How cell maintain the balance?

       We are comfortable in our classes largely because the thermostat (AC) maintains the temperature within a limited range regardless of what’s happening outside. Similarly, all living cells must maintain a balance regardless of internal and external conditions. Survival depends on the cell’s ability to maintain the proper conditions within itself.

Why Cells Must Control Materials

Your cells need nutrients such as glucose, amino acids, and lipids to function. It is the job of the plasma membrane, the flexible boundary between the cell and its environment, to allow a steady supply of these nutrients to come into the cell no matter what the external conditions are. However, too much of any of these nutrients or other substances, especially ions, can be harmful to the cell. If levels become too high, the excess is removed through the plasma membrane. Waste and other products also leave the cell through the plasma membrane. Recall that this process of maintaining balance in the cell’s environment is called homeostasis.

How does the plasma membrane maintain homeostasis? One mechanism is selective permeability, a process in which a membrane allows some molecules to pass through while keeping others out.

Some molecules, such as water, freely enter the cell through the plasma membrane. Other particles, such as sodium and calcium ions, must be allowed into the cell only at certain times, in certain amounts, and through certain channels.

Plasma Membrane Structure

Now that you understand the basic function of the plasma membrane, you can study its structure. The plasma membrane is composed of a phospholipid bilayer, which has two layers of phospholipids back-to-back. 

Phospholipid Bilayer Structure

Plasma Membrane Structure

The model of the plasma membrane is called the fluid mosaic model. It is fluid because the phospholipids move within the membrane just as water molecules move with the currents in a lake. At the same time, proteins in the membrane also move among the phospholipids like boats with their decks above water and hulls below water. These proteins create a “mosaic,” or pattern, on the membrane surface.

The other components of the plasma membrane are cholesterol (to stabilize phospholipids), integral protein (as transport protein), peripheral protein, and carbohydrate (as glycoprotein or glycolipids).