Why does the cell membrane control the entry and exit of substances?

The cell membrane is permeable.

Permeability refers to the ease with which a substance passes through a biosemipermeable membrane. The permeability of biosemipermeable membranes to certain molecules in the body can be roughly divided into the following three situations:

free passage of water molecules; It can be permeable to glucose, amino acids, urea, chloride ions, etc.; Proteins, sodium, potassium, etc., which are not easily permeable. The existence of permeability has important physiological significance for the movement of water inside and outside the cell, the exchange of various substances, and the maintenance of pH and osmotic pressure.

In some pathological situations (such as allergies, trauma, burns, hypoxia, etc.), reactions such as tissue edema occur due to the destruction of the normal structure and function of the biosemipermeable membrane, which increases its permeability.

According to the flow mosaic model, the cell membrane is made up of a phospholipid bilayer as a backbone, and there are proteins or glycoproteins and things like that (I guess a lot). First of all, it has the property of a semi-permeable membrane, that is, it can be transmitted to macromolecular substances (but it can be transmitted through endocytosis and exocytosis), and phospholipids are lipids, so they can only be transmitted by fat-soluble small molecules through concentration gradients, that is, they can diffuse freely; And then there's embedded proteins that act as channels for non-fat-soluble substances, such as water (textbooks say that water is free to diffuse, but in fact, a scientist discovered a protein called a "water channel" that assists in the permeation of water, for which he won the Nobel Prize), and glucose enters red blood cells, which also allows substances to penetrate and assist in diffusion because of the difference in concentration gradients. The focus is on active transport, because many substances are absorbed by the cell even though the external concentration is much lower than that in the cell, so the active transport is involved in ATP on the basis of assisted diffusion, and absorbs the substances needed by the cell by dissipating energy, and many kinds of ions pass through the ion pumps on the cell membrane, such as the K+ pump, the Na+ pump (the cell will constantly absorb potassium and excrete sodium, and I don't remember the reason.

Probably these three forms of substances in and out can limit the entry and exit of substances As for endocytosis, I only know that it is the invagination of the cell membrane to form vesicles that envelop macromolecular substances into the cell, and the reason for the cell's endocytocytosis and exocytosis is probably related to glycoproteins I don't know much more The above is just what I said I have learned, I hope it will help you a little!

The cell membrane is like a wall. There are various functional holes embedded in the wall, and there are special protein guards, and those who meet the conditions are allowed to enter, and those who do not meet the requirements are not allowed to enter. There are also some small holes, which ordinary substances cannot pass through, but small molecules such as water molecules are unimpeded, and they are completely determined by the concentration on both sides of the cell membrane, and the equilibrium is good.

This is not determined by the cell membrane, but by the concentration of substances on both sides of the cell membrane, which is just quite an interface, or a decomposition line, with the higher concentration moving to the side with the lower concentration. And the driving force of this movement is the theory of molecular motion in physics, where high concentrations diffuse to low concentrations. Of course, this movement is limited to substances that can pass through the cell membrane, and from this point of view, the cell membrane is equivalent to a sieve, allowing only those that can pass through, so that the cell membrane plays a role in protecting the cell.

The cell membrane is selectively permeable.

There are different carrier proteins on the cell membrane, and the amount of various substances is controlled in and out.

In addition to some of the above explanations, it is also said that the cell is a large system, and the structural mechanism of the whole system determines the function of the cell membrane.

The regulation of the nucleus is also important, the production effect of mitochondria, and so on.

This needs to be looked at holistically.

How cell membranes control the movement of substances in and out of cells.

The function of the cell membrane is to control the entry and exit of substances, so that useful substances cannot easily seep out of the cell, and harmful substances cannot easily enter the cell.

The cell membrane is mainly an elastic semi-permeable membrane composed of phosphorus fibers and lipids, with a thickness of 7 8 nm, and for animal cells, the outer side of the membrane is in contact with the external environment. Its main function is to selectively exchange substances, absorb nutrients, excrete metabolic wastes, secrete and transport proteins. The phospholipid bilayer is the basic scaffold that makes up the cell membrane.

The main components of cell membranes are proteins and lipids, which contain small amounts of sugars. Some of the lipids and sugars combine to form glycolipids, and some proteins and sugars combine to form glycoproteins. Cell membranes are mainly composed of lipids (mainly phospholipids), proteins, and sugars. Among them, proteins and lipids are the main ones.

Under the electron microscope, it can be divided into three layers, that is, there is a thick electron dense band on the inner and outer sides of the membrane, and there is a thick zona pellucida band in the middle, and the total thickness is about about This structure is not only seen in various cell membranes, but also has similar structures in various organelle membranes such as mitochondria and endoplasmic reticulum.

The cell membrane is a barrier to prevent extracellular substances from entering the cell freely, which ensures the relative stability of the intracellular environment, so that various biochemical reactions can run in an orderly manner. However, cells must exchange information, matter and energy with the surrounding environment in order to complete specific physiological functions, so cells must have a set of material transport system to obtain the required substances and discharge metabolic wastes.

