Cell Size, Phases and Division
Surface area to volume ratio
6:1
4:1
2:1
-Which SA/V ratio would be more efficient
to a cell?
A large SA/V ratio…..6:1
Surface area to volume ratio
Each time a cell doubles in size, its surface area
increases by a factor of four but its volume increases
by a factor of eight. It would mean that the cell
would need 8 times the normal amount of nutrients
and make 8 times the normal amount of wastes.
All cells are relatively the same
size. Why?
1. Surface area-to-volume ratio
• As a cell grows the volume increases
much more rapidly than the surface
area
–Diffusion is slow
–The larger the cell the more food and
the more wastes; not efficient.
Cell Size, cont.
Increase size of cell Decrease rate of
Diffusion
Oxygen
Nutrients
Wastes
Water
Cell Size, cont.
2. DNA limits the size of a cell
DNA codes for proteins, the larger
the cell, the more proteins it
needs.
The cell can’t make instructions
fast enough
DNA makes up the chromosomes
inside the nucleus
DNA and Cell Division
For the most of a cell’s lifetime,
chromosomes exist as chromatin –
long strands of DNA wrapped around
proteins.
Under an electron microscope,
chromatin looks somewhat chaotic
resembling a plate of spaghetti.
-This is necessary for the
information to be copied.
Cell Cycle
The cell cycle is a
sequence of growth
and division in a cell.
Foldable Instructions
• Fold one piece of
white paper hot dog
style.
• Cut down the middle
seam (hot dog) &
tape the short ends
together.
• Accordion fold the
paper to make 8
equal tabs.
The Cell Cycle
Draw the
diagram of
the cell cycle
on square 1
of foldable
Foldable: Tab 1
Interphase
• The majority a cell’s life cycle is spent in
a period of growth known as
Interphase.
• Three stages
–G1- Growth
–S- DNA synthesis/replication
–G2- preparation for mitosis
• No Chromosomes are visible.
• DNA exists as chromatin
Interphase
Draw the
diagram of
interphase
on square 2
of foldable
White fish blastula
Onion root tip
Foldable: Tab 2
Chromosome
centromere
Sister chromatid
Draw the
diagram of
the
chromosome
on square 3
of foldable
Foldable: Tab 3
Cell Division
• The cell then enters mitosis
or the period of nuclear cell
division in which two daughter
cells are formed, each
containing a complete set of
identical chromosomes.
Prophase
• Nuclear
membrane
breaks down
• Chromosomes
condense
(appear)
• Centrioles
develop
• Spindle fiber
appears
Draw the
diagram of
prophase on
square 4 of
foldable
Foldable: Tab 4
Metaphase
• Spindle fibers
attach to
chromosomes
• Chromosomes
“met” @ the
middle.
Draw the
diagram of
the
metaphase
on square 5
of foldable
Foldable: Tab 5
Anaphase
• Sister Chromatids
are pulled apart
towards the poles.
Draw the
diagram of
anaphase on
square 6 of
foldable
Foldable: Tab 6
Draw and identify the phase of Mitosis?
What phase of the cell cycle will the 2 daughter ell
be in?
• Sister Chromatids
are now at opposite
poles and uncoil.
• Nucleus starts to
reform
Draw the
diagram of
the
telophase on
square 7 of
foldable
Telophase
Foldable: Tab 7
Cytokinesis occurs
-Two new cells
Foldable: Tab 8
Cytokinesis
Cell plate
Cleavage furrow
Anaphase
Prophase
Metaphase
Interphase
Cytokinesis
Telophase
Mitosis
• In Mitosis, everything is identical.
• Takes place in somatic cells
(body cells, ex: lung, skin, heart,
stomach, etc.)
Results of Mitosis
•
•
•
•
Replace old or damaged cells.
Occurs fastest in skin cells.
Some cells like brain cells do not divide.
During early development, mitosis
produces the cells needed to make tissues
and organs.