AQA AS Biology Practical Work
A-LEVEL
BIOLOGY
PRACTICAL WORK
Student Handbook
2012/2013
Name: ___________________
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AQA AS Biology Practical Work
Practical Evaluation
%
Mark
Grade Comment
Points for improvement
Beetroot membranes
Microscope Onion
Cells
Food Tests on
Biological
molecules
Osmosis on Potato
cells.
Enzymes. The effect
concentration on the
activity of Amylase.
Fish Gills.
Evaluation and
scatter plot.
Mitosis in Onion or
Garlic root tips.
Transpiration
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AQA AS Biology Practical Work
At all times Biology students should show full regard for safety and the ethical
issues involved with the well being of living organisms and the environment.
There will not be time for students to do all of the practical exercises outlined
within this booklet so some will be given as demonstrations.
The sequence of practical exercises may change. Students must keep a record of
their practical marks in the front of this book.
Contents
Beetroot Practical. ........................................................................................................................................ 4
Using the Biology Calculators to Calculate Standard Deviation (S.D.) ........................................................ 10
Magnification .............................................................................................................................................. 11
Preparation of a temporary slide of Onion bulb scale epidermis. .............................................................. 11
Making Microscope Drawings. .................................................................................................................... 13
Biological Molecules – Food tests ............................................................................................................... 14
Osmosis Experiment ................................................................................................................................... 19
Enzyme practical ......................................................................................................................................... 22
Demonstration of Sheep Heart and Lung Dissection (Not included).......................................................... 24
Fish Head Practical ...................................................................................................................................... 24
Measurements of Circulatory system and Respiratory System (Not included). ........................................ 27
Mitosis root tip practical ............................................................................................................................. 28
Biodiversity Practical .................................................................................................................................. 31
Transpiration Practical ................................................................................................................................ 33
Safety in the Laboratory.............................................................................................................................. 35
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AQA AS Biology Practical Work
Beetroot Practical.
An experiment to test the effect on cell membranes of their exposure to different
temperatures. Skills; The use of water baths to change or control temperature.
Collection of reliable quantitative data where a colour change takes place. Using a
standard scientific calculator to calculate mean and standard deviations . Plotting
data as line graphs.
This exercise is designed to demonstrate to you how to write up A-level Biology practical work.
In future you should follow this format when writing up practical work.
Title: Clearly state what the experiment is about.
______________________________________________________________________________
______________________________________________________________________________
Hypothesis: Predict what will happen (1). This should be semi quantitative if possible.
Introduction: This gives background and context to the experiment. You can include reference
to background work that you and other scientists may have done.
Cells are surrounded by membranes. Enclosed within a beetroot cell is a purple dye called
Anthocyanin.
Anthocyanins are water-soluble pigments produced in
the cytoplasm of red coloured plant cells. The
attachment of the sugar molecule makes them
particularly soluble in the sap of the vacuole, where
these molecules are stored. These are responsible for the
pink-red colors of most flower petals, of most red fruits
(like apples) and almost all red leaves during the
autumn. Anthocyanins absorb light in the blue-green
wavelengths, allowing the red wavelengths to be
scattered by the plant tissues to make these organs
visible to us as red(3).
A Beet Plant (2). The root tubers
are rich in red pigment.
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AQA AS Biology Practical Work
A typical beetroot cell has an irregular shape, a cellose cell wall, plasma membrane, and sap
vacuole, surrounded by the tonoplast. Within the cytoplasm are the organelles (but no
chloroplasts, Why?), storage granules of starch and the anthocyanin dye (4).
In the space provided on the next page draw a diagram to show the structure of a typical beetroot
cell, as it would be seen using a light microscope.
During this experiment the plasma membrane will be damaged (5) so that it can no longer contain
the dye and the cell will release Anthocyanin into the surrounding water giving the water colour
(6).
The plasma membrane is formed by lipid (fats) and proteins both of which are altered by heat.
Materials and Method
List your materials
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AQA AS Biology Practical Work
Independent Variable; Immersion of blocks of beetroot cells in water of different temperatures is going
to cause different amounts of damage to the membranes. As you are able to choose and vary the
temperatures you use this factor is known as the independent (or manipulated) variable.
Dependent Variable; This is going to be what you measure so will be the results of the experiment.
The results will vary depending on the experimental conditions, that you use, so is called the dependent
variable.
Constants; You will be changing the temperature of the heat treatment to your beetroot pieces but to
make the experimental conditions fair all other factors should be kept constant. Examples of constant
factors in this experiment include;
_____________________________________________________________________________________
_____________________________________________________________________________________
Control; A control is an extra bit of the experiment that you do to ensure that your results are reliable.
For instance, how can you assess the amount of damage that you may do to the beetroot by moving it
between test-tubes? How could you measure the amount of dye leaking without the change in
temperature?
Safety. When working in the laboratories always remember the rules and take care. In your write up
outline any safety precautions necessary to ensure safe working practice OR fill in a risk assessment
form before starting the practical.
