Microscopy, Aseptic Technique and Osmosis

- Clip the slide onto the stage

- Use the lowest powered objective lens and the coarse adjustment knob to bring the specimen roughly into focus.

- Use the fine adjustment knob to create a clear image whilst looking through the eyepiece.

- Swap to a higher powered objective lens for greater magnification and refocus.

- Draw your observation with a pencil, with unbroken lines, no colouring/shading. Draw the subcellular structures in proportion, title the drawing and note down the magnification. Label the drawing using straight, uncrossed lines.

- Add a drop of water to the slide

- Cut up an onion, separate it into layers and peel off some epidermal tissue with tweezers

- Place the epidermal tissue into the water

- Add iodine solution as a stain

- Place a cover slip on top, avoiding getting any air bubbles beneath to completely cover the specimen

- Disinfect the workspace

- Use a sterilised (eg with heat) Petri dish of agar jelly

- Sterilise the inoculating loop by passing it through a flame

- Streak the bacteria onto the plate with the loop

- Lightly tape on the lid of the Petri dish

- Store the dish upside down to avoid condensation dropping onto the agar

- Place paper discs soaked in different types/concentrations of antibiotics on an agar plate that has an even covering of bacteria.

- Leave some space between the discs

- The antibiotic should diffuse into the agar. Antibiotic resistant bacteria will continue to grow, but non resistant strains will die

- The clear area left around the disc where the bacteria have died is called the inhibition zone

- A control must be used (a disc soaked in sterile water) for comparisons

- Leave the plate for 48 hours at 25°C (higher temperatures can cause harmful pathogen growth)

- The larger the inhibition zone, the more effective the antibiotic has been. The area of the inhibition zone can be calculated with πr².

- Cut up a potato into identical cylinders.

- Prep some beakers with different sugar solutions in them. One should be pure water.

- Measure the mass of the cylinders and leave one cylinder in each beaker for 24 hours.

- Take them out, blot them dry with a towel and remeasure their masses

- Cylinders that have drawn in water by osmosis will have increased in mass, giving a positive percentage change. If water has drawn out they will decrease in mass, giving a negative percentage change.

- Water always moves into the more concentrated solution, so the higher the sugar solution the smaller the mass of the cylinder.

- The percentage change can be calculated with (Change in mass / Initial mass) x 100