Cells
I. Introduction – “What is a cell?”
A cell is the smallest unit that can carry out
all the activities necessary for life. (i.e.
homeostasis, metabolism, reproduction,
heredity, cellular organization)
 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.
 From a simple magnifying glass to more
complex compound light microscopes to the
latest technology of transmission electron
microscopes and scanning electron
microscopes.

a. Robert Hooke (1635-1703)


In 1665, the English
scientist and monk,
observed a thin slice
of cork.
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 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 the
same conclusion, that
all animals were
composed of cells.
f. Rudolph Virchow (1821-1902)

In 1855, the German
physician, while
studying diseases,
determined that cells
come only from other
cells. (i.e. cells
produce 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
V. Levels of Cellular Organization “How are cells organized?”
i)
ii)
iii)
iv)
v)
Cells
Tissues
Organs
Organ systems
Organisms
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.

BY UNDERSTANDING THE STRUCTURES
IN A CELL, YOU CAN PREDICT THEIR
FUNCTIONS.
A. Nucleus
1. Termed the “brain” of
the cell.
2. Used to direct all cell
activities and serves as the
storage center for the
cell’s DNA.
3. Contains the
chromosomes (genes).
B. Nucleolus and
C. Nuclear Envelope
B1. Stores genetic
material such as RNA..
B2. Site where ribosomes
are synthesized (made).
C1. Double membrane
around the nucleus is used
to protect it and allow
nucleic acids to enter and
leave the nucleus.
D. Cell Membrane
1. The semipermeable
membrane allows
specific molecules to
come in and out of the cell.
2. They also protect the
cell and give it support.
3. The lipid bilayer is
made of hydrophilic heads
and hydrophobic tails.
E. Cytoplasm
1. A jellylike fluid
within the cell that
helps to cushion the
cell and other
organelles.
2. Cytosol is the liquid
portion, which is in
constant motion as the
particles move around.
F. Mitochondria
1. Often called the
“powerhouse” of the cell
because it is the place
where energy/ATP is
converted. (i.e. site
where cellular
respiration occurs)
2. The number of
mitochondria in a cell
will vary. (i.e. muscle
cells have more
mitochondria)
G.Ribosomes
1. These are the most
numerous of the cells
organelles because
they are they sites
where proteins are
created (synthesized).
H. Endoplasmic Reticulum (ER)

The ER directs the traffic
of the many molecules by
creating a series of
channels that act as a
“highway system” though
the cytosol.
1. Rough (has ribosomes
on it) – synthesizes
proteins.
2. Smooth (no ribosomes)
– synthesizes lipids.
I. Golgi Apparatus
1. Labels the
proteins that are to
be used inside and
outside of the cell.
2. Also packages and
distributes the
proteins to specific
destinations.
J. Lysosome
1. A type of vacuole
that contains
digestive enzymes to
break down food
particles and diseasecausing bacteria that
enter the cell.
2. “Recycling centers”
of the cell.
K. Vacuoles
1. Fluid filled space
that aids in digestion,
storage, support, and
helps maintain water
balance.
2. Often stores
enzymes and waste
products.
L. Cilia and Flagella
1. They are hair-like
projections out of the
cell membrane.
2. Used for
locomotion in
unicellular organisms
and movement of
materials in multicellular organisms.
M. Centrioles (Animal only)
1. Organizes fibers
during cell division.
(i.e. mitosis)
2. Always found in
pairs.
N. Chloroplasts (Plants only)
1. These organelles make
chemical energy in the
form of sugars, using
air, water, and energy
from sunlight. (i.e.
photosynthesis)
2. Found mostly in algae
such as seaweed and
green plants.
O. Cell Wall (Plants only)
1. Thick outer layer that
provides strength by
making the cell rigid.
2. Mostly made of
cellulose but with
some pores to allow
ions and molecules to
pass through.
P. Large Central Vacuole
(Plants only)
1. Holding tank –
stores waste products,
nutrients, and water.
2. May occupy
between 30% and 90%
of the cells volume.
VII. Categories of Cells –
“How do cells differ?
1. Prokaryotic (First Cells)
a. Small, simple cells that lack a nucleus.
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 contain a
membrane-bound compartment called
the nucleus.
b. Both plant cells and animal cells,
although different themselves, are
considered eukaryotic since they have a
nucleus.
A. Nucleus
B. Membrane
bound organelles
C. Size (microns)
D. Evolved
(billion years ago)
E. Types of cells
Prokaryote vs.
none
Eukaryote
yes
none
1-10µm
3.5bya
yes
2-1,000µm
1.5bya
bacteria
plants/animals/fungi
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. 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.
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