Lab 2

• Diffusion is the movement of molecules from areas of higher chemical potential to areas of lower chemical potential
• Molecules tend to move from areas of higher solute concentration to areas of lower solute concentration due to the laws of motion and mass action
• In an animal cell, small non-polar molecules and gases like oxygen and carbon dioxide can use simple diffusion to pass through the plasma membrane
• Factors affecting the speed of diffusion:

  • Diffusion rate increases with temperature due to increased kinetic energy of particles
  • The molar mass of a molecule impacts its rate of diffusion according to Graham's law, where lighter molecules diffuse more rapidly than heavier ones
• Osmosis is the movement of water molecules from regions of higher water potential to regions of lower water potential
• Water potential is affected by the level of solutes dissolved in water, with the addition of solute lowering water potential
• Aquaporins are protein pores in the plasma membrane that allow water to travel through for osmosis
• Tonicity of solutions:

  • Hypotonic solution has higher water potential than the inside of the cell
  • Hypertonic solution has lower water potential than the inside of the cell
  • Isotonic solution has the same water potential as the inside of the cell
• In plant cells, being in a hypotonic solution leads to water flowing in, causing the central vacuole to fill up and create turgor pressure that keeps the cell rigid
• Both simple and facilitated diffusion involve the net movement of solute down the concentration gradient without external energy input
• Transport proteins are needed for facilitated diffusion and osmosis to cross the cell membrane
• Active transport moves molecules against the concentration gradient and requires energy input