Robert Hooke was the first to describe cells in 1665 after observing cork under a microscope. He described them as "little boxes" or "little rooms". Almost 200 years later, Matthias Schleidan and Theodor Swann concluded that all plants and animals respectively are made up of cells. They along with Rudolf Vichrow wrote the three part Cell Theory: (1) all organisms are made of cells, (2) the cell is the basic unit of life, and (3) all cells come from preexisting cells.

1. The Basic Units
of Life

2.  Cells were not
discovered until the
mid-1600’s when
microscopes were
invented.
 Robert Hooke: first
man to describe
cells
 He looked at a slice of
cork
 He described it as “
little boxes” or “little
rooms”

3. He described
plant cells as
“juicy”, which
meant that they
were living
He discovered
that animal
cells do not
have a cell wall
like plant cells
do.

4.  Anton van Leewenhoek:
made his own
microscope to look at
pond scum
 Saw little organisms that
we now call protists
 Discovered differences
in blood cells
 Discovered that yeast
were unicellular
organisms

5.  Almost 200 years passed before scientists
realized that cells were present in ALL living
things!
 Matthias Schleidan: Concluded that all
plants were made of cells
 Theodor Swann: Concluded that all animals
were made of cells

6.  Wrote the first two parts of the cell theory, which is:
(1) All organisms are made up of one
or more cells
(2) The cell is the basic unit of all
living things
*Rudolf Vichrow: Wrote 3rd part of Cell
Theory, which is:
(3) All cells come from existing cells

7.  Cell Size:
 Example of large cell: yolk of
chicken egg
 Most cells are SMALL. There are
reasons why:
(1) Allows the cell to get rid of
less food and wastes
(2) As the volume of the cell
increases, its surface area
grows
(3) The volume and surface area
of
the cell limit the size that the cell
can be.
(4) We calculate this by finding
the surface area-to-volume
ratio

8. RATIO = surface area / volume
Example:
Step 1: Find surface area of
cube (# of sides x area of
cube)
If sides of cube measure 2 cm,
then surface area = 6 x (2 cm
x 2 cm)
Surface area of cube = 24 cm2

9. Step 2: Find volume of a cube
(side x side x side)
Volume = 2 cm x 2 cm x 2 cm
Volume of cube = 8 cm3
Put numbers into equation: 24 = 3: 1
8
“three to one ratio”
*The larger the cell, the smaller the surface area
to volume ratio!

10. Two Kinds of Cells
Prokaryotes: single-celled organisms that do not
contain a nucleus
PRO = NO (NUCLEUS)
*no membrane-bound organelles
*Smaller in size
*Examples: Eubacteria and Archabacteria
*They do contain cytoplasm, DNA, and a cell
membrane

11. Eukaryotes: single or multicellular
organisms that DO contain a nucleus
*Have membrane-bound organelles
*Most are larger in size, but still require
a microscope to see
*Examples: protists, fungi, plants, and
animals
*They do contain cytoplasm,
DNA, and a cell membrane

16. Who was the first person
to describe cells?

17. Which 2 scientists
wrote the Cell
Theory?

18. What are the 3 parts of
the Cell Theory?