MOVEMENT OF SUBSTANCES INTO AND OUT OF CELLS

• Diffusion

  The movement of particles from an area of high concentration to an area of low concentration down a concentration gradient through a partially permeable membrane.
• Equilibrium (n)

  To spread particles equally, in a state of balanace
• Four factors that increase the rate of diffusion

  • Larger surface area
  • Higher temperature
  • Steeper concentration gradient
  • Shorter diffusion distance
• Osmosis

  The net movement of water molecules from an area of higher water potential (dilute solution) to an area of lower water potential (concentrated solution), through a partially permeable membrane
• Partially permeable membrane

  A membrane that allows only certain substances to pass through while blocking others. E.g. water can pass through during osmosis but salt does not
• High water potential

  It is a dilute solution. There are more water molecules than there are solute molecules
• Low water potential

  It is a concentrated solution. There are more solute molecules than there are water molecules
• Active transport

  The movement of particles or ions through a cell membrane from an area of lower concentration to an area of higher concentration using energy from respiration.
• Why is energy needed for active transport?

  Particles are being moved against a concentration gradient, (lower concentration to higher concentration) in the opposite direction from which they would naturally move, by diffusion
• Concentration

  Measure of how many particles of a substance there are in a certain volume
• Factor affecting the rate of movement: concentration gradient

  The greater the difference in concentration, the faster the rate of diffusion. This is because more particles are randomly moving down the gradient than are moving against it
• Factor affecting the rate of movement: temperature

  The greater the temperature, the greater the movement of particles, resulting in more collisions and therefore a faster rate of diffusion
• Factor affecting the rate of movement: surface area to volume ratio

  The greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion
• Factor affecting rate of movement: distance

  The longer the distance, the slower it takes for molecules to pass through, resulting in a slower rate of diffusion