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Cells
Biology A
I. Introduction – “What is a cell?”
 A cell
is the smallest unit that can carry
out all the activities necessary for life.
*cellular organization *heredity
*metabolism
*reproduction
*homeostasis
*responsiveness
*growth & development
 Most
microscopic organisms are made
up of a single cell.
II. Cell Discovery –
“Who discovered the cell?”
 New
information was due largely to
the advancement of the microscope.
a. Robert Hooke (1635-1703)

In 1665, the English
scientist and monk,
observed a thin slice
of cork (dead cells).

He described what he
saw as, “a great many
little boxes,” which he
then termed the cell.
b. Anton van Leeuwenhoek
(1632-1723)

In 1675, the Dutch
microscope maker,
was the first person to
observe living cells.

For the next 150 years
very little research was
done on microscopes
or cells.
c. Robert Brown (1773 - 1858)

In 1827, the English
botanist, was the first
person to see the
nucleus inside cells.

However, by the
time he died no one
really understood
the importance of
his discovery.
d.Matthias Schleidan (1804-1881)

In 1838, the German
botanist, observed
thousands of plant
cells and concluded
that all plants were
composed of cells.
e. Theodor Schwaan (1810-1882)

In 1839, the German
zoologist, came to a
similar conclusion, he
saw that all animals
were composed of
cells.
f. Rudolph Virchow (1821-1902)

In 1855, the German
physician, while
studying diseases,
determined that cells can
come only from other
cells.

“Cells make more cells.”
III. The Cell Theory –
“Why are cells important?”
The observations of these scientists, taken
together are known as the cell theory:
1) All living things are composed of one or
more cells.
2) Cells are organisms’ basic units of
structure and function.
3) Cells come only from existing cells.
IV. Basic Materials in a Cell –
“What is a cell made up of ?”
The 4 Major Organic Molecules
1) Carbohydrates
2) Lipids
3) Proteins
4) Nucleic Acids
QUIZ
1.
2.
3.
Who saw the first cells in
cork?
What are the three parts of
the cell theory?
Who saw the first living
cells?
V. Levels of Cellular Organization “How are cells organized?”
i)
Cell (smallest unit of life)
V. Levels of Cellular Organization “How are cells organized?”
i)
ii)
Cell
Tissue (many cells working together)
V. Levels of Cellular Organization “How are cells organized?”
i)
ii)
iii)
Cell
Tissue
Organ (many tissues together)
V. Levels of Cellular Organization “How are cells organized?”
Cell
ii) Tissue
iii) Organ
iv) Organ system
(many organs together)
i)
V. Levels of Cellular Organization “How are cells organized?”
i)
ii)
iii)
iv)
v)
Cell
Tissue
Organ
Organ system
Organism
(a complete living thing)
VI. Organelles Found in a Typical Cell “What is in cell?”

Organelles (little organs) are specialized
compartments that carry out specific
functions within a cell.
VI. Organelles Found in a Typical Cell “What is in cell?”

