Microscopy Required Practical Method
This page covers three main GCSE Biology Required Practicals: microscopy, microbiology, and food tests. It also includes a section on the osmosis practical.
For the Microscopy required practical, the method involves preparing a microscope slide, staining cells with iodine, and adjusting the microscope for clear viewing. The process is as follows:
- Prepare your microscope slide
- Add iodine to stain the cells
- Place the cover slip on the slide and position it on the microscope stage
- Use the coarse adjustment knob to move the stage
- Look into the eyepiece and adjust the fine knob until the image is clear
Highlight: The use of iodine as a stain is crucial for enhancing the visibility of cell structures under the microscope.
The Microbiology practical GCSE focuses on culturing microorganisms and testing antibiotic effectiveness. Key points include:
- Using paper discs soaked in different antibiotics
- Observing zones of inhibition where bacteria have died
- Including a control (e.g., water) for comparison
- Incubating the plate for 48 hours at 25°C
Vocabulary: Zone of inhibition - A clear area around an antibiotic-soaked disc where bacteria have been killed or their growth inhibited.
Safety measures for the microbiology practical are emphasized:
- Sterilize petri dishes and culture medium to kill unwanted microorganisms
- Pass the inoculating loop through a flame to sterilize it
- Store petri dishes upside down to prevent condensation from falling onto the agar surface
The Potato osmosis experiment is outlined as part of RP3-Osmosis:
- Cut potatoes into identical cylinders
- Prepare beakers with different sugar solutions
- Measure the initial mass of potato cylinders
- Leave potatoes in beakers for 24 hours
- Dry potatoes and measure final mass
- Observe changes in mass due to osmosis
Example: If water is drawn out of the potato by osmosis, the potato will decrease in mass.
The page concludes with an overview of Food Tests for RP4:
- Sugars: Benedict's test (blue to green, yellow, or brick red if sugar is present)
- Starch: Iodine test (brown-orange to black or blue-black if starch is present)
- Proteins: Biuret test (blue to purple if protein is present)
- Lipids: Sudan III test (separation into two layers, with the top layer red if lipids are present)
Definition: Osmosis - The movement of water molecules from an area of high concentration to an area of low concentration across a partially permeable membrane.
The page also includes diagrams of a microscope and a petri dish setup, which are helpful visual aids for understanding the equipment used in these practicals.