It is estimated that 15 30% of the proteins encoded by nuclear genes are proteins involved in the transport of substances on the cell membrane, and the energy spent by cells on the transport of substances accounts for two-thirds of the total energy consumed by the cell.

Summary. In addition to the cell membrane controlling the entry and exit of substances, cells have some other mechanisms to control the entry and exit of substances. For example, cells can regulate the movement of substances in and out through the activity of cell membrane proteins, which can regulate the balance of substances inside and outside the cell through synthesis and degradation.

In addition to cell membrane controls, cells have other mechanisms to control the entry and exit of substances. For example, cells can regulate the entry and exit of substances through the activity of cell membrane protein residues, which can regulate the balance of substances inside and outside the cell through synthesis and degradation.

In addition, cells can also regulate the entry and exit of substances through the activity of membranous transporters, which can regulate the balance of substances inside and outside the cell through the synthesis and degradation of membranous transporter proteins.

Which is the cell structure where various substances are stored.

The cell structure that stores various substances is the cytoplasm. Cytoplasm is the internal structure of the cell and is responsible for storing the substances inside the cell, including enzymes, acids, bases, water, oxygen, sugars, and other substances. The cytoplasm is made up of two parts, the cell membrane and the cytoplasm, where the cytoplasm is the main part of the cytoplasm and is responsible for storing most of the substances inside the cell.

The cell membrane is composed of a layer of membrane proteins and lipids, which are responsible for protecting the substances in the cell from the external environment.

Summary. Yes, cell membranes are selectively permeable. The cell membrane is composed of a lipid bilayer embedded with various protein channels and carriers that are able to selectively control the entry and exit of substances.

They can regulate the permeability of substances according to their characteristics such as size, charge, solubility, and concentration gradient, thereby maintaining the stability of the internal and external environment of the cell.

Yes, cell membranes are selectively permeable. The cell membrane is composed of a lipid bilayer that embeds a variety of protein channels and vectors that selectively control the entry and exit of substances. They can adjust the permeability of substances according to their characteristics such as size, hail, charge, solubility and concentration gradient, so as to maintain the stability of the internal and external environment of the cell.

Fellow, I really didn't understand, I can be more specific.

Yes, cell membranes can selectively control the entry and exit of substances. This is because the cell membrane is a bilayer structure made up of many lipid molecules, which have hydrophobic and hydrophobic properties. There are many protein channels and carrier proteins present on the cell membrane that help the substance or substance to cross the cell membrane.

For small molecules and non-polar substances, they can diffuse directly into and out of the cell through the hydrophobic interior of the cell membrane. This is because hydrophobic regions within the cell membrane can interact with these substances, allowing them to pass through quickly. This is called membrane diffusion.

But for polar substances (e.g., ions) and larger molecules (e.g., glucose), they cannot easily pass through the inside of hydrophobic cell membranes. For these substances, there are specific protein channels and carrier proteins present on the cell membrane that can interact specifically with these substances to help them cross the cell membrane. This method is called passive transport and active transport with brigades.

The selectivity of the cell membrane is achieved through this purebred approach, which ensures that only specific substances enter and exit the cell as needed, thus maintaining the stability and normal function of the internal and external environment of the cell.

There are two ways for substances to enter and exit cells, which are: active transport and passive transport.

Active transport refers to the transport of substances along the inverse chemical concentration gradient (i.e., the movement of substances from the low concentration zone to the high concentration zone), and the active transport is not only completed by a specific transport protein molecule embedded in the cell membrane as a carrier (i.e., each substance is transported by a special carrier), but also must consume the energy generated by cellular metabolism.

There is no unified definition of cell, and the more common formulation is that cell is the basic structure and functional unit of living organisms.

It is known that all organisms except viruses are composed of cells, but the life activities of viruses must also be reflected in cells.

The way substances move in and out of cells has a lot to do with the structure of the cell membrane.

The main ways for substances to enter and exit cells are free diffusion, assisted diffusion, active transport, endocytosis and exocytosis.

1.Free diffusion: refers to the process of some fat-soluble substances moving from the high-concentration side of the membrane to the low-concentration side, such as water molecules or glycerol molecules, because the cell membrane is mainly composed of lipids, proteins and sugars, so these molecules can enter and exit the cell freely.

2.Assisted diffusion: is passive diffusion mediated by membrane proteins on the cell membrane. The transmembrane transport process mediated by special proteins (including carriers and channels) on the membrane is a paraelectro-chemical gradient.

3.Active transport: also diffusion mediated by membrane proteins on the cell membrane, but this process requires energy consumption.

4.Endocytosis: Because the cell membrane is fluid, it needs to be difused in this way when a larger mass of material from the outside enters the cell.

Therefore, the cell membrane structure has a great effect on the movement of substances into and out of the cell.