AQA A Level Biology Required Practicals

Required practical 1: investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

e.g. temperature, pH, substrate concentration

Method1

1) using a permanent marker pen, mark an 'X' halfway down one side of each of the three test tubes

2) add 10cm^3 of milk powder solution to each of the three test tubes

3) add 2cm^3 of trypsin to 2cm^3 pH 7 buffer to each of other set of three test tubes

4) stand all six test tubes in water bath at 20˚C and leave to equilibrate for 10 minutes

5) add trypsin and buffer solution from one test tube to milk powder solution of another test tube

6) put a bung in test tube and invert 5 times

7) place test tube back in water bath

8) time how long it takes for the milk solution to clear by measuring time taken to see 'X' and record

9) repeat steps 5,6,7,8 using the other test tubes

10) calculate average time taken for trypsin to digest casein in milk at 20˚C

11) repeat steps 1-10 using water baths of temperatures 30˚C, 40˚C, 50˚C and 60˚C

12) work out rate of reaction using 1/mean time for each temperature

13) plot graph of rate of reaction (y-axis) and temperature (x-axis)

Control group1

Test tubes containing:

-5cm^3 milk powder solution and 5cm^3 distilled water to show absence of enzyme activity

-5cm^3 milk powder solution and 5cm^3 of hydrochloric acid to show colour of completely hydrolysed sample

Variables1

Independent: temperature

Dependent: rate of reaction

Control: pH, volume of trypsin solution, volume of milk solution

Risk assessment1

Hazard: glassware breaking

Risk: injury

Safety precautions: keep apparatus away from edge of desk, take caution

Hazard: hot water bath

Risk: scalding

Safety precautions: keep apparatus away from edge of desk to reduce risk of spillage, use tongs to remove test tubes, wear goggles for eye protection

Hazard: trypsin solution

Risk: allergies, corrosive

Safety precautions: wear goggles for eye protection, wear gloves to avoid contact with skin, wash spillages off skin immediately to minimise injury to skin

Notes1

-milk contains casein protein which causes milk to become colourless when broken down

-trypsin is a protease enzyme which hydrolyses casein protein

-optimum temperature of trypsin is 37˚C

Describe how you could keep temperature constant.

-use water bath

-monitor temperature with digital thermometer

-adjust if any fluctuations occur by adding cold/hot water

Explain any measures that could have been taken to ensure temperatures of the water baths were as reliable as possible.

-measure temperature of water bath at beginning and end of the reaction period to show there was little variation in temperature

Explain why three experiments were performed at each temperature.

-enables calculation of a more reliable mean

-so that anomalous data can be identified

Suggest the purpose of control test tube containing only solutions of milk powder and pH buffer.

-to show casein was digested due to enzyme action not due to temperature changes

Suggest two better ways of determining when milk solution goes clear.

-use colorimeter and record time taken to reach constant of absorbance

-set up standard where complete hydrolysis of casein has occurred for comparison and measure time taken to reach same colour as standard

Required practical 2: preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index

Method2

1) add 10ml of 5mol^dm-3 hydrochloric acid to a beaker placed on a bench mat

2) cut small sample of root tip using scalpel

3) transfer root tip immediately to hydrochloric acid in beaker and leave for 15 minutes

4) set up microscope whilst waiting

5) remove root tip and rinse in distilled water in watch glass

6) cut off root tip (1mm) and place on microscope slide

7) place few drops of toluidine blue stain and macerate with mounted needle to separate cells

8) add cover slip and spread root tip using gentle pressure and blot simultaneously using filter paper between finger and slide

9) place on microscope stage

10) set objective lens to lowest magnification and use coarse adjustment knob to readjust focus until image clear, using higher magnification if necessary

11) calculate mitotic index

Risk assessment2

Hazard: glassware breaking

Risk: injury

Safety precautions: keep apparatus away from edge of desk, take caution

Hazard: hydrochloric acid

Risk: corrosive

Safety precautions: wear goggles for eye protection, wear gloves to avoid contact with skin

Hazard: toluidine stain

Risk: irritation

Safety precautions: wear goggles for eye protection, wear gloves to avoid contact with skin

Hazard: scalpel

Risk: injury

Safety precautions: use forceps to hold sample whilst cutting, keep away from edge of desk, wear gloves to avoid contact with skin, cut on a non-slip surface, cut away from body

Notes2

-mitotic index = number of visible chromosomes/ total number of cells in sample

-purpose of HCL is to destroy substances uniting cells to break into tissue into individual cells and the halt process of mitosis

-purpose of toluidine blue stain is to stain DNA and distinguish chromosomes

Describe how a student could use an eyepiece graticule to determine the mean diameter of an organelle.

