Question

How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?

Answer 1

Hint: Neutral solutes in a plant can move across the plasma membrane through the help of passive diffusion or osmosis. On the other hand there are polar molecules which cannot pass through the non-polar membrane.

Complete answer:
> Movement of Neutral solutes across the plasma membrane-
Neutral molecules move across the plasma membrane by simple passive diffusion. Diffusion is the movement of molecules from a region of higher level concentration to a region of lower level concentration.

> Movement of polar molecules across the cell membrane – The cell membrane is formed up of a phospholipid bilayer as well as proteins. The movement of polar molecules across the non-polar lipid bilayer needs carrier-proteins. Which are considered as integral protein particles which have certain affinity for specific solutes. As a result, they facilitate the transportation of molecules across the membrane.

There are two key ways that polar molecules can be moved across a membrane that is passive as well as active.
- Passive diffusion: Passive diffusion is a simple diffusion which allows small, non-polar molecules to move down their gradient. This can be destroyed if the diffusion distance increases. Passive facilitated diffusion is found along the transport channels.

- Active diffusion - Active diffusion transport requires energy from the cell. It usually transports molecules against the gradient. The Transportation that uses ATP hydrolysis as the energy source for transportation process is considered as primary active transport.

Note: The cell membrane is a phospholipid bilayer which is embedded in proteins and regulates the transport of molecules across to maintain homeostasis of the cell environment. The lipid soluble or a nonpolar molecule can easily pass through the cell membrane, but hydrophilic or polar molecules cannot pass easily.