The __________ (the cell’s outer border) controls the movement of materials into and out of the cell. It is called a lipid bilayer because of the type of molecules it is made up of and it has two layers
Cell membrane
The blank in the statement refers to the plasma membrane, which is the cell's outer border. The plasma membrane is composed of a lipid bilayer. To understand how the movement of materials is controlled by the plasma membrane, we need to look at its structure.
The lipid bilayer is made up of phospholipids, which are molecules with a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails. The hydrophilic heads face outward, interacting with the watery environment both inside and outside the cell, while the hydrophobic tails face inward, creating a barrier.
The plasma membrane is selectively permeable, meaning it regulates the passage of molecules into and out of the cell. It allows certain substances to move across while restricting the passage of others. This property is essential for maintaining the cell's internal environment and protecting it from harmful substances.
The movement of materials across the plasma membrane can occur through two main processes: passive transport and active transport. Passive transport includes diffusion, osmosis, and facilitated diffusion, which do not require energy expenditure by the cell. Active transport, on the other hand, involves the use of energy to move molecules against their concentration gradient.
Overall, the plasma membrane's lipid bilayer and its selective permeability are crucial for controlling the movement of materials into and out of the cell, thereby maintaining cellular homeostasis.