Writing in scientific format. Work must be written in the past tense as if it has been done and
it should be in impersonal form, so don’t use I, we, they, he or she in the method or discussion
as this relates to a person or people.
For example………
Beetroot bores, cut using a no. 3 cork bore were provided. These were trimmed to the same
length which was ____________ and washed thoroughly before the experiment.
Five bores were used by each group. Bores were immersed for exactly __________________,
each in a water bath that was set to one of the following temperatures _________, __________,
_________ and ________. A control sample was similarly immersed in water at room
temperature at ______.
Immediately the bores were carefully transferred into prepared, labeled test tubes each
containing _________ of distilled water. Care was taken to make sure that the bores went into
their correct tube.
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AQA AS Biology Practical Work
After a further __________________ the bores were removed from the tubes and discarded.
The contents of the tubes were mixed thoroughly and then viewed by placing a piece of white
paper below the tube and looking vertically down into the solution.
Qualitative Results; Colour differences were observed and recorded. This is very subjective and
is based on the quality of the colour as seen by the observer.
Quantitative Results; The absorbance of light by dye in solution can be measured using a
COLORIMETER. This puts a numerical value on the results.
Colorimeter.
The graph on the left (3) shows the
absorption peak for Anthocyanin. When
using a colorimeter it is possible to select
the wavelength that you wish to monitor
by using filters. Light that is absorbed is
not transmitted!
Results.
When creating a table us a pencil (not a pen) and make sure you use a ruler for all lines. This
time it has been done for you so simply fill it in. Units go in the heading ONLY.
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AQA AS Biology Practical Work
Table to show the relative permeability of beetroot cell membranes when exposed to water
baths of varying temperature.
Temperature
o
C
Observation
Colorimeter readings
(% Transmission of light).
First column
Mean
Standard
Deviation.
(S.D.)
contains the
independent
variable.
Graphs (On separate paper) 6 marks.
Use graphs to present your results where possible.
Chose the most appropriate type of graph. As the independent variable is a range of related
values and the graph should illustrate a relationship between the variables, a line graph is the
correct choice. In this case the mean values and S.D. range bars can be plotted against
temperature. Plot the mean values and give the upper and lower indications of standard
deviation using bars. The independent variable will be on the horizontal X-axis (A CROSS!) and
the measured (dependent) variable will be on the y-axis (VERTICAL). Label axes include units of
measurement and use keys. Give the graph a title.
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AQA AS Biology Practical Work
Discussion (on separate paper 15 marks).
2 marks will be awarded for the correct use of scientific terminology, grammar, spelling and tense.
The discussion is where one analyses and explains the results, describe trends or patterns in data
collected and outlines positive and negative aspects?
Why did these results occur (4), give biological explanations about membrane structure and the effect of
heat on its molecular structure?
What were the sources of error and limitations of this experiment?
How did these results compare to those of others and are the results reliable (relate this to the error bars
drawn on the graph)?
Did the control prove anything (was the method valid)?
If you had to measure absorbance instead of transmission would the graph have been a different shape?
How could the experiment be improved (accuracy and precision)?
What other relevant experiments could be done?
Conclusion (on separate paper 1 marks).
One line is all that is needed. Tell the reader whether the results relate to the hypothesis?
Evaluation of the practical (3 marks); be reflective about what new skills and theories you have learned
from this exercise.
References
If you have used any published material, IT sources of information or other student’s work
anywhere in your write up, this is the place to acknowledge the work of others.
Do not rewrite the introduction or method.
Total 25 points.
References (Should be presented in this format).
1.
2.
3.
4.
5.
Roberts, M. King , T. and Reiss, M. (1994). Practical Biology for Advanced Level. Thomas Nelson and
sons Ltd.
Photo courtesy of Dr Stanley Kays
http://www.uga.edu/rootandtubercrops/English/photographs/beetroot.htm
http://www.uga.edu/rootandtubercrops/English/photographs/beetroot.htm
Clyde, R. (Autumn Term) “Cell Structure” and “Movement across Membranes”. Class notes.
Jones, M. Fosbery, R. and Taylor, D. (2004). Biology 1 (8th Edn). Cambridge University Press.
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AQA AS Biology Practical Work
Using the Biology Calculators to Calculate Standard Deviation (S.D.)
Standard deviation analyses variation within the data set that you use to calculate the mean. If the
numbers are very different the standard deviation will be high but if the numbers used to calculate the
mean are similar then the deviation will be small. It is the mean variation of results contributing to a data
point!
Standard deviation gives the reader an idea of how reliable the results are and may be quoted as a ± after
the mean, implying that you can expect to add or take that number from the mean and still be within the
range of expected variation, observe the overlap of data ranges.
On the graph that you plot give a range bar. This is a vertical line through the mean showing the range if
you add the SD on to the mean or take it away from the mean. Below is a presentation of range bars on
different graph types:
Briefly describe the two graphs and
explain in terms of reliability of the
results in terms of variation and
overlap.
Top graph
______________________________
______________________________
______________________________
______________________________
______________________________
______________________________
______________________________
_______Bottom graph
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
To use our calculators to calculate S.D. press these buttons.
