Unit Title: Cell Division
Course: Biology
Cell Division
Essential Questions:
Enduring Understandings:
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All cells come from division of pre-existing
cells.
The cell cycle is regulated by internal and
external chemical signals.
Cells must divide because they cannot
maintain homeostasis if they grow too
large.
DNA (and sometimes RNA) is the primary
source of heritable genetic information
necessary for cells (and organisms) to
survive, grow and reproduce.
DNA must be replicated before cells can
divide.
Prokaryotic cell division is simpler and faster
than eukaryotic cell division because only
single circle DNA.
Mitosis produces copies of eukaryotic cells
for growth, development, repair and
asexual reproduction.
Meiosis produces gametic cells with half the
normal number of chromosomes for sexual
reproduction.
Human lifecycle: fertilization> zygote>
mitosis>mature organism>meiosis
(gametes) > fertilization
Organisms typically have two alleles for
every gene; one copy of each gene
randomly inherited from each parent.
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Organisms resemble family members
because they share common genes, but are
not identical to relatives because alleles may
be mutated, shuffled, and randomly
recombined during sexual reproduction into
trillions of possible variations.
1
How and why do cells copy
themselves?
What is the main advantage
bacteria have over eukaryotic
organism?
Why do organisms need meiosis
to engage in sexual reproduction?
How do processes in meiosis and
fertilization create genetic
variation?
How are genes from parent
organisms passed on to offspring?
Unit Title: Cell Division
Course: Biology
Cell Division
Critical Skills:
Critical Content:
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Cell cycle
Mitosis
Meiosis
Fertilization
Mutation
Genetic variation
DNA
Chromosome
Centromere
Chromatids
Interphase
S phase
Cytokinesis
Spindle fibers
Prophase
Metaphase
Telophase
Anaphase
Daughter cells
Cell differentiation cell
stem cells
Sex chromosomes
contact inhibition
cancer
Homologous chromosomes
Diploid
Haploid
Tetrad
Crossing over
Gamete
Sperm
Egg
Polar bodies
Fertilization
Zygote
Mutation
2
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Identify structures associated with
cell division from illustrations or
descriptions.
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Compare and contrast mitosis and
meiosis processes and purposes.
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Identify and organize cell division
stages from key attributes in
diagrams.
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Explain how DNA is passed from
parents to offspring.
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Analyze how a change in mitosis or
meiosis will affect chromosome
structure, gamete viability and
genetic diversity.
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Properly use a compound
microscope.
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Determine volume and surface area
of a cube.
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Calculate and compare ratios.
Unit Title: Cell Division
Course: Biology
Big Idea: Living systems store, retrieve, transmit, and respond to information
essential to life processes. Cells have a lifecycle in which heritable information is
passed to the next generation (new cells & new organisms) via DNA replication,
mitosis, meiosis and fertilization.
Synopsis: All cells come from the division of a parent cell. In eukaryotes, mitosis
is cell division in which each daughter cell receives and complete and identical set
of chromosomes. Mitosis allows organisms to grow, repair and reproduce
asexually. Conversely, sexual reproduction is the combination of gametic cells
from two parents to form a zygote (fertilization). Meiosis is the mechanism for
producing gametes, or sex cells, with a unique half set of normal chromosomes.
Meiosis and fertilization produce the genetic and phenotypic variation upon
which natural selection operates.
Approximate Instructional Days: 12
Learning Targets
3.1.1
Cells have particular structures that underlie their
functions.
3.1.2
Most cell functions involve chemical reactions.
3.1.3
Cells store and use information stored in DNA to guide
their function.
Most of the cells in a human contain two copies of each of
22 different chromosomes.
3.2.2
3.2.3
Changes in DNA (mutations) occur spontaneously at low
rates.
