Download Producing New Cells

Key Area 3: Producing New Cells
Mitosis
Why do cells divide?
• Organisms would only ever exist as
single cells – fine for bacteria but
not so good for plants and animals!
• Old and damaged cells
would never be replaced.
• Organisms wouldn’t reproduce.
Chromosomes
•Chromosomes are structures found in the nucleus of
every living cell.
•Chromosomes contain genetic material that gives us our
individual characteristics.
Centromere
Chromosome
Plant Shoots
PlantShoot Cells
What happens during mitosis?
Mitosis
Chromosomes shorten, thicken
and replicate. (become visible)
Spindle fibres attach to
the centromere.
Chromosomes line up along
the centre of the cell.
Chromatids are pulled to the
opposite ends (poles) of the
cell.
Nuclear membrane forms and cytoplasm
divides. The cell membrane pinches inward,
ultimately producing two genetically
identical cells.
Which Cell?
Chromosomes during mitosis
The stages of mitosis
Mitosis
Genetic material
When cells divide, it is essential that genes are copied
into the new cells.
Genes are the basic unit of inheritance, and are
responsible for the characteristics of an organism.
Genes are located on chromosomes.
One of a kind?
• The daughter cell produced by mitosis are genetically
identical to the parent cell.
• This ensures that there is no loss of genetic information.
Aseptic Technique
What is “Aseptic Technique”?
• A procedure or an experiment which is carried out under sterile
conditions, usually involving growing microorganisms or
sometimes human cells- e.g. for transplants.
• This requires an appropriate growth medium (where the cells are
grown) such as agar.
• Agar contains all the nutrients the cells need to grow.
• Other factors such as temperature, light and pH must be
controlled (kept the same).
Importance of sterile techniques
1. Prevents the wrong type of microbe
entering the experiment
Importance of sterile techniques
2. Prevents microbes from entering the
environment about us
– Especially important when working with
dangerous pathogens (e.g. MRSA, SAARS, HIV,
Influenza etc)
What do we mean by
“sterilisation”?
• This is how we make sure that no
microorganisms are present at the start of
our experiment
What kinds of places might this
be important?
How could you sterilise
equipment?
Sterilisation Methods
Chemical
Alcohols
Heat
Bleaches
Usually heated to ~160°C in
an autoclave
Preparing for experiments using
microorganisms
1. All apparatus must be sterilised prior
to using
2. The bench surface must be disinfected
using a chemical treatment
3. Hands should be washed thoroughly and
hair well away from the sample
Aseptic Technique: Method
Step
Reason
1
Loop is heated to kill any other microorganisms which may
be present. It is cooled a little to avoid killing microbe to be
cultured
2
Lid is left on as long as possible to stop any contamination of
the culture
3
To collect microbes which are to be cultured on the plate
4
To avoid contamination of culture with any other microbes
5
6
This allows colonies of microbes to grow on the plate.
Streaking allows small colonies to be visible
To stop any microbes entering plate. Loop is flamed to kill
any residual microbes.
The plate before incubating
Distilled Water
Yeast Suspension
After 1 week
Distilled Water:
Yeast Suspension:
No Growth
Lots of growth
Conclusions
• Only the yeast plate showed any microbial
growth
• The distilled water had no microbes grow
because the water was aseptically
transferred to the plate.
• Aseptic techniques does not allow the
growth of any unwanted environmental
microbes