Essential Biology Laboratory Investigations
Cell Observation with a Microscope
Experiment Aim
To observe, draw, and label cells using a microscope, such as onion epidermal cells or cheek cells.
Required Equipment
- Light Microscope
- Glass Slide
- Cover Slip
- Specimen (Onion or Cheek cells)
- Iodine Solution
- Pipette
- Tweezers
- Paper Towel
Experimental Procedure
- Peel a thin layer of onion skin and place it on a clean slide.
- Add a few drops of iodine stain (to make the structures visible).
- Carefully place a cover slip on top, avoiding air bubbles.
- Place the slide on the microscope stage.
- Start with the lowest magnification objective lens.
- Use the coarse adjustment knob to focus.
- Switch to a higher magnification and use the fine focus.
- Draw your observations, including clear labels and a title.
Identifying Macronutrients in Food
Experiment Aim
To identify the presence of starch, sugar, protein, and lipids in food samples.
Required Equipment
- Test tubes
- Iodine solution
- Benedict’s solution
- Biuret reagent
- Sudan III or ethanol
- Heat source (e.g., water bath)
- Food samples (e.g., bread, milk, oil)
- Dropping pipettes
Experimental Procedure
The following table outlines the tests, substances detected, reagents used, and expected results:
| Test | Substance Detected | Reagent Used | Result if Present |
|---|---|---|---|
| Starch | Starch | Iodine | Blue-black colour |
| Sugars | Glucose (reducing) | Benedict’s | Heat → green/yellow/orange/red |
| Protein | Protein | Biuret | Purple colour |
| Lipids | Lipids | Sudan III / Ethanol | Red layer / Cloudy emulsion |
pH Impact on Enzyme Reaction Rates
Experiment Aim
To investigate how pH affects the rate of amylase activity, using starch as a substrate.
Required Equipment
- Amylase enzyme
- Starch solution
- Iodine solution in spotting tile
- Buffer solutions (various pH)
- Water bath
- Stopwatch
- Beakers
- Test tubes
- Pipettes
Experimental Procedure
- Add amylase, starch, and pH buffer into a test tube.
- Place the test tube in a water bath at 37°C for a few minutes.
- At regular intervals, take a small sample and drop it into iodine on a spotting tile.
- Observe the colour change. When the iodine no longer turns blue-black, the starch has been broken down.
- Record the time required for starch breakdown.
Key Variables
- Independent: pH level
- Dependent: Time taken / rate of reaction
- Control: Temperature, enzyme concentration, volume
Osmosis Effects on Plant Tissue Cells
Experiment Aim
To observe the effect of different concentrations of sugar solution on plant cells by osmosis.
Required Equipment
- Potato cylinders
- Range of sucrose (sugar) solutions
- Distilled water
- Test tubes and rack
- Balance
- Ruler
Experimental Procedure
- Cut equal-sized potato pieces and measure their initial mass.
- Place each in a different sugar solution (e.g., 0%, 0.2%, 0.4%, etc.).
- Leave them for at least 30 minutes.
- Remove and gently blot dry.
- Measure the final mass.
- Calculate the percentage change in mass.
Key Variables
- Independent: Sugar concentration
- Dependent: Percentage change in mass
- Control: Time in solution, size of potato
Microorganism Culturing & Antibiotic Effects
Experiment Aim
To investigate the effect of antibiotics or antiseptics on bacterial growth, using aseptic technique for culturing bacteria on agar plates.
Required Equipment
- Petri dishes with sterile agar gel
- Inoculating loop or sterile swab
- Bacterial culture (usually E. coli or Bacillus subtilis)
- Antibiotic discs or antiseptic solutions (e.g., Dettol, hand gel)
- Bunsen burner (for sterilizing equipment)
- Tape
- Incubator (set at max 25°C in school labs for safety)
- Ruler
Experimental Procedure
- Sterilize the inoculating loop by passing it through a Bunsen burner flame until red hot. Let it cool.
- Open a sterile agar plate near the flame (to reduce contamination).
- Dip the loop into the bacterial culture and spread evenly across the agar surface.
- Use sterile forceps to place antibiotic discs (soaked in different antibiotics or antiseptics) onto the plate.
- Close the lid and secure with tape, but do not seal it completely (to allow oxygen in and prevent the growth of harmful anaerobic bacteria).
- Label the plate and place it upside down in the incubator (to prevent condensation dripping on the bacteria).
- Incubate at 25°C for 24–48 hours.
- After incubation, measure the diameter of the clear zones (zones of inhibition) around the discs using a ruler.
- Calculate the area of the clear zone.