Lemonade-Ed - Amylase Investigation

Activity: Amylase Investigation

Digestion of Starch

Wendy took a bite of her baguette. She thought, "The bigger the bite, the more starch there is to be digested, and the longer it takes ..."

Wendy wanted to find out whether adding a bigger amount of an enzyme to starch speeds up digestion. Starch is broken down (digested) into glucose by an enzyme called salivary amylase, which is produced in your mouth.

She used the same amount of starch each time, but added different amounts of the enzyme. She used iodine indicator to show when the starch had disappeared. The iodine indicator loses its blue-black colour when all the starch has gone. She timed how long it took for the starch to disappear each time. When the starch had disappeared, she knew it had all been digested.

Her results are shown in this table. The concentration tells you the amount of salivary amylase enzyme she added. For example, 1 cm' of 2% enzyme contains twice as much enzyme as 1 cm of 1% enzyme.

Wendy wanted to see if there was a pattern in her results, so she drew a line graph. Line graphs help you see the relationship between variables in an experiment.

Wendy put the input variable (the amount of enzyme used) along the bottom, on the x-axis. She put the outcome variable (the time taken to digest the starch) up the side, on the y-axis. She plotted her results on the graph.

Lines of Best Fit

Questions:

Draw axes like Wendy did and plot her results.
Can you draw a straight line through all the crosses?
Why do you think that lines on graphs do not always go through all the points?
What pattern do you see in the results?
Describe the relationship between the input variable and the outcome variable.

Interpreting Graphs

Wendy used her graph to predict how long it would probably take for other concentrations of amylase to digest starch. She drew a line up to the graph from 1.5% on the x-axis, and read off the time on the y-axis.

Questions

- Do this on your copy of Wendy's graph. What is the time on the y-axis?
- Why do you think she would want to do this?

She can also extend the line and predict how fast starch will be digested by a 6.5% concentration of amylase.

Do this on your copy of Wendy's graph. How long will it take for the starch to be digested by a 6.5% concentration of amylase?

Other Relationships

Charlotte decided to look at the way pH affects how an enzyme works. She used the same concentration of salivary amylase for all her tests, but she changed the pH of the starch solution by adding acid or alkali. She recorded the time it took for the starch to be digested. Her results are shown in this table.

Questions

Use the data in the table to plot a graph. Try to draw a curve of best fit to join the points.
Describe the relationship shown by your graph in terms of how the time taken to digest the starch changes with pH.

The relationship shown by the graph is not a simple relationship. To begin with, as the pH increases, the time taken to digest the starch is shorter. After a certain point, the reaction starts to take longer again.

What pH do you think will give the shortest time for amylase to digest starch? Explain your answer.