Here's why:
* Plasma membrane: This is the outer boundary of all cells, acting as a selective barrier controlling what enters and exits the cell. It's essential for maintaining the cell's internal environment.
* Internal membranes: Many cells have internal membranes forming compartments like the endoplasmic reticulum, Golgi apparatus, and lysosomes. These membranes are involved in:
* Transporting molecules: They move molecules within the cell and between organelles.
* Compartmentalization: They separate different cellular processes, allowing for efficient and organized function.
* Enzymatic activity: Some membranes contain enzymes that carry out specific metabolic reactions.
Other structures involved in transport include:
* Cytoskeleton: This network of fibers helps with the movement of organelles and vesicles within the cell.
* Motor proteins: These proteins use energy to move molecules along the cytoskeleton or across membranes.
Therefore, membranes are the primary structures responsible for transporting materials within and between cells.
