d. Movement of Substances

• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
• Diffusion is a passive process - it doesn't require energy.
• Diffusion happens in:

  • liquids
  • gases
• The bigger the difference in concentration, the faster the diffusion rate.
• Only very small molecules can difffuse through cell membranes.

  e.g. glucose, amino acids, water and oxygen.

  Big molecules (e.g. starch and protein) can't fit through the membrane.
• Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
• Active transport is the movement of particles against a concentration gradient (from an area of lower concentration to an area of higher concentration) using energy released during respiration.
• Factors that affect the movement of substances:

  • Surface area to volume ratio
  • Distance
  • Temperature
  • Concentration gradient
• Rate of diffusion, osmosis, and active transport = higher in cells with a larger surface area to volume ratio.
• When a fucntion is passive, what does it mean?

  It does not require energy.