Is endocytosis a type of active transport?

[Chap]

Is endocytosis a type of active transport? Shouldn't it be a type of an active process, but NOT active transport?

 

My argument is as follows:

Active transport by definition is; an energy consuming process that involves the movement of particles from a region of relatively low concentration to a region of relatively high concentration, AGAINST a concentration gradient.

 

Endocytosis on the other hand does not necessarily involve the movement of particles against a concentration gradient. Instead, endocytosis is used to ingest particles by a cell which are too large to pass through the plasma membrane. For example:

Consider a macrophage which has ingested two bacteria through endocytosis. Assume that the environment around the macrophage is concentrated with bacteria. Even in this scenario, the macrophage will continue to ingest more bacteria through endocytosis. The bacteria will be 'moving' DOWN a concentration gradient, not against it.

 

Therefore, if endocytosis is classified under active transport, it is wrong since active transport only involves movement against a concentration gradient.

 

P.S I only asked this question since a large number of websites classify endocytosis under active transport, even one .edu site! I would like to know the arguments of everybody on this matter. please.

[CharonY]

It is a matter of context and level of transport. The transport you think of is generally a transport across membranes (short distance transport) whereas vesicle based transport is a means of long-distance transport. From a physiological viewpoint both are transport processes, albeit in very different contexts.

[Chap]

Thanks for your reply. So I understand these are two different processes: active transport transports individual ions/molecules while endocytosis transports in bulk.

So endocytosis CANNOT be classified under active transport, right?

[CharonY]

I think it can, as a general term. But obviously not if you are talking about "active transport across membranes", which would be a more precise description to begin with.

Again, definitions such as these are highly context dependent. I would not put them into the same category, but the term "active or passive transport" is not precise enough, either. It is just a convenient distinction in a given context (and thus a convenient exam question), but quickly becomes imprecise when venturing out into other biological contexts.

For instance, does pumping blood qualify as active or passive transport? From the viewpoint of transport into cell the active part plays no role. It only does active circulation. But from the viewpoint of moving cells and other metabolites throughout the body it is.