stage 2 biology - sasta.asn.au · key ideas in biology ... this practical is a very good...

KEY IDEAS IN BIOLOGY

P R AC T I C A L M A N UA L

Ala

n C

rier

ie &

Dav

id G

reig

Alan C

rierie & D

avid Greig

STAGE 2 BIOLOGYAssessment using SACE Performance Standards

Teaching Notes

KEY IDEAS IN BIOLOGY Practical Manual

Teaching Notes - Version 14

TABLE OF CONTENTS

MATERIALS OVERVIEW 3

M1 TESTING FOR MACROMOLECULES 4

M2 NUCLEIC ACIDS 5

M3 ENZYME ACTIVITY 8

C1 CELL STRUCTURES 9

C2 MITOSIS 9

C3 RATE OF OSMOSIS 10

O1 KIDNEY STRUCTURE AND FUNCTION 10

O2 RATE OF FERMENTATION 11

O3 RATE OF PHOTOSYNTHESIS 11

E1 NATURAL SELECTION 12

E2 SUCCESSION Suggested answers 14

E3 ANTIBIOTIC RESISTANCE 16

A population of the Australian pelican (Pelecanus conspicillatus) on the Cooper Creek, 2012.

2

Publishing Information This Practical Manual is part of a series which is designed to support the teaching of Stage 2 Biology in South Australia. The 300 page colour Essentials Textbook (with student DVD) and 200 page Essentials Revision Workbook are also available and are designed to suit the requirements of the S.A. course © SACE Board 2010. The copyright of the contents of this book remain the property of the authors Alan Crierie and David Greig. This book is published by ‘Science Teaching And Resources’ (S.T.A.R.) whose office is in South Australia 5048. Email [email protected] Mobile 0418 895 560 Distributed by: SASTA, 249 Henley Beach road, Torrensville, Adelaide. 5007 Ph. 8354 0006, Fax. 8354 0008, email. [email protected], www.sasta.asn.au Authors: Crierie A and Greig D Library catalogue: 1. Biology 2. Key Ideas 3. Practical Manual 4. Teaching Notes ISBN 978-0-9804362-6-6

The authors Alan Crierie is currently a senior Biology Teacher and a Deputy Principal at St Michael’s College in Adelaide. As past Chairman of the Biology Subject Advisory Committee of SSABSA, he has been very closely involved with the design and implementation of the SACE Biology course. David Greig is no longer teaching in the classroom but most recently worked as a Key Teacher at Brighton Secondary School in Adelaide. Through his business ‘Science Teaching And Resources (S.T.A.R.)’ he is working as a consultant, author, project manager and editor on a number of science publishing projects at state, national and international level.

Copyright information All rights reserved except under the conditions described in the Copyright Act 1968 of Australia and subsequent amendments. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior permission of the publishers. While every care has been taken to trace and acknowledge copyright, the publishers tender their apologies for any accidental infringement where copyright has proved untraceable. They would be pleased to come to a suitable arrangement with the rightful owner in each case.

Acknowledgements The production of these materials has taken almost two years and could not have been done without the assistance of many people and organisations. In particular we wish to thank the following for their contributions: ó Greg Cole and Kristy Cummins at SASTA for their active involvement ó Peter Warnes for his helpful and constructive suggestions ó Brenton Cannizzaro at Enpresiv Group for designing the thematic logo and cover ó Mike Badenoch for the hand drawings ó The De La Salle Brothers for their inspirational work in education around the globe: ‘Order,

System, Method’ ó Sophie Andonopoulos for her helpful practical advice. ó Sue Lace for her practical advice ó The SACE Board of SA for permission to use extracts from the Biology Subject outline in

this Manual and the Teaching Notes. ó Our wives and families for their encouragement and support

KEY IDEAS IN BIOLOGY Practical Manual Version 12 Teaching Notes © S.T.A.R. 2012 3

MATERIALS OVERVIEW This table has been provided to assist the teacher or laboratory manager by providing, at a glance, most of the materials that may need to be prepared in advance for these Practicals. Please refer to the Materials listed for each Practical in the Manual for more details. Practical Weeks before Days before Prior to lesson M1 ● iodine solution

● potato tissue ● ethanol/onion epidermis ● aceto-orcein ● margarine, olive oil ● sodium hydroxide

● microscopes ● slides/coverslips ● rubber gloves? ● Sharp blades ● Cutting boards ● Paper towelling

