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Cell Growth & Division
Standards:
SB1 – Students will analyze the nature of the
relationships between structures and
functions in living cells.
SB2 – Students will analyze how biological
traits are passed on to successive
generations.
The larger a cell becomes, the more
demands it places on its DNA
and the more trouble it has
moving nutrients and wastes
across the cell membrane
Ratio of surface area to volume
• as the length of the cell
increases, its volume increases
faster than its surface area
V = (L x W x H) units3
A = (L x W ) units2
• this resulting change in the cell’s
ratio of surface area to volume
makes it harder to move
substances in and out
water
waste
O2
food
CO2
• before a cell becomes too large,
a growing cell divides to form 2
daughter cells by cell division –
which increases surface area to
volume ratio
Two types of cell division:
Mitosis
Meiosis
• Occurs in ALL regular body
cells
[like skin cells]
• Occurs only in sex cells
[producing egg & sperm]
• Produces EXACT copies of
first or “parent” cells
[“biological Xerox”]
• Produces genetically
DIFFERENT cells from the
“parent” cells
[variation in DNA]
Cell Division Basics
Genetic information is carried in the
DNA as chromosomes
• cells of every organism have
specific number of
chromosomes
Does more chromosomes an organism has
mean that it is more advanced/smarter?
No…for example:
King Crabs have 208 chromosomes in
each cell
Turkeys have 82 chromosomes in each cell
How many chromosomes do we
have in each of our body cells (not
sex cells)?
Humans have 46 in our body cells
Chromosome – rod-shaped, genebearing body
• DNA-containing
structure that
carries genetic
material from one
generation to
another.
• occurs in pairs
• the two members of each pair are
called homologous chromosomes
(same size and shape)
Cells that contain both
chromosomes are diploid (2N)
Humans – 46 chromosomes
23 pairs
Cells which contain one
chromosome of each
homologous pair are called
haploid or (N)
Humans – 23 chromosomes
(egg and sperm only)
(gametes)
What is the difference between diploid
and haploid?
Diploid – having two copies of each
chromosomes (2n)
Body cells are Diploid
If you see Diploid…
Fruit
flies have
have
850
Skunks
Humans
have
46
You think DOUBLE!
What is the difference between diploid
and haploid?
Haploid – cell with half the number of
chromosomes (n)
23
23
Gametes are Haploid
23
23
If you see Haploid…
Humans
have
23 (in
cells)
Fruit
flies
have
4sex
(in
Skunks
have
25
(insex
sex cells)
cells)
You think HALF!
Remember: Skunks
have 50 inhave
body cells
Remember:
Humans
46
Remember: Fruit Flies have 8 in body
(in body cells)
cells
What is the difference between
gametes & body cells?
Gamete – a haploid sex cell, formed during
meiosis, that can combine with another
haploid sex cell and produce a diploid
fertilized egg
Sperm & Egg
are gametes!
How many
chromosomes are in
human gametes? 23
Body cells reproduce using mitosis
Start with 1 diploid
Notice that they are IDENTICAL!
End with 2 diploid
Autosomes – chromosomes other
than the sex chromosomes
• first 22 pairs of chromosomes
Sex chromosomes – determines the
sex
• 23rd pair of chromosomes
• X or Y
(name of sex chromosomes)
XX = female
XY = male
Karyotype – picture of paired human
chromosomes arranged
by size and shape
Get your note cards!
• Put them in chronological order based
on what you see…
Cell Cycle
Label your diagram in the comp book now; note cards
in a minute…
Cell Cycle - process of cellular
reproduction, occurring in three
main stages
Use 3 different colors to label your
picture!
1. interphase (growth)
2. mitosis (nuclear division)
3. cytokinesis (cytoplasm division)
What occurs during Interphase
(the 1st stage in cell cycle)
There are 3 stages during interphase:
1. G1 - grows
2. S - DNA
replicates
3. G2 - continues to
grow and
prepares to
divide
NOTECARD
Interphase
centrioles
• period between cell divisions
(growth and normal cell
activities)
• nucleus clearly seen
• growth and repair
• G1, S, G2 phases
• chromosomes are not visible;
• DNA is in the form of
chromatin
nucleus
• DNA is copied or REPLICATED
• centrioles duplicate
chromatin
What is Mitosis?
Mitosis -
2nd main stage of the cell
cycle during which the cell’s replicated
DNA divides and 2 genetically identical
diploid daughter cells are produced
What occurs during mitosis?
(the 2nd stage in cell cycle)
There are 4 phases during mitosis:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
NOTECARD
1. Prophase
Nucleus disappears
• centrioles separate and move
to opposite poles
• asters form
• chromosomes form –
chromatin becomes shorter
and thicker (coils)
• spindle fibers form
• nuclear membrane and
nucleolus disappear
Centrioles separate
2. Metaphase
• paired chromatids line up at the equator
• centromere attaches to spindle fibers
Chromosomes line up in
the middle
NOTECARD
NOTECARD
3. Anaphase
• chromatids separate
•chromosomes move to opposite poles
Chromosomes move apart
NOTECARD
4. Telophase
• chromosomes lengthen
• spindle fibers disappear
• nuclear membrane and nucleolus reappear
• cytoplasm begins to divide
Nucleus reappears
Cytoplasm starts to
separate
NOTECARD
What occurs during cytokinesis?