-place stage micrometer on stage

-look through eyepiece graticule and align with stage micrometer to calibrate

-calculate how many known values on stage micrometer equal one eyepiece graticule unit

-measure each organelle using eyepiece graticule

-take number of measurements to calculate mean

Describe how you could make a temporary mount of a piece of plant tissue to observe position of starch grains in plant cells using an optical microscope.

-add drop of water to glass slide

-obtain thin section of plant tissue and place on slide

-stain with iodine dissolved in potassium iodide solution

-lower cover slip using mounted needle

Explain why the graticule needs to be recalibrated if magnification is increased.

-stage micrometer appears larger

-so each eyepiece division will be a smaller measurement

Explain why it is necessary to focus on the lowest magnification first before switching to higher magnifications.

-low magnification allows larger area of slide to be viewed

-allowing specific areas to be located more easily

-which makes focusing easier

Explain why is meristem tissue used for this experiment.

-where mitosis occurs

Explain why it is important that root tip spread out before viewing.

-to get thin/few layer of cells

-so that light can pass through

Explain why students are advised not to slide coverslip sideways.

-could roll layers of cells together making it difficult for cells to be seen clearly under microscope

-could damage chromosomes

Explain how students are able to distinguish dividing cells and non-dividing cells.

-visible chromosomes indicate cell is dividing

Explain how to ensure mitotic index calculated is reliable.

-select multiple fields of view/many cells to ensure representative sample

-pick fields of view at random (e.g. using grid and random number generator)

-repeat count to ensure figures correct

-count only whole cells

-calculate mean of different mitotic indexes

Explain why it was important student measured in several parts of leaf tissue.

-distribution may not be uniform

-so it is a representative sample/reliable mean

Required practical 3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue

e.g. potato, cucumber, tomato, lettuce

Method3

1) make a serial dilution of sucrose solutions using distilled water - at ​0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol sucrose​​

2) measure 5cm^3 of each dilution into separate test tubes

3) use cork borer to cut out six potato chips and cut down sections into identically sized chips using the scalpel

4) dry each chip using a paper towel to remove excess water

5) weigh each before start of experiment and record

6) place a potato chip in each test tube and leave for 20 minutes

7) remove each potato chip and blot dry using paper towel before weighing each again

8) calculate percentage change in mass for each potato chip

9) plot graph of percentage change in mass (y-axis) against concentration of sucrose solution (x-axis)

10) x axis intercept is equal to the concentration of the potato

11) use this to find data for the water potential of the potato

Variable3

Independent: concentration of sucrose solution

Dependent: percentage change in mass

Control: volume of sucrose solution, size of potato chips

Risk assessment3

Hazard: glassware breaking

Risk: injury

Safety precautions: keep apparatus away from edge of desk, take caution

Hazard: scalpel

Risk: injury

Safety precautions: use forceps to hold sample whilst cutting, keep away from edge of desk, wear gloves to avoid contact with skin, cut on a non-slip surface, cut away from body

Notes3

-how to carry out serial and simple dilutions

-concentration of average vegetable investigated

Explain why it is important to not squeeze potato chips when drying them.

-squeezing would decrease mass of chips

-and would vary for each potato chip so results no longer comparable

Required practical 4: investigation into the effect of a named variable on the permeability of cell-surface membranes

e.g. concentration of solvents, temperature

Method4

1) cut beetroot into slice of uniform thickness using scalpel

2) cut slice into 10 identical discs using cork borers

3) rinse discs with distilled water to remove any excess pigment

4) create a dilution series of ethanol ranging from 0 - 100% using distilled water

5) place two discs in each test tube

6) leave samples for 5 minutes

7) set colorimeter to a blue filter and zero using a cuvette with distilled water

8) filter each sample into a cuvette using filter paper

9) measure absorbance for each solution

10) higher absorbance = higher pigment concentration = more permeable membrane

11) plot graph of absorbance (y-axis) against ethanol concentration/ temperature (x-axis)

Control group4

-place two beetroot discs in distilled water to show any pigment released from action of alcohol