_______________________________
Input the values
_______________
Mode
5 sd
( value
Data)
(value
Data)
(etc)
Calibration Of Microscopes.
Get the results
Inverse
Inverse
Inverse
Inverse
Mean ẍ4
To get standard deviation
number of entrees 6n
total of Values ∑x 1
n-1 SD
5
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AQA AS Biology Practical Work
Magnification
When you have made a biological drawing you may need to calculate the
magnification of that drawing. Sometimes you can just write which objective
lens you used to view your specimen, but if you are given values, have measure
the size or have a scale bar you must use the following equation.
ALWAYS USE THE SAME UNITS OF MEASUREMENT FOR THE
TOP AND BOTTOM FIGURES IN THE EQUATION.
Magnification
=
Size of Image =
Size of object
Size of Drawing
Size of Cell
This is a ratio so has no units. You could measure both your drawing and the
cell at the same axis line to get a value in millimetres for each. Then submit
these values into the equation.
Preparation of a temporary slide of Onion bulb scale epidermis.
Microscopes.
Skills; Using an Optical Microscope, preparing temporary mounts, staining and
estimating the size of onion cells.
Safety: Take care with sharp instruments, avoid getting iodine on your hands and
remember that cover slips are made from thin glass and are sharp, particularly
when broken.
Instructions.
You will be provided with the scale leaf of an onion bulb. Remove the epidermis
from the inner concave side of the onion bulb scale. This is a thin, single layer of
cells forming a translucent membrane.
Epidermis
peeling off
Onion Scale
leaf.
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AQA AS Biology Practical Work
Peel off the epidermis using your fingernails, a pair of forceps or the blade of a
scalpel (take care). You are aiming to get a single layer of cells (a monolayer).
Only a small piece is needed about 5mm2. Larger pieces should be trimmed whilst
the specimen is being stained with iodine. Place the epidermis in a watch glass and
quickly add a few drops of iodine to flood the specimen, ensuring that the
epidermis is immersed in iodine.
Leave in iodine for at least 3 minutes. Iodine will stain skin and clothes.
After 3 minutes remove the specimen and put it on a glass slide. Use a dropper to
put two drops of water on the specimen. Avoid leaving folds in your epidermis
and ensure there are no air bubbles underneath it. Use mounted needles to unfold
it if necessary.
Clean glass slide
Two drops of
water
Place your cover slip at the edge of the water and gently
lower it onto the slide with the needle.
Cover slip
Mounted needle
Onion epidermis
Exclude air bubbles if possible.
Coverslip
Clean glass
slide
Onion epidermis in water
Dry the slide around the cover slip and view using the low power microscope
objective lens. Move up to high power and draw one cell showing the maximum
amount of detail possible. Use the scale in the eye piece to record the length and
width of your cell in eye piece units, noting the objective used. Then calculate the
magnification (enlargement) of your drawing.
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AQA AS Biology Practical Work
Making Microscope Drawings.
Sit with a straight back and focus on the specimen.
Place the paper beside you and in pencil try to draw the outline of the specimen
without looking at your drawing but continue to look at the specimen through the
microscope.
Add necessary detail to your drawing after doing the complete outline.
Your drawing should be clear unbroken lines and not shaded.
Use the space available but don’t go off the page. Keep your drawing central.
Spotting can be used to add detail.
Tissue plans should not contain any cells.
Cell diagrams should not have more than a few cells included.
An example has been given. Of course your cell will be a slightly different shape
and the walls of neighbouring cells, etc will be in different places.
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AQA AS Biology Practical Work
 Title, date and labels should be added with your name.
 Rulers must be used to provide lines to the labels away from the drawing.
Lines should not cross.
 Calculations relating to magnification should be shown.
Your microscope drawing and calculations of magnification for width and
length of the cell will be assessed.
Biological Molecules – Food tests
Skills; Using chemical tests to identify the biological molecules. Including the
Benedict’s test for reducing sugars, Iodine for starch, Biuret test for proteins,
Emulsion test for lipids and the acid hydrolysis, neutralization and Benedict’s test
for non-reducing sugars.
Lesson Objectives
By the end of this practical exercise you must know how and when to use these “food tests” and
what to expect from either a positive or negative result.
In this practical you are going to complete experiments that will identify some of the main
biological molecules. You will also carry out these tests on an unknown sample.
Biological molecule
Detection test
Carbohydrate:
-
Benedict’s test
Acid hydrolysis, neutralisation and
then Benedict’s test.
Starch
-
Iodine test.
Proteins (including enzymes)
-
Biuret test
Lipids
-
Emulsion test
Nucleic acids
-
Acidified acetic orcein is used to
stain chromosomes when studying
mitosis.
Reducing Sugar (e.g. Glucose)
Non-Reducing Sugar (e.g. sucrose)
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AQA AS Biology Practical Work
Tests for carbohydrates
There are 3 tests for carbohydrates:
- Test for reducing sugars = Benedicts test
- Test for non-reducing sugars = Acid hydrolysis, neutralisation and then Benedict’s test.
