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Cell Division
Chapter 10: Cell Growth and Division
Section 11.4: Meiosis
Vocabulary:
 Asexual Reproduction
 Chromatin
 Sexual Reproduction
 Chromatid
 Mitosis
 Centromere
 Meiosis
 Histone
 Diploid
 Nucleosomes
 Haploid
Asexual Reproduction:
 The production of genetically identical offspring
from a single parent
Sexual Reproduction:
 Offspring are produced by the fusion of two sex
cells – one from each of two parents. These fuse
into a single cell before the offspring can grow.
Mitosis:
 Division of the nucleus
of a eukaryotic cell
 Followed by cytokinesis –
division of the cytoplasm
 The two daughter cells are
identical to the original cell
Meiosis:
 Process that produces gametes from a diploid
cell. A reductive division of the nucleus that
produces four haploid gametes.
Diploid:
 Cells having two sets of chromosomes
 2N = 46
 Examples: All human body cells
 Except reproductive cells (sperm and egg)
Haploid:
 Cells containing only one set of chromosomes
 N = 23
Chromatin:
 DNA and protein (histones) in the nucleus of a
non-dividing cell
Chromatid:
 One of the two identical parts of a replicated
chromosome
Centromere:
 Point of attachment between sister chromatids
Histone:
 Protein molecule that DNA wraps around during
chromosome formation
Nucleosomes:
 The beadlike structures formed by DNA and
histone molecules
Cell Growth, Division, and
Reproduction
Section 10.1
THINK ABOUT IT
 When a living thing grows, what happens to its
cells?
 What are some of the difficulties a cell faces as it
increases in size?
Limits to Cell Size
 There are 2 main reasons why cells do not grow
indefinitely:
1. Larger cells place more demands on their
DNA
 When a cell is small, the information stored in
DNA is able to meet all of the cell’s needs
 It’s like putting a Volvo engine in a Hummer…
just doesn’t have the power to make it go.
Limits to Cell Size
2. Larger cells can’t move enough nutrients
and waste across the cell membrane
 Function of the cell membrane: help exchange
materials between outside and inside of the cell.
 A huge cell is going to need lots of food, water,
and oxygen and produce lots of wastes that
would have to travel through the cell and across
the membrane.
Limits to Cell Size
 The larger a cell becomes, the more demands the
cell places on its DNA.
 In addition, a larger cell is less efficient in moving
nutrients and waste materials across its cell
membrane.
Information “Overload”
 Compare a cell to a growing
town. The town library has a
limited number of books. As
the town grows, these
limited number of books are
in greater demand, which
limits access.
 A growing cell makes greater
demands on its genetic
“library.” If the cell gets too
big, the DNA would not be
able to serve the needs of the
growing cell.
Exchanging Materials
 Food, oxygen, and water enter a cell through the cell
membrane. Waste products leave in the same way.
 The rate at which this exchange takes place
depends on the surface area of a cell.
Exchanging Materials
 The rate at which food and oxygen are used up and waste
products are produced depends on the cell’s volume.
 The ratio of surface area to volume is key to understanding
why cells must divide as they grow.
Ratio of Surface Area to Volume
 Imagine a cell shaped like a cube...
 As the length of the sides of a cube increases, its volume increases
faster than its surface area, decreasing the ratio of surface area to
volume.
 If a cell gets too large, the surface area of the cell is not large
enough to get enough oxygen and nutrients in and waste out.
Traffic Problems
 To use the town analogy again, as
the town grows, more and more
traffic clogs the main street. It
becomes difficult to get
information across town and
goods in and out.
 Similarly, a cell that continues to
grow would experience “traffic”
problems. If the cell got too
large, it would be more difficult
to get oxygen and nutrients in
and waste out.
Division of the Cell
 Before a cell grows too large, it divides into two new
“daughter” cells in a process called cell division.
 Before cell division, the cell copies all of its DNA.
 It then divides into two “daughter” cells. Each daughter cell
receives a complete set of DNA.
 Cell division reduces cell volume. It also results in an
increased ratio of surface area to volume, for each daughter
cell.
Cell Division and Reproduction
Asexual Reproduction
Sexual Reproduction
 A single parent
 Fusion of two sex cells – one
from each of two parents
 Genetically diverse offspring
 Prokaryotic and eukaryotic
single-celled organisms and
 Most animals and plants, and
many multicellular organisms
many single-celled organisms
 Simple, efficient, & effective
 Genetic diversity helps ensure
way for an organism to produce
survival of species when
a large number of offspring.
environment changes
 Genetically identical offspring
The Process of Cell Division
Section 10.2
Chromosomes
Prokaryotic
Eukaryotic
Chromosomes
 The genetic information that is passed on from one generation of cells
to the next is carried by chromosomes.