M2

● onions ● meat tenderizer (6% papain) ● 95% ethanol ● photocopy of pattern sheets

for DNA modeling ● sheets of newspaper

● stirring rods/ pipettes ● test-tubes/ wire-loop ● onion extract(early in day) ● glue/scissors/Poster paper ● salt and shampoo

M3

· 0.1% hydrogen peroxide · pH solutions · fine sand

· fresh liver · mortar and pestle

C1 ● mini-grids/ocular grids

● prepared slides

● onion tissue ● geranium tissue ● algae tissue ● aceto-orcein ● methylene blue

● microscopes/slides ● newspaper ● teat pipettes ● sharp blades ● prepared slides

C2

● onion roots ● prepared mitosis

slides

● aceto-orcein stain ● overnight staining of root tips

● microscope slides ● other as listed

C3

● approx 1 potato per group ● potato peelers

● spoon/ paper towel ● beakers/ balance

O1

● kidneys ● dissecting board/ scalpel ● antiseptic solution ● stereo-microscope ● paper/ textas

O2

● yeast suspension ● glucose solution

● beaker/test tubes ● delivery tubes ● retort stands/ stop watches

O3

● 50mL syringes ● solutions of sodium hydrogen carbonate

● Buchner flask ● leaves/ cork borer ● OH projector ● Sheets of tracing paper ● stop watch/beakers ● sieve / forceps

E1

● photocopied sheets of frogs: red, green, yellow

● scissors ● dice

E2 second hand data only

E3

· Antibiotic multo-disks

· Agar powder

· bacterial cultures · agar plates

· cotton buds · methylated spirits · forceps · adhesive tape


M1 TESTING FOR MACROMOLECULES This Practical is a very good opportunity to revise and emphasize lab rules and safety procedures.

Materials required iodine solution potatoes Methylene blue stain aceto-orcein onions margarine olive oil ethanol sharp blades rubber gloves microscopes slides and coverslips

A. Carbohydrates This is a standard and well known test, the positive test is blue black colour. If iodine solution does not react strongly enough, you can make some fresh solution by dissolving about 0.5g of iodine crystals and 1g potassium iodide in 100mL distilled water. Emphasize care here, iodine will stain most things, including skin and paper!

B. Protein Methylene Blue stain works well but again emphasize that it stains things!

C. Nucleic acids Aceto-orcein solution can be purchased or made by dissolving 3.3g orcein in 100mL glacial acetic acid under reflux in a fume hood. This can be used as a 50:50 dilution with distilled water. The positive test is a red colour. Suggest using fingers rather than pegs when gently warming the slide or the slides will get too hot and crack.

D. Lipids Although margarine and olive oil are suggested, other materials will suffice. Students should notice a cloudy white suspension which is insoluble lipid in the alcohol. The ‘whiteness’ is quantitative. Emphasize that ethanol is flammable and toxic! Can use methylated spirits instead if you wish.


M2 NUCLEIC ACIDS

Part A EXTRACTING DNA There are several cheap and simple techniques available to schools which yield impure but nonetheless useful samples of DNA. We have chosen to use plant material to avoid the health and ethical problems associated with the use of fresh animal tissue. We have also chosen a technique that does not require the use of hazardous chemicals such as phenol or expensive equipment such as a centrifuge.

STAGE 1 Preparing the onion extract

Materials required 1 large onion (about the size of a tennis ball) clear, good quality shampoo 1 knife and chopping board 1 coffee filter bag or cheese cloth 2 Pasteur pipettes 1 large plastic filter funnel 1 litre beaker water bath set at 600C ice bath table salt (3g) large mixing spoon 100mL distilled water 250mL conical flask blender (optional) thermometer

Method 1. Dissolve 3g of table salt in 70ml of distilled water. Add 10mL of shampoo and make up to

100mL with distilled water. 2. Remove the dead outer layers and then cut the onion into quarters and then chop into 1 cm

slices. 3. Put these pieces of onion into the salty shampoo solution from step1. 4. Put the beaker in a water bath at 600C for 15 minutes and stir occasionally. 5. Cool the mixture by standing the beaker in an ice bath for 5 minutes while stirring frequently. 6. Pour the mixture into a blender and blend in several short bursts of about a second with a total

of no more than 5 seconds. (Note that an alternative technique is available which does not require a blender. Simply press the chopped pieces of onion against the side of the beaker with the back of a spoon during steps 4 and 5).

