Transport Across Cell Membrane (Powerpoint)
Transcript Transport Across Cell Membrane (Powerpoint)
Molecules in a solution or a gas move about
randomly and collide. This random
movement is called Brownian motion.
When the molecules of a solute move from
a high concentration area to a low
concentration area this is called diffusion.
Diffusion is affected by concentration,
temperature, and pressure
The increase in any of the above factors
will result in the increase of the rate of
Osmosis is the diffusion of water
molecules through a selectively permeable
The cells are bathed in isotonic solution in
which the solute concentration outside the
cell is equal to that inside of the cell
One of the blood’s major functions is to
keep the internal body environment in a
state of isotonic balance, this is called
A hypotonic solution is a solution that has
a lower concentration of solute, it results
in the swelling of cells
This is done through carrier protein
molecules located in the cell
membrane, without the expenditure of
How this is done, is not well
understood, however scientists believe
that the protein carrier speeds the
passage of molecules already moving
across the cell membrane
The use of the cells’ own energy is called
About 30 – 40 % of the total body energy
is used for active transport
Active transport includes exocytosis (for
large molecules to be transported outside
the cell) and endocytosis, which is further
classified into pinocytosis (for dissolved
molecules) and phagocytosis (for solid
The Importance of Cell surface to Volume Ratio
The rate at which these substances cross this membrane depends of the surface
area. The surface area to volume ratio of a cell is therefore very important.
1×1×1 cm cube has a surface area of 6×1×1 cm, or 6 cm² with a volume of 1 cm³.
2×2×2 cm cube has a surface area of 6×2×2 cm, or 24 cm² with a volume of 8 cm³.
So, the volume has increased by 8 times (1 to 8) but the surface area has increased by
just four times (6 to 24).