Essential Biology Experiments: Techniques and Principles

Cell Observation Techniques

Aim: Observe Cells and Subcellular Structures

• Add specimen (e.g., onion epidermis) on a slide.
• Stain (e.g., iodine) to highlight structures.
• Lower cover slip at an angle to reduce air bubbles.
• Use low → high magnification.
• Focus using coarse → fine adjustment.
• Label parts of the microscope.
• Calculate magnification.
• Measure size using a scale bar.
• Understand differences between plant and animal cells.
• Explain why staining is used (to see organelles like the nucleus).

Investigating Osmosis

Aim: Investigate Osmosis with Potato Cylinders

• Cut identical potato pieces.
• Weigh each piece, then place in sugar solutions of different concentrations.
• Leave for 24 hours, then dry and reweigh.

Experimental Variables:

• Independent Variable (IV): Sugar solution concentration.
• Dependent Variable (DV): Mass of potato.
• Controlled Variables (CV): Time, temperature, volume of solution, size of potato.

Key Concepts:

• Osmosis: Movement of water from a high water concentration to a low water concentration across a partially permeable membrane.
• Identify the isotonic point from a graph (where mass change = 0).
• Describe graph trends (e.g., increasing sugar concentration leads to mass decrease).
• Explain observations using the principles of osmosis (water moving into or out of cells).

Food Component Tests

Aim: Test for Starch, Sugar, Protein, and Lipids in Food Samples

• Starch: Add Iodine solution → positive result is blue-black.
• Reducing Sugars (e.g., glucose): Add Benedict's solution + heat → positive result is brick-red.
• Protein: Add Biuret reagent → positive result is purple.
• Lipids: Add Ethanol, then add water → positive result is a cloudy emulsion.

Controls and Safety:

• Control: Use water or a substance with no known food components.
• Safety Precautions: Wear goggles; ethanol is flammable.

Enzyme Activity Investigation

Aim: Investigate How pH Affects Enzyme Activity

• Mix amylase + starch + buffer solution.
• Drop mixture into iodine solution every 30 seconds.
• Record the time until the iodine stays orange (indicating all starch has been broken down).
• Repeat the experiment for different pH values.

Experimental Variables:

• Independent Variable (IV): pH (using buffer solutions).
• Dependent Variable (DV): Time taken to digest starch.
• Controlled Variables (CV): Temperature, amylase concentration, starch volume.

Key Concepts:

• Enzymes: Biological catalysts.
• Optimum pH: Shown by the fastest digestion time.
• Denaturation: Occurs at high or low pH, causing enzymes to lose their shape and function.

Validity:

• Ensure validity by repeating trials and controlling variables effectively.

Photosynthesis Rate Experiment

Aim: Investigate Light Intensity's Effect on Photosynthesis

• Place pondweed in water with sodium hydrogencarbonate.
• Move the light source to different distances from the pondweed.
• Count the bubbles produced or collect the oxygen gas.

Experimental Variables:

• Independent Variable (IV): Light distance (inversely related to light intensity).
• Dependent Variable (DV): Bubble count per unit time (rate of O₂ production).
• Controlled Variables (CV): Temperature, carbon dioxide concentration, type of plant.

Graph Interpretation and Limitations:

• Light Intensity Graph: Rate of photosynthesis increases with light intensity, then plateaus.
• Limitations of Bubble Counting: Not an accurate measure of oxygen volume.
• Improving Precision: Use a gas syringe for more precise oxygen collection.
• Connection to Limiting Factors: Relate findings to concepts of limiting factors in photosynthesis.