What are porins? What role do they play in diffusion?

Porins are types of proteins which form pores of large sizes in the outer membranes of plastids such as chloroplast, mitochondria and the membranes in bacteria. They help in facilitating the passive transport of small-sized protein molecules.

Carrier proteins form porin channels in the outer membranes of plastids, mitochondria and some bacteria. The porin channels allow the molecules up to the size of small proteins to pass through molecule bound to the transport protein and thus allow facilitated diffusion. 

The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules up to the size of small proteins to pass through. Thus porins facilitate diffusion. 

The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules up to the size of small proteins to pass through. Thus porins facilitate diffusion.