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Cell Growth and Division
Chapter 10
In Your Notebook
• Materials move through cells by diffusion. Oxygen and food
move into cells, while waste products move out of cells. How
does the size of a cell affect how efficiently materials get to
all parts of a cell?
• Work with a partner to complete this activity.
• 1. On a sheet of paper, make a drawing of a cell that has the
following dimensions: 5 cm x 5 cm x 5 cm. Your partner
should draw another cell about one half the size of your cell
on a separate sheet of paper.
• 2. Compare your drawings. How much longer do you think it
would take to get from the cell membrane to the center of the
big cell than from the cell membrane to the center of the
smaller cell?
• 3. What is the advantage of cells being small?
Think About It
• When a living thing grows, what
happens to its cells?
• Does an organism get larger because
each cell increases in size or because
it produces more cells?
• What is there about growth that
requires cells to divide and produce
more of themselves?
Limits to Cell Size
• All cells can increase in size
• Eventually they have to divide
• Two Reasons for division
• Larger cells place more demands
on DNA
• Larger cells less efficient moving
materials across cell membrane
Reason #1 – Information Overload
• Even though the cell gets larger its
DNA does not
• Example:
• small town – small library – limited
number of books – people have to
wait to borrow books
• If town grows – so does demand for
books – have to build bigger library
• DNA is our “genetic library”
Reason #2 – Exchanging Materials
• Need to get food in and waste out as
quickly as possible
• Want large surface area to volume ratio
Traffic Problems
• If town only had two-lane main street
leading to center of town – as town grows
– traffic gets congested –
becomes difficult to move
goods in and out
• Same for cell – can’t get
Oxygen and nutrients in
and waste products out
• So – cells don’t keep
growing larger even if
organism does
Cell Division
• Process by which a cell divides into
two new daughter cells
• DNA replicates
• Cuts down on DNA overload
• Reduces cell volume
• So materials can move in and out
quickly
In Your Notebook
• Write two short summary statements
that explain why information overload
and exchanging materials limit cell
size.
Types of Reproduction - #1
• Asexual
• Production of genetically identical
offspring from a single parent
• Simple, efficient, effective
• Population can grow quickly
• Used by single-celled organisms
• Bacteria
• Used by multi-celled organisms
• budding
Asexual – The Good & The Bad
• Advantages
• For bacteria, when conditions are
right, faster reproduction means
better chance of survival
• As long as conditions stay right
being genetically identical is also
good
• Disadvantage
• When conditions change –
everyone dies
Types of Reproduction - #2
• Sexual
• Fusion of two cells
• Need mommy and daddy
• Offspring inherit some of their
genetic information from each
parent
• Used by most animals and plants
• Also many single celled
organisms
Sexual – The Good & The Bad
• Advantages
• When seasons affect food supply it can
be better to take time to find mate and
grow and develop offspring
• Provides genetic diversity
• If environment changes some
offspring may have right combination
of characteristics to survive
• Disadvantage
• Takes a long time
• Can’t do it alone
In Your Notebook
• Use a Venn Diagram to compare
asexual and sexual reproduction
• Look on page 277 if you need ideas
10.2 – Cell Division
• The cell cycle represents the events that
take place as a cell grows, prepares for
division, and then divides into two new
cells. Once two new cells have formed,
they each begin the cycle anew.
• Like other cycles, the cell cycle is broken
into phases. Different types of cells and
cells from different organisms may show
slight variations in some of the phases of
the cycle, but the general course of events
is similar for all living things.
In Your Notebook
1. Why do you think it is advantageous for cells to
go through the different events of the cell cycle
(such as copying their genes or building
the materials needed for division) in an ordered
way? What might happen if a cell underwent all
of these activities at once?
2. Why do you think that it is important for a cell to
grow in size during its cell cycle?
3. What might happen to a cell if all of the events
leading up to cell division took place as they
should, but the cell did not divide?
Think About It
• What role does cell division play in your
life?
• What happens when you are finished
growing?
• Does cell division stop?
• What if you break a bone or get a cut?
• What about general wear and tear
• Like on your skin, digestive system or
even your blood?
Chromosomes
• Bundled packages of DNA
• Read “What is the role of
chromosomes in cell division” on
page 279
Prokaryotic Chromosomes
• Prokaryotes have no nucleus
• DNA
• Found in cytoplasm
• Single, circular chromosome
Eukaryotic Chromosomes
• More DNA than prokaryotes
• Multiple chromosomes in cell
• Fruit flies – 8
• Humans – 46
• Carrots - 18
• Found in nucleus
• Contain DNA and proteins (histones)
Eukaryotic Chromosomes
• Which side, left or right, shows the
smallest structures, and which shows
the largest?
The Cell Cycle
• A series of events during which the
cell grows, prepares for division then
divides into two daughter cells.
Prokaryotic Cell Cycle
• Binary Fission
• Result: Two genetically
identical daughter
cells
In Your Notebook
• Why does the cell duplicate its DNA?
• What might happen if
the membrane did not
indent and pinch off?
