SAIntS Biology Department 2013/14 AS Core Practicals Handbook
AS Biology – Core Practical Handbook Contents Page :
AS Core Practical Titles
Page: 2
Practical 1.1 - The effect of caffeine on heart rate.
Page: 3
Practical 1.2 - The vitamin C content of fruit juice.
Page: 6
HSW activity - Lifestyle factors & heart disease
Page: 8
Key Word / Aspect
Definition / Notes
Accuracy
The difference between the actual values and the measured values. If the difference is high, then accuracy is low and vice versa. Accuracy can be improved by using appropriate apparatus and methods for making measurements. There is little difference between your results and the recorded “true” results
Anomalous Result
A result that appears „out of place‟, often as a result of human error.
Bias
Calculations Choosing the correct graph / chart Control Variable
When drug companies / scientists (who have a big stake in the outcome of an experiment) promote certain hypothesis / website / source / article; without reference or cross checking. Show the Working out – it may get you marks! Data is a shown as a percentage that adds up to 100% - Pie Chart Both variables are quantitative (i.e. numerical) or one is d iscrete – Bar Graph Both Variables are continuous – Line Graph A factor that is kept constant so that its effects on the DV are consistent throughout all experiments
Key Word / Aspect
Graph
Definition / Notes Axes: IV on X-axis. DV on Y-axis. Label both aappropriately ppropriately with units. Scale: The curve should cover more than 50 % of the graph paper. Plot all points accurately. Mark the plotted point with a dot and a circle cir cle or with a cross. Line: Either draw a best fit line / curve to show trends or join each point with a neat straight line, passing exactly through the point. Do not extrapolate.
Graph / table titles
Must refer to the IV & the DV
Independent Variable (IV)
The factor that affects the DV. The factor you change.
Limitations
Experimental failings or restrictions
Null Hypothesis
Opposite of the working hypothesis: i.e. that the IV has no effect on the DV. Aim to disprove this hypothesis experimentally
Preliminary
Work that is carried out prior to actually starting to collect c ollect results in an investigation. Allows consideration of amounts, equipment suitability & r ange of
Key Word / Aspect Spearman Rank Correlation
Systematic Error
Tables
-test t -test
Definition / Notes Statistical test which allows students to find out whether 2 variables are correlated (i.e does increasing one cause the other to increase or decrease?) Usually down to an uncontrolled factor, a systematic error affects the entire experiment, usually shifting the results by a consistent amount each experiment. Systematic errors always produce inaccurate results, but in some cases the data produced may still be reliable & as a trend may still be observable, valid to a degree. The IV comes in the 1 st column. Arrange values in ascending order. Label all columns and rows appropriately and accurately. Include SI units (International Standard units – i.e. Metric units) in the headings of the columns and rows. Be consistent with significant figures / decimal places. Used to compare 2 means (mean = normal "average"). Involves choosing between 2 hypotheses . For the t-test, the null hypothesis (H0) is always that the 2 means are equal – e.g. "mean length of leaves at the top of the tree = mean length of leaves at the bottom of the tree". It can never be that the means are different, or that one i s bigger/smaller than the other. You always start out assuming that the null hypothesis hy pothesis is true, and only change your mind if the evidence is good enough. A combination of accuracy and reliability. Valid r esults are representative and can be
A level Biology - How Science Works
HSW Criteria 1) Use theories, models and ideas to develop & modify scientific explanations
Learning Outcome
Practical
a) Explain how the development of scientific theories involves hypothesising, collecting & interpreting data & using creative thinking. b) Explain the importance of modelling as way of developing scientific
The Core Practicals cover the HSW criteria. Complete Complete the last column, noting which practical fulfil each criteria.
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understanding. 2) Use knowledge & understanding to pose scientific questions, define scientific problems, present scientific arguments and scientific ideas
a) Distinguish between questions that science can address, and those which science cannot address. b) Identify scientific questions or problems within a given context. c) Apply scientific theories to answer scientific questions or address scientific problems.
3) Use appropriate methodology, including ICT, to answer scientific questions & solve scientific problems
Justify methods, techniques and processes used during scientific investigations, including use of ICT, to collect valid & reliable data and produce scientific theories for a chosen question or problem.
4) Carry out experimental and investigative activities, including appropriate risk management, in a range of contexts
Produce a risk assessment before carrying out a range of practical work.
