The reason is: the supporting function of cell wall.
The cell wall of plants is mainly composed of cellulose and pectin, which has certain toughness and can support and protect cells.
Cell wall has the function of protecting and supporting fine white blood cells; Cell membrane protects the structure of du part in the cell and controls the entry and exit of zhi substance inside and outside the cell. It is selective to substances, allowing useful substances to enter the cells, keeping other substances out of the cells, and at the same time, it can discharge the waste generated in the cells. Nuclear-plays an important role in biological inheritance. The nucleus contains genetic material; There are many substances in the cytoplasm, and the cytoplasm of living cells has fluidity, which is beneficial to the exchange of substances between cells and the external environment.
According to the above, the main reason why plant cells keep a certain shape is the support of cell walls.