What is the difference between osmosis , active transport and passive transport ? Can you please help me with this .↑
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The Difference Between Osmosis and Active Transport
• Categorized under Science | The Difference Between Osmosis and Active Transport
A cell has many requirements in order to grow and replicate, and even cells that aren’t actively growing or replicating require nutrients from the environment to function. Many of the cell’s requirements are molecules that can be found outside the cell, including water, sugars, vitamins and proteins.
The cell membrane has important protective and structural functions, and it acts to keep cellular contents separate from the exterior environment. The lipid of the cell membrane is composed of , which have hydrophobic (oil soluble, “water-fearing”) tails that form a barrier to many solutes and molecules in the environment. This feature of the cell membrane allows the cell internal environment to differ from the external environment, but also acts as a major barrier to taking up certain molecules from the environment and expelling waste.
The lipid does not pose a problem for all molecules, however. Hydrophobic (or oil soluble), molecules can freely diffuse through the cell membrane unimpeded. This class of molecules includes gases such as oxygen ), carbon dioxide , and nitric oxide (NO). Larger hydrophobic organic molecules can also pass through the plasma membrane, including certain hormones (such as estrogen) and vitamins (such as vitamin D). Small, polar molecules (including water) are partially hindered by the lipid but can still pass through.
For molecules that can freely pass through the cell’s membrane, whether they travel into or out of the cell depends on their concentration. The tendency of molecules to move according to their concentration gradient (that is from higher concentration to lower concentration) is called diffusion. This means that molecules will flow out of the cell if there are more inside the cell than outside. Likewise, if there are more outside the cell, molecules will flow into the cell until a balance is met. For example, consider a muscle cell. During exercise, the cell converts to . As oxygenated blood enters the muscle, travels from where the concentration is higher (in the blood) to where it is lower (in the muscle cells). At the same time, travels out of the muscle cells (where it is higher) to the blood (where it is lower). Diffusion does not require energy expenditure. The diffusion of water is given a special name, osmosis.
For larger polar molecules and any charged molecules, entering and leaving the cell is more difficult as they cannot pass through the lipid . This class of molecules includes ions, sugars, amino acids (the building blocks of proteins) and many more things the cell needs to survive and function. To fix this problem, the cell has transport proteins that allow these molecules to move into and out of the cell. These transport proteins make up 15–30% of the proteins in the cell membrane.
Transport proteins come in several shapes and sizes, but all extend through the lipid , and each transport protein has a specific type of molecule that it transports. There are carrier proteins (which are also known as transporters or ), which bind to a solute or molecule on one side of the membrane and transport it to the other side of the membrane. A second class of transport proteins includes channel proteins. Channel proteins form hydrophilic (“water loving”) openings in the membrane to allow polar or charged molecules to flow through. Both channel proteins and carrier proteins facilitate transport both into and out of the cell.
Molecules can travel through transport proteins from high concentration to lower concentration. This process is called passive transport or facilitated diffusion. It is similar to diffusion of molecules or water directly through the lipid , except that it requires transport proteins.
Cells also use active transport to maintain the proper concentration of ions. Ion concentration is very important for the cell’s electrical properties, controlling the amount of water in cells and other important functions of ions. For example, Magnesium ions are very important for many proteins involved in DNA repair and maintenance. Calcium is also important in many cell processes, and active transport helps maintain a calcium gradient of 1:10,000. Transport of ions across the lipid depends not only on the concentration gradient, but also on the electrical properties of the membrane, where like charges repel. The sodium-potassium ATPase or Na+-K+ pump maintains a higher concentration of sodium outside of the cell. Almost one third of the cell’s energy requirement is consumed in this endeavor. This huge energy expenditure for the active transport of ions corroborates the importance of maintaining a balance of molecules in proper cell function.
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