Diffusion and Facilitated diffusion

What is the definition of diffusion?

• Net movement of molecules from an area of high concentration to an area of low concentration

What is facilitated diffusion?

• Movement of molecules from an area of high concentration to an area of low concentration, across a partially permeable membrane via protein channels or carrier proteins

What is another factor that affects facilitated diffusion?

• The number of available proteins to diffuse substances through the cell surface membrane

What are examples of molecules that move through the cell surface membrane using facilitated diffusion through a channel protein?

• K+

• Na+

• H2O(aquaporins)

What are examples of molecules that move through the cell surface membrane using facilitated diffusion through a carrier protein?

• Glucose

• Amino Acids

Does a carrier protein need energy to undergo facilitated diffusion?

• No, it does not need any energy to change shape during facilitated diffusion

What type of molecules are able to pass through cell membranes by simple diffusion?

• Small molecules

• non-polar molecules

• Fat-soluble molecules such as hormones

Why can fat-soluble molecules undergo simple diffusion through cell membranes?

• Because They can dissolve into the phospholipid bilayer and move down the concentration gradient

How is diffusion through cell membranes different in water?

• It is different because water is polar molecule which means that it cant under go simple diffusion through the phospholipid bi layer

• However, due to such a high conc of water, direct diffusion can happen

What is the name of the channel protein which allows for the movement of only water across the membrane

• There is sometimes a specific water channel known as aquaporins which allow water molecules to cross the membrane without the challenge of moving through the phospholipid bilayer

how is the concentration gradient maintained in cells and organelles

• It is maintained by the fact that many of the molecules which pass through into the membrane are used for metabolic reaction which means that the conc of that molecule then decreases again due to the reaction taking place

What are the 5 factors which affect rate of simple diffusion?

• Temperature

• Distance

• Surface area

• Size of molecule

• Concentration gradient

How does temperature affect rate of simple diffusion?

• When temperature increases, the kinetic energy of molecules increases, and so the movement of the molecules will increase and therefore the rate of diffusion will increase

How does Distance affect rate of simple diffusion?

• The longer the diffusion distance

  which molecules have to diffuse across, the slower the rate of diffusion

How does Surface area affect rate of simple diffusion?

• If a tissue has a large surface area that means that there is more space for molecules to diffuse through the membrane which therefore increases the rate of diffusion

How does the Size of molecules affect rate of simple diffusion?

• The larger the molecules, the harder it will be for the molecules to pass through the membrane therefore decreasing the rate of diffusion

How does the concentration gradient affect rate of simple diffusion?

• The steeper the concentration gradient, the faster the rate of diffusion to the side which there are fewer molecules

What are 2 examples of when membranes control what goes in and out of cell membranes and why are they important in both?

• neurone plasma membranes have channels which are specific to either sodium or potassium ions. The diffusion of these ions is important for the conduction of nerve impulses

• The plasma membrane of epithelial cells that line your airways have chloride ion channels, and these play crucial role in regulating the composition of mucus to trap particles and pathogens