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 Alcohols Bleaches 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

StepReason 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