The cells that make up multicellular organisms come in a wide
variety of sizes and shapes.
•Two Examples
1.Red blood cell (8 micrometers in diameter)
2.Nerve cells ( can be 1 meter in large animals)
The cell with the largest diameter is an ostrich egg.
Surface Area-to-Volume Ratio
p. 202
***As the cell grows…the outer surface of a cell
grows more slowly than the volume of material
inside the cell.
 When the surface of a cell is no longer large
enough to let in the proper amounts of food and
let out wastes, the cell divides. This is the
parent cell. If the cell grew too big, its surface
area would be too small to permit enough food
and oxygen to enter or waste products to leave.
Cellular Characteristics
•
Each cell has its own characteristics
1. Size
2. Rate of Growth
3. Timing of Cell Division
•
Sometimes the controls that regulate cell division do
not operate properly-the cell divides in an
uncontrolled manner (cancer)
D. All body cells (somatic or autosomes) have the same
set of genes, but use only the ones necessary for
their functions.
Example: Blood cells produce only what blood cells need.
E. Specialized cells: Cells that perform a specific
function in addition to all the ordinary activities that
keep a cell alive.
Example: Muscle cells – also contract
Cell Division
A.
B.
C.
D.
E.
F.
G.
A.
Parent Cell: The cell that divides.
Daughter Cell: The two cells that result. They have the same traits as the
parent cell..
Traits: Characteristics that are passed on from parent to offspring.
Example: hair color, eye color, tall, short
Chromosomes: Hereditary information that determines the traits of an
individual. They are thick rod-shaped bodies.
Chromatin: Before cell division, a long molecule of DNA covered
(wrapped) with proteins.
Genes: A segment of DNA that controls a hereditary trait.
Diploid (2n): The full complete set of chromosomes.
Found in all Body Cells. (Autosomes/somatic)
Haploid (n): Half the chromosome number. Found in sex cells. (Gametes)
A. male sex cell (sperm)
female
sex cell (egg)
(XY) male sex
chromosomes
23
(XX) female sex
chromosomes
23
Cell Division Continued
I.
Fission: Simplest form of
reproduction. A unicellular
organism splits in two and
forms two organisms.
J. Budding: The growth of a
small fragment on a larger
parent cell. It contains
complete genetic instructions
but only a small amount of
cytoplasm.
NOTE: Fission and Budding are
both forms of asexual
reproduction. (single parent)
• Sex Cells (Gametes)
have only half of the
(2n) diploid number
haploid consist of one
member of each
chromosome
Human Haploid #: 23
Cat Haploid #: 19
Structure of a Chromosome
The Cell Cycle
Interphase: longest busiest
phase
(G-1 Phase – Growth)
(S-Phase – Replication)
(G-2 Phase – Synthesis)
Mitosis: division
(1st) Prophase
(2nd) Metaphase
(3rd) Anaphase
(4th) Telophase
Cytokinesis: cytoplasm
divides
The Cell Cycle
**Sequence of growth and division**
MITOSIS:
The division of chromosomes into two identical
cells.
1. Not dividing (period
of growth)
2. DNA Replicates
3. Stage that cells
spend most of their
time.
4 Phases of Mitosis
Metaphase
PROPHASE
• Chromosome become
visible
• Nuclear membrane
disappears
• Spindle Fibers appear
• The longest phase of
mitosis
Metaphase
• Chromosomes line up
along the equator
(middle of the cell)
Centromeres attach to
spindles
• Centromeres split
• Sister Chromatids
separate
• Chromatids move to
opposite poles
(ends of the cell)
Anaphase
Telophase
• Last phase of mitosis
• Chromatids reach poles
• Chromosomes are not
visible
• Spindle disintergrates
(disappears)
• Nuclear membrane
reappears
• New cell wall or cell
membrane appears
Cytokinesis (cytoplasm divides)
• Following telophase, the
cell’s cytoplasm divides.
• In cytokinesis: a cleavage
furrow pinches the cell in half.
Cytokinesis In Plants
• The division begins in the middle with a cell plate laid
across the equator
Cytokinesis in Animals
•The division begins from
the outside (pinching
inward)
Mitosis (stays the same)
• Each daughter cell has the same number of
chromosomes as the parent cell that produced
it.
46
46
46
46
46
46
46
Meiosis
• Process by which diploid cell divides to produce
four haploid cells. These cells are called
gametes (sex cells), they combine through
sexual reproduction to form a diploid zygote.
The zygote is the first cell of a new organism.
Therefore, meiosis is essential for sexual
reproduction.
• Spermatogenesis: production of sperm cells
• Oogenesis: production of eggs
Meiosis (produce gametes)
(reduce the chromosome number)
cell
46
92
Cell replicated
End of Meiosis I
46
46
23
23
23
23
End of Meiosis II
Meiosis I and Meiosis II
• During Meiosis two nuclear divisions occur
1st Division: called Meiosis I
2nd Division: called Meiosis II
• Reduces the chromosome number to half
• The end result……4 haploid cells
Stages Of Meiosis - Meiosis I
• Prophase I - The beginning phase – DNA which was unraveled and spread all over
the nucleus is condensed and packaged
– Homologous chromosomes (each made of
two identical chromatids) come together and
form tetrads (4 chromatids)
– Crossing over, in which chromatids within
tetrads exchange genetic material, occurs
• Metaphase I - Middle stage - Tetrads line up
along the equator of the cell
Stages Of Meiosis - Meiosis I
• Anaphase I - One copy of each
chromosome still composed of two
chromatids moves to each pole of the cell
• Telophase I - End stage - New nuclear
membranes are formed around the
chromosomes and cytokinesis (cytoplasm
division) occurs resulting in two haploid
daughter cells
Stages Of Meiosis - Meiosis II
• Prophase II - Cells do not typically go into
interphase between meiosis I and II, thus
chromosomes are already condensed
• Metaphase II - Chromosomes line up at the
equator of the two haploid cells produced in
meiosis I
• Anaphase II - Chromosomes made up of two
chromatids split to make chromosomes with one
chromatid which migrate to the poles of the cells
• Telophase II - Cytokinesis and reformation of
the nuclear membrane in haploid cells each with
one set of chromosomes made of one
chromatid
Mother cell
Stages Of Meiosis:
Meiosis I
Interphase
Prophase I:
Condensing
Prophase I:
Chromosomes
Tetrad formation/
Metaphase I
crossing over
Meiosis II
Telophase I
Anaphase I
Stages Of Meiosis:
Meiosis II
TelophaseIII
Prophase
The products of meiosis are 4
haploid cells each with a
unique set of chromosomes.
Metaphase II The products of
mitosis are 2 diploid
cells with identical
chromosomes.
Anaphase II
Telophase II
Crossing Over
Prophase I:
Tetrad formation/
crossing over
Because of crossing over, every
gamete receives a unique set of
genetic information.
Telophase II
Metaphase I
Anaphase I
Telophase I
Meiosis I
Meiosis II
Mitosis (worksheet)
1. Humans have how many chromosomes?
2. Which mitotic stage does the cell spend most
of its time?
3. What is the most rapid dividing cells in the
body?
Fill – in – the blank
The body cells of a cat is 38. That means its’
(4)____ number is 38. An egg cell would have
(5) __ chromosomes. Sex cells are called
(6)__. When an egg was fertilized it would
have