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Diocesan School for Girls
BIOLOGY
Level Two
Achievement Standard 90457 vs 2
Biology 2.1
Internal Assessment
Carry out a practical biological investigation with supervision
Credits: 3
ENZYME ACTION
TEACHER GUIDELINES
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Teacher Guidelines:
The following guidelines are supplied to enable teachers to carry out valid and consistent assessment
using this internal assessment resource.
Context/setting:
Students are expected to carry out an investigation in the laboratory on the action of an enzyme on a
substrate. This investigation uses the action of the enzyme renin on milk as the biological reaction to
illustrate the process of enzyme action. Students will be required to investigate a factor that affects
the action of this enzyme action.
Students will need considerable practice at developing investigations: to plan, carry out, record,
process and interpret data; developing a conclusion; discussing biological concepts and processes
relating to the investigation (i.e. what the investigation showed about the concept or process) and
analysing the investigation process to develop a critical evaluation.
The investigation is to be carried out with teacher supervision by giving the students guidelines for the
investigation (EN 6). The investigation must be at the level 7 of Biology in the New Zealand
Curriculum (EN 3).
It is expected that students will have opportunity to make changes to their initial methods as they
work through the investigation (EN 4).
Conditions:
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This is a practical activity, which should be completed individually in class.
It is suggested that students are given approximately an hour to plan and trial their
investigation.
Students will be provided with a total of five 50-minute periods to carry out the investigation,
process data and write a report.
Any student absent for a period during the week will be given time to complete their work
when they return to school.
No books or resources will be available to students during the class time.
Pens, calculators etc will be taken into class in a clear plastic bag.
No electronic translation devices will be allowed in the class.
The students will not take the task sheet or any material that they write on out of the
classroom at any time.
All task sheets and rough notes will be handed in to the teacher at the end of each of class
period. These task sheets will be kept by the class teacher, in a secure area in the science
department until the next allocated period.
It is not possible to call this a closed book activity, as there is the potential for students to go
home between periods and access books or knowledge from other people.
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Resource requirements:
All equipment is to be provided in a general space in the lab (or in its normal place in the lab for test
tubes, beakers etc). Students are not to be presented with a set of equipment that is specifically for
their use.
During the investigation, students are to be provided with equipment that they request wherever
possible.
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Full cream homogenised milk (allow for at least 250mL per student during the week). This will
have the same number of days left to run before its use by date each lesson.
Renin – as Renco Solution. Quantities per student will vary according to the nature of their
investigation. The use level should be monitored during the week to ensure there is an ample
supply at all times. Please ensure that fresh Renco is purchased – left over solution from the
previous year is not to use put out for use.
The Renco packets should be available to students so that they can read the instructions for
general use of this enzyme in cooking.
Fine disposable pipettes (these must be new)
10mL measuring cylinder - 1 per student
5mL syringe –1 per student
1mL syringe – 1 per student
Test tubes – as per in labs. At least 100 clean test tubes in any teaching lab at any time.
Test tube racks – enough for 1 per student
Stop watch – enough for 1 per student
Thermometers – enough for at least two per student
Equipment that could be used to make a water bath – these must not be set up for students.
(ie beakers as per lab equipment; ice; hot water)
Buffer solutions covering the range pH 4 – 10 with a choice of at least 7 different pH values in
that range. (increasing by a value of 1, i.e. 4.0, 5.0, ……….9.0, 10.0. These buffers must be
accurate to within 0.1 and have been checked for accuracy before the task.
Distilled water – must be neutral pH and be checked daily.
Universal indicator solution and pH paper
Polystyrene cups (at least 4 per student) for insulated water baths.
Additional information:
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Students have been studying enzyme action and the factors that affect the rate of enzyme action
in class for the week prior to this investigation.
Students will have carried out an investigation into a different enzyme controlled reaction in class
time leading up to this task. They will not have carried out this specific reaction.
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Student Name: _____________________________
Assessment Date: _______________
Teacher: ___________
Diocesan School for Girls
BIOLOGY
Level Two
Achievement Standard 90457 vs 2
Biology 2.1
Internal Assessment
Carry out a practical biological investigation with supervision
Credits: 3
ENZYME ACTION
Time: 5 class periods will be allocated to this task.
Conditions: Individual work.
Achievement
Achievement with Merit
Achievement with Excellence
 Carry out a practical
biological investigation.
 Carry out a quality practical
biological investigation.
 Carry out and evaluate a
quality practical biological
investigation.
Check that this booklet has pages 1 - 3 in the correct order and that none of
these pages are blank.
YOU MUST HAND THIS BOOKLET AND ALL PAPER THAT YOU USE TO THE
SUPERVISOR AT THE END OF EACH PERIOD OF THIS ASSESSMENT
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Introduction
Renin is an enzyme that is found in the stomach of young mammals. It is responsible
for solidifying (setting) the milk when it enters the stomach. This slows down the rate
at which the milk moves through the stomach and into the small intestine of the
mammals. This process increases the ability of the mammal to digest the milk and
therefore gain the maximum nutrient value from the food.
