Small lipid soluble molecules would move through the plasma membrane by
A.
Diffusion
B.
Filtration
C.
Osmosis
D.
Active transport
The Correct Answer and Explanation is:
The correct answer is A. Diffusion.
Explanation:
Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. It is a passive transport mechanism, meaning it does not require energy. Small, lipid-soluble molecules, such as oxygen (O₂), carbon dioxide (CO₂), and certain steroid hormones, are able to diffuse directly through the plasma membrane because of their solubility in lipids.
The plasma membrane is primarily composed of a lipid bilayer, made up of phospholipids with hydrophobic (water-fearing) tails and hydrophilic (water-attracting) heads. Because the interior of this bilayer is hydrophobic, lipid-soluble molecules can easily pass through it without assistance from transport proteins or energy input. These molecules move along their concentration gradient, traveling from areas of high concentration (e.g., oxygen in the lungs) to areas of low concentration (e.g., oxygen in tissues).
In contrast, other transport mechanisms are used for molecules that are not lipid-soluble or are too large to pass through the lipid bilayer. Filtration involves the movement of water and solutes through a membrane due to hydrostatic pressure, but it is not specific to lipid-soluble molecules. Osmosis refers to the movement of water across a membrane, not solutes, so it is not applicable to lipid-soluble molecules. Active transport is a process that requires energy in the form of ATP to move molecules against their concentration gradient, but it is not necessary for lipid-soluble molecules, as they can passively diffuse through the membrane.
In summary, small lipid-soluble molecules move across the plasma membrane via diffusion, a passive, energy-free process that takes advantage of the lipid nature of both the molecule and the membrane.