Cell Division
Mitosis
Why study cells?
•  Cells → Tissues → Organs → Bodies
–  bodies are made up of cells
–  cells do all the work of life!
The Jobs of Cells
•  Cells have 3 main jobs
–  make energy
ATP •  need energy for all activities
•  need to clean up waste produced
while making energy
–  make proteins
•  proteins do all the work in a cell,
so we need lots of them
–  make more cells
•  for growth
•  to replace damaged or diseased cells
Our organelles
do all these
jobs!
Making more cells is OUR focus
•  Think about it… why do we need to make
more?
Before we get too far...
•  What limits cell size?
–  How do you think the size of the cell affects
the distribution of chemicals throughout the
cell?
–  Write your hypothesis to this question: If…
then____
Modelling Limits to cell size
•  We will use different sized agar cubes as
models of living cells.
–  You will submerge them in a NaOH solution
for 10 min. and observe whether it diffuses to
the centre
–  We will investigate a relationship between the
surface area and the volume of different sized
cells, and drawing conclusions about
maximum size
I need a volunteer!
•  Measure the three cubes, and record the
values on the blackboard
–  Everyone needs to copy this table down, and
calculate the first 3 columns while we wait
Cube Small Medium Large Surface area (cm2) Volume (cm3) SA/Volume ra7o Diffusion Depth (mm) Diffusion Rate (mm/
min) Analysis:
Answer in your notes:
1.  What does the colour
change in the cells
indicate about the
diffusion of NaOH?
2.  Did all the cells change
colour all the way
through?
3.  Calculate the diffusion
rate per min for each
cell, and record it in
your table
4. Compare the results to
your hypothesis. Was
your prediction correct?
5. If the coloured part of the
cell is thought of as the
part that gets a lot of
food and oxygen, and
can get rid of wastes by
diffusion, which of the
three cells is best able to
carry out these
functions? Explain
Analysis
6. If all cell activity takes
place in the cell’s
interior, but all
materials enter and
exit through the cells
surface, explain the
importance of the
surface area to
volume ratio.
7. So... Why do cells
divide!?
8. How might
temperature affect the
results of this activity?
How would this relate
to your cells?
Why Do Cells divide?
•  Growth
•  Repair damage
•  Reproduction
–  To reproduce, repair & grow,
the cell must…
•  copy their DNA
•  make extra organelles
•  divide the new DNA & new organelles
between 2 new daughter cells
Cell Division for Growth
•  One main characteristic of life is that all
organisms grow. As multicellular cells
grow, the number of cells increases. The
size of the cell does not just get bigger.
•  When a cell gets too large, water and
nutrients cannot move through the cell fast
enough.
Cell Division for
Growth:
•  Chemical signals
cannot get across a
cell efficiently if they
are too large, so they
must divide
Cell Division for Repair:
•  Dead/ injured cells
•  Your body sheds
millions of cells daily!
All of which need to be
replaced
•  Broken bones, blisters,
cuts, you need new
cells to heal the break
•  All organisms need to
repair themselves to
stay alive.
Cell lifespans
•  Not all cells are created equal,
they all have a predetermined
self-destruct time!
–  red blood cells live 120 days
–  liver cells live 200 days
–  intestine lining cells live 3 days
–  skin cells live 20 days
–  stomach lining cells live 2 days
–  brain cells live 30-50 years
Cell Division for Reproduction
•  The ability to reproduce is an important
characteristic of all living things.
•  All cells, including single celled organisms,
use cell division to reproduce.
•  Asexual reproduction involves only one parent and
the offspring are exact genetic copies of the
parent.
•  Sexual reproduction is when a cell from one parent
joins with a cell from another parent. The offspring
has genetic information from each parent.