Cellular Transport

• Passive transport does not require energy and involves molecules moving from an area of high to low concentration
• Homeostasis refers to the balanced internal condition of cells, also known as equilibrium, maintained by the plasma membrane controlling what enters and leaves the cell
• Diffusion is a passive process where molecules move down the concentration gradient without the use of energy, driven by their natural kinetic energy
• Types of cell transport:

  • Passive Transport, Requires NO energy, molecules move from an area of high to low concentration
• The plasma membrane's chemical and physical properties allow only certain types of molecules to enter and exit a cell by simple diffusion
• Lipid-soluble molecules like alcohols can diffuse through the membrane because lipids are the main structural components of the membrane
• Gases can diffuse through the lipid bilayer, which is how oxygen enters cells and carbon dioxide exits cells
• Facilitated diffusion:

  • Aided by a concentration gradient and transport proteins
  • Doesn't require energy
  • Uses transport proteins to move molecules from high to low concentration
  • Examples include glucose or amino acids moving from blood into a cell
• In facilitated diffusion, molecules move through the pores in Channel Proteins
• Diffusion of water across a membrane:

  • Water moves from HIGH water concentration to LOW water concentration
  • Water is attracted to solutes (like salt) so it will also travel to areas of low solute concentration to high solute concentration
• Osmosis:

  • Hypotonic solution: has a lower solute concentration than inside the cell
  • Isotonic solution: solute concentration is the same as inside the cell
  • Hypertonic solution: has a higher solute concentration than inside the cell
• In an Isotonic solution:

  • 5 solutes inside the cell and 5 outside
  • Water will flow in both directions, outside and inside the cell, as the cell is at equilibrium
• In a Hypotonic solution:

  • 5 solutes inside the cell and 3 outside
  • Water will flow into the cell due to the higher concentration of solutes outside
• In a hypotonic solution, where the solute concentration is lower outside the cell, water moves inside the cell, causing it to swell and potentially burst in a process called cytolysis
• Osmosis in red blood cells:

  • Isotonic: no net movement of water
  • Hypotonic: water moves into the cell, potentially causing it to burst
  • Hypertonic: water moves out of the cell, leading to cell shrinkage
• Filtration is the movement of liquid from high pressure to low pressure, such as the passage of water and solutes through a membrane by hydrostatic pressure
• An example of filtration is in capillaries, the smallest blood vessels, where small molecules passively diffuse across the walls due to the difference in concentration, aided by blood pressure pushing water and dissolved solutes out of the capillary through tiny pores between capillary cells
• Endocytosis is the process by which cells take in substances from outside of the cell by engulfing them in a vesicle, including nutrients to support the cell or pathogens that immune cells engulf and destroy
• Active transport allows a molecule to cross the membrane from lower concentration to higher concentration