3
Focused
Assessed
Unit Title: Cell Division
Course: Biology
Suggested Learning Experiences with Ideas for Differentiation
R)=Remediation E)=Extension
Vocabulary
Cell Size Lab - investigate changing ratios of
surface area to volume
Determine changes in surface area relative to
volume as a cell grows
E: Cell surface area/volume affected by
other factors http://www.mhhe.com/biosci/
genbio/biolink/j_explorations/ch02expl.htm
Model mitosis and meiosis with magnetic toys,
sockosomes, string & pipe cleaners, etc
R: Mitosis & Meiosis video animations –
(google each for pbs, mcgraw-hill; cells
alive, etc)
Create flipbooks for mitosis & meiosis
R: Shorten flipbook assignment or use
premade flipbooks for coloring and
labeling
Compare & Contrast mitosis and meiosis
E: Compare/contrast poster for cell
division: binary fission, mitosis and
meiosis
Identify stages of mitosis in Allium root tip
slides
Extension ideas
 Cancer – unregulated cell division
 Stem cell research – potential in
undifferentiated cells
 Fun cell cycle game at
http://www.nobelprize.org/
 Mitosis thrillionare game
 Quia quizzes online
4
Unit Title: Cell Division
Course: Biology
Resources
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Biology by Miller & Levine. Pearson (2010) Chapter 10 – Cell cycle and Mitosis;
Chapter 11.4 – Meiosis
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Teacher notes for cell division – major concepts, student misconceptions and link to a
modeling exercisehttp://serendip.brynmawr.edu/exchange/files/MitosisMeiosisConceptsTN.pdf
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Cell size Lab – Biology (p275) or http://www.biologyjunction.com/cell_size.htm or
http://colgurchemistry.com/Sc10/Sc10BIOLOGY/PDFS/Sc10BiologyAct10SurfaceAreaVo
lumePDF.pdf
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Flipbook templates http://sciencespot.net/Media/mitosisbook.pdf ;
http://sciencespot.net/Media/meiosispg1.pdf
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CELL DIVISION UNIT OUTLINE (attached)
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Vcell cell cycle with mitosis video - http://vcell.ndsu.edu/animations/mitosis/movieflash.htm
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Mcgraw-Hill animations- cell cycle: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_
works.html; mitosis: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokin
esis.html; meiosis: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter3/animation__how_meiosis_works.
html ; compare mitosis and meiosis: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__comparison_of_mei
osis_and_mitosis__quiz_1_.html
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PBS Nova mitosis & meiosis compared http://www.pbs.org/wgbh/nova/miracle/divi_flash.html
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Cell Cycle game http://www.nobelprize.org/educational/medicine/2001/cellcycle.html
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Mitosis Thrillionaire game (review mitosis) http://www.syvum.com/cgi/online/tgamem.cgi/squizzes/biology/mitosis.tdf?0
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Quia Quiz – compare - http://www.quia.com/pa/44116.html?AP_rand=12254302
5
Unit Title: Cell Division
Course: Biology
Unit Outline
I. CELL COPIES FOR GROWTH, REPAIR AND ASEXUAL REPRODUCTION
A. Why can’t cells just get bigger and bigger?- Can’t maintain homeostasis!
1. DNA Overload - If a cell get too big, then there isn’t enough DNA directions to make
all of the needed proteins.
2. Problems moving materials
 If the cell gets too big, food, gases, etc. cannot easily travel across the cell
 Surface area and volume: The volume of the cell grows faster than the surface
area of the cell membrane.
 There isn’t enough room on the membrane to get enough stuff in and out
of the cell for the increasing volume that needs materials.
B. CELL DIVISION - Process by which a cell becomes two daughter cells
 Each daughter cell has increased surface area relative to volume = better exchange of
materials
1. Why do we need more cells?
1. Make more organisms (asexual reproduction = make clones!)
2. Growth and Development - all multi-cell creatures start out as a single cell
3. Repair and Replacement – millions of our cells die every second of every day
2. Cell Division Requires Preparation!
1. cells only have one set of DNA instructions!!
2. First step to making an identical second cell is making a copy of the DNA.
3. Once done, the copies must be separated and sorted into the two sides of the cell.
4. Then the cell can split into two.
BINARY FISSION – Prokaryotes Divide = asexual reproduction
1. Circular DNA copied
2. DNA separates to opposite sides of the cell
3. The cell membrane/wall divides into two cells
MITOSIS – Eukaryotes Divide - The nucleus must divide before the cell can
C. CELL CYCLE - the series of events that eukaryotic cells go through as they grow and
divide.
