Third Grade
Worksheets
What Is a Cell?
Cells are the building blocks of all living things. A cell is the smallest part of a living thing that carries out actions that keep the thing alive. Some living things are made of only one cell-they are unicellular. People are multicellular. The human body is made of more than one hundred trillion cells!
Cells are usually placed into two groups. There are cells with a nucleus and cells without. Cells without a nucleus are very simple cells. The cells of bacteria lack a nucleus. The cells of plants and animals do have a nucleus. Cells are also classified as either plant or animal cells.
All cells are filled with cytoplasm. This jelly-like fluid has many chemicals in it that help the cell stay alive.
