The matter is made up of small particles known as atoms and molecules which are believed to be in constant motion. Scientific researchers have identified several means by which these molecules move from one point to another especially in living things and they include osmosis, absorption, and diffusion (King & Reiss, 2001). The essay discusses diffusion as one of the most common means of transport across the cell membrane.
Diffusion is one of the most important processes in biological sciences by which molecules move across the cell membrane due to the presence of a diffusion gradient (Starr & Taggart, 2006). Diffusion gradient refers to the relative difference between the concentrations of molecules across the cell membrane. By implication, molecules will always move from areas of a higher concentration to areas of lower concentration to attain equilibrium. This process, just like osmosis, is a type of passive transport since there is no energy used for the molecules to move across the cell membrane (King & Reiss, 2001).
For instance in the mammalian lungs, due to the difference in concentration of oxygen and carbon dioxide gases, there will be constant movement of the gases in and out of the lung alveolus (Starr & Taggart, 2006). Carbon dioxide concentration is higher in the lung bloodstreams and will diffuse out while oxygen will diffuse into the lung blood capillaries where concentration is lower through the lung alveoli. This process facilitates the constant exchange of gases across the lung membrane which is highly adapted through the large surface area.
References
King, T. & Reiss, M. (2001). Practical advanced biology (2nd ed). Nelson Thornes.
Starr, C. & Taggart, R. (2006). Biology: the unity and diversity of life (11th ed). Cengage Learning.