Download The Discovery of Cells

Chapter 1 Section 2

Cells were discovered
in 1665 by Robert
Hooke.

He observed them by
looking at a thin slice
of cork.

He saw hundreds
of Little boxes and
called them cells,
which means “little
rooms.”

Hooke believed that
cells were only
found in plants.

In 1673, Anton van
Leeuwenhoek
observed pond water
and scum and saw
small creatures he
named animalcules,
which means “little
animals.”

He also observed blood from different
animals and teeth scrapings.

He was also the first person to see
bacteria, a unicellular organism.

It took nearly two
centuries after Hooke’s
discovery of cells that
anyone realized, cells
are present in all living
things.

Matthew Schleiden, a
German scientist who
studied animals also
stated that they are
made of cells.

Schleiden wrote the
first two parts of
what is known as
the Cell Theory.

In 1858, a German
doctor, Rudolf
Virchow wrote the
third part of the Cell
Theory.

All organisms are composed of one or
more cells.

The cell is the basic unit of life in all living
things.

All cells come from existing cells.

Cells come in different shapes, sizes, and
perform different functions but they share
many similarities.
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•
•
•
Cell Membrane
Hereditary Material
Cytoplasm and Organelles
Small size

All cells are surrounded by a cell
membrane.

This membrane acts as a barrier between
the inside and outside of the cell.

It controls the passage of materials into
and out of the cell.

When new cells are made, they receive a
copy of the hereditary material of the
original cells.

DNA

All cells have organelles, chemicals and
structures that enable it to live, grow, and
reproduce.

The chemicals and structures of a cell are
surrounded by fluid called the cytoplasm.

Almost all cells are too small to be seen
with the naked eye and must be observed
under high power of a microscope.

A cell’s outer wall (surface area) needs to
be able to accommodate its inner
activities (volume).

If a cell gets too large, its surface will have
too few openings to allow enough
materials into and out of it.

A single cell as big as us would
have an incredibly small
surface-to-volume ratio.

The cell would not survive
because its outer surface would
be too small to allow in the
materials it would need.

Multicellular organisms grow by
producing more small cells, not
by getting larger.

Multicellular organisms have cells that
specialize in a particular area and do a
particular job.

These cells can form tissues and organs
with different functions.

Prokaryotic Cells
 No membrane-covered nucleus, free floating DNA

Eukaryotic Cells
 Membrane-covered nucleus that contains DNA

These cells are also called bacteria and are
the world’s smallest cells.

Their DNA is one long, circular strand.

They do not have any membrane-covered
organelles.

Most bacteria are covered by a hard cell wall
outside a softer cell membrane.

These cells were probably the first types of
cells on Earth.

These cells are more complex than
prokaryotic cells and about 10 times
larger.

These cells first appeared about 2
billion years ago.

All living things that are not bacteria are
made of one or more eukaryotic cells
(plants, animals, fungi, and protists.)

They have a nucleus and several
membrane-covered organelles.
Prokaryotic Cells
*No nucleus
Eukaryotic Cells
*Nucleus
*No membrane
covered organelles
*Membranecovered organelles
*Circular DNA
*Linear DNA
*Bacteria
*All other cells