Cellular Organization and the
Cell Cycle
Cell Specialization and Organization
Cells throughout an organism become
specialized, or develop in different ways,
in order to perform a specific function.
Ex. Red blood cells – transport oxygen
Notice they are flat, bi-concave disks with no
nuclei
Levels of Organization
TISSUES:
As cells become specialized, they are
grouped into units called tissues. A tissue
is a group of similar cells that perform a
particular function.
Most animals have four main types of tissue:
muscle, epithelial, nervous, and
connective (you will learn about these
later)
ORGANS:
Many tasks in the body are too complicated
to be carried out by just one type of
tissue. Many groups of tissues, in these
cases, work together as organs.
Ex. Each muscle in your body is an
individual organ, by definition. Within a
muscle, however, there are nerve tissues
and connective tissues performing
essential tasks to help the organ (muscle)
function.
ADIPOSE (FAT) TISSUE
CARDIAC MUSCLE TISSUE (FOUND IN
HEART)
SKELETAL MUSCLE (IN ARMS, LEGS,
ETC.)
SMOOTH MUSCLE (LINES VESSELS
AND ORGANS)
NERVE CELLS TO
THE LEFT JOIN
TOGETHER TO
FORM NERVOUS
TISSUE, WHICH
THEN FORMS
NERVES (BELOW)
Individual bone cells join together to form bone
tissue, which in turn forms bones and the skeletal
system.
LINES
LUNGS
AND
BLOOD
VESSELS
ALSO
LINES
OUTER
SKIN
LINES KIDNEYS
LINES DIGESTIVE TRACT
ORGAN SYSTEMS:
A group of organs that work together to perform a
specific function is called an organ system.
Ex. Blood cells, blood vessels, and your heart are
all composed of various cell and tissue types,
and all must work together to deliver essential
components to other cells in your body.
Together, they form the circulatory system.
ORGANISM:
All organ systems combined form the organism!
Cell Size and Growth
Surface Area to Volume Ratio
Why Do Cells Divide?
Cells divide before they become too large. The larger a cell
becomes, the less efficiently it moves materials in and
out.
Reasons why a large cell is less efficient than a small one:
 The rate at which cells move materials in and out is
determined by the amount of cell membrane it has
(surface area).
 The rate at which food and oxygen are used up and
waste products are produced depends on the cell’s
volume (the amount of space it has inside).
Therefore, for a cell to be most efficient, it wants as much
surface area as possible, and as little volume as possible.
Thus, it wants a high surface area to volume ratio.
Notice that the volume of each cube gets larger faster
than the surface area increases. Therefore, a smaller
cell has a higher surface area to volume ratio. It is more
efficient because it has a lot a cell membrane as
compared to the space inside of it.
Real Life Examples of High Surface
Area to Volume Ratios
Elephant Ears
Red Blood Cells
Small Intestines (villi)
Car Radiator
Leaves
The Cell Cycle
Remember, cells divide before they get too
large, in order to be more efficient. The
cell cycle consists of many phases:
G1 PHASE
(growth)
CYTOKINESIS
Telophase
Anaphase
M PHASE
(mitosis)
division of the
nucleus
S PHASE
CELL
CYCLE
Metaphase
Prophase
G2
PHASE
(growth)
(synthesis)
DNA
replication
occurs
Interphase

G1, S, and G2 are all part of interphase.
During this time, the cell is growing, DNA
is replicating, and then the cell begins to
prepare itself to divide again in order to
stay small.
M Phase (Mitosis)


Mitosis is division of the cell’s nucleus. Before a
cell divides in two, it must divide up the
chromosomes to ensure that each new cell will
receive it’s own complete copy of the DNA.
(Remember that DNA made a copy of itself
during the S phase for this reason.)
There are 4 phases of mitosis: prophase,
metaphase, anaphase, and telophase.
Prophase
PHASE 1:
PROPHASE
Cell membrane
Spindle
chromosome
spindle
Centriole
Nuclear
Nuclear
envelope
envelope
Centrioles and
spindle form,
nuclear envelope
disappears, and
DNA condenses
into chromatids,
and sister
chromatids pair
together to form
chromosomes. This
is the longest
phase of mitosis.
Metaphase
PHASE 2:
METAPHASE
centriole
spindle
centriole
Chromosomes
line up in the
middle along
spindle.
Anaphase
PHASE 3:
ANAPHASE
Spindle shortens,
thus pulling
chromatids apart
toward opposite
poles
chromatid
chromatid
centriole
Sister chromatids
are pulled apart
as the
microtubules of
the spindle
shorten. As a
result, the
chromatids are
pulled toward
opposite poles.
Telophase
PHASE 4:
TELOPHASE
Chromatids are
now at opposite
poles. New nuclear
envelopes form, as
spindle and
centrioles
disappear. There
are now two nuclei
in the same cell,
each containing a
complete copy of
the DNA.
What Happens Once Mitosis is
Over?

Now that each nuclei has its own copy of
the DNA, the cell can divide into two new
ones, each taking one nucleus with it. This
process is called Cytokinesis.
Cytokinesis
Cytokinesis is the division of the cell’s
cytoplasm. It occurs differently in plants
and animals.
Cytokinesis in Animal Cells
Cytokinesis in Plant Cells
Cytokinesis in animal cells
Cleavage
furrow
What Phase Of the Cell Cycle Is It?
A
D
B
E
C
F
What Phase Of the Cell Cycle Is It?
A ANAPHASE
D INTERPHASE
B TELOPHASE
C CYTOKINESIS
E METAPHASE
F PROPHASE
Cell Timing
All phases of the cell cycle are controlled by
specific hormones. One of these is called
cyclin.
Sometimes, cells continue dividing, even
though they are not needing to.
Uncontrolled growth of cells is called
cancer. Cancer cells form tumors, which
effect the organs in which they are
forming in.
BRAIN TUMOR
PANCREATIC CANCER
BREAST TUMOR
ORAL CANCER
The picture on the left shows a healthy right lung, and a small discolored left
lung. This indicates the presence of tumors, as seen in the picture on the right.