BY UNDERSTANDING THE
STRUCTURES IN A CELL, YOU CAN
PREDICT THEIR FUNCTIONS.
A. Nucleus
CELL
NUCLEUS
1. Directs all of the
cell activities and
serves as the storage
center for DNA.
2. Sometimes called
the “brain” of the cell.
B. Nucleolus
NUCLEOLUS
1. Place where the ribosome's are made
by RNA (ribonucleic acid).
2. It is in the center of the nucleus.
C. Nuclear Envelope
NUCLEAR
ENVELOPE
1. Membrane
around the nucleus
that protects it and
allows the RNA to
enter & leave the
nucleus.
D. Cell Membrane
1. Semi-permeable
membrane that allows
only certain
molecules to enter
and leave the cell.
CELL MEMBRANE
2. Protects the cell
and as well as gives it
support.
E. Cytoplasm
1. Jelly-like fluid
within a cell that
helps to cushion the
cell.
CYTOPLASM
2. It is constantly in
motion, as particles
enter and leave the
cell through the cell
membrane.
F. Mitochondria
1. The place where energy
(ATP) is made.
2. Where cellular
respiration occurs.
MITOCHONDRIA 3. Often called the
“powerhouse” of the cell.
G. Ribosomes
1. The site where
proteins are made
(synthesized).
2. These are the
most numerous of
all the organelles.
Cell Quiz 2
1.
2.
3.
What are the levels of
organization?
What is the function of the
ribosome?
What is the function of the
mitochondria?
H. Endoplasmic Reticulum (ER)
1. Directs the traffic
of all the molecules
by creating a series
of channels.
2. Often called the
“highway system”
of the cell.
H. Endoplasmic Reticulum (ER)
1. Rough ER (has ribosomes on it) –
synthesizes (makes) proteins.
2. Smooth ER (has no ribosomes on it) –
synthesizes (makes) lipids.
I. Golgi Apparatus
1. Labels packages
and distributes the
proteins that are to
be used inside and
outside of the cell.
2. Often called the
“post office” of the
GOLGI APPARATUS cell.
J. Lysosomes
1. Breaks down food
particles and diseasecausing bacteria that
enter the cell.
2. Often called the
“janitors” of the cell.
K. Vacuoles
1. Aids in storage and
support of the cell by
helping to maintain
water balance.
VACUOLE
2. Often called the
“storage center” of the
cell.
L. Cilia and Flagella
1. Hair-like projections that stick out of the
cell membrane and used for movement.
2. Often called the “hairs” of the cell.
CILIA
FLAGELLA
M. Centrioles
(Animals only)
1. Assists the cell
during reproduction
by pulling the cell
into two halves.
2. Always found in
pairs during mitosis.
N. Chloroplasts
(Plants only)
1. Makes energy for
the cell by using air,
water, and sunlight
in a process called
photosynthesis.
CHLOROPLASTS
2. Found in all of the
green plants.
O. Cell Wall
(Plants only)
1. Thick outer layer
that provides extra
strength and
support to the cell.
2. Made of cellulose,
but has few pores to
allow only certain
molecules to enter
and leave the cell.
P. Large Central Vacuole
(Plants only)
1. Storage tank that
holds waste
products, nutrients,
and water.
2. May occupy
between 30% and
90% of the total
plant cell.
VII. Categories of Cells –
“How do cells differ?
1. Prokaryotic (First Cells)
a. Small, simple cells that lack a nucleus.
VII. Categories of Cells –
“How do cells differ?
b. Bacteria are living prokaryotes and are the
most numerous.
VII. Categories of Cells –
“How do cells differ?
2. Eukaryotic (True Cells)
a. Large, complex cell that contains a
membrane-bound compartment called a
nucleus.
VII. Categories of Cells –
“How do cells differ?
b. Both plant cells and animal cells, although
different themselves, are considered
eukaryotic since they have a nucleus.
Comparison of
Prokaryotes and Eukaryotes
Eukaryote Eukaryote
Prokaryote
Animal
Plant
Avg. Size
1 – 10 um
10 – 20 um 30 – 50 um
Cell
Membrane
YES
YES
YES
Cell
Wall
NO
NO
YES
Nucleus
NO
YES
YES
Comparison of
Prokaryotes and Eukaryotes
Eukaryote Eukaryote
Prokaryote
Animal
Plant
Ribosomes
YES
YES
YES
Endplasmic
Reticulum
NO
YES
YES
Golgi
Apparatus
NO
YES
YES
NO
YES
YES
Mitochindria
Comparison of
Prokaryotes and Eukaryotes
Eukaryote Eukaryote
Prokaryote
Animal
Plant
Vacuoles
Lysosomes
Cilia and
Flagella
YES
MANY
ONE
NO
YES
YES
MOST
SPERM
SOME
Chloroplasts
NO
NO
YES
VIII. Theory of Endosymbiosis –
“Why do cells differ?”

Mitochondria and chloroplasts are
descendants of prokaryotic cells so it is
believed that 1.5 billion years ago some
prokaryotic cells were “swallowed” by
larger cells but were not digested.
VIII. Theory of Endosymbiosis –
“Why do cells differ?”

Thus the prokaryotic cells remained inside
the larger cells and gradually lost the ability
to live alone. The partnership that the two
cells formed is called endosymbiosis.
IX. Limits of Cell Size –
“Why are all cells so small?”
1. Since cells are continuously in contact with
their surroundings their parts cannot be to
far from the membrane.
IX. Limits of Cell Size –
“Why are all cells so small?”
2. Cell volume increases faster than surface area. (i.e.
ratio of surface area to volume limits how large a
cell can get):
a. Surface area = measurement of exterior of cell
b. Volume = measurement of interior of cell
Any Questions?

“An education is not how much you have
committed to memory. It is knowing where to
go to find out what you need to know and it is
knowing how to use the information that you
get.”
--William Feather