State that some substances move into and out of cells by diffusion through the cell membrane

Some substances move into and out of cells by diffusion through the cell membrane. This process is essential for maintaining cellular functions and homeostasis.

Key Points

1. Cell Membrane Structure:
   • The cell membrane is selectively permeable, meaning it allows certain substances to pass while restricting others. This permeability is influenced by factors such as the size, charge, and solubility of the molecules.
2. Substances That Diffuse:
   • Gases: Oxygen and carbon dioxide can easily diffuse across the lipid bilayer of the cell membrane due to their small size and nonpolar nature.
   • Small Molecules: Water and other small, uncharged molecules can also diffuse through the membrane, although water may utilize specialized channels (aquaporins) for more efficient transport.
   • Ions: While ions typically cannot diffuse freely through the lipid bilayer due to their charge, they can still move across the membrane through specific ion channels.
3. Importance of Diffusion:
   • Diffusion allows cells to acquire essential nutrients, eliminate waste products, and regulate internal conditions without the expenditure of energy.