Instructions:
You are to develop and carry out and investigation into ONE factor that may affect the
rate of the reaction between renin and milk.
Task 1
Your teacher will demonstrate a simple trial so that you can see the effect of renin on
a small volume of milk. To do this, 5mL of fresh milk will be prepared to a suitable
temperature (remembering that this enzyme is active in the stomach of mammals),
0.5mL Renco solution will be added. Your teacher will show you how to observe the
reaction as it proceeds and what you can expect the end point of a standard milk /
renin reaction to look like.
Task 2
Write a plan to investigate the effect of your chosen factor on the reaction between
renin and milk.
The following equipment is available:
 Renin (in the form of the commercial enzyme Renco)
 Milk – this is full fat homogenised milk (i.e. blue box from the supermarket).
This will have the same number of days left to run before its use by date each
lesson.
 Buffer solutions covering the range pH 4 - 10 with a choice of at least 5 different
pH values in that range.
 Distilled water
 Thermometers
 Stop Watches
 Universal indicator solution / pH paper
 Normal lab equipment - beakers, test tubes, measuring cylinders, syringes etc.
Your plan should state:
 a statement of purpose for your investigation (a testable question, prediction,
hypothesis, or an aim) in relation to the reaction of renin with milk.
 the range over which the independent variable will be changed
 how the dependent variable will be measured.
 how you will control other variables that could have a significant impact on your
investigation
 how you will collect, record, process and graph your data
 the equipment you will need
 how you will ensure your results are accurate, valid and reliable
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Task 3
Trial your investigation plan, then use the information you found out in your trial to
develop your plan into a step-by-step method.
Task 4
Carry out your investigation, recording any changes that you make to your initial
method developed in task 3.
Ensure that your data is reliable and valid to test the purpose of your investigation
Record observations throughout your investigation.
Measure and reliably record all valid data relevant to your investigation.
Task 5
Process your data to produce results that can be compared directly with each other.
Graph the processed data in a way that allows you to interpret the trend in the data.
Task 6
Write a well-organised report on your investigation which includes:
 The purpose of the investigation including your initial methods
 The final method you used in the investigation
 Recorded measurements and observations
 All processed data, including a graph
 A conclusion interpreting the trend shown by the data in relation to the purpose of
the investigation.
 A discussion of what your conclusion shows.
 A critical evaluation of the validity of the investigation. This could consider reliability
of the data, sources of error, limitations, or bias as appropriate to your investigation
method.
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Assessment schedule AS 90457 vs 2
Based on AS90457 Bio/2/1 –A version 4 from NCEA web documents provided by TKI site December 2004 for use in
internal assessment from 2005.
To be awarded the grade (A, M or E) the student must meet the holistic judgement statement at the top of the column.
Evidence
Achieved
Achieved with Merit
The report shows the development
and carrying out of an
investigation.
Development of an investigation:
 A purpose for the
investigation, describing what
will happen to the rate of the
reaction between the milk and
renin(qualitative or quantitative
prediction) as a result of
changing the chosen factor.
The report shows the development
and carrying out of a quality
investigation.
Aim: To investigate the effect of temperature of reaction
solutions OR concentration of renin OR pH of milk OR
concentration of milk on the rate at which the enzyme renin is
able to solidify milk.
Hypothesis: e.g. That the rate of reaction will increase as
temperature increases, peaking at close to 37°C as this is the
body temperature of young mammals, and decreasing to no
reaction at all past approx 60°C as we would expect the
enzyme to denature at apporx. 60°C.
Method:
 A method that includes a
 A method that includes a
1. Measure 5mL of full fat homogenised milk (x days pre-best
description of:
description of
before date) into a test tube using a 5mL plastic syringe.
 The independent variable by
 The independent variable as a
2. Measure 1.0mL renco solution into a second 1mL syringe.
valid range of either conc. of
giving a range of either conc. of
3. Make a water bath set at 37°C by using warm water in a
renin; temp of reaction solutions;
renin; temp of reaction solutions;
polystyrene cup (for insulation) placed within a large beaker
pH of reaction solutions
pH of reaction solutions
(further insulation). Check that the water temperature is
 Dependent variable – time taken  Dependent variable – valid
between 37°C and 40°C at all times.
for milk to set
measurements of the time taken
4. Place both the test tube of milk and the syringe of renco
for milk to set
into the water bath.
Some other aspects of the
Some other aspects of the
5. Place a thermometer into the milk and watch constantly
investigation identified or described investigation identified or described
until the milk reaches 37°C.
e.g. other variables
e.g. control of other variables.
6. When the milk reaches 37°C, use the syringe of renco to
These should include the control
place the 0.5mL of prepared renco into the test tube. Start
of whichever of the following are
the stop watch immediately.
not being used as the independent
7. Every 20 sec, gently rock to tube to see whether the milk is
variable – i.e. temperature, pH
set. Stop the stop watch when the milk sets. It is
(note this does not necessitate the
presumed that the water bath temperature will remain
use of a buffer), volumes of
constant during this time.
reaction solutions, concentration of
8. Repeat steps 1 – 7 at least 4 times to show that consistent
reactions solutions
results are being produced.