- Test for starch = iodine.
You will be working to distinguish between reducing sugars such as glucose and non-reducing
sugars like sucrose. You will also identify starch, a polysaccharide, proteins and fats, (lipids).
Reducing sugars include monosaccharides and most disaccharides (but not sucrose).
Non-reducing sugars include some polysaccharides and some disaccharide, such as sucrose.
Safety notes.



You will be using acetone which is highly flammable so NEVER have it near a naked
flame, DO NOT heat acetone.
Safety goggles where appropriate.
Do not touch hot test tubes with bare hands.
Start by carrying out each test on the correct solutions to see how they work. Then you can
identify those molecules in the unknown samples by elimination.
Test for Reducing Sugars
Method
1. In a boiling tube, take 2cm3 of the solution to be tested and add 2cm3 (10 drops) of
Benedict’s reagent. Mix the reagents thoroughly.
2. Place the boiling tube in a water bath in which the water has boiled, but the source of the
heat has been turned down. Leave for 5 minutes, shaking occasionally.
Result
Positive test: Reducing sugar present = The blue copper (II) sulphate in the Benedict’s reagent is
reduced to brick-red copper (I) oxide. The test is partially quantitative and so the colour will
range from green, through yellow, orange and brown to deep red, as the quantity of reducing
sugar increases.
Negative result: The solution will remain blue in colour.
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AQA AS Biology Practical Work
Test for Non-Reducing Sugars
Information
There is no specific test for a non-reducing sugar but a non-reducing sugar can be detected by its
inability to reduce Benedict’s reagent directly.
However if the non-reducing sugar is first hydrolysed by boiling with hydrochloric acid it will be
broken down into its monosaccharides.
After neutralisation these can then reduce Benedict’s reagent in the normal way.
So a non-reducing sugar is identified by a negative reaction to Benedict’s before
hydrolysis/neutralisation and a positive result after hydrolysis/neutralisation.
Method
1. Carry out the reducing sugar test. If negative get a NEW sample.
2. PUT THE FRESH SAMPLE in a boiling tube, add 2cm3 (10 drops) of dilute
hydrochloric acid (0.1M) to the solution and boil for 2-3 mins
3. Then add sodium hydroxide (0.1M), to the boiling tube until the solution is neutral, (over
neutralise with 12 drops), or preferably alkaline. Use the pH paper to test for this. (This is
important because Benedict’s is not effective in acid conditions).
4. Carry out the reducing sugar test again by adding Benedict’s solution.
Result: A negative result (solution remains blue), after the first reducing sugar test, followed
by a positive result, (solution turns red/brown), after the second reducing sugar test, is an
indication of a non-reducing sugar.
Test for Starch
Method
1. Place two drops of the solution to be tested in a test-tube.
2. Add a drop of Iodine in Potassium Iodide Solution. (No heating is required).
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AQA AS Biology Practical Work
Result : If starch is present the yellow-orange iodine in potassium iodide solution becomes
a blue-black colour.
Test for Lipids
Method
1. Place 2cm3 of the test solution in a test tube and add 5cm3 of acetone. CARE- Keep
acetone well away from naked flames as it is extremely flammable.
2. Shake the tube thoroughly.
3. Add 5cm3 off water and shake gently.
4. As a control repeat procedures 1-3 using water instead of the test solution.
Result: A milky suspension indicates the presence of a lipid.
Test for protein
Biuret Test
Method
1. To 2cm3 of the test solution add an equal amount of Biuret Reagent
drops of Biuret Reagent B and shake the tube to mix the contents.
2. No heat is required for this test but the contents of the tube can be
warmed by rolling in the hands.
A. Then add 10
Result: The presence of protein is indicated by a purple-mauve colouration.
Now use your skill to detect which two biological molecules are in the
‘unknown’ sample. Fill in the table provided as you complete the tests.
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AQA AS Biology Practical Work
Biological Molecules – Food tests results table
Test
Test summary and results observed
Benedict’s test
Acid hydrolysis, Neutralisation and
Benedict’s test.
Iodine Test
Emulsion Test
Biuret Test
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AQA AS Biology Practical Work
Osmosis Experiment
Measuring the amount of water movement in and out of cells.
Skills; Producing an appropriate dilution series when provided with stock solutions
of reagents.
Collection of reliable quantitative data where there are changes in mass or length.
Collect and present raw data in a suitable table conforming to conventions (IOB).
Take all measurements to an appropriate level of accuracy and precision.
Using a standard scientific calculator to calculate mean, standard deviations and
percentage change. Plotting data as line graphs.
An experiment to determine the water potential of bulky plant tissue (potato).
Work in groups of 3
SAFETY
Take care when using the scalpels.
The chemicals are not dangerous
Apparatus required for each group:
18 potato bores per group
paper towel
distilled water
1 pair forceps
6X 250ml beakers
0.2M Sucrose solution
1 scalpel
1 tile
0.4M Sucrose solution
Ruler
0.6M Sucrose solution
0.8M Sucrose solution
1.0M Sucrose solution
Instructions
Read through all this before you start.
