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?

MitosisChromosomes 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 materialWhen 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

AlcoholsBleaches

Chemical Heat

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

2

3

4

5

6

Loop is heated to kill any other microorganisms which may be present. It is cooled a little to avoid killing microbe to be cultured

Lid is left on as long as possible to stop any contamination of the culture

To collect microbes which are to be cultured on the plate

To avoid contamination of culture with any other microbes

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:

No Growth

Yeast Suspension:

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