Cells and Cell Theory: Grade 11 Biology

CELLS & THE CELL THEORY

Cells were discovered by Robert Hooke in 1665.

The Cell Theory states:

1.   All living organisms are composed of cells. They may be unicellular or multicellular.

2.   The cell is the basic unit of life.

3.   Cells arise from pre-existing cells.

The modern version of the Cell Theory includes the ideas that:

• The activity of an organism depends on the total activity of its individual cells.
• Heredity information (DNA) is passed on from cell to cell during cell division.
• Energy flow (metabolism) occurs within cells.
• All cells have the same basic chemical composition.

There are two different categories of cells:

1.   Prokaryotes lack a nucleus (though they do have DNA) and other membrane-bound organelles.  The two kingdoms of prokaryotes are Bacteria & Archaea

1. Eukaryotes have distinct nuclei bound by a nuclear membrane and membrane-bound organelles (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles).                 

There are four kingdoms of eukaryotes:    Animal, Plant, Fungus and Protist