7. Filter the mixture through the coffee filter or several layers of cheesecloth into a 250 mL flask and keep it cold until it is dispensed to students in 10mL amounts in test tubes (see student method).

More information about this and similar topics may be found at the Biotech Education Homepage of the Iowa State University. http://www.biotech.zool.iastate.edu/Biotech_Public_Ed.html ● The detergent dissolves the fatty molecules that are present in the cell membranes, which

releases the DNA into solution. ● The heat treatment causes the lipids and proteins to precipitate. ● The salt improves the cohesion between the DNA strands. ● Filtration is necessary to remove larger particles whilst leaving soluble and suspended

materials in the filtrate. ● Most meat tenderisers contain papain (check the packaging information if unsure) which is a

protease and will digest the histones which are associated with the DNA when gently mixed. ● DNA will precipitate in very cold and concentrated ethanol.


● Spooling is rotating rather than stirring, and it is useful to score the glass or wire with a diamond pencil (if available) to allow the DNA to adhere initially.

This technique is rather sensitive with some variables that are difficult to control (e.g. shampoo), some trial and error may be necessary. The DNA may be dried using a hair drier forming a white film. So far as the further investigations go, forcing DNA through a syringe will shear some of the molecules and reduce viscosity. It is recommended that Part 1 of this preparation be performed by the laboratory technician early in the day, our trials indicated that the extract did not keep well overnight. These materials and this technique will produce about 60mL of solution, which is enough for 6 groups. Quantities can be varied according to class size.

Part B MODELS OF NUCLEIC ACIDS We have developed, carefully trialled and can recommend these patterns and the idea of students making posters. The patterns should be photocopied and given to students in advance to save time in lesson. It may also be useful to do one as a transparency for use on an OHP. The bases can be glued or stapled to TAB 1 on the DNA and RNA models and to TAB 3 on the transfer RNA models. The tRNA molecules should be given the same number as their specific amino acid and then clipped together with a paper clip. You can work out the actual amino acid that is carried by the particular tRNA, by referring to a table of mRNA codons that lists the corresponding amino acids that are coded for. The peptide bonds can be represented by gluing or stapling TABS 4 together. Posters which are well done, particularly using colour, can be used for display in the classroom or laboratory.

Transfer RNA number_____ Amino acid____________

TAB 3

T2 T2 T2


TAB 3

T2 T2 T2


TAB 3

T2 T2 T2

T4 Amino acid___________________ T4

T4 Amino acid___________________ T4

T4 Amino acid___________________ T4


A

G C

G C

G C

G C

G C TAB 1

Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

TAB 1 Sugar

A T/U

A T/U

A T/U

A T/U

A T/U


M3 ENZYME ACTIVITY Fresh ‘stock’ hydrogen peroxide is usually 6% by volume. To make 1% simply add 17 mL of this solution to 83 mL of distilled water. Then simply do a serial dilution of this to make the 0.1% solution. Remember that hydrogen peroxide will deteriorate in the presence of both light and heat. Consequently it is strongly advised that Staff do a ‘trial run’ to ensure that the substrate concentration is suitable. Fresh liver from a butcher is ideal although other sources of catalase (yeast, blood cells, potatoes and other vegetables) can be used if more convenient. Good idea to use plastic gloves, if not wash thoroughly with hot soap and water or anti-bacterial gel.

A guide to making up substrate solutions of various pHs. It is suggested that at least 4 different pH levels should be tested. The following method is suggested to make 100 mL of stock solutions (scale up as necessary) Use a pH meter if possible, pH papers give less reliable results. CAUTION: It is wise to use eye protection when making up or using strong acid or strong alkali solutions. pH 1 60 mL of 6% H2O2, 40 mL of bench strength (dilute) Hydrochloric Acid.

pH 3 To 60 mL H2O2 add 38 mL of distilled water. Test the pH. It will be approx 5. Add

drops of HCl until the pH is 3 and then top up to 100 mL with distilled water.

pH 6, 7, 8, 10 Take 10 mL of bench strength dilute sodium hydroxide and make it up to 100 mL

with distilled water. Reserve this solution.

Take 60 mL of H2O2 and add 30 mL of distilled water. Add the NaOH solution until the

required pH’s are reached and then make the solution up to 100 mL with distilled water.

pH 12 To 60 mL of H2O2 add 35 mL of the diluted NaOH solution and measure the pH. If it is

approximately 12, add distilled water to make it up to 100mL. If not, add drops of bench NaOH

before making up to 100 mL.

pH 13 To 60 mL of H2O2 add 40 mL of bench strength NaOH.

