INTRODUCTION
The cell membrane is selectively permeable. It allow certain molecules into the cell. It can be more or less permeable to different type of molecules. These molecules diffuse passively across the membrane. Passive transport differ from active transport because it does not involve any chemical energy. Passive transport is the movement of biochemical and other atomic or molecular substances across cell membranes without need of energy input. There are 3 main type of Passive Transport; Diffusion, Facilitated Diffusion, Osmosis Diffusion is the movement of molecules or atoms from a region of high concentration to a region of low concentration. Facilitated Diffusion also called facilitated transport or passive-mediated transport is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins. Osmosis, is the movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentration on the two sides.
ABOUT PICTURE
The picture represents on how the molecules transport across the cellular membrane from to a region of higher concentration to a region of lower concentration. It shows how it imports molecules with the two out of three passive transport, Diffusion and Facilitated Diffusion. They both don’t require chemical energy and the molecules move down their concentration gradient (plus a channel or carrier protein for facilitated diffusion). It also show the difference between the two. Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. Facilitated diffusion is the movement of a substance using a transport molecule from high concentration to low concentration.
Diffusion is through the phospholipid layer and tends to transport small, non-polar molecules. It contains water, gases (O2 and H20) and steroid hormones. Facilitated Diffusion is through the transport protein and tends to transport large, polar molecules. It contains water, glucose, and amino acid. The glucose and amino acid enter the cell by a protein carrier. Diffusion and facilitated diffusion move substances down a concentration gradient and does not require the use of ATP. |
SUMMARY
The most important and repeated sentence is that passive transport does NOT require energy, active energy does. Passive transport is the diffusion of substances across membrane. Molecules will move from where the substance is more concentrated to where it is less concentrated. There are different types of easy movements of molecules. There are molecules that move freely like osmosis or diffusion. Diffusion is the when molecules move from a higher to lower concentration. It doesn’t need energy to move its molecule and doesn’t need proteins to carry any of its molecules.
The proteins in cell membranes act like channels to help transportation. There is a semi-permeable membrane which is in between transport where very small molecules are able to cross. In the cell membrane, proteins help move molecules move quickly which is called facilitated diffusion. It is as simple as transporting glucose into the membrane. The cell notices fluid rushing by with free glucose molecules. Then the protein grabs one glucose molecule and shift its position to bring molecules into cell. The glucose moved from a higher to lower concentration and it’s moving down a concentration gradient. A big example of passive transport is osmosis. It is a water specific process. It is the movement of water across the cell membrane. The cell pumps ions in and out of the cell keeping it balanced to stay alive. The ion concentration has to be equal on both sides because if it is not balanced the cell can end up swelling then explode.
The proteins in cell membranes act like channels to help transportation. There is a semi-permeable membrane which is in between transport where very small molecules are able to cross. In the cell membrane, proteins help move molecules move quickly which is called facilitated diffusion. It is as simple as transporting glucose into the membrane. The cell notices fluid rushing by with free glucose molecules. Then the protein grabs one glucose molecule and shift its position to bring molecules into cell. The glucose moved from a higher to lower concentration and it’s moving down a concentration gradient. A big example of passive transport is osmosis. It is a water specific process. It is the movement of water across the cell membrane. The cell pumps ions in and out of the cell keeping it balanced to stay alive. The ion concentration has to be equal on both sides because if it is not balanced the cell can end up swelling then explode.