Cells
Chapter 6 Notes
What does the word ‘Cell’
Mean?
 The
word cell is derived from the Latin
word 'cellula' which means small
compartment.
A Famous Man in Science –
Robert Hooke
 In
1663 an English scientist, Robert Hooke,
discovered cells in a piece of cork, which
he examined under his primitive
microscope.
 Hooke
only observed cell walls because
cork cells are dead and without
cytoplasmic contents.
 Hooke
drew the cells he saw and also
coined the word CELL.
Anton van Leeuwenhoek
 Today,
he is known as
the “Father of
Microbiology” and
discovered bacteria

Used his own (single
lens) monocular
microscopes and was
the first person to
observe bacteria and
protozoa
Anton van Leeuwenhoek
 Built
microscopes that magnified over 200
times, with clearer and brighter images
than any of his colleagues at that time.
Cell Theory
 The
CELL THEORY, or cell doctrine, states that
all organisms are composed of similar units
of organization, called cells.
 The
concept was formally articulated in
1839 by Schleiden & Schwann and has
remained as the foundation of modern
biology.
Cell Theory Components

1.
2.
3.
4.
5.
6.
There are 6 Components to Cell Theory:
All known living things are made up of cells.
The cell is structural & functional unit of all living
things.
All cells come from pre-existing cells by division.
(Spontaneous Generation does not occur).
Cells contain hereditary information which is
passed from cell to cell during cell division.
All cells are basically the same in chemical
composition.
All energy flow (metabolism & biochemistry) of life
occurs within cells.
Two Major Classes of Cells
1.
2.
Prokaryotic Cell

Lacks a nucleus and most other organelles.

Bacteria and another group of organisms called
the archaea are prokaryotic cells. Prokaryotic
organisms appear earliest in Earth's fossil record.
Eukaryotic Cell

Has a nucleus surrounded by its own membrane,
and has other internal organelles bounded by
membranes.

Protists, fungi, plants, and animals consist of
eukaryotic cells. Organisms with eukaryotic cells
appeared later in Earth's history.
Prokaryotic Cells
A
bacterium is an example of a prokaryotic cell
(pro means "earlier than").
 Prokaryotic
cells are much simpler in structure
 They
do not have a true nucleus or membrane
bound organelles that a eukaryotic cell would
have.
 The
DNA in a prokaryotic cell is concentrated in
an area called the nucleoid region:

This is not separated from the rest of the cell by a
membrane. ONLY EUKARYOTIC CELLS HAVE
MEMBRANE BOUND ORGANELLES
Prokaryotic Cells


Notice how everything is floating around together
– not bound separately from one another!
Example:

The DNA is not bound separately from the ribosomes
Eukaryotic Cells

Protists, fungi, plants, and animals consist of
eukaryotic cells.

Eukaryotic cells are much more complex in
structure

They do have a true nucleus and membrane
bound organelles

The DNA in a eukaryotic cell is concentrated
in an area called the nucleus
Eukaryotic Cells
 Notice
how everything is bound in a
membrane separate from one another.
Example:

The DNA is seen inside the nucleus which
has a nuclear membrane separate it from
everything else!
Compare, Compare!
 Prokaryotic
Cell
 Eukaryotic
Cell
o What are some similarities?
o What are some differences?
Stop and Freeze!
Question:
Do you have
prokaryotic or eukaryotic
cells? EXPLAIN!!
All of this Membrane talk!
--Membrane Structure
1.
2.
Membranes help keep the functions of a
eukaryotic cell organized.
Act as partitions,

3.
The membranes isolate teams of enzymes within
a cell's compartments.
Regulate the transport of substances across
the boundary, allowing only certain
substances to pass.

NOT A WALL!
Plasma Membrane
 The
plasma membrane and other
membranes of a cell are composed mostly of
proteins and a type of lipid called
phospholipids
Phospholipids

A phospholipid molecule is structured much like
the fat molecules but has only two fatty acids
instead of three.

Composed of 2 Main Parts:
Head
1.

Made up of a phosphate group,

Negatively charged

Hydrophilic (water loving)
Tail
2.


The two fatty acids at one end (the tail) of the
phospholipid are hydrophobic.
So the tail end of a phospholipid is pushed away
by water, while the head is attracted to water
Phospholipids
The structure of
phospholipids allows
them to form
boundaries, or
membranes,
between two watery
environments.
Phospholipid Bilayer
 The
phospholipids
form a two-layer
"sandwich" of
molecules, called
a phospholipid
bilayer, that
surrounds the
organelle or cell.
Inside the Phospholipid Bilayer

Many types of proteins are
embedded in the
membrane's phospholipid
bilayer.

Other molecules, such as
carbohydrates, may be
attached to the
membrane as well, but the
proteins perform most of
the membrane's specific
functions.
Protein Function Inside Cells
 Help
Other Cells (especially cells that are part of a
multicellular organism)
1.

Proteins help cells communicate and recognize
each other.
Example, chemical signals released by one cell may
be "picked up" by the proteins embedded in the
membrane of another cell.
 Transport
1.
Proteins (Protein Channel)
Help move certain substances such as water and
sugars across the plasma membrane
Moving Across the Plasma
Membrane

Molecules in a fluid are constantly in motion,
colliding and bouncing as they spread out
into the available space.

So how do particles move across the plasma
membrane?!
1.
Diffusion!

The net movement of the particles of a
substance from area of where they are in
high(more) concentration to where they are in
low(less) concentration
Diffusion
 Diffusion
across a membrane is called
passive transport because no energy is
expended by the cell in the process.
 Only
the random motion of the molecules
is required to move them across the
membrane.
Passive Transport
 Cellular
membranes are barriers to the
diffusion of some substances.
 A selectively permeable membrane
allows some substances to cross the
membrane more easily than others and
blocks the passage of some substances
altogether.
Osmosis
 The
passive transport (diffusion) of water
across a selectively permeable
membrane is called osmosis.