The Basic Units of Life

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”

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.

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

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

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

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

RATIO = surface area / volumeExample: 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

Step 2: Find volume of a cube (side x side x side)Volume = 2 cm x 2 cm x 2 cmVolume 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!

Two Kinds of CellsProkaryotes: 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

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

Cell Theory Video

Who was the first person to describe cells?

Which 2 scientists wrote the Cell

Theory?

What are the 3 parts of the Cell Theory?