The movement of materials in biological systems takes place through various processes that include osmosis, diffusion, facilitated transport, and active transport. Osmosis involves movement of molecules from regions of low concentration to regions of high concentration while diffusion involves movement of molecules from high-concentration regions to low-concentration regions.
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Facilitated transport is the movement of molecules across a biological membrane through the aid of transport proteins while active transport is the movement of molecules from high-concentration regions to low-concentration region. The two processes differ because active transport involves the use of chemical energy while facilitated transport does not. These processes have several similarities and differences, which make them effective for the transport of different types of materials in biological systems.
Osmosis and diffusion
Osmosis refers to the process through which a solvent’s molecules move through a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration (Dubitzky, Southgate, & Fub, 2011). It is a critical biological process that facilitates the movement of molecules across semi-permeable membranes. The major aspects of molecule movement that differentiate osmosis from other transport methods include osmotic pressure, concentration gradient, and solute potential.
In diffusion, molecules move from a high concentration gradient to a low concentration gradient while in osmosis, molecules move down a concentration gradient (Truskey, Yuan, & Katz, 2009). Diffusion refers to the movement of molecules from a region of higher concentration to a region of lower concentration, and unlike osmosis, does not involve a semi-permeable membrane (Dubitzky et al., 2011).
Diffusion is not affected by solute potential while osmosis is highly dependent on solute potential. It usually occurs in the gaseous state but can also take place in the solid and liquid states. On the other hand, osmosis occurs when the concentrations of two solutes are different, and it is applicable to the solvent parts of the solutions only. Unlike other means of transport, osmosis can only take place in the presence of water and involves the movement of the solvent only (Truskey et al., 2009). In contrast, diffusion involves the movement of all types of substances and can take place in any medium.
Facilitated transport and active transport
Facilitated transport refers to the movement of materials across a biological membrane through the aid of transport proteins (Dubitzky et al., 2011). This process does not require chemical energy, and like osmosis, takes place down a concentration gradient. It differs from diffusion because movement of substances depends on the successful binding of molecules to transmembrane integral proteins (Truskey et al., 2009).
The existence of a concentration gradient means that substances move without using energy. However, their molecules are polar. Therefore, they are repelled by the cell membrane, hence the need for transport proteins. Transport proteins facilitate diffusion by eliminating the repulsion of polar molecules by the hydrophobic parts of the cell membrane (Dubitzky et al., 2011).
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Active transport refers to the movement of molecules from a region of lower concentration to a region of higher concentration through the aid of chemical energy (Truskey et al., 2009). Unlike other transport processes, active transport utilizes energy because molecules move against a concentration gradient. It is similar to facilitated transport because it uses carrier proteins that enhance movement of molecules. Like osmosis, it involves movement of molecules from a lower to a higher concentration gradient. However, it differs from osmosis and diffusion because it uses chemical energy (Truskey et al., 2009).
Dubitzky, W., Southgate, J. & Fub, H. (2011). Understanding the Dynamics of Biological.
Systems: Lessons: Learned from Integrative Systems Biology. New York, NY: Springer Science & Business Media.
Truskey, G. A., Yuan, F., & Katz, D. F. (2009). Transport Phenomena in Biological Systems. New York, NY: Prentice Hall.