5) Analyse & interpret data to provide evidence, recognising correlations and causal relationships
a) Analyse data including use of: descriptive statistics (mean, mode & median, error bars, standard deviation identification of outliers and range); graphic representation to identify patterns & relationships (eg correlation and cause) with appropriate statistical tests (A2 tests (A2 only). b) Interpret data with reference to methods of analysis used.
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As you complete complete the core practicals practicals - make a note note in the table table of which criteria criteria the practical practical meets.
HSW Criteria
Learning Outcome
6) Evaluate methodology, evidence & data & resolve conflicting evidence
Evaluate the validity of inferences made from data in terms of the methods, techniques and processes used to collect & analyse the data, recognising any systematic or random errors present or conflicting evidence.
7) Appreciate the tentative nature of scientific knowledge
Explain how scientific theories are developed, refined, supported or refuted as new data or new interpretations of data become available.
8) Communicate information & ideas in appropriate ways using appropriate terminology
Present scientific information using text, graphics and other media as appropriate using scientific terminology with reference to data and credible sources.
9) Consider applications & implications of science & appreciate their associated benefits and risks
10) Consider ethical issues in the treatment of humans, other organisms & the environment
11) Appreciate the role of the scientific community in validating new knowledge & ensuring integrity
12) Appreciate the ways in which society uses science to inform decision-making
a) Evaluate activities in terms of their associated benefits and risks to humans, other organisms and the environment. b) Discuss the risk associated with an activity in terms of the actual level of the risk and its potential consequences, associated associated uncertainties, and the factors affecting people’s perception of the risk. a) Identify ethical issues arising from the application of science as it impacts on humans, other organisms and the environment. b) Discuss scientific solutions from a range of ethical viewpoints. a) Discuss the importance of critical evaluation of new data or new interpretations of data which challenge established scientific theories or propose new theories. b) Describe how the process of communication through journals, conferences & peer review contribute to validation of new scientific theories by the scientific community. Discuss how science influences decisions on an individual, local, national or international level.
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Practical
Name of practical; IV / DV Effect of caffeine on Daphnia heart rate n IV: IV: caffeine caffeine conc DV: DV: heart rate of Daphnia The effect of temperature on cell membranes IV: IV: temperature of water DV: DV: % transmission of light through resulting solution The effect of temperature on cell membranes IV: IV: temperature of water DV: DV: % transmission of light through resulting solution
The effect of changing enzyme concentration on rate of reaction. IV: IV: concentration of enzyme DV: DV: time taken for enzyme to break down substrate
Other variables to be controlled Temperature Volume of solutions Stress of Daphnia Size of Daphnia Time of acclimatisation Temperature Concentration of DCPIP solution (1%) Shake each tube same no. times Same end point colour. i.e. until blue colour of DCPIP just disappears Volume of distilled water Time left in water Size of beetroot piece
Temperature Volume of enzyme Volume of substrate Concentration of substrate pH
Other equipment
Method and outcome
Microscope, counter, cavity slide, dropping pipettes, stop clock, distilled water, test tubes, stop clock
Method: Remove 1 Daphnia and place in cavity slide. Remove pond water and replace with distilled water. Leave for 5mins to acclimatise then observe & count heart rate under microscope for 30s, multiply number by 2 to calculate beats/min. Repeat with 2 n more Daphnia. Repeat again, this time with small conc of caffeine solution in place of n n distilled water. Carry out for 5 conc of caffeine = 3 repeats at 3 conc . n Outcome: Outcome: as caffeine conc increased, heart rate i ncreased
1% DCPIP solution, 1% vitamin C solution, range of fruit juices, test tubes/conical flasks, beakers, pipette 3 accurate to 1cm , burette, safety goggles
Method: pipette 1cm3 blue DCPIP into test tube. Using burette (or accurate pipette) add 1% vitamin C solution drop by drop. Shake tube gently after each drop. Continue until the blue colour just disappears. Record volume of solution needed to decolourise the DCPIP. Repeat further 2 times and calculate mean result. Repeat procedure with different fruit juices. 3 Calculations: 1cm of 1% vitamin C solution contains 10mg Vitamin C, therefore mass 3 3 in 1cm = 10mg x volume of 1% vitamin C to decolourise 1cm of DCPIP. Mass in sample = mass of vitamin C to decolourise 1cm3 DCPIP volume of sample 3 required to decolourise 1cm DCPIP
Raw beetroot, size 4 cork borer, white tile, knife, ruler, beaker, forceps, water baths, boiling tubes, thermometer, colorimeter & cuvettes, stop clock, distilled water, syringe Protease e.g.1% trypsin, casein solution, small beakers, thermometer, distilled water, syringes, stopclock, large beaker
Method: using cork borer and knife, cut pieces of beetroot into 1 cm length cylinders. Place in distilled water overnight to remove any dye released on preparation. Wash and blot dry. Place 8 boiling tubes of distilled water into 8 water baths of different temperature. Once at temperature, temperature, add a piece of beetroot to each and l eave for 30 mins. Remove beetroot and shake tubes to disperse dye. Set colorimeter to % absorbance on blue/green filter. Calibrate using distilled water in a cuvette first then add 2cm3 of beetroot solution from the first temp to a new cuvette. Place into colorimeter to read % absorbance. Repeat for all other pieces. Calculations & outcome: to calculate % transmission = 100 - % absorbance. As temperature increased, % transmission slightly increased to a point at which it greatly increased due to membrane molecules gaining more heat energy, vibrating more to a point where the vibrations caused large gaps in the membrane enabling the release of dye also proteins in membrane denatured leaving large pores.
