chap 2 movement of sustances

• diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentraton gradient
• all particles are in continuous, random motion
• what are the 4 factors affecting rate of diffusion ?

  temperature, concentration gradient, mass of particle and surface area to volume ratio
• at higher temperatures, the particles have higher kinetic energy and move more quickly, hence diffusion rate is higher
• the steeper the concentration gradient, the greater the rate of diffusion
• the smaller the mass of particles, the faster they travel, hence, rate of diffusion is higher
• the greater the surface area to volume ratio, the greater the rate of diffusion
• osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
• when placed in a solution of lower water potential:

  animal cell shrinks and spikes form on the surface of the cell, and the cell becomes dehydrated and eventually dies. The process is called crenation

  plant cell decreases in size and becomes flaccid, the cell membrane shrinks away from the cell wall and becomes plasmolysed
• when placed in a solution of higher water potential:

  animal cells expands and eventually bursts, leading to lysis

  plant cells expand and its vacuole expands and pushes the cytoplasm against the cell wall. The rigid, inelastic cell wall prevents the cell from bursting and the cell becomes turgid
• active transport is the net movement o particles from a region of lower concentration to a region of higher concentration against the concentration gradient, through a partially permeable membrane