Biology: 3

• Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration
• Diffusion is important for:

  1. Gas exchange in the alveoli
  2. Nutrient absorption in small intestine
  3. Gas exchange in stomata
• The factors which affect diffusion include:

  1. Temperature
  2. Distance
  3. Surface area
  4. Concentration gradient
• The higher the temperature, the faster the rate of reaction
• The shorter the diffusion distance, the faster
• The greater the surface area per unit volume, the faster the rate of diffusion
• The lighter the concentration gradient, the faster the diffusion
• Osmosis is the net movement of water molecules through a partially permeable membrane, from a region of high to low water potential
• Concentrated solution:

  1. Low water potential (because it's mostly not water)
  2. Water leaves the cell (as there's more water in the cell)
  3. Cell becomes flaccid and plasmolysed in plant cell
  4. Cell become crenated in animal cell
• Dilute solution:

  1. High water potential
  2. Water enters cell (As there's more water particles outside)
  3. Cell becomes turgid in plant cell
  4. Cell bursts in animal cell