Fundamentals of Anatomy and Physiology

42

look at a thin slice of cork. Cork is nonliving plant tissue
that comes from the bark of trees. Because this was dead
plant tissue, he observed the cell walls of dead cells. They
resembled tiny rooms, so he called them cellulae (small
rooms) from the Latin. Thus, the term cells has been used
ever since.
Living cells were observed a few years later by the
Dutch naturalist Antonie van Leeuwenhoek. He observed
pond water under his microscope and was amazed at what
he saw in what he believed was pure water. He called the
tiny organisms in the water animalcules- (meaning lit-tle
animals). It took, however, almost another 150 years before
the significance of cells as the building blocks of biologic
organization was to take hold.
Two German scientists laid the foundation of what we
call today the cell theory. In 1838, Matthias Schleiden, a
botanist, after careful study of plant tissues, stated that all
plants are composed of individual units called cells. In
1839, Theodor Schwann, a zoologist, stated that all animals
are also composed of individual units called cells. Thus, the
foundation of our modern cell theory was formed.

Chapter 3

The modern cell theory consists of the following

principles:

1. Cells are the smallest complete living things—they
   are the basic units of organization of all organisms.^


2. All organisms are composed of one or more cells in
   which all life processes occur.^


3. Cells arise only from preexisting cells through the
   process of cell division.^


4. All of today’s existing cells are descendants of the
   first cells formed early in the evolutionary history of
   life on earth.

Anatomy Of A Typical

eukaryotic Cell

The following structures are parts of a typical eukaryotic

cell: cell membrane, cytoplasm, nucleus, nuclear mem-

brane, nucleoplasm, chromatin, nucleolus, mitochon-dria,

lysosomes, endoplasmic reticulum (both rough and

smooth), Golgi apparatus, and ribosomes.

Carbohydrate

chains

Phospholipid

Cholesterol

Nonpolar region

of membrane protein

Integral

protein

Peripheral globular protein chain

Figure 3- 3 The structure of a plasma (cell) membrane.

(^) ®
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