Using catalase in yeast and hydrogen peroxide
Method: make up different concentrations of enzyme using distilled water. Ensure different syringes for different chemicals to prevent cross contamination. Set up water bath for 3 temperature to keep constant. Place 1 test tube of 5cm casein solution into water bath 3 alongside second tube containing 2cm of 0.2% trypsin. Allow to acclimatise for 3 mins so that at same temperature then add trypsin to casein, start stop clock. Time how long it takes for casein solution to turn transparent. (mark a ‘X’ on the other side of tube, as soon as seen through n solution stop clock). Repeat a further 2 times then repeat for next conc Calculations & outcome: rate = 1/time n As conc of enzyme increases, rate of reaction increases until a plateau point where all enzyme has metabolised all substrate immediately. immediately. n
Method: using first conc of yeast solution, acclimatise to desired temperature alongside separate tube of hydrogen peroxide. Set up gas syringe and set to 0. Quickly add peroxide to yeast and attach gas syringe. Read off the volume of O 2 gas produced n every 10 mins until 3 readings the same. Repeat 3x for each conc of yeast solution. Calculations & outcome: rate = initial rate of reaction = gradient at steepest point
Possible evaluation issues Ensuring Daphnia were same size e Left too long under microscope, temp (due to lamp) = increased heart rate Ensuring enough data is collected n Too high conc of caffeine kills Daphnia Counting of heart beat can be inaccurate Difficulty in controlling temperature Amount of shaking (too much adds oxygen which will slightly restore the DCPIP to blue) End point difficult to judge as needs to be just when blue colour disappears disappears especially in highly coloured juices Some loss of solution when transferring
Some beetroot may have skin on affecting surface area. Difficulty in maintaining temperature Accurate reading of the colorimeter Accurate size of beetroot From the different parts of the root Ensuring same amount of time at the different temperatures
Maintaining constant temperature Accurately making up the different concentrations Identifying end point consistently Difficult to see the cross through the solution
Attaching syringe can be slower allowing loss of gas Inaccurate reading of gas syringe in making up dilutions Reaction going too quickly to read
n
from graphs of volume against time for each conc . Outcome as protease.
Name of practical; IV / DV Observing Mitosis Chromosomes stained blue using orcein ethanoic stain
Other variables to be controlled
Other equipment
Method and outcome
Garlic roots, sharp knife, 1M hydrochloric acid, Ethanoic alcohol, Orcein ethanoic stain, ice-cold distilled water, water bath @
Method: place test tube of 2cn3 1M HCl into 60˚C waterbath. Cut off 1 -2cm of root tip from garlic root. Put in watch glass containing 2cm3 of acetic alcohol for at least 12 mins. Remove then place into another watch glass containing 5cm3 ice cold distilled water. Leave for 4-5 mins, then remove and dry. Place tips into heated HCl for 5mins then repeat process again by placing tips back into acetic alcohol etc. Tips will be very fragile at this
Possible evaluation issues
Resolution of microscope Human error in counting numbers of cells Enough time in the solutions to enable successful maceration or staining.
