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Cell Theory, Microscopes, and
Cell Types
Pages 171-174
Discovery of Cells
• Early scientists believed in spontaneous
generation, the idea that life could come from
nonliving things.
• This was disproved through the experiments
of Francesco Redi and Louis Pasteur.
• However, because the microbes that Pasteur
theorized caused spoilage were too small to
see, his ideas were not easily accepted.
• The first cells were not
observed until the 1600s.
• Anton van Leeuwenhoek
was the first to create a
microscope to observe
“animalcules” in pond
• These animalcules are now
called microorganisms.
Further Cell Discoveries
• Robert Hooke used an
early compound
microscope to observe
• He observed small
block-like structures.
He called these
structures cells.
• Schleiden conducted studies of plant tissues
and found that plant cells arose from
preexisting plant cells.
• Schwann conducted similar studies of animal
• Virchow formally concluded that new cells
came from preexisting cells.
The Cell Theory
• The work of Leeuwenhoek, Hooke, Schleiden,
Schwann, and Virchow was formally
recognized as the Cell Theory. There are three
main points to the Cell Theory.
1. All living things are composed of cells.
2. Cells are the basic unit of structure and
function in living things.
3. New cells are produced from preexisting
• Microscopes were essential to the discovery and
study of cells.
• The first microscopes were light microscopes.
• They use light and lenses to illuminate and
magnify an object.
• Simple light microscopes use a single lens.
Compound light microscopes use two or more
• Light microscopes can magnify objects up to 1500
times their actual size.
Compound light microscope
Iris root
• More powerful microscopes use a beam of
electrons to magnify objects. These are called
electron microscopes. They can magnify
objects up to 500,000 times their actual size.
• Scanning electron microscopes (SEM) are used
to scan surfaces and determine threedimensional shape.
• Transmission electron microscopes (TEM) are
used to determine the internal details of cells.
• Scanning tunneling microscopes (STM) are
used to create images of atoms on molecular
Electron microscope
Blood cells SEM
Human cell TEM
Cell Types
• There are two major cell types as determined by
internal structures.
• Prokaryotic cells are cells whose genetic material
is not enclosed by a membrane. They lack
membrane-bound internal structures
(organelles). These are the cells of bacteria.
• Eukaryotic cells are cells whose genetic material
is enclosed by a membrane (a nucleus). They also
have numerous membrane-bound organelles.
These are the cells of protists, fungi, plants, and
• All cells are surrounded by a cell membrane (or
plasma membrane), contain ribosomes, and
contain DNA.
• Prokaryotic cells are surrounded by a cell wall
made of peptidoglycan. They lack a nucleus and
• Fungal cells are surrounded by a cell wall made of
chitin. They have a nucleus and all organelles
except the chloroplast.
• Plant cells are surrounded by a cell wall made of
cellulose and contain chloroplasts. They have a
nucleus and all organelles.
• Animal cells do not have a cell wall. They have a
nucleus and all organelles except the chloroplast.
Animal cell
Plant cell