Biology Forums - Study Force

My biology notes say that one of the differences between phagocytosis and pinocytosis is that pinocytosis makes an indent in the cell membrane and phagocytosis is an outstretching of the cell membrane.
I tried researching this on the internet but failed to find any answers.

Could someone please clarify this for me? Is there actually a difference between how each one affects the cell membrane?

Sure thing -- there is a huge difference between pinocytosis and phagocytosis.

Pinocytosis occurs by creating a "pit" in the surface of a cell, just like you were reading. An indent. That pit eventually pulls more and more toward the inside of the cell until a certain protein comes along and "pinches" the pit off, forming a vesicle that is now inside the cell and can travel to where it needs to go. Pinocytosis is mostly a non-specific process in that it literally engulfs an area of extracellular "stuff" and brings it inside the cell.

Phagocytosis is a very specific ingestion of a particle. It is usually mediated by signals that occur between the cell membrane and the particle that will be ingested (be it a bacterium, part of a dead cell, or other biological debris). You are right in that phagocytosis literally outstretches or "crawls" along the particle to be ingested, eventually enclosing the particle in a vesicle called a phagosome.

So yeah, huge differences between the two. Pinocytosis works by forming a pit and then closing the pit off. Imagine using a plastic bag to catch a fish in water. You'd catch the fish along with the water that the fish was swimming in.

Phagocytosis works by slowly crawling up and along the particle to be digested and engulfing it. It's also important to know that phagocytosis does its best to exclude all fluid and other molecules aside from the particle its ingesting. Imagine putting a sock on. The sock is snug against your feet and ankles.

Hope that helps!