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AQA AS Biology Practical Work
1. Choose a recorder from within your group to record all the measurements and recordings.
Use the table provided to record your group’s results. You only need to initially record one copy
per group, but you will all need a table of results to submit with your report.
2. Check that you have 6X 250ml labeled beakers.
Pour 50mls of the particular molar sucrose solution, into the correct beaker.
3. You need to carry out steps 4 to 10 quickly and carefully to avoid the bores drying out, as this
may affect your results.
4. Take 18 prepared potato bores; divide them into 6 sets of 3.
5. Place 3 of them side by side on a white tile. Lay a ruler down the edge of the bores and trim
the ends with a scalpel, so that they are all the same length. This is clearly shown on the attached
diagram. Use this as guidance.
6. Repeat this with the remaining 5 sets of 3 bores, keeping each set of 3 separate.
It may be an idea to place each set of 3 bores on a separate scrap of paper to prevent confusion.
Call these sets 0.2, 0.4, 0.6, 0.8, 1.0 and distilled water.
7. Gently roll the bores on a piece of paper towel or filter paper to lightly dry the surface.
8. Measure and record the length of all the bores, accurate to 0.5mm. Do this keeping them in
their sets of 3.
9. Weigh and record the total mass of the 3 bores of each set.
10. Quickly place each set of bores in their respective beakers of solution.
11. Leave the apparatus for 20 minutes.
12. Whilst you are waiting you can calculate and record the average initial length and average
initial mass for each set of potato bores. You can also start to write up your experiment. Use the
separate sheet as a guide.
13. After 20 minutes remove the bores using forceps and place each set on the appropriately
labeled paper.
14. Gently roll each set of bores, re-measure and record the final lengths of the bores.
15. Weigh and record the final mass for each set of 3 potato bores.
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AQA AS Biology Practical Work
16. You can now calculate and record the average final length and average final mass for each
set of potato bores.
17. For each of the 6 separate solutions, calculate and record the following ratio for each set of
bores:
final average length ÷ Initial average length
18. Repeat step 17 for mass, so that you calculate the ratio for each solution.
19. Plot 2 graphs. The first one should be the concentration of sugar solutions (molarity),
against:
Final average length ÷ Initial average length (ratio)
The second graph should be the concentration of sugar solutions (molarity), against:
Final average mass ÷ Initial average mass (ratio)
20. From your graphs state the concentrations of sucrose solution, which are isotonic with the
potato bores, from the length and mass results. This will be where the ratio is 1:1.
Write up and assessment.
Write up
You need to hand in the completed results table, the 2 graphs and a discussion.
Points to consider in the discussion:









Which is the more accurate – mass or length?
Why? Consider the limitations of the measuring equipment for mass verses length.
For the rest of the discussion use either the mass or the length results. Use thee set of
results which you think are most reliable.
Discuss which solution is isotonic. What does this mean? What is happening at a cell
level in the potato bore?
Discuss which solution is hypertonic. What does this mean? What is happening at a cell
level in the potato bore?
Discuss which solution is hypotonic. What does this mean? What is happening at a cell
level in the potato bore?
What were the sources of errors in this practical?
How could the practical be improved upon to reduce the errors? (Consider method and
equipment used here).
Errors and Improvements.
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AQA AS Biology Practical Work
Mark
/ 15 =
%
=
Grade
Enzyme practical: How varying the concentration of amylase affects the rate
of conversion of starch to maltose.
The affect of Concentration on the rate of Amylase activity.
Skills;. Carry out an investigation in a methodical and organized way,
demonstrating competence in the required manipulative skills and efficiency in
managing time. Collection of reliable quantitative data where a colour change
takes place. Take all measurements to an appropriate level of accuracy and
precision. Using a standard scientific calculator to calculate mean and rates.
Plotting data as line graphs.
Demonstration of the activity of Catalase (Not included)Skills; Collection of
reliable quantitative data where a gas is evolved.
Background Information
Amylase is an enzyme. Enzymes are biological catalysts. That is they speed up the rate of
chemical reactions.
Amylase catalyses the reaction of Starch → Maltose
Starch = a polysaccharide. This is insoluble and so makes a good storage polysaccharide for
plants.
Test for starch – iodine turns blue/black in its presence.
Maltose = a disaccharide. It is soluble and a reducing sugar.
Test for maltose – Benedict’s. It will turn from a blue colour to a brick red/orange precipitate.
Producing the dilutions of the enzyme amylase.
Concentration
of amylase (%)
100
80
60
40
20
Volume of
amylase
(enzyme) (ml)
5
4
3
2
1
Volume of
Water (ml)
0
1
2
3
4
Total volume of
enzyme solution
(ml)
5
5
5
5
5
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AQA AS Biology Practical Work
Take 5ml of each dilution and 5mls of starch for each practical.
Procedure
Read the instructions completely before starting the procedure. Working in pairs:
1. Set up the water bath at 250C. This must be maintained throughout the practical.
2. Place 1 drop of iodine into each well of the spotting tile.
3. As a control, place 1 drop of starch solution into 1 of the wells, in the spotting tile, with 1 drop
of iodine.