During the cell cycle a cell grows; prepares for division; divides to form two
daughter cells, each of which begins the cycle again
1. Interphase – period between cell divisions in which cells grow, function and prepare
for division (longer phase)
◦ 3 phases: G1; S; and G2
6
Unit Title: Cell Division
Course: Biology
2. M phase = period cell is actually dividing (quick phase)
1. Mitosis = division of the nucleus
4 phases: Prophase, Metaphase, Anaphase and Telophase
1. Cytokinesis = division of the cytoplasm
D. 3 PHASES OF INTERPHASE
1. G1phase- cell grows and does its special jobs
2. S phase - DNA replicates (copied)
3. G2 phase - organelles and other materials needed for division are reproduced
E. STAGES OF MITOSIS
Centromere
1. PROPHASE (first)
a) DNA condenses
b) Spindles form at poles
c) Nuclear membrane
dissolves
DNA Condenses into Chromosomes.
 Chromosomes- condensed DNA coiled around proteins in the nucleus; two copies
of genetic code (made during S phase)
 chromatids -duplicated chromosomes attached at the center by the centromere
 Centromeres - like a “twist tie” that holds the sister chromatids together.
o Number of centromeres = number of chromosomes
2. METAPHASE (middle)
a) Spindles force chromosomes to line up on cell “equator”
3. ANAPHASE (apart)
a) Spindles pull chromatids apart
4. TELOPHASE (Far end)
a) Single chromosomes move to poles
b) nuclear membrane reforms around each group
c) Cytokinesis begins
CYTOKINESIS - division of cytoplasm
 Starts during telophase
 animal cells – cytoplasm is pinched inward by cell membrane
 plant cells –a cell plate forms midway to become cell wall &
membrane
Mitosis makes 2 cells that are
 Identical to original cell
 Same chromosome number and exact genes
Some cells stop mitosis after cell differentiation (specialization)
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Unit Title: Cell Division
Course: Biology
 Skin cells divide often - constantly renewed and repaired.
 Liver cells - can divide to repair minor damage
 Most nerve and muscle cells do not divide - Why? Critical functions might be
interrupted
G. CELL CYCLE REGULATORS
1. Proteins regulate the timing of the cell cycle in eukaryotic cells (cyclins)
Two types of regulatory proteins
◦ internal regulators = control events inside the cell (regulate mitosis phases)
◦ external regulators = respond to signals from outside the cell (growth
hormones, contact inhibition)
2. Cell division can be turned on and off
a) Hormones
b) Contact Inhibition - when cells come into contact with each other, normal cells
stop dividing.
◦ When space is found between cells, cells begin dividing once again
H. CANCER - uncontrolled cell division.
 If cells continue to divide over and over, eventually a mass of cells can be formed
called a tumor that may interfere with normal tissue or cell functions.
 Cancer cells do not respond to the signals that regulate the growth in most cells
Causes
a) Carcinogens – known cancer causing agents
a. (Tobacco, asbestos, chemicals)
b) radiation exposure (X-ray, sun)
c) viral infections (HIV, Leukemia, EBV)
d) high number of cancer cells have a defect in a gene called p53, which normally
halts the cell cycle until all chromosomes have been properly duplicated
Types of Cancer
a) Benign
b) Malignant/ metastasis
II. MEIOSIS
A. CHROMOSOME NUMBER
 Organisms have different numbers of chromosomes.
Fruit flies =8, dogs = 78, chimps = 48
 Chromosomes occur in pairs because organisms have one set of from each parent.
 Human cells (except sex cells) have 23 pairs of chromosomes: 23 from mom and
23 from dad for a total of 46 chromosomes
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Unit Title: Cell Division
Course: Biology
1. HOMOLOGOUS CHROMOSOMES - Matched set from each parent which contain the
same type of genetic information although not necessarily the exact same gene
expression.
 Sister chromatids are exactly the same, but homologous chromosomes are not
 EX: a pair of homologous chromosomes may have genes for eye color, but
the one from mom codes for brown eyes and the one from dad codes for
blue.
a) DIPLOID (2n) = “two sets” - a cell that contains two sets of homologous
chromosomes, usually one from mom and one from dad
N = number of chromosomes from each parent
Human diploid (2n) cells = 46 chromosomes
2 x23 from each parent = 46
b) HAPLOID (n) - a cell that contains only one set of chromosomes
Human haploid cells (n) = 23
What was the purpose of mitosis?
