the sum of two components:
      • Pd: permeability through the lipid bilayer, which is small, mercury-insensitive, and temperature-dependent
      • Pf: permeability through water channels, which is large, mercury-sensitive, and temperature-independent
    • Aquaporins are proteins that mediate Pf, and cells express different isoforms to regulate water permeability

    Gradients across the Cell Membrane

    • Concentration gradients: non-charged molecules diffuse down their concentration gradients
    • Electrical gradients: ions are influenced by the membrane potential in addition to their concentration gradient
    • The selective permeability of the membrane enables the establishment of concentration and electrical gradients across the membrane
    • Cells maintain concentration and electrical gradients at a cost of energy (~30% of resting energy)

    Selective Permeability and Diffusion

    • The cell membrane is selectively permeable, allowing certain substances to cross while excluding others
    • The lipid bilayer is permeable to nonpolar, uncharged molecules (e.g. O2, N2, benzene) and lipid-soluble molecules (e.g. steroids, fatty acids, some vitamins)
    • The lipid bilayer is impermeable to large uncharged polar molecules (e.g. glucose, amino acids) and ions (e.g. Na+, K+, Cl-, Ca2+)

    Diffusion

    • Diffusion is the random mixing of particles in a solution due to kinetic energy
    • Diffusion occurs from an area of high concentration to an area of low concentration
    • Factors affecting the rate of diffusion:
      • Concentration gradient: the greater the difference in concentration, the faster the rate of diffusion
      • Temperature: higher temperatures increase the rate of diffusion
      • Particle size: larger particles diffuse slower
      • Surface area: increasing surface area increases the rate of diffusion
      • Distance: increasing diffusion distance slows down the rate of diffusion

    Osmosis

    • Osmosis is the diffusion of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration
    • Osmosis occurs to eliminate osmotic gradients
    • Cell membranes are permeable to water but not to certain solutes, allowing osmosis to occur

    Membrane Permeability to Water

    • The cell membrane has a permeability coefficient (Pw) that is the sum of two components:
      • Pd: permeability through the lipid bilayer, which is small, mercury-insensitive, and temperature-dependent
      • Pf: permeability through water channels, which is large, mercury-sensitive, and temperature-independent
    • Aquaporins are proteins that mediate Pf, and cells express different isoforms to regulate water permeability

    Gradients across the Cell Membrane

    • Concentration gradients: non-charged molecules diffuse down their concentration gradients
    • Electrical gradients: ions are influenced by the membrane potential in addition to their concentration gradient
    • The selective permeability of the membrane enables the establishment of concentration and electrical gradients across the membrane
    • Cells maintain concentration and electrical gradients at a cost of energy (~30% of resting energy)

    Gradients across the Cell Membrane

    • A concentration gradient is the difference in concentration of non-charged molecules between the inside and outside of the cell membrane, causing molecules to diffuse down their concentration gradients.
    • An electrical gradient, or membrane potential, is the difference in electrical charge between the inside and outside of the cell membrane, influencing the movement of ions.
    • The selective permeability of the cell membrane allows for the establishment of concentration and electrical gradients across the membrane.
    • The membrane's selectivity enables cells to maintain differences in charged ions between the inside and outside of the membrane, establishing an electrical gradient.

    Ion Gradients across the Membrane

    • The concentration of ions (Na+, K+, Cl-) is higher in the extracellular fluid than in the cytoplasm.
    • The cell membrane acts as a capacitor, separating and storing charge.

    Osmosis

    • Osmosis is the diffusion of water through a selectively permeable membrane from an area of high water concentration to an area of low water concentration.
    • Osmosis occurs when the membrane is permeable to water but not to certain solutes.
    • Water moves to eliminate osmotic gradients.

    Membrane Permeability to Water

    • The permeability of the cell membrane to water is determined by the presence of aquaporins (9 isoforms) and the lipid bilayer.
    • Cells have different permeability to water due to the expression of different aquaporin isoforms.

    Selective Membrane Permeability

    • The cell membrane is selectively permeable to small uncharged polar molecules (water, urea, glycerol, CO2) and impermeable to large uncharged polar molecules (glucose, amino acids) and ions (Na+, K+, Cl-, Ca2+, H+).
    • Membrane proteins mediate the transport of substances across the membrane that cannot permeate the hydrophobic core of the lipid bilayer.

    Diffusion

    • Diffusion is the random mixing of particles in a solution as a result of kinetic energy.
    • The rate of diffusion is influenced by the concentration gradient, temperature, and surface area.
    • Diffusion is limited by the size of the cell (approximately 20 µm).

    Membrane Fluidity

    • Membranes are fluid structures, and lipids can move around within the plane of the membrane.
    • Fluidity is determined by lipid tail length, number of double bonds, and the amount of cholesterol.

    Membrane Proteins

    • Integral proteins extend into or across the cell membrane and are amphipathic, with hydrophobic regions spanning the hydrophobic core of the lipid bilayer.
    • Peripheral proteins are attached to the inner or outer surface of the cell membrane and are easily removed.
    • Membrane proteins can act as receptors, cell identity markers, linkers, enzymes, ion channels, and transporter proteins.

    Selective Permeability of Membrane

    • The molecular organization of the membrane results in selective permeability, allowing some substances to cross while excluding others.
    • The lipid bilayer is permeable to nonpolar, uncharged molecules and lipid-soluble molecules.

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