CHAPTER 3 CELLS
3.1 Cell Theory
KEY CONCEPT Cells are the Basic unit of life.
Discovery of Cells
• The cell theory grew out of the work of many
scientists and improvements in the microscope.
• A cell is the smallest unit capable of carrying out
life functions
• More was learned about cells as microscopes
improved.
• The cell theory is a concept of biology.
Examples of Cells
Amoeba Proteus
Plant Stem
Bacteria
Red Blood Cell
Nerve Cell
Wacky theory of cell history
• Cell Theory
Discovery of Cells
• Zacharias Jannsen
• Man who invented the
compound microscope
Discovery of Cells
• Robert Hooke
• In 1665 he used a
microscope to look at a
thin slice of cork
• Responsible for naming
cells after looking at
cork
• Named them after the
chambers that monks
lived in
Discovery of Cells
• Anton van Leeuwenhoek
• In 1674, first scientist to
observe and describe living
cells from looking at pond
water
• Called them
Animalcules
The Cell Theory
• Matthias Schleiden
• German Scientist
• 1838, concluded all
plants are made of cells
• Cofounded the Cell
Theory
The Cell Theory
• Theodore Schwann
• German Zoologist
• 1839, concluded all
animals were made of
cells
• Cofounder of cell theory
The Cell Theory
• Rudolph Virchow
• German Scientist
• 1855, concluded all cells
come from other cells
• Cell Division
Cell Theory
• 3 major principles of
the Cell Theory
1. All organisms are
made of cells
2. All existing cells are
produced from other
living cells
3. The cell is the most
basic unit of life
• There are two types of cells: Prokaryote and
Eukaryote
• All cells share certain characteristics.
• Cells tend to be microscopic.
• All cells are enclosed by a membrane which regulates the flow of
materials into and out of the cell.
• All cells are filled with cytoplasm – a jelly like cell membrane
substance containing dissolved molecules
like proteins and minerals.
cytoplasm
Bacterium
(colored SEM; magnification 8800x)
There are two types of Cells: Prokaryotes
and Eukaryotes
• Prokaryotes
• Do not have a nucleus.
• DNA in cytoplasm
• Do not have membrane-bound
organelles
• Single celled organisms
• Less complex
 Ex Bacteria
cell membrane
cytoplasm
There are two types of Cells: Prokaryotes
and Eukaryotes
• Eukaryotes
• Have a nucleus.
nucleus
• DNA in nucleus
• Eukaryotic cells have
membrane-bound organelles.
• Single or Multicellular
organelles
• More complex and
Specialized
cell membrane
 Ex. Most plant and
animal cells