Membrane
The membrane has a double lipid layer through which fat- soluble
substances will
move, by passive transport or diffusion. The molecules will
only move through if
they are small enough. There are globular protein
regions, which are
hydrophilic. These regions allow water and water soluble
substances through, but
only if they are small enough, for example starch
grains are too big. These
substances move through by passive transport or
diffusion. Diffusion is the
passive movement of substances from a high
concentration to a low concentration
( N.B., you don't need a membrane
present, e.g. diffusion occurs in the air). In
CONTRAST, diffusion of
water across a semi- permeable membrane is called
OSMOSIS. Active
Transport Active transport requires energy from ATP, and
involves carrier
molecules studding the membranes. The carrier combines with the
molecule on
the outside, which requires ATP. It then moves across, (which also
requires
ATP), and returns. An example is glucose being transported by
active
transport by insulin. Why is it called the Fluid Mosaic Model? Fluid-
it is
called a fluid because proteins are said to wander through the membrane
(hence
fluid) Mosaic- it is a mosaic because it is a collection (or mosaic)
of
structures Model- because no matter how real the diagram looks, it is not
real.