All cells are derived from pre-existing cells, is the famous saying of German biologist Schwann.

Schwang is one of the main advocates of the cell theory. He and the German botanist Schleiden jointly proposed the cell theory, which believes that all animals and plants develop from cells and are developed from cells. It is composed of cells and cell products that both develop from previous cells and contribute to the life of the whole that is composed of other cells.

Test points:

The discovery of cells, the establishment, content and development of cell theory Special topic: Analysis: The cell theory was proposed by the German botanist Schleiden and the zoologist Schwann of.

(1) A cell is an organism. All animals and plants develop from cells and are composed of cells and their products.

(2) A cell is a relatively independent unit, which not only has its own life, but also contributes to the life of the whole composed of other cells.

(3) New cells can be produced from old cells. "All cells are derived from pre-existing cells" is Virchow's famous saying, which is consistent with the experimental results "showing that new cells are produced by the division of original cells". This is the development of the content of cell theory.

Existence of cells

All cells are derived from pre-existing cells, and cells are produced by division of pre-existing cells. The inside of the cell wall is attached to a very thin membrane called the cell membrane. This film is composed of protein molecules and a phospholipid bilayer. Small molecular substances such as water and oxygen can pass freely, but certain ions and macromolecule substances cannot pass freely.

Therefore, in addition to protecting the inside of the cell, it also has the function of controlling the entry and exit of substances into the cell: it neither allows useful substances to leak out of the cell at will, nor allows harmful substances to easily enter the cell. In addition, it can communicate information between cells.

When the concentration of the cell fluid is less than the external concentration, the water in the cell fluid passes through the protoplasm layer and enters the external solution, causing both the cell wall and the protoplasm layer to shrink to a certain extent.

Because the protoplasm layer is more flexible than the cell wall, when the cell continues to lose water, the protoplasm layer separates from the cell wall, which is plasmolysis. When the concentration of the cell fluid is greater than the concentration of the external solution, the water in the external solution penetrates the protoplasm layer into the cell fluid to restore the protoplasm layer, and the restoration of plasmolysis gradually occurs.