Transporter proteins are specialized proteins that facilitate the movement of substances across cell membranes. They play a crucial role in maintaining cellular homeostasis by allowing essential molecules, such as nutrients and ions, to enter or exit the cell. These proteins can be found in various types of cells and are vital for processes like nutrient absorption and waste removal. There are two main types of transporter proteins: facilitated diffusion and active transport. Facilitated diffusion allows substances to move down their concentration gradient without energy input, while active transport requires energy to move substances against their gradient. Both types are essential for proper cell function and overall organism health.