Question

in simple diffusion • Only O2
, CO2
, NH3
can transverse. Why

Answer 1

Simple diffusion refers to the passive movement of molecules from an area of higher concentration to an area of lower concentration without the need for energy input. The ability of certain molecules to transverse or cross biological membranes through simple diffusion is primarily determined by factors such as size, polarity, and solubility.

1. **Oxygen (O2)**: Oxygen is a small, nonpolar molecule. Nonpolar molecules can easily pass through the lipid bilayer of cell membranes because the membrane is composed primarily of phospholipids, which create a hydrophobic (water-repellent) interior. Oxygen's small size and nonpolar nature allow it to diffuse freely across the membrane.

2. **Carbon Dioxide (CO2)**: Carbon dioxide is also a small, nonpolar molecule. Like oxygen, it can diffuse through the cell membrane effortlessly due to its size and nonpolar characteristic. While CO2 has a polar covalent bond between carbon and oxygen, its linear shape makes it overall nonpolar and able to traverse lipid membranes easily.

3. **Ammonia (NH3)**: Ammonia is a small and slightly polar molecule. It can diffuse through membranes, but it does so less readily than O2 and CO2. However, its small size allows it to cross membranes through simple diffusion, especially in environments where concentrations differ.

Other larger or more polar molecules (e.g., sugars, ions) typically cannot diffuse across membranes through simple diffusion due to their size or charge, which would require facilitated diffusion or active transport mechanisms to cross lipid membranes.