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A Handbook of Biology

Types of Transport

a) Passive Transport: It is the movement of molecules across the membrane

along the concentration gradient (i.e., from higher concentration to the

lower) without the expenditure of energy. It is of 2 types:

Simple diffusion: It

is the movement of

neutral solutes across

the membrane.

Osmosis: It is the

movement of water

by diffusion across

the membrane.

Polar molecules cannot

pass through the non-polar

lipid bilayer. So they require

membrane carrier protein for

transport.

b) Active transport: It is the movement of molecules across the membrane

against the concentration gradient (i.e. from lower to the higher

concentration). Such a transport is an energy dependent process in

which ATP is utilized, Eg. Sodium/potassium pump.

2.

Cell Wall

It is a non-living rigid structure

found outer to the plasma

membrane of fungi and plants

Cell wall of algae is made of

cellulose, galactans, mannans and

minerals like CaCO3. In other plants,

it consists of cellulose, hemicellulose,

pectins and proteins

Cell wall of a young

plant cell (primary

wall) is capable of

growth. It gradually

diminishes as the

cell matures and

the secondary wall

is formed on the

inner side (towards

membrane).