Answer:
The cell membrane component responsible for controlling which polar and large substances are allowed to enter and exit the cell is the phospholipid bilayer along with membrane proteins, particularly transport proteins.
Phospholipid Bilayer: The cell membrane consists of a double layer of phospholipid molecules. Phospholipids have a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. This structure creates a selective barrier that prevents the free diffusion of polar molecules and ions through the hydrophobic interior of the membrane.
Transport Proteins: Embedded within the phospholipid bilayer are various types of membrane proteins, including transport proteins. These transport proteins facilitate the movement of specific polar or large substances across the membrane. There are two main types of transport proteins:
Channel Proteins: These form channels or pores in the membrane, allowing the passage of ions or water molecules. Examples include aquaporins (for water) and ion channels.
Carrier Proteins: These undergo conformational changes to transport specific molecules across the membrane. They are highly selective and may require energy for active transport.
Together, the phospholipid bilayer and these membrane proteins control the permeability of the cell membrane, regulating which substances are allowed to enter and exit the cell. This selective permeability is crucial for maintaining the internal environment of the cell and ensuring proper cellular function.
Step-by-step explanation: