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
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
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