(the 3rd step (LAST) in cell cycle)
Cytokinesis - the last stage of the cell
cycle, during which the cell’s
cytoplasm divides, creating a new
cell.
Daughter Cells
Cytokinesis
Animals
Plants
•cytoplasm pinches
near equator
•plasma membrane
does not pinch
•called cleavage
furrow
•cell plate forms
across equator
• two new cells form
• two new cells form
Results of
Mitosis
• guaranteed genetic
continuity
• two new cells with
identical chromosomes
to the parent cell
Mitosis
Start with 1 diploid
Notice that they are IDENTICAL!
End with 2 diploid
Meiosis
Meiosis – cell division in which there
is a reduction of
chromosomes by half (one
of each chromosome pair)
• occurs in gametes
• occurs only in sexually
reproducing organisms
• from Diploid (2N) to Haploid (N)
Meiosis = 1 duplication and 2
divisions
Results in : 4 fertile sperm cells
1 fertile egg cell
There are 2 stages during Meiosis:
1. Meiosis I
2. Meiosis II
Meiosis I is exactly like mitosis EXCEPT that
Homologues form a
tetrad
Crossing-over occurs
during prophase I
Then there is meiosis IIa second division.
Meiosis I – separates the
homologues
• homologous chromosomes line up synapsis
• twisted homologous
chromosomes - tetrad
• crossing over occurs
Crossing over - exchange of chromosomal
segments between a pair of homologous
chromosomes during prophase I of
meiosis
Meiosis I
Meiosis II
• crossing over results in additional
variety
• this makes us all genetically unique
• leads to genetic diversity
Diversity is Good!
Genetic diversity allows some
individuals of the same species to
continue as their environment
changes…even if others can’t
Hypothetical…lets say you are a
caveman
Which of these would
be LESS likely to
survive?
Because all these cave people have
genetic diversity, but one lacks an
important trait (ability to build tools), he
will not survive his environment… but
the others will!
Meiosis II
• the division process happens again…BUT
the DNA does NOT
copy before dividing
Meiosis I
and
no crossing over
Meiosis II
Results in 4 haploid cells that are NOT
identical
Spermatogenesis – meiosis in
sperm cells
• the beginning of sperm
x
Meiosis I
X
X
Spermatogonial cell
x
46 chromosomes
(2n)
Primary spermatocyte
xx
XX
46 chromosomes
x
x
X
X
(2n)
Secondary spermatocyte
23 chromosomes (n)
_________________________________
I
I
I
I
I
I
I
I
Meiosis II
II
II
II
II
Spermatids
23 chromosomes
(n)
Sperm
23 chromosomes
(n)
Oogenesis – meiosis in an egg cell
• oo = egg
• the beginning of an egg
x
X
X
Oogonial cell
x
46 chromosomes
Meiosis I
(2n)
Primary oocyte
xx
XX
46 chromosomes
x
Secondary oocyte
x
X
(2n)
X
_________________________________
23 chromosomes (n)
I
I
I
I
I
I
I
I
Meiosis II
II
II
II
II
Ootid
23 chromosomes
(n)
Egg
Polar bodies 23 chromosomes (n)
23 chromosomes
(n)
Purpose of the polar bodies is to get
rid of excess chromosomes
The gametes come together to make
a zygote.
This restores the diploid number of
chromosomes in the resulting
individual.
Click here to watch a cool video—from
fertilization to early development (5 min)
Click here to watch a cool video—from
conception to birth (first 6 min of 9 min)…
Many Bacteria & protozoans do not need a partner
to reproduce.
Are they reproducing using mitosis?
Answer: NO...They are using Binary Fission
Binary Fission – an Asexual form of
reproduction used by some prokaryotes in
which a cell divides into two genetically
identical cells. (creates a new individual)
It is like “cloning” themselves
What are the advantages &
disadvantages to being asexual &
sexual?
Asexual Reproduction
Advantages
Disadvantages
Can reproduce without a
partner…
No genetic variation…They are clones. Its
putting all your
in one basket. If a
No eggs
genetic
something kills the parent, it WILL kill ALL the
variation
offspring too. Easily
becomes extinct with little
change to environment.
No
partner
They
don’t haveneeded
to find a
mate/partner.
Able to reproduce quickly.
The greater the number of
Can reproduce
offspring,
the better the
survival
rate of the
quickly
population.
Quick reproduction is also a disadvantage
Quick
reproduction
because
too many
individuals will be
competing
with each other for for
food & space
= Competition
resources
What are the advantages &
disadvantages to being asexual &
sexual?
Sexual Reproduction
Advantages
Disadvantages
Genetic diversity!
Has the ability to create endless
recombination of genes (crossing-over)
coming from 2 parents, all individuals
are different in some way.
Must find a partner. Very difficult if the
population is low and spread out.
Difficult to recover if the species is
endangered.
The species is more able to adapt to
environmental changes
Slow reproduction….takes time…
Slow population growth
Genetic diversity
Species is adaptable
Must have partner
Slow reproduction