Facilitated diffusion:

It is difficult for substances that have hydrophilic moiety to pass through membrane so their movement has to be facilitated by protein present on membrane. Such process is called facilitated diffusion. It is a passive process

• Cell selects substances for uptake, so it is a specific process.
• Substances are pass through channels formed by proteins.

Channels vary in size and some are open while some can be controlled.

 :-  Proteins that form huge pores in the outer membrane of plastids, mitochondria and some bacteria through which proteins can pass.

Aquaporins: Porins that form water channels.

Passive symport and antiports:

Symport: Both molecules cross membrane in some direction.

Antiport: Both molecules move in opposite direction.

Uniport: When molecules move along membrane independent of other molecules.