P.13 Explaining Experimental Results

Purpose of Explaining Results

• Goal: To interpret results by connecting observed trends or patterns in the data with scientific principles or theoretical knowledge.
• Importance: Demonstrates understanding of the underlying scientific processes influencing the relationship between the independent and dependent variables.

Example: Enzyme Activity in the Rennin Experiment

• In the rennin experiment, we observed that increasing rennin concentration decreases the time taken to reach the reaction end-point, which implies an increase in reaction rate as enzyme concentration increases.

Scientific Explanation

1. Enzyme-Substrate Interaction:

• Rennin is an enzyme that catalyzes the breakdown of casein in milk, leading to milk clotting.
• As enzyme concentration increases, more active sites are available to bind with substrate molecules (casein), increasing the frequency of enzyme-substrate collisions.
• This leads to a higher reaction rate, meaning the end-point (milk clotting) is reached faster.

1. Saturation Point:

• In the experiment, the graph shows that at higher enzyme concentrations, the rate of reaction increases at a decreasing rate. This is seen by the flattening curve in Figure P1.6.
• This trend occurs because as enzyme concentration increases, substrate molecules become limiting. Eventually, all available casein molecules are bound to active sites, so adding more rennin no longer significantly increases the reaction rate.
• This results in a non-linear relationship, where further increases in rennin concentration yield diminishing effects on the reaction rate.

1. Optimal Conditions:

• Enzyme activity is also affected by environmental factors such as temperature and pH. The experiment likely kept these constant to isolate the effect of enzyme concentration.
• If conditions were optimal, enzyme efficiency would be maximized, contributing to a higher reaction rate until substrate saturation is reached.

Key Points for Explaining Results

• Reference the Trend: Start by stating the trend in the data, such as the relationship between enzyme concentration and reaction time.
• Scientific Reasoning: Connect observed patterns to scientific concepts, such as enzyme-substrate interactions and saturation effects.
• Acknowledge Limitations: Recognize when additional factors (e.g., substrate limitation) start influencing the results, leading to non-linear relationships.

Example Explanation Structure

“As rennin concentration increases, the time to reach the end-point decreases, indicating an increase in reaction rate. This is because more rennin provides more active sites for casein binding, increasing enzyme-substrate collisions. At higher concentrations, the effect diminishes as substrate becomes limiting, showing a non-linear trend due to substrate saturation.”

Practical Tips for Explaining Results

1. Use Clear Scientific Terms: Relate data trends directly to biological processes, such as “enzyme-substrate collisions” or “saturation point.”
2. Link Theory to Observations: Use theoretical knowledge, like enzyme kinetics, to explain why trends occur in the data.
3. Be Concise but Thorough: Provide a clear, focused explanation that addresses each aspect of the trend observed.