Movement across cell membranes

• Diffusion


  Molecules traveling from an area of high concentration to an area of low concentration across a semi permeable membrane
• Diffusion concentration gradient

  Down
• Does diffusion require energy?

  No, it's a passive process
• Selectively permeable membrane


  Only allows small molecules to diffuse through because larger molecules are too big for the pores.
• Cell membrane


  Site of diffusion. Semi permeable membrane
• Cell membrane replica


  Visking tubing as the pores are of similar size
• Solute molecules


  Too large
• Diffusion site in mammals


  Alveoli and cells
• What does diffusion supply?

  Important cells and substances for plants, animals and mammals.
• Osmosis


  The movement of water molecules from an area of high water concentration to an area of low water concentration across a semi permeable membrane
• Does osmosis require energy?

  No, it is also a passive process
• Equilibrium


  When water molecules move into and out of the cells at an equal rate. Happens in osmosis.
• Exam tips

  • Always use Molecules
  • Never use amount when describing variables. Mass or volume
• Independent variable - Change

  Dependent variable _ Measure

  Controlled variable - Keep
• Higher temperature


  Rate of reaction increases
• How does a membrane maintain mass?

  Through equalibrium
• Active transport


  The movement of molecules from an area of low concentration to an area of high concentration using ATP.
• Difference between Diffusion/Osmosis and active transport

  Diffusion/Osmosis - Down a concentration gradient. Area of high to low concentration. Passive process

  Active transport - Against a concentration gradient. Area of low to high concentration. Requires energy (ATP)
• How is active transport carried out

  Through proteins in the cell membrane
• Active transport steps

  1. Molecule binds with protein on low concentration side
  2. Protein uses ATP to rotate and transfer the molecule to the high concentration side
  3. ATP is made in aerobic respiration
• What does active transport gain?

  Substances from dilute solutions
• What must a cell have to carry out active transport?

  Mitochondria
• If respiration stops...


  Active transport stops because there is no energy.