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magnified 30 mes. He used this microscope to examine very thin slices of cork,
a material made from dead plant ssue. He observed that the cork has a
honeycomb of ny compartments and, because the cork cells were dead, the
compartments were empty. He called the compartments in the cork cellulae
and coined the term cell. Hooke, however, did not know the real structure and
funcon of cells and his observaons gave no indicaon of the nucleus and other
organelles found in most living cells.
In the 1670s, the Dutch scienst Anton van Leeuwenhoek used
microscopes capable of magnifying 300 mes and discovered bacteria and
protozoa which he collecvely called animalcules.

For almost two centuries, biologists failed to recognize the importance
of cells. Then, in 1839, the German biologists Mahias Schleiden (a botanist) and
Theodor Schwann (a zoologist) invesgated plant and animal ssues, and
reported that all living things consist of cells. In 1858, Rudolf Virchow
concluded that all cells come from pre-exisng cells, thus compleng the classical
cell theory.
The idea that all living things are composed of cells is called the Cell
Theory. In its modern form, the cell theory includes three principles:

1. The cell is the fundamental unit of structure and funcon in all
organisms. Nothing smaller than a cell can ever be considered alive.

2. All living things are composed of one or more cells. Life processes
occur within a cell.
3. Cells arise from previously exisng cells through cell division. Life
onEarth evolved from early cells, and that no addional cells originate
spontaneously.

PROKARYOTIC AND EUKARYOTIC CELLS
Cells make up all living things and all cells possess certain structures
namely:
(1) plasma membrane – made of phospholipids, it controls the
movement of materials into and out of the cell;

(2) cytoplasm – a semi-fluid substance, it is where chemical reacons
take place; and

(3) genec material (DNA) that provides the informaon necessary for
cellular acvies such as growth and reproducon.

Cells are classified into two main types, according to the way their
genec material is organized. Prokaryoc cells (Greek; pro, before, and karyon,

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