Here's why:
* Cell Membrane: Both plant and animal cells are enclosed by a cell membrane, also known as the plasma membrane. This thin, flexible barrier is essential for regulating what enters and exits the cell.
* Selective Permeability: The cell membrane is selectively permeable, meaning it allows some substances to pass through while blocking others. This selectivity is crucial for maintaining the cell's internal environment.
* Mechanisms of Transport: Substances can cross the cell membrane through various mechanisms, including:
* Passive Transport: Movement of substances across the membrane without requiring cellular energy. Examples include diffusion, osmosis, and facilitated diffusion.
* Active Transport: Movement of substances against their concentration gradient, requiring energy from the cell. This allows the cell to accumulate needed substances or eliminate waste products.
In summary, the cell membrane is the gatekeeper of the cell, controlling the passage of substances in and out. This process is essential for the cell's survival and function.
