4-1
Introduction to
the Cell
Important events in
the discovery of the
cell and the
development of the
cell theory…..
1665 – Robert Hooke
Observed cells in cork.
Coined the term "cells”.
Cork Cells
1673- Anton van Leeuwenhoek
Created a powerful
microscope
1827-33 - Robert Brown
-noticed that pollen grains in water jiggled around
called “Brownian motion”
-discovered the nucleus
Nucleus
Human Cheek Cell
1838 - Matthias Schleiden
A botanist who concluded that all plants are made of cells.
Typical Plant Cell
1839 - Theodor Schwann
A zoologist who concluded that all animals
are made of cells.
Nerve Cells
1855 - Rudolph Virchow
A physician who did
research on cancer cells
and concluded
“Omnis cellula e cellula”.
“All cells are from other
pre-existing cells.”
The Cell Theory
1. All living things are composed of
one or more cells.
2. Cells are the basic units of
structure and function in an
organism.
3. Cells come only from existing
cells.
Cells are Diverse…
both in size,
shape, and
internal
organization.
Why Are Cells So Small?
• Transport- Cell volume to surface
area ratios favor small size.
• Control- Nucleus to cytoplasm
consideration.
• Metabolic requirements……..we’ll come back to this later.
How small can a cell be?
Mycoplasmas - bacteria that are 0.1 to 1.0 mm.
(1/10 the size of regular bacteria).
Note: 1.0 mm = one millionth of a meter
All cells have……
•
•
•
•
Plasma (cell) Membrane
Nucleus (eukaryotes only)
Cytoplasm (an area)
Organelles (structures with
specialized functions)
Cell Types
Prokaryotes- simple cells that do
not have internal membranes
example = bacteria
Eukaryotes- more complex cells
that do have internal, membranebound structures
examples = plants and animals
Timeline
Prokaryotic
Organisms:
First appeared
3.5 BYA
include bacteria
and cyanobacteria
Eukaryotic
Organisms:
First appeared
2.0 BYA
include protists,
fungi, plants and
animals
Key Differences:
Prokaryotes
• Lack a nucleus and
other membrane
bounded structures.
• Have small ribosomes
• DNA is not organized
into chromosomes
• Flagella are not made of
microtubules and does
not have a 9+2 structure
• Cell walls are made of
peptidoglycan, not
cellulose
Eukaryotes
•
•
•
•
•
Have a nucleus and other
membrane bounded
structures.
Have large ribosomes
DNA is organized into
chromosomes
Flagella are made of
microtubules and have a
9+2 structure
Cell walls are made of
cellulose
Examples
Prokaryotic
Eukaryotic
Nucleus
Eukaryotic
Prokaryotic