Variables4

Independent: alcohol concentration/temperature

Dependent: absorbance

Control: size of beetroot disks, volumes of solution, time beetroot in solution

Risk assessment4

Hazard: glassware breaking

Risk: injury

Safety precautions: keep apparatus away from edge of desk, take caution

Hazard: scalpel

Risk: injury

Safety precautions: use forceps to hold sample whilst cutting, keep away from edge of desk, wear gloves to avoid contact with skin, cut on a non-slip surface, cut away from body

Hazard: ethanol

Risk: irritant, flammable

Safety precautions: wear goggles for eye protection, keep away from flames

Hazard: hot water bath

Risk: scalding

Safety precautions: keep apparatus away from edge of desk to reduce risk of spillage, use tongs to remove test tubes, wear goggles for eye protection

Notes4

-beetroot contains purple pigment betalain, which is contained within vacuole

-can indicate permeability as betalain leaks out of cell membrane when membrane permeability increased

-ethanol is non-polar so acts as solvent for phospholipids, dissolving them

Use of a colorimeter in this investigation would improve the repeatability of the student’s results. Give one reason why.

-quantitative

-colour change is subjective

-standardises the method

Describe a method a student could use to determine concentration without a colorimeter

-prepare a dilution series using known concentrations of a pigment solution

-creating colour standards that will then be labelled

-compare results of unknown sample with colour standards to calculate estimated concentration

Explain why it was important to wash the beetroot discs at start of investigation.

-to wash off any betalain pigment on the disc

-to show that any pigment released is from the effect of alcohol/temperature

Explain why you were instructed to pour the alcohol immediately from the experimental test tube into a clean test tube.

-limit variation in time discs are in alcohol

-make sure all discs in contact with alcohol for same length of time

-so no more pigment can diffuse out of discs

Explain why your results would have been different if you had used cooked beetroot.

-heating would damage plasma membranes

-denatures proteins and disrupts phospholipid bilayer

-lots of pigment released during cooking

A student started drawing his curve from the origin, was he correct to do this? Explain why.

-no

-curve drawn should not extend beyond data collected, no control carried out with water

Explain why you were instructed to shake the test tubes every minute.

-increase contact of all surfaces with alcohol/prevent discs sticking together/ maintain diffusion gradient for pigment

Suggest a suitable control for the investigation and explain why it is necessary.

-distilled water and two discs of beetroot

-to show that the alcohol/temperature was causing leakage of pigment

-to compare it with the effects of alcohol

Required practical 5: dissection of animal or plant gas exchange system or mass transport system or of organ within such a system

Risk assessment5

Hazard: disinfectant

Risk: flammable

Safety precautions: keep away from flames

Hazard: scalpel

Risk: injury

Safety precautions: use forceps to hold sample whilst cutting, keep away from edge of desk, wear gloves to avoid contact with skin, cut on a non-slip surface, cut away from body

Hazard: biohazard

Risk: contamination

Safety precautions: use disinfectant, wash hands with soap, keep sample on board at all times

Required practical 6: use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth

Method6

1) use sterile pipette/wire hoop to transfer bacteria from broth to agar plate

2) spread bacteria evenly over plate using plastic spreader

3) use sterile forceps to place multi-disc antibiotic ring on plate by holding its centre

4) tape lid on (do not tape around entire lid), invert and incubate at 25°C for 48 hours

5) sterilise equipment and disinfect surfaces

6) measure diameter of inhibition zone for each antibiotic ensuring lid of agar plate not removed

7) calculate area of inhibition zone A = πd / 4

8) plot bar chart of area of inhibition zone (y-axis) against antibiotic (x-axis)

Control group6

-add water to bacteria on agar plate

-to show bacteria do not die regardless of antibiotic

Variables6

Independent: antibiotic

Dependent: area of inhibition zone

Control: time disk in antibiotic concentration

Risk assessment6

Hazard: biohazard

Risk: contamination

Safety precautions: aseptic techniques

Hazard: naked flames

Risk: burns

Safety precaution: caution, ensure no loose materials

Hazard: disinfectant

Risk: flammable

Safety precaution: keep away from flames

Notes6

-aseptic techniques

-expected inhibition zone of antibiotics

Aseptic techniques

-wash hands to remove/kill microbes

-wear gloves and apron to prevent contamination

-burning Bunsen close by to create upward current of air

-disinfect bench on disinfected cloth to kill microbes/prevent contamination

-flame equipment to sterilise/kill microbes/prevent contamination

-lift lid slightly to prevent entry of microbes

State factors that affect bacteria growth.

