Practicals

• What is the purpose of using a Colorimeter in practicals?

  To measure the absorbance of solutions
• What is critical analysis of data in the context of exams?

  Evaluating data and methods
• What is the aim of the enzyme practical with trypsin?

  To investigate the effect of pH on activity
• What is the predicted optimum pH for trypsin activity?

  pH 9
• What is the first step in the method for the trypsin experiment?

  Attach film to a straw
• Why is it important to leave the test tube in the water bath for five minutes?

  To allow the solution to reach temperature
• What should be done if no change occurs in the film after 25 minutes?

  Record it as infinity
• How should results be presented in a table?

  To three significant figures
• How do you calculate the rate of reaction?

  1 divided by the time taken
• Why convert reaction rates to $10^{-3}$?


  To simplify data for plotting
• What is the correct way to plot data on a graph?

  Independent variable on x-axis
• What is a line of best fit?

  A line that represents data trends
• When should a curve be used instead of a straight line for a graph?

  When data points suggest a non-linear trend
• What variable is deliberately changed in an experiment?

  Independent variable
• What variable is measured in an experiment?

  Dependent variable
• Where does the independent variable go on a graph?

  X-axis
• Where does the dependent variable go on a graph?

  Y-axis
• How should the scale on a graph be chosen?

  To fill at least half the paper
• When should a dot-to-dot line be used on a graph?

  With fewer than 10 data points
• What does a curve in a graph indicate?

  Non-linear relationship between variables
• Why can't we conclude the exact optimum pH from limited data points?

  Not enough intermediate points tested
• What was the predicted optimum pH for trypsin?

  pH 9
• What conclusion can be drawn at pH 4 regarding trypsin?

  Trypsin was denatured at pH 4
• Why can't we conclude the alkaline pH at which trypsin denatured?

  Rate of reaction didn't drop to zero
• What is a common question regarding method evaluation in experiments?

  Evaluate the method's limitations
• What is a subjective endpoint in an experiment?

  Determining when a solution is clear
• What effect does an uncontrolled water bath have on results?

  Temperature decreases during the experiment
• What is the purpose of using hydrochloric acid in the experiment?

  To soften root tissues
• Why is acetic orcein used in the experiment?

  To stain chromosomes for visibility
• What part of the onion is used for the experiment?

  Last five millimeters of the root tip
• Why is it important to cut the root tip carefully?

  To avoid injury and ensure safety
• What temperature should the water bath be set to during the experiment?

  60 degrees Celsius
• What is the purpose of rinsing the root tip in distilled water?

  To remove hydrochloric acid
• Why is filter paper used during the staining process?

  To absorb excess stain
• What is the purpose of squashing the root tip?

  To create a thin layer for viewing
• What is the mitotic index?

  Percentage of cells undergoing mitosis
• How is the mitotic index calculated?

  Cells in mitosis / total cells × 100
• Why should multiple fields of view be examined?

  To ensure a representative sample
• What is osmosis?

  Diffusion of water through a membrane
• What does a hypertonic solution do to plant cells?

  Causes them to lose mass