All organisms are composed of cells. May exist singly as unicellular organisms or as subunits of multicellular organisms. The invention of the microscope led to the discovery of the cell and the formulation of the cell theory. The significance of this discovery was not recognized until 150 years later. This formed the basis for the cell theory.
Animal cells lack cell walls.
Cells are controlled by their DNA . In cells other than bacteria, this DNA is organized with proteins into chromosomes. The largest organelle in most cells is the nucleus which contains the chromosomes. Cytoplasm surrounds the nucleus and contains various organelles of different functions. Found only the Kingdom Monera, the bacteria and blue-green algae.