Cells and Cell Theory
Early Microscopes
Robert Hooke built a
microscope in 1665
He looked at cork from
trees and saw tiny boxes.
He called them cells.
Hooke spent most of his
time looking at plants
and fungi. He thought
that only plants had cells
because they were easier
to see.
Anton van Leeuwenhoek
•Van Leeuwenhoek built a microscope
in 1673
•He examined pond scum and saw
organisms
•He named the “wee beasties”
animalcules because they looked like
little animals.
•Today, we call these organisms
protists.
Finding Cells in Other
Organisms
Leeuwenhoek also examined
blood.
He noticed that the animal
blood was different from
human blood.
He was the first person to
view bacteria
He discovered that the yeast
that makes bread rise was a
single-celled organism.
CELL THEORY . . . 200 years later
• In 1839, Schwann (who studied animals) and
Schleiden wrote that
• ALL organisms are made of one or more cells
• The cell is the basic unit of life
Virchow (1858) added
• All cells come from existing cells
Cell Similarities
All cell have a membrane to
keep the inside separate from
the outside environment.
All cells have cytoplasm (fluid)
and small parts called
organelles
All cells have some hereditary
material called
Deoxyribonucleic Acid (DNA)
Most cells are small in size.
Why Are Cells Small?
• Cells are small because if a cell’s volume gets too
large, the cell’s surface area will not be able to take in
enough nutrients or get rid of wastes fast enough to
keep cells alive.
• They need to keep a large surface area/volume ratio.
TWO TYPES OF CELLS
Prokaryotic Cells
*Pro means NO nucleus
These cells were the first
type of cell on Earth.
They are the smallest cells
They have circular DNA
and no membrane covered
organelles
These cells are found in
organisms like bacteria.
You have Eukaryotic Cells!
Eukaryotic Cells
*Eu mean true nucleus
These cells are found in plants,
animals, fungi, and protists.
The cells are larger in size (10x) than
prokaryotic cells
They have a large, obvious nucleus
and membrane covered organelles.
They have DNA that is linear (in a
line) and coiled up.
What’s the Advantage of a Eukaryotic
Cell?
Different chemical reactions can
happen at the same time
Benefits of Being Multicellular
•Larger Size
•Multicellular organism are larger than
unicellular organisms. They have less predators
and more choice of prey.
*Live Longer
Multicellular organisms can loose cells and not
die.
Specialization
Multicellular organisms can do more things .
Cells can specialize to do different jobs.
Multicellular organisms grow by producing more
cells!