Science Biology
Two of the main ways in which diffused substances are transported across cells are
osmosis
and
diffusion . Diffusion is the movement of a fluid across a concentration gradient useful to
the cells; osmosis is the movement of
water across a semi-permeable membrane . However,
sometimes substances need to be transported
against a concentration gradient or
membrane, which is when
active transport takes place.
By active transport, cells are able to move substances from
an area of low concentration to
an area of high concentration
. This is what is meant by moving against the gradient. Because
the substances are being transported against a gradient,
energy is required for an active
transport system
to carry a molecule across the membrane and then return to its original
position (see below diagram).
The energy required for active transport to take place comes from
cellular respiration. The
rate of active transport
and rate of respiration in cells are closely linked. The process of
respiration releases energy – so in other words, the more respiration happening, the more
active transport is tak
- Created by: Ashley Batchelor
- Created on: 20-11-12 09:09
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