Progress in the study of cells is associated with the development of microscopy in the 19th century. By this time, ideas about the structure of cells had changed: the main thing in the organization of the cell was not the cell wall, but its actual content – protoplasm. In protoplasm, a constant component of the cell, the nucleus, was discovered.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.