-increased concentration of glucose so increased respiration

-increased concentration of oxygen so increased respiration

-increased temperature so increased enzyme activity

-increased concentration of phosphate so increased ATP/DNA/RNA

-increased concentration of nucleotides so increased DNA synthesis

Give two reasons why it would be important to use sterile techniques during this investigation.

-to prevent release of bacteria into air

-to prevent contamination of apparatus with bacteria

Explain why students do not tape around entire dish.

-this prevents oxygen entering

-and so promotes growth of more harmful anaerobic bacteria

At the start of the investigation, the agar was sterilised. Explain why.

-to ensure that no unwanted bacteria will be present

Explain why some bacteria were able to grow on antibiotic plates.

-some bacteria were resistant

-some areas of dish not covered in antibiotic

Explain why student passed the forceps through a Bunsen flame before and after each time she used them.

-to sterilise/kill bacteria

-to prevent contamination so only one bacteria

Explain why there are clear zones around some of the discs containing antibiotic.

-antibiotic has diffused into agar

-killed bacteria

Suggest why an effective antibiotic may produce only a small clear zone.

-antibiotic may diffuse slowly

Required practical 7: use of chromatography to investigate the pigments isolated from leaves of different plants

E.g. leaves from shade-tolerant and shade-intolerant plants or leaves of different colours

Method7

1) set up two boiling tubes, adding 3cm^3 of solvent to each and placing a bung in the top of each tube standing them upright in a test tube rack

2) label tubes A and B

3) draw a pencil line 2cm from the bottom of chromatography paper (origin) that fits into boiling tube, labelling top of paper as 'leaf A'

4) cut disc from leaf A with cork borer, avoiding veins and midrib of leaf

5) place leaf disc on chromatography paper at centre of line marking origin, crushing disc into the paper with the end of a glass rod which leaves a stain on paper

6) pin chromatography paper to bung with drawing pin and place in tube A, ensuring end of chromatography paper is in solvent in a way that the solvent line does not come above the origin

7) place tube A in a rack ensuring it is not moved again

8) remove chromatography paper from tube when solvent line almost reaches the top of the paper, immediately drawing a pencil line to show how far the solvent has moved up the paper (solvent front)

9) let filter paper with coloured spots (chromatogram) dry

10) draw around each coloured spot on the chromatogram using a pencil

11) repeat experiment steps 1-10, labelling the piece of paper 'leaf B' at step 3

12) calculate Rf value = distance moved by pigment from origin to centre of pigment spot/ distance from origin to solvent front

Analysis:

-compare Rf values with at a base to identify pigments present in each leaf

Control group7

*

Variables7

Independent: leaf

Dependent: Rf value (type of pigment)

Control: area of leaf disc, time spent in solvent

Risk assessment7

Chromatography solvent: flammable, causes irritation to eyes and skin, harmful by inhalation

-ensure good ventilation

-no naked flames

-wear eye protection

-wash immediately if physical contact occurs

Notes7

Chlorophyll main pigment that absorbs light energy during photosynthesis

-most plants have other photosynthetic pigments that are not green

Examples of common pigments:

-chlorophyll a: blue-green pigment which absorbs violet/blue and red light

-chlorophyll b: yellow-green pigment which absorbs blue and orange/red light

-carotenoids: yellow or yellow-orange pigment which absorbs violet, blue and green light (accessory pigments that absorb wavelengths of light chlorophyll cannot)

-anthocyanins: red, purple or blue pigments which are not involved in photosynthesis

Factors affecting Rf values include:

-affinity​​: pigments have different affinities to the chromatography paper, those with lower​​ affinities will ​travel further​​ up the paper

-solubility​​: pigments that are more soluble ​travel faster​​ up the paper and will end up closer to the top ​​at the ​solvent front​​

Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin.

-level of solvent below origin line

-remove before solvent reaches top

Explain why chromatograms are marked with pencil quickly after being taken out of the solvent.

-chromatograms will fade very quickly, particularly in the light

-so marking rapidly allows calculation of Rf value

Explain the advantage of this method that does not need to be mixed with acetone to release pigment.

-simple

-avoids need to grind leaves to extract pigment

-fewer hazards without acetone usage

Explain why the student marked the origin using a pencil rather than using ink.

