What is mandatory in the process of facilitated diffusion?
a)	Presence of concentration gradient	b)	A carrier protein
c)	A hydrophilic moeity	d)	All of the above

(d)

Movement of hydrophilic moiety substance is facilitated by aquaporin and ion channels, which is the constituent of cell membranes. They plays a role in passive transport of water soluble substances and do not set up a concentration gradient. Hence, diffusion of hydrolphilic substances along the concentration gradient through transporter carrier protein, with no energy involvement is termed as facilitated diffusion