Recall that membranes have two major components: phospholipids i ordered it in a bilayer, and also membrane proteins.


Click below for a an ext elaborate picture of a cabinet membrane.

One of the features of membranes is to manage what passes into and also out the the cell. In this module you will evaluation mechanisms of membrane transport.

You are watching: How does facilitated diffusion differ from diffusion

There are numerous different species of membrane transport, depending on the attributes of the substance gift transported and the direction the transport.


In basic diffusion, tiny noncharged molecules or lipid dissolve molecules pass in between the phospholipids to go into or leave the cell, moving from areas of high concentration to areas of short concentration (they movedown your concentration gradient). Oxygen and carbon dioxide and also most lipids enter and also leave cells by basic diffusion.

Illustrations of an easy diffusion.

Note the the arrows show that the problem is relocating from whereby there is much more of the substance to where there is much less of it, and that the substances space passing between the phospholipids the the membrane.


Osmosis is a type of basic diffusion in i m sorry water molecule diffuse v a selectively permeable membrane from areas of high water concentration to locations of reduced water concentration. (Note the the an ext particles liquified in a solution, the much less water over there is in it, therefore osmosis is sometimes explained as the diffusion of water from locations of low solute concentration to locations of high solute concentration).

Illustration the Osmosis. Assume the the membrane is permeable come water, yet not to sucrose (represented by the small black squares). The sucrose molecules will not leaving the cell due to the fact that they cannot pass v the membrane. However, due to the fact that there is much less water top top the side with the sucrose, water will go into the cabinet by osmosis.

Another method to define the two services in the example of over is to use the terms hypertonic and also hypotonic. A hypertonic equipment has more solutes and less water than a hypotonic solution. So, in the instance above, the solution inside the cabinet is hypertonic come the solution external the cell. During osmosis, water move from the hypotonic systems (more water, much less solutes) come the hypertonic systems (less water, more solutes).

In every of the examples displayed below, i beg your pardon of the options is hypertonic?




In facilitated diffusion, building materials move right into or the end of cells down their concentration gradient v protein networks in the cabinet membrane. Basic diffusion and also facilitated diffusion are similar in the both involve movement down the concentration gradient. The difference is how the problem gets v the cabinet membrane. In basic diffusion, the problem passes between the phospholipids; in facilitated diffusion there room a specialized membrane channels. Charged or polar molecules that cannot fit between the phospholipids usually enter and also leave cells through assisted in diffusion.

Illustrations of helped with diffusion.

Note that the problem is moving down that concentration gradient v a membrane protein (not between the phospholipids)



The types of membrane transport disputed so far always involve substances moving down your concentration gradient. The is also feasible to move substances throughout membranes against their concentration gradient (from locations of low concentration to areas of high concentration). Because this is an energetically unfavorable reaction, power is necessary for this movement. The source of energy is the malfunction of ATP. If the power of ATP is directly used come pump molecules versus their concentration gradient, the carry is dubbed primary energetic transport.

Illustration that primary energetic transport.

Note the the substance (indicated by the triangles) is gift transported indigenous the next of the membrane with tiny of the substance to the side of the membrane with a many the substance with a membrane protein, and also that ATP is being damaged down come ADP.


In part cases, the usage of ATP might be indirect. For example, if a cell supplies ATP come pump the end Na+ and then supplies the Na+ concentration gradient to carry in glucose, the transport of glucose would be an example of secondary active transport.

On the left next of the photo below, a substance (represented by one X) is gift transported from the inside of the cabinet to the outside also though over there is an ext of the substance top top the outside (indicated by the letter X being larger on the outside of the cell. This is primary active transport.

In the snapshot on the right side, problem S, already at higher concentration in the cell, is brought into the cell v substance X. Since S is being transported there is no the straight use that ATP, the transport of S is an example of an additional active transport. For substance X primary active transport that X is occurring. The high concentration the X outside the cell is being supplied to carry in problem S against its concentration gradient.



It is possible for huge molecules to go into a cell by a process called endocytosis, whereby a small piece that the cabinet membrane wraps about the particle and is brought into the cell. If the fragment is solid, endocytosis is additionally called phagocytosis. If fluid droplets space taken in, the processes is called pinocytosis.

Illustration the endocytosis. Note the the particle gotten in the cell surrounding by a piece of cell membrane.

The the opposite of endocytosis is exocytosis. Cells usage exocytosis to secrete molecules too huge to pass v the cell membrane by any kind of other mechanism.

Other Links and animations:


For an computer animation of active transport, endocytosis, exocytosis, see:


For much more information on an additional active transport, inspect out: http://www.lib.mcg.edu/edu/eshuphysio/program/section1/1ch2/s1ch2_36.htm

DICHOTOMOUS an essential FOR cabinet TRANSPORT



Click top top the button above to open a problem solver to help you practice your understanding of membrane transport through the following examples:

1. A white blood cabinet engulfs a bacterium as you fight off an infection.

2. Carbon dioxide (a small uncharged gas molecule) beginning the lungs (where that is less concentrated) indigenous the blood (where the is more concentrated).

3. Cell of the stomach wall transport hydrogen ions with a ATP-dependent membrane protein to the inside of the stomach, developing a pH the 1.5.

The pH the the cytosol (fluid within the cells) the stomach wall cells is roughly 7. (Recall the a low pH method high hydrogen ion concentrations).

4. The lung cell of a victim that drowned in fresh water space swollen as result of water start the cells.

5. Salient gland cells create the enzyme outstanding amylase and also secrete it right into the outstanding ducts come be ceded to the mouth.

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6. A Paramecium (a solitary celled organism) swims into an area of salty water.. The Paramecium shrivels up as it loses water with its cabinet membrane.

7. Some bacteria usage the energy of ATP to pump H+ the end of their cells. They usage the H+ concentration gradient to drive the transport of sugars right into the cabinet

versus their concentration gradients. What mechanism of transport ideal describes how the sugars are entering bacter cells?

8. Part cells engulf droplets that extracellular fluid. What mechanism of move would this be?