B1.6

• Molecules have kinetic energy which means that they'll constantly be moving around randomly.
• In which of the states can molecules diffuse?

  Gas and Liquid
• Cell membranes are said to be 'partially permeable'. 


  Only some molecules can pass through the membrane
• Which molecules are able to diffuse into and out of cells?

  Only small molecules such as water, glucose, and amino acids, can diffuse into/out of cells. Large molecules like proteins and starch are too big. 
• List three factors that affect the rate of diffusion.

  Concentration gradient 

  Temperature 

  Surface area

  Distance to diffuse across (if diffusing across a membrane)
• Will a larger surface area increase or decrease the rate of diffusion?

  Increase as a larger surface area means a larger area over which molecules can diffuse.

  More particles can fit around its surface.
• Why does a higher temperature increase the rate of diffusion?

  Higher temp = More kinetic energy = Move faster = Diffuse quicker
• How does the conc. gradient affect diffusion?

  Larger conc. gradient = higher rate of diffusion
• Conc gradient


  Difference between the concentration of two places.
• Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney
• A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.