60˚C, 2 watch glasses, test tube, 2 pipettes, microscope slides, forceps, mounted needle, filter paper, microscope with mag x100 & x400
Seeds of white mustard, agar, distilled water, damp sponge, cling film, McCartney bottles, weighing scales, plastic tray, 250ml beaker, glass rod, scissors, sunny window sill
Totipotency & Tissue Culture
The strength of plant fibres IV: IV: source and type of fibre DV: DV: mass that can be held
Length of fibre Size of each individual mass
Stems of stinging nettles or celery, bucket, gloves, paper towels, clamp stands, slotted masses and holders, white tile, sharp knife
point. Transfer 1 tip to microscope slide, cut 4-5mm from growing tip (site of mitosis) and keep the tip. Gently break up (macerate) with mounted needle, add 1 small drop of orcein ethanoic stain and leave for 2 mins. Add coverslip and blot with filter paper. View under microscope and identify the stages of mitosis. Calculations: percentage of cells in each stage of mitosis Mitotic index: number of cells containing visible chromosomes total number of cells in the field of view Method: sprinkle seeds on damp sponge and allow to germinate. Use when just starting to unfold their cotyledons (seed leaves). Make up Agar gel and pour 2cm height of gel into McCartney bottles and allow to set. With sharp scissors, cut the tops off just below the shoot apex (including the cotyledons). This is called an explants. Push the stem of the explant into the gel (making sure cotyledons don’t touch agar) cover with cling film and place on sunny windowsill. Observe over 10 days. Outcome: explant grows roots and leaves continue to grow. You need to be able to explain why they are covered in cling film and why they continue to grow even when covered. Also why they shouldn’t be opened again. Method: plant material should be left to soak in a bucket of water for about a week in order for the fibres to be easily extracted (called retting). Or celery stalks should be left in beaker of coloured water in order for fibres to be easily seen and pulled out. Once fibres removed, connect between 2 clamp stands and gradually add mass in the middle until the fibre snaps. Try with individual fibres from different plants and different ways of combining fibres eg twists and plaits. Can also compare stem to individual fibres. Outcome: the more fibres combined together the stronger it is.
Unwanted pathogens growing in the gel as it is a good source of water and nutrients Wrong part of the plant cut and inserted into gel.
Maintaining length of fibres Ensuring consistency when twisting or plaiting Using fibres of the same age (as they get older they become more brittle) Extracting whole fibres that are useful
Name of practical; IV / DV Investigating plant mineral deficiencies IV: IV: minerals present DV: DV: physical c charact of the plant Effect of garlic and mint on bacterial growth IV: IV: presence of garlic or mint DV: DV: zone of inhibition around disc
Other variables to be controlled Volume of mineral solution Species of plant Size of container Amount of light received
n
Conc of plant material Lawn of bacteria on petri dish Contamination of petri dish by other microbes Same volume of plant material on each disc
Other equipment
Method and outcome
Mexican hat plantlets or geranium leaves, 7 test tubes, test tube holder, different mineral solutions:each lacking 1 nutrient and 1 containing all, aluminium foil
Method: half fill a tube with the ‘all nutrients present’ solution. Cover the top of the tube with foil or paraffin and push down on covering so that there is a well in the centre. Gently push the geranium stem/roots of Mexican hat plantlet through the hole so it is i n solution below. Repeat with solutions lacking in nitrogen or phosphate or potassium or magnesium or calcium or lacking all. Wrap all tubes in aluminium foil and place in tube holder on sunny window sill. Observe regularly. Outcome: the ‘all nutrients present’ plant will look healthy whereas the others will all have some abnormality. Make sure you know what nutrient deficiencies affect plants.
Agar plate seeded with bacteria, plant material e.g. garlic & mint, pestle & mortar, 10cm3 industrial denatured alcohol, sterile pipette, paper discs, sterile petri dish, sterile forceps, hazard tape, marker pen.
Method: make plant extract by crushing 3g of plant material with 10cm3 industrial denatured alcohol. Shake occasionally occasionally for 10 mins. Pipette 0.1cm3 of extract onto sterile paper disc. Allow to dry on sterile petri dish. Meanwhile label agar plates with date and split into 4 sections. 1 for each type of plant extract. Place 1 disc of each extract in each quadrant of the agar plate, close and tape with hazard tape. Leave to incubate over night and observe zone of inhibition. Carry out controls with just distilled water on discs. Outcome: the control discs completely covered with bacteria, some plant extracts will create larger zones of inhibition than others, meaning they are more effective at lower concentrations.
Possible evaluation issues
Ensuring accurate measurement of solutions No air bubble caught in xylem of geranium possible microorganism growth in nutrient solution Insufficient time to see an effect.
Growth of unwanted microbes on agar plates due to bad aseptic techniques Not shaking extract enough to ensure enough active ingredient Inconsistency when adding plant extract to paper discs. Contaminating controls Using wrong species of bacteria for lawn