 Factors that could cause bias
9. Repeat steps 1 – 8 at the following milk temperatures:,
or sources of error are
15°C; 25°C; 50°C; 70°C
identified
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Achieved with Excellence
The report shows development,
carrying out and evaluation of a
quality investigation.
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Results:
Temp. of
milk °C
Time taken for milk to solidify (s)
Trial 1
Trial 2
Trial 3
Trial 4
15 °C
25 °C
37 °C
50 °C
70 °C
Appropriate graph of the data (to be inserted)
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Average
Collecting, recording and
processing of data relevant to
the purpose e.g.
 Measurements of time taken for
milk to solidify recorded against
rennin conc. or pH or temp of
solutions.
 Data is processed appropriately
to enable a trend or pattern (or
absence) to be identified e.g.
Averaging of results OR
appropriate graph
Collecting, recording and
processing of data relevant to
the purpose e.g.
 Sufficient data recorded
 Data range OR number of
repeats will enable a reliable
trend or pattern to be identified,
 Data processing allows a trend
or pattern (or absence) to be
interpreted.
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Conclusion:
The rate of reaction was slowest at 15°C, increasing up to a peak at
37°C. The reaction was still active at 50°C but was not active at
70°C.
Discussion: e.g. All enzymes are specific and have specific
conditions which they are designed to operate within. We can expect
that each enzyme will be most effective in these conditions. Renin is
found naturally in the stomach of young mammals so we would expect
the optimum temperature to be approx. 37°C and the optimum pH to
be approx 4. In this investigation I have only changed one factor, the
temperature of the milk and renin solutions. The results show that as
expected, the rate of reaction for this enzyme peaked at approx. 37°C.
While increasing temperature normally increases the rate of a reaction
due to increase particle motion and increased rate of collisions,
enzymes will denature at a temperature normally around 60°C. This
is why we would have expected there to be no reaction at 70°C. At
this temperature, the enzyme will have denatured, changing the
shape of the enzyme and therefore destroying the active site.
Enzyme action can be described using either the lock and key or
induced fit theory. In both cases, the shape of the active site on the
enzyme is important. The substrate (in this case milk) fits into the
active site and when fitted, induces the reaction (in this case the
setting of the milk). If the enzyme (a protein) is heated beyond 60°C,
the enzyme will denature. This involves the unfolding of the structure
of the protein, and in doing so the destruction of the active site,
rendering the enzyme ineffective.
Evaluation e.g.
Although the method used was designed to maximise the validity of
the data collected, there are a number of factors which may contribute
to potential sources of error in the data. These include the following:
Temperature of the solutions: In order to minimise the volume of
renin lost in transfer of the renin from the syringe to the reaction tube,
I chose to retain the renin in the 1mL syringe within the water bath
rather than transfer this to a test tube where the temperature of the
renin could have been checked specifically. A volume of 1mL in a test
tube is minimal and would have been difficult to get an accurate
temperature measurement of. It is not likely that the renin heated at
the same rate as the milk as there is a 5:1 volume difference. By
maintaining the temperature of the water bath as close as possible to
the experimental temperature, I have attempted to minimise this
problem, as once heated, the renin should have been retained at the
set temperature so that it would not matter that it reaching this
temperature prior to the milk.
Water bath maintenance: My method presumed that I could
manage the process of maintaining the water bath at the set
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Interpreting and reporting on the
findings, eg
 Conclusion links the findings of
the investigation to the purpose
of the investigation.
Interpreting and reporting on the
findings, eg
 A valid conclusion links the
processed data to the purpose
of the investigation.
 Discussion uses knowledge of
enzyme action and factors
affecting this action to explain
the trend or pattern in the
results
Evaluation of the investigation,
eg
 Justification of the conclusion
in terms of the method used,
such as the reliability of the
data and the validity of the
method.
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temperature, at the same time as checking the milk temperature or
progress of setting. In reality this would have been more effectively
controlled if two people were working together on this investigation.
While I attempted to maintain the bath at all times, at higher
temperatures there was more potential for this to vary. By measuring
the temperature of the milk to signify the start of the reaction, this
minimised the potential effect of variation in the water bath
temperature. Once the experiments were running, it was difficult to
maintain the 20sec checks on the solution and the water bath
temperature. Insulation was added to the water bath system to
minimise this problem. This issue was more marked at the lower
temperatures where the reaction rate was slower.
Timing of end points: The solution was tipped gently every 20s to
check for solidification. In longer experiments, the potential for the
solidification to occur at the beginning of one of these periods,
therefore putting the results out by up to 15 - 18s was not a significant
factor. In the experiments where the total time taken to solidify was
approx.. 30 – 40 s, this had the potential to reduce the reliability of the
results. The ability to make multiple repeats at these temperatures
due to the short time involved in the reaction assisted in reducing the
potential effect of this problem.
Subjectivity of solidification point: The point of solidification is
somewhat subjective. While the use of a single observer in
determining this point gives a level of consistency, the general
subjectivity of this point should not be overlooked and has the
potential to reduce the reliability of the investigation. Once again –
the use of multiple repeats can eliminate this uncertainty to a degree.
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