Biology: Cell Membrane Structure and Functions
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Questions and Answers

What is the main function of the phospholipid bilayer in the cell membrane?

  • Regulate waste removal
  • Enable cell signaling
  • Maintain selective permeability (correct)
  • Facilitate cell-cell interactions

    • Integral proteins are primarily involved in cell signaling.

    False

    What type of proteins attach to the surface of the cell membrane?

    Peripheral proteins

    The fluid mosaic model describes the cell membrane as a fluid structure due to the movement of ________ and ________.

    <p>proteins, lipids</p> Signup and view all the answers

    Match the passive transport mechanism with its description:

    <p>Diffusion = Movement of molecules from high concentration to low concentration Osmosis = Movement of water across a semipermeable membrane Facilitated diffusion = Transport of molecules with the help of integral proteins</p> Signup and view all the answers

    What is the main component of the cell membrane according to the fluid mosaic model?

    <p>Phospholipids and proteins</p> Signup and view all the answers

    Increasing temperature leads to decreased permeability of the cell membrane.

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

    Explain the function of channel proteins in the cell membrane.

    <p>Channel proteins provide channels for certain substances to move across the cell membrane.</p> Signup and view all the answers

    Osmosis is the movement of _ molecules across a differentially permeable membrane.

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

    Match the following terms with their descriptions:

    <p>Hypotonic solution = Has a higher water potential compared to another solution Isotonic solution = Has the same water potential as another solution Hypertonic solution = Has a lower water potential compared to another solution</p> Signup and view all the answers

    Is diffusion an active or passive process?

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

    Is osmosis an active or passive process?

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

    Does active transport require energy?

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

    Is phagocytosis an active or passive process?

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

    Study Notes

    Cell Membrane

    Structure

    • Phospholipid bilayer: two layers of lipid molecules with phosphate heads and fatty acid tails
    • Hydrophilic (water-loving) heads face outward, hydrophobic (water-fearing) tails face inward
    • Embedded proteins:
      • Integral proteins: span the membrane, involved in transport and signaling
      • Peripheral proteins: attached to the surface, involved in signaling and cell-cell interactions

    Functions

    • Selective permeability: regulates what enters and leaves the cell
    • Cell signaling: receives and transmits signals through embedded proteins
    • Cell-cell interactions: facilitates interactions with other cells through adhesion molecules
    • Waste removal: aids in the removal of waste products from the cell

    Fluid Mosaic Model

    • Phospholipid bilayer is fluid, allowing for lateral movement of proteins and lipids
    • Embedded proteins are mobile, enabling dynamic interactions and signaling

    Transport Across the Cell Membrane

    • Passive transport: diffusion, osmosis, and facilitated diffusion
    • Active transport: energy-dependent transport of molecules against their concentration gradient

    Cell Membrane

    Structure

    • The phospholipid bilayer is composed of two layers of lipid molecules with phosphate heads and fatty acid tails.
    • Hydrophilic (water-loving) heads face outward, while hydrophobic (water-fearing) tails face inward.
    • Embedded proteins are classified into two types:
      • Integral proteins that span the membrane, involved in transport and signaling.
      • Peripheral proteins attached to the surface, involved in signaling and cell-cell interactions.

    Functions

    • The cell membrane exhibits selective permeability, regulating what enters and leaves the cell.
    • It plays a crucial role in cell signaling, receiving and transmitting signals through embedded proteins.
    • The cell membrane facilitates cell-cell interactions through adhesion molecules.
    • It aids in the removal of waste products from the cell.

    Fluid Mosaic Model

    • The phospholipid bilayer is fluid, allowing for lateral movement of proteins and lipids.
    • Embedded proteins are mobile, enabling dynamic interactions and signaling.

    Transport Across the Cell Membrane

    • Passive transport occurs through diffusion, osmosis, and facilitated diffusion.
    • Active transport involves energy-dependent transport of molecules against their concentration gradient.

