When does a diffusion occur across a cell membrane
Diffusion occurs across a cell membrane when there is a concentration gradient of a substance. To understand when diffusion occurs, you need to consider the following factors:
1. Concentration gradient: Diffusion occurs when there is a difference in concentration of a substance on either side of the cell membrane. For example, if there is a higher concentration of a particular molecule outside the cell compared to inside, it will diffuse into the cell.
2. Permeability of the membrane: The cell membrane is selectively permeable, meaning it allows some substances to pass through while restricting others. Diffusion can occur if the substance is small enough and can pass freely through the membrane.
3. Lipid solubility: The lipid bilayer of the cell membrane is composed of fatty acid chains. Substances that are lipid soluble, such as oxygen and carbon dioxide, can diffuse through the membrane easily. However, substances that are not lipid soluble, like ions or polar molecules, require specific transport proteins or ion channels to facilitate their diffusion.
In summary, diffusion across a cell membrane occurs when there is a concentration gradient, the substance is small and lipid soluble, and the membrane is permeable to that substance.