Transport in Plants
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Temperature and pressure
Size (density) of the substances. Smaller substances diffuse faster.
Substances soluble in lipids diffuse through the membrane faster.
2. FÅÇÏLÏTÅTËD DÏFFÜSÏØÑ
It is the diffusion of hydrophilic substances with the help of membrane
protein channels and without expenditure of ATP energy.
It also needs a
concentration gradient.
It is very specific. Cell
selects substances for
uptake. It is sensitive to
inhibitors that react with
protein side chains.
Porins form huge pores in the
outer membranes of plastids,
mitochondria & some
bacteria. Molecules having
size of small proteins can
pass through them.
An extracellular molecule
binds to the transport
protein. Then, it rotates and
releases the molecule inside
the cell. E.g. water channels
– made up of 8 types of
aquaporins.
Transport rate reaches a maximum when all the protein transporters are
being used (saturation).
Some protein channels are always open; others can be controlled. Some
are large sized. E.g. Porins.
PÅSSÏVË ÜÑÏPØRTS, SÝMPØRTS ÅÑD ÅÑTÏPØRTS
Uniport: A molecule alone moves across a membrane independent of
other molecules.
Symport: Two molecules together cross the membrane in same
direction.
Antiport: Two molecules move in opposite directions.
ÅÇTÏVË TRÅÑSPØRT
It is the transport of molecules against a concentration gradient (from
lower concentrated region to higher concentrated region) with the
expenditure of energy.
It is carried out by membrane-proteins. Pumps are proteins that use
energy to transport substances across cell membrane (‘uphill’ transport).
(AIPMT 2009)