To divide into two cells that are Identical to original cell
Same chromosome number and exact genes
Diploid cells undergo mitosis and produce diploid daughter cells
HOW DO WE AVOID CHROMOSOME DOUBLING EACH GENERATION?
 If sex cells (gametes) had the usual number of 46 chromosomes, they would produce
a zygote with 92 chromosomes.
 If this happened again in the next generation, then 92 + 92 = 184
chromosomes…and in the next generation we would have 368, and each generation
would keep doubling.
 Obviously, this can’t happen
1. Cell would have too many instructions
2. Nucleus would burst with too many DNA molecules
 A single DNA strand is about 5cm (2 inches) long
B. GAMETES - haploid sex cells
 Sperm(male) and egg (female)
 contain half the normal number of chromosomes (hapliod) than other cells
 produced by meiosis, not mitosis.
C. MEIOSIS - cell division in which the number of chromosomes per cell is cut in half by
separating homologous chromosomes in a diploid cell
 Produces haploid gametes from a diploid starting cell
2 STAGES:
 Meiosis I – separates homologous chromosomes to form two new haploid cells
 Meiosis II – separates chromatids in the two cells from first stage to form four
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Unit Title: Cell Division
Course: Biology
haploid
cells
MEIOSIS I
1. INTERPHASE I
Cells undergo a round of DNA replication, forming duplicate chromosomes
2. PROPHASE I
 Each chromosome pairs with its corresponding homologous chromosome to form
a tetrad.
 There are 4 chromatids in a tetrad.
 Tetra = four
CROSSING OVER - Homologous tetrads exchange portions of their chromatids
during prophase I
 Crossing-over produces new combinations of GENES.
3. METAPHASE I
 Tetrads line up in center and spindle fibers attach to the chromosomes.
4. ANAPHASE I
 Fibers separate tetrads
 homologous chromosomes pulled toward opposite ends of the cell.
5. TELOPHASE I & CYTOKINESIS
 Nuclear membranes form.
 The cell separates into two cells.
New cells are haploid and genetically different
MEIOSIS II
The second stage of meiosis is exactly like mitosis but with haploid cells.
Chromosomes line up, chromatids travel to opposite sides of the cell, and the cell splits.
Prophase II>MetaphaseII>Anaphase II>Telophase II> cytokinesis
D. MAKING GAMETES
1. Sperm - four equal-sized MALE gametes formed by meiosis
2. Egg - one female gamete formed by meiosis.
o POLAR BODIES - the other three cells made but usually not involved in
animal reproduction
E. FERTILIZATION = SEXUAL REPRODUCTION - The union of two haploid gametes to
form a diploid zygote
 Combining gametes from two different parents leads to a variety of people with
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Unit Title: Cell Division
Course: Biology
high genetic diversity
 Humans - sperm with 23 chromosomes combines with egg with 23 chromosomes
to form a zygote with 46 chromosomes.
Zygote = fertilized egg > will undergo mitosis and cell differentiation to become a
multicellular organsism
Meiosis allows for sexual reproduction which increases genetic variation in the
offspring. More variation = more adaptable population
How?
1. Produces haploid cells so don’t constantly double DNA each generation
2. DNA mixed up during crossing over of prophase I & random alignment in
Metaphase I
Mutations – permanent changes to your DNA, most occur during DNA replication but
some can occur during mitosis and meiosis
1. Separation mistakes (nondisjunction)
2. Chromosome breaks (deletions, inversions, translocations)
Somatic chromosomes - 22 pairs of our chromosomes have the same type of information
(same genes) on both copies
Sex chromosomes - determine gender, X and Y code for different sets of genes
X X= female & XY = male
Meiosis
Mitosis
 Start with a diploid cell
 Start with a diploid cell
 Occurs in two phases:
 Occurs in one phase.
 Genetic information remains the same.
Meiosis I & Meiosis II
 Genetic information is shuffled
 Results in 2 identical diploid daughter
cells.
 Results in 4 different haploid
daughter cells
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