Cells are the basic unit of life.
What are Cells?
History of Cells & Cell Theory
The cell theory grew from the work and
research of many scientists.
Who Was Involved?
Hooke's Microscope
First to View Cells • In 1665, Robert
Hooke was the first
to use a light
microscope to
examine a thin slice
of cork (dead plant
tissue)
• What he saw looked
like small boxes Hooke's drawing of Cork Cells
First to View Cells
• Hooke is responsible
for naming cells.
• Hooke called them
“CELLS” because
they looked like the
small rooms that
monks lived in
(called cells).
• Dutch microscope maker.
• One of the first people to
use a microscope to study
living things in nature &
was the first to view
microorganisms .
• Leeuwenhoek used a
simple, handheld
microscope to view pond
water & scrapings from
his teeth.
• Observed living cells, which
he called “animalcules.”
Anton van Leeuwenhoek (LAY-vuhn-hook)
Beginning of the Cell Theory
• In 1838, a German botanist named Matthias Schleiden concluded that all plants were made of cells
• Schleiden is a cofounder of the cell theory
Beginning of the Cell Theory
• In 1839, a German zoologist named Theodore Schwann concluded that all animals were made of cells.
• Schwann also cofounded the cell theory.
Beginning of the Cell Theory
• In 1855, a German
medical doctor named
Rudolph Virchow
observed, under the
microscope, cells dividing.
• He reasoned that all
cells come from other
preexisting cells by cell
division.
Three Principles of Cell Theory
1. All living things are made
of one or more cells.
2. Cells are the basic unit of
structure and function in
an organism (they are the
smallest unit that can
perform life functions).
3. Cells come from the
reproduction of existing
cells (cell division).
Why is the Cell Theory called a Theory and not a Fact?
Cell Theory
All organisms are made of one or more cells.
• Some organisms are made up of one cell or
unicellular
• Others are multicellular or made up of many cells
Principle #1
The cell is the most basic unit of life.
Principle #2
All existing cells are produced by other living cells.
Principle #3
1. They are flexible in function
• Become different types of tissues and material
• Ex: fetal development
2. They can let things in and out
• Communication
• Getting nutrients, energy
3. They have their own command center
• DNA tells cells what to do
4. They have the ability to divide and make more
• Ex: growth & reproduction
Characteristics of Cells
Cells are small so they
can exchange materials
with their surroundings.
Surface area relative to the volume decreases as
size of cell increases.
- limits the size of cells
Cells need a large surface area to absorb enough
nutrients.
Cell Size
Surface area = 96 (only 4 times greater)
Volume = 8
Factors Affecting Cell Size
• Volume of a cell is
determined by
multiplying length
times width times
height (L x W x H).
• Surface area (cell
membrane) is the total
area (L x W) of all sides
(the entire surface of
the object).
• Therefore, Volume
increases FASTER
than the surface area.
4
4
4
2 2
2
Surface area = 24
Volume = 64 (8 times greater)
• When the surface area is no longer
great enough to get rid of all the
wastes and to get in enough food
and water, then the cell must divide.
• Therefore, all of the cells in an
organism are close in size.
Cell Size
Cell Size
Question: Are the cells in
an elephant
bigger,
smaller, or
about the same
size as those in
a mouse?
Cell Size Answer:
The elephant’s
cells are about
the same size
as those of the
mouse, but the
elephant has
MANY MORE
cells than the
mouse.
Sizes of living things
The Cellular Level of Organization
Living things are constructed of cells.
Living things may be unicellular or multicellular.
Cell structure is diverse but all cells share
common characteristics.
Types of Cells
Prokaryote: Lacking a true
nucleus Bacteria
Eukaryote: With a nucleus
bounded by a membrane
Plant
Animal
Fungi
Protists
Types of Cells
Cell Size and Types
• Cells, the basic units of organisms, can only
be observed under microscope
• Three Basic types of cells include:
Animal Cell Plant Cell Bacterial Cell
_________ > _____________ > ___________
Which Cell Type is Larger?
Plant cell Animal cell bacteria
Number of Cells Although ALL living things are made of
cells, organisms may be:
• Unicellular – composed of one cell
• Multicellular- composed of many cells that may
organize into tissues, etc.
How Big is a Micron ( µ ) ?
1 cm = 10,000 microns 1” = 25,000 microns
Cell Features ALL cells have these parts:
• Ribosomes – make protein for use by the organism
• Cytoplasm – fluid material within cell
• DNA – genetic material
• Cytoskeleton – internal framework of cell
• Cell Membrane – outer boundary, some things can cross the cell membrane
Prokaryotes – The first Cells
• Cells that lack a nucleus or membrane-
bound organelles
• Includes bacteria
• Simplest type of cell
• Single, circular chromosome
Eukaryotes
• Cells that have a nucleus and membrane-bound intracellular organelles
• Includes protists, fungi, plants, and animals
• More complex type of cells
Organelles With DNA • Mitochondria and chloroplasts have their own DNA (separate
from the nucleus)
• This supports the ENDOSYMBIOSIS THEORY which states that eukaryotic cells evolved when prokaryote cells engulfed or absorbed other cells.