Cellular Respiration & Osmosis
- Molecules tend to diffuse into available space, with the movement of the molecules running from a more concentrated environment to a less concentrated environment. Diffusion is spontaneous and happens without the expenditure of energy.
- Osmosis is a particular type of diffusion. In osmosis, water molecules move across a semi-permeable membrane from low solute concentration solutions (hypotonic solution) to high solute concentration solutions (hypertonic solutions.)
- Cellular respiration is the catabolic process through which cells convert the organic molecules from food into adenosine triphosphate (ATP.) ATP is an energy-yielding molecule that is the major carrier of chemical energy in cells.
- Cell membranes possess channels that pump hydrogen ions (protons) across the membranes. When proton concentrations outside a cell membrane rise higher than the concentrations inside the membrane, the protons diffuse back across the membrane. In 1961, Peter D. Mitchell published a research study on cellular respiration in which he compared the diffusion of ions across cell membranes with osmosis. He called the process chemiosmosis.
- The formation of ATP from adenosine diphosphate (ADP) and a phosphate molecule is an endergonic reaction, that is, one requiring the input of energy. During chemiosmosis, protons move across a cellular membrane via the enzyme ATP synthase (a transport protein.) The subsequent chemical changes release energy, which is used to convert ADP to ATP.
