Question

What information must be considered to determine whether a specific molecule will pass through a biological membrane?

Answer 1

The cell membrane is selectively permeable, meaning that only certain things like small unchanged molecules and ions are able to diffuse across, can pass through the membrane whilst other molecules require a transport protein as seen in passive transport, active transport and facilitated diffusion.

Answer 2

Size, polarity, and direction of concentration gradient

Step-by-step explanation:

A biological membrane is a semipermeable lipid bilayer.

Size

Only small, nonpolar molecules can move through the lipid bilayer. Oxygen, and carbon dioxide are examples. Even though they are polar, water and ethanol are also small enough to pass through the membrane

Polarity

Smaller lipids (nonpolar) can also pass through the membrane. Polar molecules (like glucose and amino acids) and ions (like Na⁺ and K⁺) cannot pass through without assistance.

Concentration gradient

Small molecules diffuse spontaneously from an area of high concentration to an area of low concentration. Such movement is called passive transport.

Special channels allow polar glucose and amino acids to diffuse through the membrane while avoiding the lipid bilayer. This is facilitated diffusion.

Ions and molecules that must be moved against a concentration gradient must go through special channels using energy from ATP. This is active transport.