-ink and leaf pigments would mix

-with ink origin line in different position

-with pencil origin line in same position

-with pencil origin line still visible

Required practical 8: investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

e.g. light intensity, light wavelength, ammonium hydroxide

Method8

1) place 50cm^3 of isolation medium into beaker

2) tear 8 spinach leaves into small pieces and place into isolation medium in beaker, ensuring there are no pieces of midrib or leaf stalk

3) half fill a large beaker with ice, placing small beaker on top of the ice

4) put three layers of muslin over top of filter funnel, wetting it with isolation medium and resting filter funnel in small beaker on ice

5) pour spinach and isolation medium into blender and blend for 15 seconds, pouring blended mixture back into beaker

6) pour a small amount of blended mixture through muslin in filter funnel, carefully folding and squeezing muslin to assist the filtering process - repeat this process until most of blended mixture has been filtered

7) label filtrate in small beaker on ice as 'chloroplast suspension'

8) label five test tubes A, B, C, X and Y and stand these tubes in ice in large beaker

9) position lamp about 10cm^3 from beaker so all tubes are equally illuminated, turning it on afterwards

10) set up control test tubes A and B as follows:

-tube A: Put 5 cm^3 DCPIP solution + 1 cm^3 water + 1 cm^3 chloroplast suspension in the tube. Immediately wrap the tube completely in aluminium foil to exclude light.

-tube B: Put 5 cm^3 DCPIP solution + 1 cm^3 water + 1 cm^3 isolation medium in the tube.

11) set up tube C: put 6 cm^3 water + 1 cm^3 chloroplast suspension in the tube (standard to help determine when any colour change is complete)

12) set up test tube X: put 5 cm^3 DCPIP solution + 1 cm^3 water in the tube

13) add 1 cm^3 chloroplast suspension to tube X, quickly mix the contents and start the timer

14) record in seconds how long it takes for the contents of tube X to change colour from blue-green to green, using tube C as a standard to determine when colour change complete

15) repeat steps 11-14 four more times

16) set up test tube Y: put 5 cm^3 DCPIP solution + 1 cm^3 ammonium hydroxide in the tube

17) add 1 cm^3 chloroplast suspension to tube Y, quickly mix the contents and start the timer

18) record in seconds how long it takes for the contents of tube Y to change colour from blue-green to green using tube C as a standard to determine when colour change complete (if not occurred within 5 minutes, record colour at this point)

19) repeat steps 16-18 four more times

20) record the colour of the mixtures in tubes A and B

Analysis:

-determine optimum concentration of inhibitor to use as weedkiller

Control group8

Test tubes A and B

Variables8

Independent: ammonium hydroxide

Dependent: time taken for decolorisation

Control: source of chloroplasts, volume of chloroplast suspension, volume of DCIP, concentration of DCIP

Risk assessment8

DCPIP: irritant to skin and eyes, staining

-wear eye protection

Lamps: temporary damage to eyes

-do not look directly at lamp

Electrical appliances: liquids near electrical appliances

-do not touch lamp/wires with wet hands

-keep liquids away from lamp/wires

Notes8

-DCIP is blue dye that acts as electron acceptor: blue when oxidised, decolourises when reduced

The solution that the student used to produce the chloroplast suspension had the same water potential as the chloroplasts. Explain why it was important that these water potentials were the same.

-osmosis does not occur

-chloroplast/organelle does not burst/shrivel

Explain why the scientists measured the rate of production of oxygen in this investigation.

-oxygen produced in light-dependent reaction

-the faster oxygen is produced, the faster the light-dependent reaction

Explain why radioactive carbon used to investigate photosynthesis.

-radioactivity can be traced

-carbon is used in the light independent reaction

Required practical 9: investigation into the effect of a named variable on the rate of respiration of cultures of single-celled organisms

e.g. temperature, pH, inhibitors, type of respiratory substrate

Method9

1) use the beaker to set up a water bath at 35 °C

2) label five test tubes 1 to 5

3) shake yeast and glucose mixture, adding 2cm^3 of this mixture to all five test tubes

4) place all five test tubes in water bath and leave until contents reach 35°C, ensuring water bath stays at this temperature

5) add 2cm^3 methylene blue to test tube 1, immediately shaking this tube for 10 seconds and replace tube in water bath and note time

6) record how long it takes for blue colour to disappear in test tube 1 using standard test tube to compare

7) repeat steps 5-6 for other four test tubes

8) repeat steps 1-7 for each other temperatures

Analysis:

