The structure of the cell membrane can be divided into two main parts: the outer lipid bilayer and the inner protein. The functions of the cell membrane are as follows:

1. Maintain cell morphology and integrity: The lipid bilayer structure of the cell membrane can maintain the shape of the cell, protect the cell from damage by the external environment, and also maintain the internal contents of the cell. of integrity.

2. Control the movement of substances in and out of cells: Proteins on the cell membrane can identify and transport substances, including nutrients, ions, water, etc., thereby controlling the movement of substances in and out of cells. This is essential for the survival and proper functioning of cells.

3. Participate in cell signaling: Proteins on the cell membrane can receive and transmit external signals, thereby participating in cell signaling. This plays an important regulatory role in cell growth, division, apoptosis and other processes.

4. Participate in cellular immunity: The proteins on the cell membrane can recognize and defend against external pathogens, thus participating in the cell's immune response. This helps protect cells from germs.

Characteristics of the cell membrane:

1. Lipid bilayer structure: The main structure of the cell membrane is a lipid bilayer composed of two layers of lipid molecules. This structure has a certain degree of fluidity and can allow small molecular substances to pass through, but large molecular substances cannot. This allows the cell membrane to control the movement of materials in and out of the cell, maintaining a stable internal environment within the cell.

2. Protein diversity: There are a variety of proteins distributed on the cell membrane. These proteins have a variety of functions, such as recognizing and transporting substances, participating in signal transduction, etc. The diversity of proteins gives cell membranes complex functions and regulatory capabilities.

3. Fluidity and stability: The cell membrane has certain stability and fluidity. Cell membrane stability is very important in maintaining cell morphology and integrity. At the same time, the protein and lipid molecules on the cell membrane are also constantly moving and exchanging, which makes the cell membrane have a certain degree of fluidity, which is conducive to the cells' adaptation and response to the external environment.

4. Have receptors and channels: There are a variety of receptors and channels on the cell membrane, which can sense external environmental signals and transmit these signals to the interior of the cell. At the same time, these receptors and channels can also control the entry and exit of substances into the cell and maintain the stability of the cell's internal environment.