The Eukaryotic Cell Cycle
• Four phases
• G1, S, G2 and M
• Timing of cycle
depends on the
type of cell
Phases of Cell Cycle
• G1
• Most growing happens here
• Cell increases in size
• Makes new proteins
and organelles
G = Gap
Phases of Cell Cycle
• S phase
• S = Synthesis
• DNA replicated
Phases of Cell Cycle
• G2
• Preparing for division
• Organelles and
molecules for division
produced
G1, S and G2 are
together known as
Interphase
Phases of Cell Cycle
• M Phase
• Cell division
• Includes mitosis and cytokinesis
• Mitosis
• Division of nucleus
• Cytokinesis
• Division of cytoplasm
What’s a Chromosome?
• Chromatin – uncoiled DNA
• Chromatid – coiled DNA
• Centromere – where duplicate
strands attach
Mitosis – Four steps to divide nucleus
prophase, metaphase, anaphase & telophase
• Prophase
• Genetic material in nucleus condenses
• Chromosomes become
visible
• Spindle starts to form
• Centrioles move toward
poles
• Nucleolus disappears
• Nuclear envelope starts
to break down
Mitosis – Four steps to divide nucleus
prophase, metaphase, anaphase & telophase
• Metaphase
• Chromosomes line up in middle of
cell
• Spindle fibers
connect to
centromeres
Mitosis – Four steps to divide nucleus
prophase, metaphase, anaphase & telophase
• Anaphase
• Sister chromatids separate and move
apart
• Move along spindle
fibers to opposite
ends of cell
Mitosis – Four steps to divide nucleus
prophase, metaphase, anaphase & telophase
• Telophase
• Chromosomes spread out into tangle
of chromatin
• Nuclear envelope
reforms
• Spindle breaks
apart
• Nucleolus reforms
In Your Notebook
• Create a chart that lists two important
pieces of information about each
phase of mitosis.
Cytokinesis
• Now that the nucleus is split we have
to divide the cytoplasm
• Animals
• Membrane drawn in
and pinches apart
• Plants
• Cell plate forms
between new nuclei
Cells Alive
• http://cellsalive.com/mitosis.htm
In Your Notebook
• You are going to write a memoir as if you
were a cell that just divided. Answer the
following as you go:
• Why did you decide to divide?
• Were there signals that told you it was time?
• Describe how you divided.
• What happened?
• In what order?
• Talk about why each process you went through
was important to you and your daughter cells.
10.3 & 10.4
• Regulating The Cell Cycle and
• Cell Differentiation
• In Your Notebook
• Name two things that might go
wrong if the cell cycle is not
carefully regulated.
Controls on Cell Division
• Cells grown in dish in lab will stop dividing when
they touch other cells
• Scrape away neighboring
cells and the cells left start
dividing again
• When you are injured the
cells at the edge start dividing
until healing process is done.
Cyclins and Regulatory Proteins
• Cyclins
• Family of proteins that tell cell when it is time
to divide, duplicate chromosomes of enter
next phase of cell cycle
• Internal Regulators
• Respond to events inside cell
• Won’t let cell enter mitosis without duplicating
chromosomes first
• External Regulators
• Looks at things outside the cell
• Growth factors stimulate growth and division
Apoptosis
• Programmed cell death
• Helps shape structure of tissues and organs
• We don’t have webbed feet because cells in
between toes are
programmed to die
• If they don’t you
have disease known
as syndactily
Cancer
• These cells don’t respond to
signals that control growth
• Divide uncontrollably
• Caused by:
• Gene defect
• Smoking
• Chewing tobacco
• Radiation exposure
• Viral infection
Cancer Treatments
• Surgery
• Physical removal of tumor
• Radiation
• Targeted beam that kills rapidly dividing cells
• Chemotherapy
• Targets rapidly dividing cells throughout body
• Hair, skin and digestive system cells normally divide
rapidly so the healthy cells as well as the cancer cells
are damaged
• This makes your hair fall out
• Gives you mouth sores
• Intense nausea
In Your Notebook
• What makes cancer cells different from healthy
cells?
• When researchers develop drugs to fight
cancer, what characteristics of cancer cells do
you think they target?
• The human body contains 100,000,000,000,000
cells. Starting with one cell – how many
divisions would you need to get to this number?
One Cell To Many
• We are start out as a single cell, become
embryo, then adult
• Differentiation
• Process by which cells become specialized
Pg 293
Stem Cell Development
• Embryo
• Totipotent
• Can become anything
• Blastocyst
• Four days of development
• Hollow ball with cluster
of cells inside
• Pluripotent
• Can become
almost anything
Stem Cell Development
• Embryonic Stem Cells
• The cluster of cells inside the blastocyst
• Pluripotent
• Can become practically anything in the body
• Adult Stem Cells
• Multipotent
• More limited potential but can develop into many
different types of cells
• Bone marrow stem cells can become several
different types of blood cells
• Stem cells in brain can produce neurons or nerve
cells
Stem Cell Research
• Benefits
• These cells could be used to repair or replace
damaged cells and tissues
• Heart attack
• Paralysis
• Ethical Issues
• Right now using embryonic stem cells kills embryo
• Is the embryo entitled to the rights and protections of
any human being?
• On the horizon
• Working to extract cells without harming embryo
• Finding ways get adult stem cells to act like
embryonic ones
In Your Notebook
• Why is differentiation important to
multicellular organisms?
• What are the three different types of stem
cells and their respective potential to
differentiate?
• How might technological advances help
address the ethical concerns surrounding
stem cell research?