DYO possibilities Some of the obvious variables for the ‘Design Your Own’ (DYO) Practicals are temperature, pH (above), surface area and source of catalase. In addition internet references indicate that sodium azide and ammonia are competitive inhibitors for the enzyme although the authors have not verified this.


C1 CELL STRUCTURES It is important that students use microscopes to gain an appreciation of the structures such as cells that are discussed in class. Viewing cells helps students to visualise their size, and, by using stains, links can be made to molecular composition. This practical links to Practical M1 (Testing for Macromolecules), in particular looking at nucleic acids and protein. In practical C1 we suggest that ocular scales (or ocular micrometers) may be used in addition to mini-grids so that more accurate measurements can be made. It is also important that students work with the one microscope to become familiar with it and calibrate it for its field of view. A video-microscope is a useful tool when teaching skills in this area. We have suggested onion cells for plant issue, but the possibility of using leaf tissue, for example Geranium, would also enable students to observe chloroplasts. Likewise, if students were to examine human cheek cells the nucleus would be visible, whereas this will not be the case in the red blood cells. The electron micrographs included should enable students to see the internal structure and detail not seen with the light microscopes in a school laboratory. Part C in order: A - mitchondria, B - chloroplast, C - rough ER, D - Golgi body nucleus, E - cell wall, and D - cell membrane.

C2 MITOSIS In this practical we recommend that garlic root tips be used for the source of tissue to make the squash preparations. It seems best to grow the garlic from bulbs that have had the base trimmed off with a sharp razor blade. Place the bulb on top of a small beaker or a conical flask so that the base is suspended in water. Some schools have indicated that other plants like onions and leeks also work well. Tooth picks can be used to hold the bulb(s) in place. Each bulb should give a minimum of 5-6 roots after a period of about a week or two so you can plan according to your class size.

Preparation of the aceto-orcein stain: (1% orcein stain in 45% acetic acid) Add 5 g of synthetic orcein powder to 250 mL of boiling conc. acetic acid. It is best to add glass beads to the flask to prevent bumping when boiling. Boil for approximately one minute and then cool the solution and make up to 500 mL by the addition of distilled water. It is suggested that this step be conducted in a fume cupboard. Let it stand overnight and filter the solution before use. Practical Tips Obtaining a slide showing the different stages of cell division is a difficult task, however, if the students follow these instructions carefully, they will be rewarded with good slides showing stained nuclei for each phase as required. In assessing their slide preparations you can assess how well they have followed instructions by observing some of the following: ● cells that are smaller and cuboidal have come from the growing tip whereas larger, elongated

cells have been taken too far from the tip. ● if the cells are all crushed and fragmented it probably indicates rough handling. ● the depth of stain is a reasonable indication of how well the staining procedures were

followed. Refer to the Key Ideas Textbook (p94) for a diagram of the Cell Cycle.


C3 RATE OF OSMOSIS What really appeals to us about using potato tissue is that they are very cheap, clean and safe to use. It is obviously important to remove excess water each time before weighing the potato cubes.

DYO possibilities ● predicting and testing the salt concentration which will result in no change in mass due to

osmosis (this isotonic point is about 1%) ● predicting and testing whether particular materials pass through the membrane. ● Predicting and testing the effect of smaller and larger size cubes of potato with different

surface area/volume ratios ● Predicting and testing the effect of changing the shape of the potato pieces to change SA/V

ratios and model different cell types. ● predicting and testing whether temperature will affect the rate of osmosis.

O1 KIDNEY STRUCTURE AND FUNCTION

Part A: Kidney dissection Kidneys are easily available from either your butcher or the local supermarket. If ordering from your butcher you may be able to put in a special request to try to better preserve a little more of the blood vessels and ureter. In this activity you could ask your students, using toothpicks and sticky labels, to mark the various parts for identification so that you can give them feedback on the accuracy of their identification of the kidney parts. Using a good stereo - microscope will enable close identification of important structures, but to examine nephron details, a more sophisticated sectioning of kidney tissue would be required. Students should be encouraged to use good hygiene, disposing of the kidneys as required and to wash their hands and the bench area with disinfectant.

Part B: Modelling of filtration and re-absorption This should be a good opportunity to provide students with a task in which they can work together with other students to investigate more about the functions of the nephrons. It is also a good opportunity for you to give students some formative practice in oral communication skills while they explain the processes of filtration and re- absorption on their model. For an alternative method of communication, a poster would work very well.


