Required Practical Investigations in Biology

Microscopy - Aim

To observe cells using a light microscope.

Microscopy - Method

Place a thin layer of onion epidermis on a slide, add iodine stain, carefully place a coverslip, and observe under the microscope.

Microscopy - Equipment

Microscope, slide, coverslip, iodine, onion.

Microscopy - Variables

Dependent: What you see under the microscope. Independent: Type of cell. Control: Stain, magnification.

Microscopy - Conclusion

Cell structures like nucleus, cytoplasm, and cell wall (plant) can be seen; magnification calculations can be done.

Osmosis - Aim

To investigate the effect of sugar solution concentration on the mass of potato cylinders.

Osmosis - Method

Cut equal-sized potato pieces, measure mass, place in different concentrations of sugar solution, leave for 24 hours, dry and reweigh.

Osmosis - Equipment

Potato, cork borer, ruler, balance, sugar solutions, beakers.

Osmosis - Variables

Independent: Sugar concentration. Dependent: Change in mass. Control: Time, temperature, size of potato pieces.

Osmosis - Conclusion

In pure water, potato gains mass; in high sugar solution, it loses mass due to osmosis.

Food Tests - Aim

To identify starch, sugars, proteins, and fats in food samples.

Food Tests - Method

Grind food, add distilled water, then test for: starch (iodine), sugar (Benedict's and heat), protein (Biuret), fat (ethanol + water).

Food Tests - Equipment

Food sample, pestle and mortar, test tubes, iodine, Benedict's, Biuret, ethanol.

Food Tests - Variables

Dependent: Colour change. Independent: Type of nutrient. Control: Amount of reagent, heating time.

Food Tests - Results

Starch = blue-black, Sugar = brick red (after heating), Protein = purple, Fat = cloudy white emulsion.

Enzymes - Aim

To investigate how pH affects the activity of amylase on starch.

Enzymes - Method

Add iodine to spotting tile. Mix amylase, starch, and buffer. Take samples every 30s, drop into iodine. Record when iodine stays orange (no starch).

Enzymes - Equipment

Amylase, starch, buffer solutions, iodine, spotting tile, stopwatch, water bath.

Enzymes - Variables

Independent: pH. Dependent: Time for starch to break down. Control: Volume, temperature, concentration of amylase/starch.

Enzymes - Conclusion

Enzymes have an optimum pH (often ~7); activity decreases above or below this due to denaturation.

Photosynthesis - Aim

To investigate how light intensity affects the rate of photosynthesis using pondweed.

Photosynthesis - Method

Place pondweed in water with sodium hydrogen carbonate. Vary distance of lamp. Count oxygen bubbles or measure gas volume in set time.

Photosynthesis - Equipment

Pondweed (e.g. Elodea), lamp, ruler, beaker, stopwatch, gas syringe or bubble counter.

Photosynthesis - Variables

Independent: Light intensity (distance). Dependent: Number/volume of bubbles. Control: Time, temperature, CO₂ level.

Photosynthesis - Conclusion

More light increases photosynthesis (until limiting factors apply); results can be graphed.