Cell Reproduction
Chapter 9
Cell Growth
Main Idea: Cells grow until they reach their
size limit, then stop growing or divide
 Objectives:

Explain why cells are relatively small
 Summarize the primary stages of cell cycle
 Describe the stages of interphase


Review: What’s the cell theory say?
All organism are made of cells
 Cells are the smallest unit of living organisms
 Cells only come from other cells

Cell Size

Imagine yourself on a tennis court playing 1
on 1.
Wouldn’t it be hard if the court were the size of a
football field?
 Cells have a size limit to ensure all the needs of
the cell are met

Surface Area to Volume

Limits to cell size: ratio of its surface area to its volume

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Surface area is the area covered by the plasma membrane
Volume is the space inside the cell
Figure 9.1 and Pg. 244 Connection to Math
By remaining small, cells have a much higher ratio of
surface area to volume and can sustain themselves easier
Demo!
So: Do large cells perform their tasks more efficiently than
small cell?
Mini Lab pg. 245
More About Size…


Small cells can transport substance easier than
large cells
Diffusion would not be efficient, since it is
passive transport, if the cell were large


It would be like trying to float a toy boat across a
small puddle or across a large pond
Cell size also limits the ability of a cell to
communicate

Signals for processes might not occur fast enough
to signal another reaction

Signals for protein synthesis need to reach the ribosomes
in time to continue the cycle
What happens when a cell
reaches its size limit?

It will either:

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Most cells divide because it prevents the cell
from becoming too large and it helps the cell
reproduce
Cell Cycle: the growing and dividing of cells
There are 3 main stages


Stop growing
Divide
Interphase, Mitosis, Cytokinesis
Time of division varies with the cell

Most cells take 12-24 hours to divide in animals
Cell Cycle
During Interphase, the cell grows, develops,
duplicates its DNA and prepares for division
 Three stages of Interphase: G1, S and G2

Cell Cycle

Interphase:
Cells spend most of their life
 G1 stage- Time immediately after the cell
divides; cells grow to mature size

G
stands for “Gap” time between cell reproductions
 Some cells don’t divide after this

Example: nervous system cells only divide once
S Phase- DNA is copied
 G2 stage- Cell prepares for division


Find your 7 o’clock partner
Designate partner A and partner B
 Partner A asks: What are the stages of the cell
cycle?
 Partner B: What occurs in G1?
 PA: What happens in G2?
 PB: What’s the S phase?

Review
Main Idea: Cells grow until they reach their
size limit, then stop growing or divide
 Objectives:

Explain why cells are relatively small
 Summarize the primary stages of cell cycle
 Describe the stages of interphase

Section 9.2
Main Idea: Eukaryotic cells reproduce by
mitosis, the process of nuclear division and
cytokinesis, the process of cytoplasm
division.
 Objective: Describe the events of each
stage of mitosis
 Objective: Explain the process of
cytokinesis


Think of events in your life that are cyclical
Example: The passing of comets in the year
 Deer in the rut
 Turkeys in spring breeding season
 Day routine

Mitosis

Goal: replicated genetic material separates
and the cell prepares to split into two cells

Why?
 It
allows genetic information to be passed onto
daughter cells

Uses?
 Replace
damaged cells
 Increases the cell number of an organism- in other
words, the organism grows

SQR3 for “The Stages of Mitosis”, pg. 248
Chromosomes
Contain coiled DNA and proteins
 Chromatin is the relaxed form of DNA in the
cell’s nucleus, looks like a single strand
 Sister chromatids are structures that contain
identical copies of DNA
 Centromere holds the sister chromatids
together
 Socks!!

Mitosis

Prophase:


Longest phase
Chromatin tightens into chromosomes
The chromosomes become shaped like an X
 Centromeres are present

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Nucleus disappears
Microtubules called spindle fibers form in the
cytoplasm
Centrioles (also microtubules) migrate to the end of
the cell (only in animal cells)
Spindle apparatus: name given to the group of
spindle fibers, centrioles, etc. that help move the
chromosomes around in the cell
Mitosis
Prophase Cont’d:



Nuclear envelop
disappears
Spindle fibers attach
to the sister
chromatids to move
the chromosomes
around
Mitosis
Metaphase
Chromosomes are easy
to identify
 Spindle fibers move
chromosomes to center
of cell

Anaphase
Chromatids are separated
and move toward
opposite poles caused by
shortening spindle fibers
 Whiles the chromatids
separate, they are
considered to be
individual chromosomes
 Centromere first

Telophase
Spindle fibers disappear
after chromosomes are
separated
 Chromosomes loosen up
 Nuclear envelope and
nucleus reappears

Mitosis

Cytokinesis:
Cell pinches inward
and cytoplasm
seperates cell into two
new cells
 Cleavage furrow
appears and cell
divides (animals)
 Cell Plate (plants)

Animations

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Mitosis Video
Fly Mitosis
Cells Alive
Mitosis
Interactive Classroom
Video
Onion Root Tips

http://www.biologycorner.com/flash/onion_mi
tosis.swf
Review

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Main Idea: Eukaryotic cells reproduce by
mitosis, the process of nuclear division and
cytokinesis, the process of cytoplasm division.
Objective: Describe the events of each stage of
mitosis
Objective: Explain the process of cytokinesis
Card Sort on Mitosis Stages
What are the two differences between plant and
animal cells in mitosis?
Cell Cycle Regulation

The timing and rate of cell division are
important

Cyclins (proteins) bind to an enzyme, cyclindependent kinases, to start the different stages
of cell cycle
Cancer
Although cell cycle has a system of checks
for quality, sometimes things go wrong
 Cancer is the uncontrolled growth and
division of cells (caused by the failure of the
regulation of the cell cycle)
 Cancer cells spend less time in interphase
 Pg. 254 picture

Stomach Cells

Normal Chicken
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Interphase
Prophase
Metaphase
Anaphase
Telophase
120 min
60 min
10 min
3 min
12 min

Cancerous Chicken

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Interphase
Prophase
Metaphase
Anaphase
Telophase
16 min
15 min
2 min
1 min
3 min
What effect do you think the difference in times have
on the organism?
Causes of Cancer
Does not just occur in weak organisms
 Mutations or changes in the DNA, usually
that control the cell cycle, cause cancer

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Often, the mutations are repaired
Environmental factors
Smoking, asbestos, chemicals, etc
 Radiation, x-rays

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Not all cancers can be prevented

Genetics
Apoptosis
Programmed cell death
 Why would cells WANT to die?

