Fundamentals of Anatomy and Physiology

Cell Structure

called the cytoplasm. Cells vary in size and most cells are
too small to be seen with an unaided eye. Cells are
measured in terms of microns- (MY-kronz), more com-
monly called micrometers -(my-KROM-ee-terz). One
micrometer (μm) equals one-thousandth (10^23 ) of a
millimeter. Most eukaryotic cells range in size from 10 to
100 micrometers in diameter (10 to 100 millionths of a
meter). Light microscopes allow us to see general fea-tures
of cells with magnifications from 103 to 10003. These are
the microscopes we use in the laboratory-. However to
“see” or study the details of cells, an elec-tron microscope
must be used. These microscopes use a beam of electrons
to visualize structures and are quite complex. A person
must be specially trained to use one of these sophisticated
instruments. Our current knowledge- of cellular structure
comes from research

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done on cell structure using electron microscopes. The

diagrams of a typical animal cell (Figure- 3-1) and a typical

plant cell (Figure 3-2) illustrate a three--dimensional view

of ultrastructure-. Plant cells have a cell wall in addition to

a cell membrane and chloroplasts that al-low them to make

their own food via the process of photosynthesis. Animal

cells do not have cell walls or chloroplasts.

History Of The Cell Theory

Because cells are too small to be seen with the naked eye,

they were not observed until the invention of the first

microscope in the mid-17th century. Robert Hooke was an

English scientist who first described cells in 1665. He built

one of the first primitive microscopes to

Cell wall

Cell wall of

adjoining cell

Plasma

membrane

Cytoplasmic

strand

Cytoplasm

Nuclear pore

Nucleus

Nucleolus (^)
Rough (^) Ribosome
endoplasmic (^)
reticulum (^)
Chloroplast
Vacuole
Mitochondrion
Golgi complex
Smooth
endoplasmic

Endoplasmic Reticulum

(^) ®
Learning
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Figure 3- 2 A diagram of a typical plant cell illustrating a three-dimensional view of cell
ultrastructure.