Methods of transport By: Sean Jensen - 12M

Methods of transport By: Sean Jensen - 12M

1. Diffusion

   • Facillitated diffusion
     • Facilitated diffusion in many respects is similar to diffusion, it operates on the same principles of the net movement of particles from region of higher potential to a region of lower potential, it is also a passive process.
       • However, facilitated diffusion requires the presence of an intrinsic carrier protein
         • Each protein has a specific substance that it transports
           • The protein can be a channel protein or a carrier protein
             • Channel proteins tend to be selective, water filled pores allow for the transport of certain ions. Channel proteins can be gated, only opening in specific conditions
             • Carrier proteins can change shape when a particle binds to the protein, this allows the particle to move through
   • Diffusion is the net movement of particles from a region of higher potential to a region of lower potential, down the concentration gradient
     • This is a passive process, meaning it doesn't require an external form of energy, it only requires the energy derived from kinetic energy
     • Factors that affect the rate of diffusion
       • Temperature
         • Increased temperature increases the rate of reaction, this is because an increase in temperature leads to an increase in kinetic energy, this increases the randomness of the particles inside the substance and prompt them to be more likely to move
       • Surface area
         • A large surface area to volume ratio will increase rate of diffusion. This is because as the surface area to volume ratio increases, there is more area for the particles to interact and a lower volume ratio decreases the net diffusion distance
       • Diffusion distance
         • The greater the distance, the lesser the rate of reaction, this is because it takes more time to reach the centre of the object, requiring more time to diffuse
       • Difference in concentration
         • A greater difference in concentration means a faster rate of diffusion, this is because the particles will be more likely to want to stabilise particle weighting
       • Nature of the molecule
         • Larger molecules will diffuse slower due to the size they occupy, non-polar molecules also tend to diffuse faster with the exception of water due to its size

2. Active transport

   • Active transport, as the name suggests is a process that's active, meaning it requires external energy in the form of Adenosine Triphosphate (ATP), Active transport is described as the net movement of particles from a region of lower potential to a region of higher potential, against the concentration gradient. This process, like facilitated diffusion requires the presence of an intrinsic protein

3. Bulk transport

   • Bulk transport involves the movement of a large amount of particles in and out of cells, endocytosis and exocytosis respectively
     • Endocytosis involves the engulfing of substances by the cell surface membrane to form sacs/endocytotic vacuoles
       • Endocytosis is classified in two forms, Pinocytosis and Phagocytosis
         • Pinocytosis is the uptake of liquids, and Phagocytosis is the uptake of solids
       • Exocytosis involves the secretion of materials by the cell surface membrane