 Every cell must copy its genetic information before cell division begins.
 Each daughter cell gets its own copy of that genetic information.
 Cells of every organism have a specific number of chromosomes.
Prokaryotic Chromosomes
 Prokaryotic cells lack nuclei. Instead, their DNA
molecules are found in the cytoplasm.
 Most prokaryotes contain a single, circular DNA molecule,
or chromosome, that contains most of the cell’s genetic
information.
Eukaryotic Chromosomes
 In eukaryotic cells, chromosomes are located in the nucleus, and are
made up of chromatin.
 Chromatin is composed of DNA and histone proteins.
 DNA coils around histone proteins to form nucleosomes.
 The nucleosomes interact with one another to form coils and supercoils
that make up chromosomes.
The Prokaryotic Cell Cycle
 Binary fission is a form of asexual reproduction during
which two genetically identical cells are produced.
 For example, bacteria reproduce by binary fission.
Binary Fission (1:02)
The Eukaryotic Cell Cycle
 The eukaryotic cell cycle
consists of four phases: G1, S,
G2, and M.
 Interphase is the time between
cell divisions. It is a period of
growth that consists of the G1,
S, and G2 phases. The M phase
is the period of cell division.
Eukaryotic Cell Cycle | Biology | Genetics (4:19)
G1 Phase: Cell Growth
 In the G1 phase, cells
increase in size and
synthesize new proteins
and organelles.
G0 Phase
 Cells that leave the cell cycle
 Do NOT copy their DNA
 Do NOT prepare for cell division
 Example: cells of the central nervous system
S Phase: DNA Replication
 In the S (or synthesis)
phase, new DNA is
synthesized when the
chromosomes are
replicated.
G2 Phase: Preparing for Cell Division
 In the G2 phase, many
of the organelles and
molecules required
for cell division are
produced.
McGraw Hill Control of Cell Cycle
McGraw Hill - How the Cell Cycle Works
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Cell: B
M Phase: Cell Division
 In eukaryotes, cell division
occurs in two stages:
mitosis and cytokinesis.
 Mitosis is the division of
the cell nucleus.
 Cytokinesis is the division
of the cytoplasm.
Mitosis (1:29)
Important Cell Structures
Involved in Mitosis
 Chromatid – each strand of a duplicated chromosome
 Centromere – the area where each pair of chromatids is
joined
 Centrioles – tiny structures located in the cytoplasm of
animal cells that help organize the spindle
 Spindle – a fanlike microtubule structure that helps
separate the chromatids
Prophase
 During prophase, the first phase




of mitosis, the duplicated
chromosome condenses and
becomes visible.
The centrioles move to opposite
sides of nucleus and help organize
the spindle.
The spindle forms and DNA
strands attach at a point called
their centromere.
The nucleolus disappears and
nuclear envelope breaks down.
This is the longest stage of
mitosis.
Metaphase
 During metaphase, the
second phase of mitosis, the
centromeres of the duplicated
chromosomes line up across
the center of the cell.
 The spindle fibers connect the
centromere of each
chromosome to the two poles
of the spindle.
 This is the shortest phase of
mitosis.
Anaphase
 During anaphase, the third
phase of mitosis, the
centromeres are pulled apart
and the chromatids separate
to become individual
chromosomes.
 The chromosomes separate
into two groups near the
poles of the spindle.
Telophase
 During telophase, the fourth and
final phase of mitosis, the
chromosomes spread out into a
tangle of chromatin.
 A nuclear envelope re-forms
around each cluster of
chromosomes.
 The spindle breaks apart, and a
nucleolus becomes visible in each
daughter nucleus.
 Chromosomes uncoil.
Stages of Mitosis (4:30)
Cytokinesis
Animal Cells
Plant Cells
 The cell membrane is drawn
 In plants, the cell membrane
in (cleavage furrow)until the
cytoplasm is pinched into
two equal parts.
 Each part contains its own
nucleus and organelles.
McGraw Hill - Mitosis and Cytokinesis
Animation
is not flexible enough to draw
inward because of the rigid
cell wall.
 A cell plate forms between
the divided nuclei that
develops into cell
membranes.
 A cell wall then forms in
between the two new
membranes.
The Stages of the Cell Cycle
Mitosis (6:10)
Video clips and Animations
 Mitosis (1:29)
 Eukaryotic Cell Cycle | Biology | Genetics (4:19)
 Stages of Mitosis (4:30)
 Mitosis (6:10)
 Meiosis (5:27)
 PBS (Mitosis vs Meiosis) Interactive