Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the
learning and teaching of Biology at a variety of levels.
|
Site author Richard Steane
|
The BioTopics website gives access to interactive resource material, developed to support the
learning and teaching of Biology at a variety of levels.
|
|
As with the previous work: The substrate will be starch. In these experiments, enzyme activity will be measured by the time taken for starch to disappear, monitored by testing with iodine/potassium iodide solution, using individual drops in a recessed tile. In other words, you will not be not testing for the products of the reaction, which you have already found out about.
This work will extend the theme of the previous work, by which you should have learned what amylase does to starch.
Each of the 4 experiments is designed to show the effect of a different ([continuously] variable) factor on the action of this enzyme on its substrate. In each case the principles behind the experiment will be similar, i.e. holding several factors constant whilst varying only one other.
1% starch sol
iodine/potassium iodide (I/KI) solution - for testing
Expt 3 only: acid - 0.1M hydrochloric acid (HCl) alkali - 0.1M sodium carbonate
universal pH indicator and narrow range pH papers
plastic pipettes recessed tile paper towel marker pen timer
electrically heated waterbaths (36 °C) - shared with next bench
Expt 2 only: also 0 °C (ice-water), 18 °C (Lab?) 36 °, 54 °, 72 °C (electrically heated waterbaths)
Experiment 3 only: use indicator paper to measure the pH of a drop of liquid from each tube, taken in the same way as the drops for testing on the tile. Record these results in the table on the last page.
| Tube number |
Temperature
/ °C |
Starch
/ml |
Other additions |
Amylase
/ml ADD LAST! |
|---|---|---|---|---|
| 1 | 36 | 10 | - | 0.5 |
| 2 | 36 | 10 | - | 1.0 |
| 3 | 36 | 10 | - | 2.0 |
| 4 | 36 | 10 | - | 4.0 |
| 5 | 36 | 10 | - | 8.0 |
Experiment 2
| Tube number |
Temperature
/ °C |
Starch
/ml |
Other additions |
Amylase
/ml ADD LAST! |
|---|---|---|---|---|
| 1 | 0 | 10 | - | 2.0 |
| 2 | 18 | 10 | - | 2.0 |
| 3 | 36 | 10 | - | 2.0 |
| 4 | 54 | 10 | - | 2.0 |
| 5 | 72 | 10 | - | 2.0 |
Experiment 3
| Tube number |
Temperature
/ °C |
Starch
/ml |
Other additions |
Amylase
/ml ADD LAST! |
|---|---|---|---|---|
| 1 | 36 | 10 | 2.0 ml acid | 2.0 |
| 2 | 36 | 10 | 0.5 ml acid | 2.0 |
| 3 | 36 | 10 | - | 2.0 |
| 4 | 36 | 10 | 0.5 ml alkali | 2.0 |
| 5 | 36 | 10 | 1.0 ml alkali | 2.0 |
Experiment 4
| Tube number |
Temperature
/ °C |
Starch
/ml |
Other additions |
Amylase
/ml ADD LAST! |
|---|---|---|---|---|
| 1 | 36 | 2.5 | - | 2.0 |
| 2 | 36 | 5 | - | 2.0 |
| 3 | 36 | 10 | - | 2.0 |
| 4 | 36 | 20 | - | 2.0 |
| 5 | 36 | 40 | - | 2.0 |
Your experiment no. >
Reminder: Record dark or light blue-black as starch present, orangey-red as starch absent.
| Time /min | Presence (++,+) or absence (-) of starch in tube number | ||||
|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | |
| ................. | ................. | ................. | ................. | ................. | ................. |
| ................. | ................. | ................. | ................. | ................. | ................. |
| ................. | ................. | ................. | ................. | ................. | ................. |
| ................. | ................. | ................. | ................. | ................. | ................. |
| ................. | ................. | ................. | ................. | ................. | ................. |
| ................. | ................. | ................. | ................. | ................. | ................. |
| ................. | ................. | ................. | ................. | ................. | ................. |
When the starch is used up (result of the iodine test consistently turns from + to -) , the time taken for the change in your experiment can be transferred to the table below. If there is no such change, then the result should be recorded as "greater than" the last time of testing.(> x min )
| Time taken for disappearance of starch in tube number | ||||
|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 |
| ................. | ................. | ................. | ................. | ................. |
The whole class results will then be shared and transferred to tables overleaf, so that conclusions can be drawn from these by all class members, because these results form an integrated set of data.
Examine the tables detailing the treatments in each experiment in turn. You should be able to see the trend shown in the variations in the experimental details.
Which tube number has the same values for each of the factors in all of the experiments?
> 3
What are the exact values for these factors in this treatment?
> 2.0 ml amylase > temperature 36 C > no pH additions > 10ml starch
In the following section, remember that the shorter the time taken for starch to disappear, the higher the
rate of reaction. Compare the results obtained in the various tubes. At each end of the table, put a simple
description to explain how the treatments varied. Make sure you understand what you are asked.
What factor was varied in experiment 1? Which ones were held constant?
varied:>amount of amylase constant:>temperature> pH >starch concn
Give a title for experiment 1.
> The effect of amylase concn on the rate of starch disappearance
Summary of results:
| treatment this end | Time taken for disappearance of starch in tube number | treatment this end | ||||
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | ||
| low enzyme | ................. | ................. | ................. | ................. | ................. | high enzyme |
What do you conclude from these results?
>More amylase causes quicker breakdown of starch
What factor was varied in experiment 2? Which ones were held constant?
varied:>temperature constant:>amount of amylase >pH >starch concn
Give a title for experiment 2.
>The effect of temperature on the rate of starch disappearance
Summary of results:
| treatment this end | Time taken for disappearance of starch in tube number | treatment this end | ||||
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | ||
| low temperature | ................. | ................. | ................. | ................. | ................. | high temperature |
What do you conclude from these results?
> Amylase breaks down starch quicker at 54° or 36° and not at all at 0° or 72°C.
What factor was varied in experiment 3? Which ones were held constant?
varied:> pH constant:> amount of amylase >temperature >starch concn
Give a title for experiment 3.
>The effect of pH on the rate of starch disappearance
Summary of results:
| treatment this end | Time taken for disappearance of starch in tube number | treatment this end | ||||
|---|---|---|---|---|---|---|
| 1 - pH .. | 2 - pH .. | 3 - pH .. | 4 - pH .. | 5 - pH .. | ||
| low pH | ................. | ................. | ................. | ................. | ................. | high pH |
What do you conclude from these results?
> Amylase works best in slightly acidic conditions.
What factor was varied in experiment 4? Which ones were held constant?
varied:>starch concn constant:> amount of amylase >temperature > pH
Give a title for experiment 4.
> The effect of quantity of starch on the action of amylase.
Summary of results:
| treatment this end | Time taken for disappearance of starch in tube number | treatment this end | ||||
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | ||
| low substrate | ................. | ................. | ................. | ................. | ................. | high substrate |
What do you conclude from these results?
>Smaller amounts of starch are broken down the quickest!
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