Diffusion, Osmosis and Active Transport

• Diffusion is the net movement of particles from an area of high concentration to an area of low concentration and can only happen if there is a concentration gradient.
• Active transport requires energy input as it goes against the concentration gradient.
• Osmosis is the diffusion of water molecules through a partially permeable membrane from an area of higher water potential (higher concentration) to an area of lower water potential (lower concentration).
• Many dissolved substances move into our body through diffusion like water, oxygen, and carbon dioxide.
• Factors that affect the rate of difussion:

  • The concentration gradient - the bigger the, the faster.
  • The temperature - the higher, the faster.
  • The surface area - the larger, the faster.
• A hypertonic solution - more water inside the cell, than outside.
• Hypotonic solution - less water inside the cell, than outside.
• An isotonic solution - equal amounts of water on both sides of the membrane.
• Energy needed for active transport comes from respiration, so there are lots of mitochondria in cells that use this method of diffusion.