Â­Mesoamericans began writing during the mid-Pre-classic period. The Mayans were the first to keep any sort of historical record, and the beginnings of the calendar were born. The Mayans used stelae, or stone monuments, to carve their civil events, calendars and astronomy knowledge. They also inscribed their religious beliefs and mythology on pottery.
The nucleus is a membrane bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction. It is commonly the most prominent organelle in the cell. The nucleus is surrounded by a structure called the nuclear envelope.
Animal cells and plant cells. Animal cells usually have an irregular shape, and plant cells usually have a regular shape. Cells are made up of different parts. It is easier to explain what these parts are by using diagrams like the ones below. Animal cells and plant cells both contain: cell membrane, cytoplasm, nucleus.