-calculate rate of respiration = 1 / mean time

-plot graph of temperature (x-axis) against rate of respiration (y-axis)

Control group9

Add boiled mixture of glucose and yeast to test tube as control test tube

-to show any change is due to respiration

Variables9

Independent: temperature

Dependent: rate of respiration

Control: volume of glucose and yeast mixture, volume of methylene blue

Risk assessment9

Methylene blue: irritant to skin and eyes, staining

-wear eye protection

-wash off immediately if physical contact occurs

Biohazard of yeast: allergies

-wash hands after use

Broken glass: cuts from sharp pieces

-take care when handling glass objects

-keep away from edge of desk

Hot liquids: scalding

-handle with care

-use tongs to remove boiling tubes from water bath

-wear eye protection

Notes9

Methylene blue is an electron acceptor: blue when oxidised, decolourises when reduced

Yeast has optimum temperature for respiration:

-any higher can cause denaturation of respiration enzymes

-so enzyme activity decreases and rate of reaction decreases

-meaning methylene blue will take longer to decolourise

During the experiment, the coloured liquid in the tubing moved towards tube B. Explain what caused this. (respirometer)

-oxygen taken up/used by seeds

-CO2 given out is absorbed by KOH solution

-volume/pressure in B decreases

Suggest and explain why the chosen temperature was 20 °C for this experiment.

-optimum temperature/temperature for normal growth of seeds

-optimum temperature for enzymes involved in respiration

Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature.

-so the oxygen is used/absorbed/respired

Many yeast cells die during the death phase. Suggest one reason why.

-decrease/no glucose/substrate

-increase in ethanol/carbon dioxide/acidity

Suggest why a layer of oil is required in this investigation.

-prevents oxygen being taken up/ entering/ being absorbed

-so yeast respires anaerobically

Suggest and explain what would happen to the volume of gas in the syringe if the yeast were only respiring aerobically.

-stays the same/relatively constant

-same volume of oxygen uptake and carbon dioxide release

For the first 10 minutes, the tap attached to tube A was left open and the syringe from tube B was removed. Suggest three reasons why the apparatus was left for 10 minutes.

-equilibrium reached

-allow for expansion/pressure change in apparatus

-allow respiration rate of seeds to stabilise

Required practical 10: investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze

e.g. light, humidity, light and humidity, temperature

Method10

1) set up the choice chamber with nothing in the base quarters

2) place 12 maggots in the chamber through the central hole, using the teaspoon

3) wait four minutes and then record the number of maggots in the left and right halves of the choice chamber

4) if left and right halves have no effect, expected result would be six in each half which will not occur because of chance distribution

-if results are not six in each half do statistical test to discover probability of them occurring by chance

-if test shows a greater than 5% probability of the results occurring by chance then you can proceed with the experiment

5) if investigating light:

-cover half the choice chamber with black paper to make it dark

-place 12 maggots in the chamber through the central hole, using the teaspoon

-wait 4 minutes and then record the number of maggots in the dark and the light halves

-if light has no effect on the distribution of maggots the expected results would be six in each half

-repeat experiment several times

-do a statistical test on your results to find the probability of them occurring by chance

6) if investigating humidity:

-place damp paper towel in one half of the choice chamber and silica gel in the other, using the humidity test strips (using forceps) to ensure that a humidity gradient exists in the chamber before adding the maggots

-place 12 maggots in the chamber through the central hole

-wait 4 minutes and then record the number of maggots in the humid and the dry halves

-if humidity has no effect on the distribution of maggots the expected results would be six in each half

-repeat experiment several times

-do a statistical test on your results to find the probability of them occurring by chance

7) if investigating light and humidity:

-create four areas in the choice chamber using black paper, damp paper and silica gel: dark and dry, dark and humid, light and dry, light and humid

-place 12 maggots in the chamber through the central hole

-wait 4 minutes and then record the number of maggots in the four quarters

-if no effect on the distribution of maggots the expected results would be six in each quarter

-repeat experiment several times

-do a statistical test on your results to find the probability of them occurring by chance

Control group10

First steps of experiment indicate control

-can carry out another control to directly compare with experiment

Variables10

Independent: environmental variable

Dependent: number of organism in area of choice chamber

Control:

Risk assessment10

Biohazard from living organism: contamination

-wash hands after handling

Notes10

-research environments organism used prefers

-write null hypothesis

-investigating kineses