O2 RATE OF FERMENTATION This is essentially a simple practical which lends itself to many investigations and variations. The following concentrations are suggested: ● 10% glucose can be made up by dissolving 10g glucose in 100mL distilled water or varied as

you wish. ● Yeast suspension can be made by mixing 25g compressed yeast with 100mL water. Allow

this to stand for 10 minutes or so before use. It is also a good idea to add a small amount of ammonium phosphate (NH4PO4) to the mixture.

Collecting the total volume of CO2 is only one technique. You may also be able to count bubbles/minute at various intervals as an indication of rate. Another technique is to put glucose and yeast into a syringe and admit some air so the level of the liquid is below the outlet when it is horizontal and then placed it into a container of warm water (35-400C) and count the bubble rate (see diagram below). If your school has electronic sensing equipment it may be possible to use heat production as your dependent variable. To do this you will need insulated containers like thermos flasks and temperature sensors. Physics students may even be able to do calculations of kJ. Be careful when inserting or removing glass tubing from rubber stoppers.

DYO possibilities The obvious variables are temperature, yeast concentration and sugar concentration. The less obvious variables, probably for better students, include age of yeast, type of sugar, presence of phosphate in yeast suspension and you can probably think of more. As a matter of interest, lactose does not react at all and sucrose is first digested by extra-cellular enzymes before glucose is absorbed and respired. Most yeast species are very temperature sensitive.

Yeast and sugar

Syringe


O3 RATE OF PHOTOSYNTHESIS We found that this exercise works a lot better with leaves that were not too fibrous and those that had been freshly picked a few minutes before the lesson. Ivy with dark green leaves is ideal. Smaller discs work better than larger ones. A 10% bicarbonate solution can be made by dissolving 100g NaHCO3 in 1 litre of distilled water and then other concentrations can be made by diluting this as required. It is important to ensure that the first discs that are loaded in the bicarbonate are not exposed to more light than the last ones to be loaded. A solution to this problem is to put the beakers in a dark place as they are loaded and then put them on the OHP at the same time. Traditionally this Practical has been done using a vacuum pump which is attached to a water tap and a Buchner flask. However this is rather unsatisfactory for a number of reasons and a much simpler method has been developed. This technique makes use of disposable plastic or glass syringes (without the needles). The technique is described in detail in the text of the Practical but it is probably a good idea to try it beforehand. If the finger over the end is a bit too painful you may try some small plastic hose with a kink in it, or a rubber stopper. If some students have difficulty pulling out the plunger it may be necessary for two students to work together. These syringes can usually be obtained from medical clinics or hospitals provided that they have not been used for blood products. Otherwise they may be purchased from medical suppliers for about $1.20 each. A problem that you may encounter is that the discs may not sink in the bicarbonate solution even though they do in water. Although this is quite a good problem-solving exercise for the students if time permits, the simplest solutions are to use a softer leaf type or tap the disc(s) gently to dislodge any small air bubbles which may be adhering to the surface. Also ensure that they are vacuumed in the syringe until they sink quickly in the water, rather than drift down slowly. When varying the amount of light as suggested using sheets of tracing paper, it is vital to restrict light from other directions.

DYO possibilities Other variables include the type of leaf, the part of a leaf, light colour, bicarbonate concentration, temperature and pH.

E1 NATURAL SELECTION This activity is suggested as a formative exercise. Simulating the process of natural selection and evolution can be a good learning activity that can illustrate clearly to students the principles involved. There are several good computer simulations in the marketplace, but this activity can achieve its goals with minimal materials and costs in a short period of time. The authors have found that the exercise can be completed quite comfortably in a double lesson. The investigation could be a good starting point for teaching the concepts of variation, natural selection, geographical and reproductive isolation and ultimately speciation. The discussion questions lead students to compare real life selection and this model, so that a better understanding of the processes operating in natural populations can be appreciated. Photocopying the frog template (page 13) on to red, green and yellow card and then cutting out the individual frogs has been found to work well.


E2 SUCCESSION (second hand data) Suggested answers Part A 1. (a) Important factors include

o Sandy soil with low nutrient levels

o Low rainfall

o Little shade and not much leaf litter

(b) Only those species that are adapted to dry harsh conditions and low nutrient levels (above) will survive. Examples include mallee scrub insects and small reptiles.

