B3.1 - Movement of Molecules In and Out of cells

B3.1 - Movement of Molecules In and Out of cells

1. Diffusion

   • Particles move from an area of high concentration to low
     • For example, different gases can simply diffuse through one another. Alternatively, dissolved particles can diffuse in and out of cells through cell membranes.
   • The structure of leaves let gases diffuse in and out of cells
   • Diffusion through cell membranes
     • Gas exchange happens in the lungs
     • The villi provide a really really big surface area

2. Osmosis

   • Similar to diffusion, but only refers to water
     • Water moves across a partially permeable membrane (eg. cell membrane) from an area of high water concentration to low

3. Active Transport

   • Root hairs are specialised for absorbing water and minerals
   • Sometimes substances need to be absorbed against a concentration gradient - ie. from a lower to higher concentration
   • Root hairs take in minerals using active transport
   • We need active transport to stop us starving