Record the result on separate paper:
(1 mark)
4. Using the syringe, put 5ml of the enzyme, (amylase), into one of the test tubes.
5. Using a pipette, put 5mls of starch into a separate test tube.
6. Add the 5ml of amylase to the 5ml starch. Start the stop clock. Immediately test for starch by
placing 1 drop of the solution into the first well of the spotting tile. Now every 10 seconds, test
another drop from the boiling tube in a different well of the spotting tile, with iodine. Continue
doing this until the test for starch is negative, (that is the iodine remains orange). Record the time
taken, (in seconds), for no colour change to occur.
7. Repeat steps 1 – 4 for each of the 4 other dilutions. If there is no end result after 5 minutes,
then terminate the run at that point but record your results.
8. Before you start the procedure produce an individual results table on separate paper. You can
then use this to record your results as you go. Make sure that you record dilutions, time taken for
all the starch to be converted into maltose for each dilution. Record the rate too. (1/time (s-1)).
Think about the design of your table.
(5 marks)
9. Plot a graph of concentration of amylase (%) against rate. Consider what goes on what axes,
units, spacing, plotting accuracy, labels and title.
(5 marks)
You will also be marked on how well you work safely and how well you follow the instructions
you have been given. Consideration will also be given to your efficiency when carrying out these
task
(4 marks)
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AQA AS Biology Practical Work
Demonstration of Sheep Heart and Lung Dissection (Not included).
Fish Head Practical
Demonstration of Fish Head Dissection to observe Fish Gill Structure. Skills;
Plotting data as scatter diagrams and using these to identify correlation.
Lesson Objectives.
1. Use knowledge and understanding to pose scientific questions and define scientific problems.
2. Carry out investigative activities, including appropriate risk management, in a range of
contexts.
• analyse and interpret data you have collected to provide evidence.
• evaluate your methodology, evidence and data, resolving conflicting evidence.
You will require specific knowledge of the following skills and areas of investigation.
• collection and analysis of data relating to intraspecific variation.
• use of an optical microscope to examine temporary mounts of cells, tissues or organs.
Fact File:
Common Name: Hake
Scientific (Latin) Name: Merluccius merluccius
Usual Size: Norm:1m Max:1.8m
UK Record Weights from rod/line:
Shore:3lb-8oz-2dr (2kg1g) Morfa Beach, Port Talbot
W.S.Parry 1984
Boat: 25lb-12oz-14dr (11kg706g) Loch Etive, Scotland
R.Roberts 1997
http://www.uk-fish.info/pages/hake.html
This week five AS classes are going to examine the heads of 20 Hake (Merluccius merluccius)
donated by a fishmonger in Aberdare, the fish meat was all sold to paying customers and the
heads were frozen on the day that the fish were caught. Hake are heavily over fished and the
species is now comparatively rare.
Examine the fish head that has been provided to you. Below sketch a QUALITATIVE record of
the structure of a single gill arch, use a hand lens to see detail. Try to create a diagram that is to
life size, so use a ruler. Label gill filaments and gill lamellae. Also indicate the direction of
water flow across the gill filament. Annotate with a full description of the gaseous exchange
process in fish.
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AQA AS Biology Practical Work
Gills and boney fish breathing
Consider what QUANTITATIVE data you could collect that may demonstrate intraspecific
variation.
1. Use your knowledge of gaseous exchange in fish to suggest a testable hypothesis
relating the size of hake to its gaseous exchange surface area.
2. What investigative activities could you (and fellow AS students) undertake in order to
test this hypothesis?
3. a) Outline any health and safety risks that need to be considered when collecting data
suggested in 2.
b) Explain how the identified risks (3a) can be minimised?
4. On the table provided make and record reliable and valid observations for one fish
making measurements with appropriate precision and accuracy.
Intraspecific Variables
Mass of head (g).
1
2
3
Mean
Width of mouth (mm)
Corner to corner.
Depth of mouth from nose
to corner (mm).
Cephalic index (mm)
circumference of head just
behind eyes.
*Total number and length of
Gill Arches in fish (mm).
Mean Length of gill
filaments (mm).
Mid-width of gill Arch
(mm).
Look for the tiny lamellae! What would you need to measure
them? ____________________
Calculation of total surface
area of lamellae (M2).
You will be provided a piece of graph paper
and with the collated year group data.
Name the type of plot you will need to make
to demonstrate a correlation to support your
hypothesis.
Which two data sets would be best for the
purpose of demonstrating a correlation
linked to the hypothesis and why?
Mass of head, mouth length, length or width
of gill arch, Cephalic Index and/or Surface
area of Gills.
What could you calculate to test the
variability of the data?
Note.
1000mmx1000mm=1 M2
1000umx1000um=1mm2
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AQA AS Biology Practical Work
5.
6.
7.
8.
Outline any risks (factors) that could make these measurements invalid.
How could the accuracy of this study be improved?