    Movement of Substances across Cell Membrane

    • Cell membrane structure: fluid mosaic model, composed of phospholipids and proteins
      • Phospholipid bilayer with hydrophilic heads and hydrophobic tails
      • Proteins interspersed among phospholipid molecules, some attached to surface, others embedded or spanning the bilayer
      • Carbohydrates attached to proteins to form glycoproteins

    Structure of Cell Membrane and its Properties

    • Phospholipid bilayer:
      • Hydrophilic heads face outwards, hydrophobic tails face inwards
      • Phospholipid molecules can move laterally
    • Protein functions:
      • Channel proteins: provide channels for certain substances to move across the cell membrane
      • Carrier proteins: bind to certain substances and transport them to the other side of the cell membrane
      • Receptors: bind to chemical messengers outside cells, triggering cell activities
      • Antigens: glycoproteins for cell recognition
      • Enzymes: speed up chemical reactions

    Relationship between Structure, Properties, and Functions of Cell Membrane

    • Cell membrane structure related to properties and functions:
      • Phospholipid bilayer makes membrane differentially permeable
      • Small, non-polar molecules can dissolve in and move across phospholipid bilayer
      • Small, polar molecules and ions are transported by channel proteins or carrier proteins
      • Phospholipid molecules can move laterally, making the cell membrane fluid and able to change shape and fuse during phagocytosis and cell division

    Factors Affecting Cell Membrane Structure and Permeability

    • Temperature: increases permeability, boiling can damage the membrane
    • Organic solvents: dissolve phospholipids, increase permeability, and damage the cell membrane

    Movement of Substances across Membranes

    Diffusion

    • Diffusion: net movement of particles from higher to lower concentration
    • Factors affecting rate of diffusion:
      • Concentration gradient: steeper gradient increases rate
      • Surface area: larger surface area increases rate
      • Distance: shorter distance increases rate
      • Temperature: higher temperature increases rate
      • Particle size: smaller particles diffuse faster
      • Nature of particles: non-polar substances diffuse faster than polar substances
    • Importance of diffusion: enables cells to exchange materials with the environment, involved in absorption of nutrients and gas exchange

    Osmosis

    • Osmosis: net movement of water molecules from higher to lower water potential across a differentially permeable membrane
    • Water potential: pure water has highest water potential (0), solutions have lower water potential (negative value)
    • Types of solutions:
      • Hypotonic: higher water potential than the cell
      • Isotonic: same water potential as the cell
      • Hypertonic: lower water potential than the cell
    • Changes in animal cells in solutions of different water potentials:
      • Hypotonic: swell and burst
      • Isotonic: no change
      • Hypertonic: shrink and become wrinkled
    • Changes in plant cells in solutions of different water potentials:
      • Hypotonic: become turgid
      • Isotonic: no change
      • Hypertonic: become flaccid and plasmolysed
    • Importance of osmosis: main mechanism of water entry and exit in cells, involved in water absorption in human intestines and plant roots

    Active Transport

    • Active transport: movement of substances across the cell membrane from lower to higher concentration using energy
    • Process of active transport:
      1. Particle binds to carrier protein
      2. Carrier protein changes shape using energy
      3. Particle is released on the other side of the membrane
    • Importance of active transport:
      • Allows uptake of additional useful substances already high in concentration in cells
      • Involved in absorption of nutrients in human small intestine and absorption of minerals from soil into plant roots

    Phagocytosis

    • Phagocytosis: uptake of large particles into cells by forming vacuoles from the cell membrane
    • Process of phagocytosis:
      1. Pseudopodia surround the particle
      2. Cell membrane fuses to form a vacuole
      3. Vacuole is fused with other vacuoles containing digestive enzymes
      4. Particle is broken down into digested products
    • Importance of phagocytosis:
      • Allows unicellular organisms to engulf food particles for nutrition
      • Involved in white blood cell engulfment of harmful microorganisms for body defense against diseases

    Comparison of Membrane Transport Processes

    • Diffusion: passive, no energy needed
    • Osmosis: passive, no energy needed
    • Active transport: active, energy needed
    • Phagocytosis: active, energy needed

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    Description

    Learn about the structure and functions of the cell membrane, including the phospholipid bilayer, embedded proteins, and selective permeability.

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