10 – 1: Cell Growth and
Division
How do living things grow?
• Grow by producing more cells. (Cells do
not increase in size)
– A human adult has about 10 trillion – 100
trillion cells in their entire body.
– About how many cells does a newborn
baby have?
Answer: Much less
Cells Dividing
Blood Lily
Limits to Cell Growth
•
2 reasons why cells divide rather than grow?
1. The larger cell has more trouble moving
nutrients and waste across the cell membrane.
2. The larger the cell, the more demand the cell
places on its DNA.
Exchanging Material
• What substances may move through the cell
membrane?
Answer: Food, oxygen and water enters.
Waste leaves the cell.
• The rate materials exchange depends on the
surface area of the cell
• The rate materials are used depends on the
cell’s volume (size).
Ratio of Surface Area to Volume
• Surface to volume ratio
• Volume increases faster than
surface
– The cell uses materials faster
than it can get them in
Asexual Reproduction
– Asexual reproduction - a single parent
producing an offspring. The offspring
produced are, in most cases, genetically
identical to the parent.
–
Asexual reproduction is a simple,
efficient, and rapid way for an organism to
produce a large number of offspring.
Sexual Reproduction
– In sexual reproduction, offspring are
produced by the fusion of two sex cells –
one from each of two parents.
– The offspring produced inherit some
genetic information from both parents,
therefore they are genetically different.
10.2 The Process of Cell Division
• Cells divide to form two new cells called daughter
cells
• This process is called mitosis (cell division)
• Before it can occur, what has to happen? The cell
replicates, or copies, all its DNA
• DNA is condensed into a manageable form
(chromosome) so it can be divided precisely
Chromosomes
• Chromosomes – bundled packages of DNA that contain
genetic information
• Every organism has a specific number of chromosomes
–
–
–
–
Fruit flies – 4
Dog - 78
Carrots – 18
How many chromosomes do humans have? 46 (23 pairs)
• Chromosomes are only visible
when the cell divides.
• Why is this?
DNA and protein molecules
are spread throughout the
nucleus in the form of
Chromatin.
Sister chromatids
Exact copies of
each other
Centromere
TEM
36,000
Chromosomes
Chromosomes (a closer look)
• Before division, the chromosome (DNA) is replicated
• The replicated chromosome consists of 2 identical
“sister” chromatids.
– Held together near the center by centromere
• The chromosome “X” shape we usually see drawn is a duplicated
chromosome made of supercoiled chromatin
Eukaryotic Cell Cycle
The cell cycle represents the events in the
life of a cell.
Interphase  Growth Phase most time
spent in this phase
G1  Cell growth
S  Replication of DNA
G2  Final growth and prepare for
division
Mitosis (M phase)  Division of the
nucleus (can last hours to a few days)
4 Phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Mitosis – 4 Stages of Cell
Division
• Chromatin condenses into chromosomes.
• The nucleus begins to disappear
• Spindle fibers begin to form at centrioles
• Chromosomes move to the center of the cell
• Centrioles migrate to opposite ends of the cell
• Spindle fibers attach to the chromosomes at the
centromere
• Sister Chromatids are pulled apart by spindle
fibers (microtubules) connected to the centromere
• Nucleus begins to re-form
• Cleavage furrow forms
• Nucleus continues to form
• Cytokinesis Occurs (cells actually divide)
• Two diploid cells have been formed
Cytokinesis
• Division of the cytoplasm
• Occurs at the same time as telophase
Actin (blue) and microtubules (orange) at the
end of cytokinesis in a green urchin zygote.
Cytokinesis - Animal
• Animal cells are surrounded by a
cell membrane
Cleavage
furrow
Cleavage furrow
SEM 140
Animal Cell  Formation of a
cleavage furrow
Contracting
ring of
microfilaments
Daughter cells
Cytokinesis - Plant
Cell plate
forming
•
Wall of
parent cell
Daughter
nucleus
Plant cells are surrounded by a
cell wall
TEM 7,500
Plant Cell  Formation of cell
plate
Cell wall
Vesicles containing
cell wall material
New cell wall
Cell plate
Daughter cells
Mitosis Animation
2.
1.
3.
4.
5.
1.
2.
3.
4.
Cleavage
furrow
Sister chromatids
separate
1.
2.
3.
4.
Haploid daughter cells
forming
5.
Questions for whiteboards:
• Show how a cell looks normally while it’s
doing it’s job as a tissue, muscle, bone or
nerve cell. Focus on what genetic material
looks like in nucleus
Questions for whiteboards:
• Show how a cell would look as it’s getting
ready to divide. Again, focus on nucleus
and genetic material
Questions for whiteboards:
• Using two circles, “X”s and a mitochondria
show why efficiency is different between
large and small cells.
Questions for whiteboards:
• List some problems that cells might
encounter if they were to grow to large.