Cells in hands and feet
 Tree leaves falling in autumn
 Cells that are damaged

Stem Cells
Discovered in 1998
 Unspecialized cells


Embryonic
 Results
after a sperm fertilizes an egg
 controversial

Adult
 Found
in tissues in body
 Can be used to maintain/repair the same kind of
tissue they came from
 Newborns have adult stem cells
 Less controversial
Paralysis Cured?
Pg. 258
 Mapping Stem Cells
 MJF Video
 Video- Terra Incognita

Meiosis- Sect. 10.1
Main Idea: Meiosis produces haploid
gametes
 Objectives: Explain the reduction in
chromosome number that occurs during
meiosis
 Recognize and summarize the stages of
meiosis
 Analyze the importance of meiosis in
providing genetic variation

Which Cells?

The only cells that go through meiosis are
the reproductive cells

The results of meiosis are sperm or egg cells
In females: meiosis takes place in the
ovaries, before birth
 In males: meiosis takes place in the testes,
usually starting at puberty

Chromosomes

Instructions for traits are
located on chromosomes

Found in the nucleus
DNA on chromosomes is
arranged as genes (which
control the production of
proteins)
 Chromosomes consist of
hundreds of genes

Homologous Chromosomes
Human body cells have 46
chromosomes
 At conception, each parent
contributes 23 chromosomes
 The chromosomes that match
from each parent make
homologous chromosomes
 They have the same length,
same genes and same
centromere position

Haploid and Diploid
Gametes: sex cells that have half the
number of chromosomes
 Gamete number change with the species
 n represents the haploid chromosome
number
 Fertilization is the process when one haploid
gamete combines with another

n + n = 2n
 2n represents the diploid number

Numbers

Different species have different number of
chromosomes
Meiosis

Remember: Gametes
are formed during
meiosis

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It reduces the number of
chromosomes in the cell
When the gametes
combine (sperm and egg)
a zygote is formed (a
diploid group of cells that
grow into an embryo)
Meiosis consists of two
stages
Meiosis I

Meiosis I:

MOST of the phases are the
same as mitosis:
 Interphase,
prophase, metaphase,
anaphase and telophase

Exception:
 Prophase
I-Instead of pairing on top
of each other, they pair side by side
with the homologue – Synapsis is
the name given to the pair
Meiosis I

Crossing-over occurs in
Prophase I: genes are
shared from each pair
 Norwegian

wrestling…
Results in genetic
recombination
Meiosis I
Metaphase I: the pairs
of homologous
chromosomes line up at
the equator of the cell
 Can we borrow you
shoes?

Meiosis I
Anaphase I- Instead of
pulling apart the single
chromosome, the
homologous pairs are
separated
 Chromosome number is
reduced from 2n to n
when the pairs get
separated

Meiosis I

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Telophase I: new cells
are haploid, but still has
it’s sister chromatid
The chromatids might
not be identical anymore
After cytokinesis, the
cells go into interphase
before the second set of
divisions

But, the DNA is not
duplicated
Meiosis II

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Cytokinesis results in four
haploid cells, each with n
number of chromosomes.
Four cells are produced
instead of two
Visualizing Meiosis
Meiosis Video
Comparison Video
United Streaming Video
Two interactive games
online to quiz yourself with
Questions for you
1. How many chromosomes will there be in
the gametes of an organism with 18
chromosomes?
 What would happen if the sister chromatids
of one pair did not separate during anaphase
II?


Down Syndrome
Numbers

Karyotype:
Picture of the pairs
Of chromosomes in
a cell

Why is Meiosis Important?

It results in genetic variation
In Prophase I the
homologous chromosomes
line up randomly
 Depending on the order they
line up in determines who
they “cross over” with

Asexual Reproduction

Asexual- one parent
Does not involve meiosis or the union of
gametes
 Bacteria- prokaryotes
 Offspring are identical to parents
 Rely on binary fission or mitosis

Cell Division- Prokaryotes

Use binary fission

Three steps:
 Chromosome
copies itself
 Cell grows double it’s size
 New cell wall forms between the two chromosomes
and the cell splits

Bet you wish Eukaryotes were that easy…
Sexual Reproduction
Offspring are genetically different from
parents because genes are combined in
meiosis
 Twins, contain unique combinations of
parents’ genes
 Advantage, through evolution, offspring can
adapt rapidly to new conditions


If disease strikes a crop of grain, the plants that
survive have the genes to overcome the disease
Cell Division- Eukaryotes
Mitosis- results in new cells with genetic info
identical to the old
 Meiosis- reduces chromosome number by
half, then join other cells to restore the
diploid number

Review Sect. 10.1
Main Idea: Meiosis produces haploid
gametes
 Objectives: Explain the reduction in
chromosome number that occurs during
meiosis
 Recognize and summarize the stages of
meiosis
 Analyze the importance of meiosis in
providing genetic variation
