Active transport in cells?

Question

Is active transport used only to remove substances from a cell, or can it also take in substances?

Thank you in advance :)

Answer 1

Active transport can both import and export materials across the phospholipid bilayer

Answer 2

The general answer is that active transport may transport material into or out of the cell.  Keep in mind that "active transport" is a general term that describes many different processes.  In cases of passive transport, material moves only from high concentration to low concentration.  Active transport expends energy in order to go "uphill"--transporting material from low to high concentration.  So, a transport process is labeled "active transport" if it uses energy and is capable of transporting from low to high concentration ("against a concentration gradient").  There are two kinds of transport.  One is diffusion, in which molecules randomly bounce their way through the cell membrane (consisting of a lipid bilayer plus proteins).  This diffusion is nonspecific and depends on the size of the molecule and its lipid solubility.  It is also passive, since its net direction is from high to low concentration.  The other is carrier-mediated, in which the molecule binds to a structure in the membrane, such as a protein.  This process is specific, since the membrane structure will only bind to certain molecules.  Some passive transport systems are carrier-mediated--their net direction is from high to low.  All active transport systems are carrier-mediated and so are specific.  Also, most active transport systems are only one way--either into or out of the cell.  For example, the Na+ pump transports sodium ions out of the cell.  Therefore we can say there are active transport systems that transport material into the cell only and other systems that transport other materials out of the cell.  The following is a chart that breaks this down:

 

TRANSPORT TYPE    SPECIFICITY               CARRIER OR               DIRECTION                  ENERGY

                                                              BINDING AGENT

Diffusion                non-specific                no carrier                   from high to low            none

 

Passive                    specific                     carrier                       from high to low            none used

Carrier

 

Active                      specific                     carrier or                   from low to high            uses

                                                              binder

 

We may find examples of any of these which may have a net direction from out to in or in to out of the cell.

Answer 3

Active transport can move a substance against a concentration gradient - in other words, from low concentration to high concentration.  Active transport requires the expenditure of energy, and is used to move substances both into and out of the cell.  For example, endocytosis is the active transport of substances into a cell via the movement of the cell membrane to form membrane vesicles.  An amoeba engulfing food, or a white blood cell engulfing a bacteria are examples of endocytosis into a cell. Active transport also occurs through transport proteins, which are protein channels or "doorways" in the cell membrane.  Again, energy is expended as the transport protein changes shape,  and the movement can be into or out of the cell.  

 

Good luck with your studies!

Kathleen

Answer 4

It is based on the concentration gradient and the biological/metabolic need of the cell in question. It can remove substances that cell may not need or are toxic to cell above threshold level. It definitely helps in the intake of glucose, ATP and other ions necessary for proper cell function.

 

Hope it helps.

 

Dr. Naina B.