How could the reliability of this study be improved?
What are the limitations of this study? Identify the limitations of the material, apparatus
and/or techniques used.
9. Hake are heavily overfished and the species is now comparatively rare. Starting
with the Latin name for Hake written in its correct format, evaluate the ethics of this
investigation (attach sheets as necessary).
Hake Head Investigation Class Data
Mass of Heads (g)
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Mean
S.D
364
204
294
510
219
333
336
255
289
201
295
239
258
300
251
310
345
337
273
190
290.15
69.22515026
Cephalc Index (mm)
223
190
180
230
163
180
196
197
207
150
215
174
185
181
194
190
199
205
160
157
188.8
20.54171134
Estimated Gill Surface area
(M2)
[mm2/1000000 =M2]
1.5
0.45
0.75
1.54
0.49
2.82
1.91
0.55
2.46
0.41
1.69
1.31
1.34
1.91
0.69
1.04
2.82
0.92
0.58
0.52
1.285
0.784860028
10. Plot the data (Mass Vs S/A) as a scatter plot and draw in the best line of correlation
possible. Put mass on the X-axis.
11. Interpret you graph as fully as possible. Describe any correlation you observe. Are there
any anomalies? Can you draw any conclusions? What further experiments could enhance
this study?
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AQA AS Biology Practical Work
Past paper homework question.
1.The electron micrograph shows a section through a fish gill. The directions of flow of water and of
blood are indicated by arrows.
10 m
Key
Direction of flow of water
Direction of flow of blood
Source: www.ucdavis.edu/mjguinan
(a) Calculate the minimum distance that a molecule of oxygen would have to
travel from the water to a red blood cell. Give your answer in micrometres and show
your working. Answer .......................................... µm.
(2)
(b) Explain how the relationship between the direction of flow of water and of
blood shown in the micrograph is useful to a fish.
(3)
(Total 5 marks)
Measurements of Circulatory system and Respiratory System (Not
included). Pulse, Blood pressure, Spirometer (data logger). Skills; Take all
measurements to an appropriate level of accuracy and precision. Using a standard
scientific calculator to calculate mean, rates and standard deviation. Plotting data
as bar charts and histograms. Plotting data as scatter diagrams and using these to
identify correlation.
27
AQA AS Biology Practical Work
Mitosis root tip practical
Mitosis – Onion/Garlic tips. Using microscopes to examine root tips and to
calculate the proportion of cells undergoing mitosis within the field of view.
Skills; Using an Optical Microscope, preparing temporary mounts and staining
cells.
1. Support a garlic clove over water. Leave until the roots develop, (3 - 4 days).
2. Cut off the root tips 1 - 2 cm long. Put them in a small volume of acetic alcohol for 10
minutes.
3. Wash root tips in ice cold water for 4 - 5 minutes, then dry them on filter paper.
4. Transfer root tips to pre-heated 1M hydrochloric acid at 60°C for 5 minutes. Do this by placing the tips into a
watch glass containing the 1M HCL resting on top of a small beaker containing water at 60°C. Repeat step 3. Take
care - they will be very fragile.
5. Transfer two root tips to a clean microscope slide. Cut each root tip about 2 mm from the growing tip. Keep the
tips, discard the rest.
6. Macerate the root tips with a mounted needle. Add one small drop of lacto-propionic orcein
stain for 2 minutes.
7. Cover with a cover slip, and blot firmly with several layers of tissue or filter paper and press
gently to spread root tips.
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AQA AS Biology Practical Work
8. View under the microscope (x400 magnification is adequate) and look for cells with
chromosomes
Tasks
Identify cells in the following stages of mitosis: interphase, prophase, metaphase, anaphase and
telophase. Draw outline sketches of a cell to illustrate each stage if possible but at least two
different stages. Label your diagrams.
Fig. 1. Typical and disturbed stages of mitosis in the meristematic cells of Allium cepa L. roots
treated with lead (E, G–J) or cadmium (F): 1440×. (A–D) Control stages of mitosis: prophase
(A), metaphase (B), anaphase (C), telophase (D); (E–G) chromosome disturbances: c-metaphase
(E), lagging chromosomes in anaphase (F), chromosome bridges (G); (H–J) nucleus
disturbances: nucleoli partly outside nucleus (H), “budding” nuclei (I), micronuclei (J).
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AQA AS Biology Practical Work
http://www.google.co.uk/imgres?hl=en&sa=X&rlz=1C1SVEC_en-gbGB403GB403&biw
4. In a given field of view, count the number of cells at each of the five stages of mitosis. Record
this in a suitable table.
5. Calculate the mitotic index.
Mitotic index = number of cells containing visible chromosomes divided by the total
number of cells in field of view
Assessment of Drawings.
Two cell drawings must represent two different stages of mitosis. Drawings must have continuous lines
and not be sketchy and all lines must be clear and continuous.
Stages of mitosis must be recognisable. Chromosomes must be drawn. Alignment of chromosomes
must be correct, the nuclear envelope will only be present in early prophase or very late telophase just as
the phragmoplast forms. Splitting into new cells is not a stage of mitosis not is interphase.
