Topic 4: Plasma membrane

• What surrounds all living cells?

  A membrane, also known as a plasma membrane
• What is the primary function of the cell membrane?

  It separates cell contents from the outside environment
• How does the cell membrane contribute to cell recognition and signaling?

  It facilitates communication between cells
• What role does the cell membrane play in metabolic pathways?

  It holds components of some metabolic pathways in place
• How does the cell membrane regulate transport?

  It regulates the transport of materials in and out of the cell
• What is the permeability characteristic of membranes?

  Membranes are partially permeable
• Why is it important to study the structure of biological components?

  To understand their function
• What are the two main parts of a phospholipid?

  • Hydrophilic heads (glycerol and phosphate group)
  • Hydrophobic tails (two fatty acid chains)

  
• What does it mean for a phospholipid to be amphiphilic?

  It has both polar and non-polar regions

  
• How do phospholipids arrange themselves in a bilayer?

  • Two layers of phospholipids
  • Hydrophobic tails face inward
  • Hydrophilic heads face outward

  
• What is the basic structure of membranes?

  The phospholipid bilayer

  
• What substances can pass through the phospholipid bilayer?

  Lipid-soluble substances
• What does the fluid mosaic model describe?

  The structure of cell membranes
• Why is the term "fluid" used in the fluid mosaic model?

  Because phospholipids and proteins can move freely within the layer
• What does "mosaic" refer to in the fluid mosaic model?

  The pattern produced by scattered protein molecules
• What are the main components of the cell membrane?

  • Phospholipids
  • Proteins
  • Cholesterol
  • Glycolipids
  • Glycoproteins

  
• How do cholesterol molecules affect membrane stability?

  They increase stability and maintain fluidity
• How does temperature affect membrane fluidity?

  Higher temperatures increase fluidity
• What happens to membrane permeability at higher temperatures?

  It increases, making the membrane leaky
• What are integral proteins?

  Proteins that span the two layers of the membrane
• What is the function of glycoproteins?

  They bind to substances the cell needs to import
• What are the two types of transport across the plasma membrane?

  • Passive transport (does not require energy)
  • Active transport (requires energy)
• What is diffusion?

  The net movement of molecules from high to low concentration
• What factors affect diffusion rates?

  Concentration gradients, mass of molecules, temperature, solubility, surface area, distance, and pressure
• What is facilitated diffusion?

  Diffusion of large polar molecules through channel or carrier proteins
• What is osmosis?

  The diffusion of water molecules down a water potential gradient
• What does water potential (ψ) indicate?

  The tendency of water molecules to move from one place to another
• How does adding solute affect water potential?

  It lowers the water potential
• What are the three types of tonicity?

  • Hypertonic: higher osmolarity than cytosol
  • Isotonic: same osmolarity as cytosol
  • Hypotonic: lower osmolarity than cytosol

  
• What is osmoregulation?

  The process by which cells modify volume by altering their water content
• What happens to cells in a hypertonic solution?

  Water leaves the cell

  
• What happens to cells in a hypotonic solution?

  Water enters the cell

  
• What is plasmolysis?

  The detachment of the plasma membrane from the cell wall in hypertonic solutions
• How do freshwater protists manage osmoregulation?

  They use contractile vacuoles to pump water out
• What is active transport?

  Transport of molecules against their concentration gradient requiring energy
• What are the two types of active transport?


  • Primary active transport: uses ATP for energy
  • Secondary active transport: uses an electrochemical gradient for energy

  
• What is the Na+-K+ pump?

  A primary active transport mechanism that moves 3 Na+ out and 2 K+ in using 1 ATP

  
• What is secondary active transport?

  Transport that uses an electrochemical gradient created by primary active transport
• What is bulk transport?

  • A type of active transport
  • Used for importing or exporting large molecules
  • Requires energy
• What is receptor-mediated endocytosis?

  A form of endocytosis using receptor proteins to capture specific target molecules