transport in cells

• Diffusion


  Spreading out of particles from an area of higher concentration to an area of lower concentration
• Diffusion happens in solutions and gases
• Concentration gradient


  The difference in concentration
• Bigger the difference in concentration


  Faster the diffusion rate
• Higher temperature


  Faster diffusion rate
• Cell membranes


  • Let stuff diffuse in and out of the cell
  • Only very small molecules can pass through
  • Big molecules like starch and proteins can't fit through
• Molecules flow through the membrane

  1. From higher concentration to lower concentration

  2. Move both ways but net movement is from higher to lower
• Larger surface area of membrane

  Faster diffusion rate
• Active transport


  Process to absorb substances against the concentration gradient
• Active transport needs energy from respiration to work
• The body uses active transport to move nutrients like glucose from lower concentration in the gut to higher concentration in the blood
• Osmosis


  Movement of water molecules from a less concentrated solution to a more concentrated solution through a partially permeable membrane
• Osmosis acts to equalise the concentration on both sides of the membrane
• Potato cylinders in sugar solutions of different concentrations

  • Potato cylinders in pure water
  • Potato cylinders in 1 mol/dm³ sugar solution
  • Potato cylinders in 0.2 mol/dm³, 0.4 mol/dm³ etc. sugar solutions
• Measuring the change in mass of the potato cylinders shows if water has moved into or out of the cells