At least two visible features must be labeled. The plasma membrane is not visible. Arrows or the ends
of lines must be on the labeled structure.
The stages drawn must be identified and spelt correctly.
HCL is used to break down the cell walls. This causes the cells to separate so a monolayer forms when
the root tip is squashed. Also because the cells are no longer connected the stain can penetrate into
more of the cells.
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AQA AS Biology Practical Work
Biodiversity Practical
Biodiversity Index Calculations (seeds). Using a sample of seeds and beans to
calculate a biodiversity index.
Objective: Use an index of Diversity (d) to calculate the biodiversity of a habitat, using the
formula provided;
Five communities of seeds and beans (A,B,C,D and E) have been provided. Using the artificial
habitat grids and random coordinates, sample the biodiversity and determine the diversity index
for the communities of seeds and beans in the 5 samples. Each group should calculate for a
different sample.
Results.
Sample ____
Sampling Table.
Square (quadrat) Number
1
2
3
4
5
6
7
8
9
10
Total
(n)
Red Kidney
Bean
Black Kidney
Bean
Haricot
Bean
Maize
(Sweet corn)
Cardamom
Seeds
N= ________
d = N (N – 1) =
Σ n (n – 1)
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AQA AS Biology Practical Work
Sample
d = N (N – 1)
Σ n (n – 1)
A
B
C
D
E



Identify which two samples have the same biodiversity.
Which is the most diverse community?
Which is the least diverse community?
Discussion;
Why were samples taken? (why didn’t the whole lot get counted?) How could accuracy have
been improved?
What assumptions were made? Comment on the variation between quadrats from the same
sample (You could calculate Standard Variation (SD), what would that mean?) Were the
results reliable? What was done to improve reliability? How could better reliability be
incorporated into this study?
To get an assessment of the true biodiversity of the bean and seed populations are there any other
factors that might be considered? (clue; consider the genetic relationships between the species of
organisms being sampled).
Discuss whether this is a Valid (of value) experiment for measuring biodiversity (be
constructively critical).
Give ethical reasons as to why we should not do a similar experiment with rare animals.
32
AQA AS Biology Practical Work
Transpiration Practical
Transpiration using a potometer. Investigation into how environmental
factors such as wind, temperature and light intensity alter the rate of
transpiration. Skills; Take all measurements to an appropriate level of accuracy
and precision. Using a standard scientific calculator to calculate mean, rates and
standard deviation. Plotting data.
Comparing rates of transpiration using a Potometer.
Label the diagram.
It is difficult to measure the rate water is lost form leaves but can measure how quickly it is taken
up by the stem. Most of this water is lost through transpiration, (approx 99%).
Use a potometer.
Needs to be water and air tight, so no air bubbles break the continuous column of water.
So set up under water.
Cut the stem at an angle so less chance of air bubbles & increase the surface area and so the
number of xylem vessels exposed to the water. Use a fresh stem from a plant with lots of leaves,
so it is living and known to be transpiring.
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AQA AS Biology Practical Work
As water evaporates from leaves more water is drawn up the capillary tubing. Record the
position of the meniscus at set time intervals.
Can plot a graph of distance moved against time. What additional information would you need
to calculate volume lost?
Exposure of the plant to different conditions, enables comparison of the rate of transpiration.
Using a potometer above design experiments to test the variation of named environmental
conditions on the water loss of a plant.
List environmental factors that could be tested and suggest a method for testing;
Environmental factor
Method Outline
Question
1. Suggest how an increase in wind speed and a rise in temperature may cause the rate of
transpiration to increase.
2. How does this cooling method compare to the main cooling mechanism in mammals?
Answer
1. Increased wind speed moves water vapour away from leaf more rapidly and so maintains
a steeper water potential gradient between air spaces of leaf and surrounding air.
2. Rise in temp increases kinetic energy of water molecules which move and therefore
diffuse more rapidly. High temp may also decrease humidity of the air (as warm air can
hold more water), so increasing the diffusion gradient.
3. Mammals use the evaporation of sweat (water) for cooling. Water evaporates from skin
surface absorbing heat energy. So is similar to plants.
34
AQA AS Biology Practical Work
Safety in the Laboratory
We have modern, well equipped laboratories here at Morgannwg and
every student will, at some point, be required to work in the lab. Here is
a brief introduction to the lab and the safety requirements you will take.
However you will receive a full induction on health and safety in the
laboratory and each practical has its own risk assessment. Hazards will
be drawn to your attention at the start of each piece of practical work.
*
Listen carefully to your tutor and follow all instructions.
*
Lab coats to be worn at all times during practical when required by
staff.
*
Do not taste or smell any chemicals.
*
No food or drink in the lab.
*
Do not smoke in the lab - lots of flammables!
*
Protective eye wear is essential.
*
Long hair must be tied back - guys as well!
*
Report any accidents, spillages or breakages immediately.
*
Observe the correct disposal of all chemicals, waste, broken glass
and sharps.
*
Clear up after yourself and your group.
35