Which of the following is the "regulated membrane transfer"?: (A) Insulin secretion by pancreatic b-cell, (B) O2 diffusion across the respiratory membrane, (C) Folate entry into the cells, (D) Mucus secretion by goblet cells
Answer is A. Regulated membrane transfer is the transpo across/through the membrane which is regulated by a specific signal or ligand. Exocytosis is a regulated membrane transfer. E.g. Neurotransmitter secretion at a synaptic junction. The transmitter is released only when the signal/impulse arrives at the nerve terminal. Insulin secretion, by exocytosis, occurs when a signal, i.e. increased blood glucose, is delivered to the pancreatic beta cell. Options (B), (C), and (D) do not occur after a specific signalling ligand has arrived at those respective cells.