2. Competition:

Different species of birds competing for the same insects

Predation: Geckos feeding on ants and beetles

Symbiosis: Geckos sheltering in spinifex grass and their droppings provide nutrients for the spinifex.

3. According to the definition a species is a breeding group. Geckos that do not interbreed under natural conditions to produce fertile offspring are separate species.

4.

5. The productivity of this ecosystem will be low because of poor nutrient levels and lack of

water.

mallee shrubs spinifex

insects kangaroo

ticks scorpions geckos

birds

Bacteria and fungi

3rd order Second order First order Producers Decomposers


Part B 1. C cristatus would seem to need the accumulation of fallen logs etc. hence it will tend to

be found in greater numbers a long time after the fire. C fordi/N stellatus on the other hand are at an advantage just after a fire as they can burrow in recently burnt area and possibly feed on colonizing insects.

2. No fires for decades would lead to low numbers of early successional species i.e. those

that can survive just after a fire. Late successional species have a lower survival rate just after a fire and may not survive and reproduce.

3. Faster reproducing birds increase in number quickly after a fire as they feed on new

insects. As new insect and beetle numbers fall due to heavy predation bird numbers will also fall. Over time the slower reproducing birds (K strategists) will tend to predominate.

4. Generally productivity is greater in the early stages because the colonizing species (r

strategists) grow and breed more quickly. 5. Less biodiversity e.g. reduced spinifex plants would reduce the number of geckos that

could shelter there. This has the potential to alter significantly the mix of species in the post burn fragment. Less mallee trees and shrubs will reduce leaf litter and reduce the number of insects geckos which in turn will lead to little food supply for birds and a decrease in their number also.

Part C 1. (a) Fires will destroy leaf litter thereby reducing shelter and food source. If the fire is

severe some species may be destroyed and the community may take many more years to regenerate. (b) The fire could clear undergrowth and allow new plants to germinate and grow (r strategists)

2. Fires are normal events in natural ecosystems such as mallee. To actively reduce fires may lead to an increase in fuel and a more serious fire at a later stage which will cause more serious damage and possibly the risk of extinction of some species. If scientists can study patterns of recolonization they can make better recommendation about fire management policies.


E3 ANTIBIOTIC RESISTANCE · Most standard texts will provide information about aseptic techniques which are probably

well known anyway but here are a few tips:

· Together with many other living resources, cultures of non-pathogenic bacteria (e.g. Sarcina lutea, E. coli, Staph albus, Bacillus subtilise and Rhodospirillum rubrum) are available from The Nature Education Centre which is now located at: Urrbrae Agricultural High School, 505 Fullarton Rd., Netherby 5062. Phone (08) 8357 3413 URL: www.nature.sa.edu.au (this shows their catalogue) email: [email protected]

· Cultures cost $10 each and are available as broths or slopes. Slopes only can be sent through the mail. Antibiotic test rings or multodiscs are available from the Scientific Equipment scheme and listed in the catalogue at a cost of $102 for 50.

· It is a good idea to put several drops of distilled water or sterile isotonic saline in the middle of the agar and then to put the bacteria in this before trying to spread them around the plate.

· students find it easier to spread a culture of bacteria evenly using a sterile cotton bud than with the traditional wire inoculating loop which tends to dig into the agar. This will provide a more even 'lawn' which will make observation a lot easier later.

· other possible antimicrobial agents may include soaps, antiseptics, disinfectants, chlorine, methylated spirits, salt, toothpaste, herbal remedies and no doubt many more.

· a well known and quite successful technique is to soak filter paper discs in test solutions and then place them on the agar at a spacing of several cm and clearly labelled so that they are not confused.

· to preserve aseptic conditions as far as possible, the hole punch should be sterilised possibly in boiling water and the filter paper taken from a new pack (using rubber gloves if you like).

· ensure that the plates are labelled on the bottom, sealed, stored upside down and then disposed of properly by your lab manager. They must not be re-opened.

DYO possibilities Include testing other antimicrobial agents such as household disinfectants and antiseptics.

We are keen to include any new, interesting and relevant Practicals and/or better ways to record marks and judge performance standards. We will be happy to acknowledge and/or pay for good ideas, please contact us to discuss. Please feel free to contact us with any questions or comments as follows:

David Greig ([email protected] Ph 0418 895 560) or

Alan Crierie ([email protected] Ph 8298 1619)

Alan Crierie and David Greig November 2012

stage 2 biology - sasta.asn.au · key ideas in biology ... this practical is a very good...

Documents