P.02 Experiments

Overview of Experimental Investigations

• Purpose: In biology experiments, we often investigate how changing one variable affects another.
• Examples of Variables in Investigations:
  • Enzyme Concentration: Effect on enzyme activity (e.g., rennin’s effect on milk clotting).
  • Temperature: Effect on catalase activity.
  • Surface Area: Effect on the rate of diffusion.
  • Solution Concentration: Effect on the percentage of plasmolysed onion cells.

Case Study: Effect of Enzyme Concentration on Rennin Activity

1. Background on Rennin:

• Rennin (Chymosin): An enzyme found in the stomachs of young mammals; used in cheese-making.
• Function: Rennin clots milk by acting on casein, a milk protein.
• Process:
  • Casein molecules in fresh milk form micelles (small, organized groups) dispersed throughout the milk, creating a uniform emulsion.
  • Rennin Action:
    • Rennin breaks down casein into smaller molecules.
    • Disrupted micelles cause casein to coagulate (clump together), forming curds.

1. Milk Clotting Mechanism:

• Micelles: Casein molecules in micelles give milk its smooth texture.
• Action of Rennin:
  • Rennin acts on casein micelles, splitting them into smaller molecules.
  • Result: Casein molecules stick together, causing milk to clot and form curds (solid) and whey (liquid).

Approach to the Experiment: Investigating Enzyme Concentration and Clotting Rate

1. Define Variables:

• Independent Variable: Enzyme concentration (different concentrations of rennin).
• Dependent Variable: Rate of milk clotting (time taken for milk to coagulate).

1. Set Up the Experiment:

• Prepare different concentrations of rennin solution.
• Add each concentration to separate samples of fresh milk under controlled conditions (e.g., same temperature).

1. Data Collection:

• Observe and Record:
  • Measure the time taken for visible clotting to occur in each milk sample.
  • Record time accurately for each concentration level.
• Expected Results:
  • Higher rennin concentrations should result in faster clotting rates, as more enzyme molecules are available to act on casein.

1. Control Variables:

• Keep all other factors constant:
  • Temperature: Rennin activity is sensitive to temperature changes.
  • Milk Volume: Ensure equal milk volume across samples.
  • Mixing: Stir each mixture similarly to distribute the enzyme evenly.

1. Analyze Results:

• Plot a graph of enzyme concentration vs. clotting rate.
• Determine how changes in rennin concentration influence clotting time and rate.

Key Points to Remember

• Clotting Process:
  • Rennin splits casein, causing micelle breakdown and coagulation.
• Data Collection:
  • Accurately measure clotting time for each enzyme concentration to assess the rate of reaction.
• Graph Interpretation:
  • Higher enzyme concentration typically correlates with a faster rate of reaction due to more active sites being available.