Question

Which process can involve active transport?

A. carbon dioxide intake through stomata.
B. mineral ion intake through root hairs.
C. mineral ion transport through xylem vessels.
E. water leaving mesophyll cells.

Answer 1

Active transport requires energy to move substances from a low concentration of that substance to a high concentration of that substance, in contrast with the process of osmosis. Active transport is most commonly accomplished by a transport protein that undergoes a change in shape when it binds with the cell’s “fuel,” a molecule called adenosine triphosphate (ATP).

For example, one type of active transport channel in the cell membrane will bind to the molecule it is supposed to transport – such as a sodium ion – and hold onto it until a molecule of ATP comes along and binds to the protein. The energy stored in ATP then allows the channel to change shape, spitting the sodium ion out on the opposite side of the cell membrane. This type of active transport directly uses ATP and is called “primary” active transport.

Another type of active transport is “secondary” active transport. In this type of active transport, the protein pump does not use ATP itself, but the cell must utilize ATP in order to keep it functioning. This will be explained in more depth in the section on Symport Pumps below.

Lastly, active transport can be accomplished through processes called endocytosis and exocytosis. In exocytosis, a cell moves something outside of itself in large quantities by wrapping it in a membrane called a vesicle and “spitting out” the vesicle. In endocytosis, a cell “eats” something by wrapping and re-forming its membrane around the substance or item.