As Core Practicals Handbook_2013_14

SAIntS Biology Department 2013/14

AS Core Practicals Handbook

Edexcel Specification

Edexcel AS Biology – Core Practical Handbook 1

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

Practical 2.1 - The effect of temperature on membranes. Page: 9

Practical 2.2 - Enzyme concentration and rate of reaction. Page: 12

Practical 3.1 - Observing mitosis. Page: 14

Practical 3.2 - Totipotency and plant tissue culture. Page: 19

Practical 4.1 - The strength of plant fibres. Page: 22

Practical 4.2 - Investigating plant mineral deficiencies. Page: 25

Practical 4.3 - The antimicrobial properties of plants. Page: 26

HSW Criteria / Learning Outcomes Page: 30

AS Core Practicals - Key Expressions (Paper 3B) Page: 33

AS Core Practicals - Summary Sheet Page: 35













Alternative practical set-up for catalase & H2O2

concentration

















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.

BiasWhen 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.

Calculations Show the Working out – it may get you marks!

Choosing the correct graph

/ chart

Data is a shown as a percentage that adds up to 100% - Pie ChartBoth variables are quantitative (i.e. numerical) or one is discrete – Bar GraphBoth Variables are continuous – Line Graph

Control Variable

A factor that is kept constant so that its effects on the DV are consistent throughout all experiments

Dependent Variable (DV)

The factor that is measure to give the results & is affected by the IV. DV depends upon the IV.

Describing Trends

Describe the trend in the graph without making theoretical assumptions. Make conclusions based on the experimental data. Refer to the hypothesis being investigated, while making conclusions. Limitations are genuine sources of error. Look out for variables like temperature, pH, etc. not being controlled. Also check if the experiment has been replicated.

Economic Implications An issue that is money / business related – e.g. loss of revenue / jobs

Environmental

Implications

An issue that is effects the environment (animals and plants) – e.g. deforestation.

Ethical Implications

Whether an issue is right or wrong (moral or immoral). E.g. keeping animals in zoos; testing medicines / drugs on animals; hunting animals (wrong of for ornaments / trophies / dubious medications). Could lead to extinction.

Experimental Hypothesis

The working hypothesis that the IV does have an effect on the DV. By disproving the Null Hypothesis you can accept your Experimental Hypothesis. NB. It’s virtually impossible to prove something correct, yet very simple to prove something incorrect. Therefore, scientists aim to disprove their Null Hypothesis, which then allows them to accept their Experimental Hypothesis.



Graph

Axes: IV on X-axis. DV on Y-axis. Label both appropriately 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 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

Work that is carried out prior to actually starting to collect results in an investigation. Allows consideration of amounts, equipment suitability & range of results to take. Adjustments would then be considered before starting the actual procedure.

Random ErrorA mistake in the method or malfunction in the equipment which leads to the production of a single anomalous result, inconsistent with the trend. Once spotted, a random error should be either repeated or ignored.

Raw Data Data that has not yet been organized, analysed or evaluated

References / Bibliographie

s

Always need specific dates / details of website; authors; reference to additional of suitable non-web resources; ICUN red list reference to book; title of article / newspaper / journal

Reliability

When the variability in replicated results is very high, the reliability is relatively low. Due to certain variables not being controlled or faulty experimental procedures. Range bars / error bars on graphs give a fair indication of the reliability. If there is considerable overlap between error bars, then variability is very high and reliability is low. Students should be able to identify factors that may decrease the reliability of the results. The same results are recorded if the experiment is repeated. Standard deviation / standard error are excellent measures of reliability.

Risk Assessments

1) Identify risk (e.g. powdered enzyme could affect respiratory system / get into eyes / skin cuts2) Minimise risk - e.g. wear mask / goggles / gloves / cover any cuts with plasters3) Action if risk occurs – e.g. wash with copious water

Social Implications An issue that affects people – e.g. loss of homes; increase in disease / famine



Spearman Rank

Correlation

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?)

Systematic Error

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.

Tables

The IV comes in the 1st 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.

t-test

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 is bigger/smaller than the other. You always start out assuming that the null hypothesis is true, and only change your mind if the evidence is good enough.

ValidityA combination of accuracy and reliability. Valid results are representative and can be used to make accurate predictions.


A level Biology - How Science Works

The Core Practicals cover the HSW criteria. Complete the last column, noting which practical fulfil each criteria.

HSW Criteria Learning Outcome Practical

1) Use theories, models and ideas to develop & modify scientific explanations

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 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 only).b) Interpret data with reference to methods of analysis used.


HSW Criteria Learning Outcome Practical

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

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 uncertainties, and the factors affecting people’s perception of the risk.

10) Consider ethical issues in the treatment of humans, other organisms & the environment

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.

11) Appreciate the role of the scientific community in validating new knowledge & ensuring integrity

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.

12) Appreciate the ways in which society uses science to inform decision-making

Discuss how science influences decisions on an individual, local, national or international level.

As you complete the core practicals - make a note in the table of which criteria the practical meets.


Name of practical; IV / DV

Other variables to be controlled

Other equipment Method and outcome Possible evaluation issues

Effect of caffeine on Daphnia heart rate IV: caffeine concn

DV: heart rate of Daphnia

Temperature Volume of solutions Stress of Daphnia Size of Daphnia Time of

acclimatisation

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 more Daphnia. Repeat again, this time with small concn of caffeine solution in place of distilled water. Carry out for 5 concn of caffeine = 3 repeats at 3 concn . Outcome: as caffeine concn increased, heart rate increased

Ensuring Daphnia were same size Left too long under microscope, tempe

(due to lamp) = increased heart rate Ensuring enough data is collected Too high concn of caffeine kills Daphnia Counting of heart beat can be inaccurate

The effect of temperature on cell membranes IV: temperature of water DV: % transmission of light through resulting solution

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

1% DCPIP solution, 1% vitamin C solution, range of fruit juices, test tubes/conical flasks, beakers, pipette accurate to 1cm3, 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. Calculations: 1cm3 of 1% vitamin C solution contains 10mg Vitamin C, therefore mass in 1cm3 = 10mg x volume of 1% vitamin C to decolourise 1cm3 of DCPIP. Mass in sample = mass of vitamin C to decolourise 1cm3 DCPIP volume of sample required to decolourise 1cm3 DCPIP

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 especially in highly coloured juices

Some loss of solution when transferring

The effect of temperature on cell membranes IV: temperature of water DV: % transmission of light through resulting solution

Volume of distilled water

Time left in water Size of beetroot piece

Raw beetroot, size 4 cork borer, white tile, knife, ruler, beaker, forceps, water baths, boiling tubes, thermometer, colorimeter & cuvettes, stop clock, distilled water, syringe

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, add a piece of beetroot to each and leave 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.

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

The effect of changing enzyme concentration on rate of reaction. IV: concentration of enzyme DV: time taken for enzyme to break down substrate

Temperature Volume of enzyme Volume of substrate Concentration of

substrate pH

Protease e.g.1% trypsin, casein solution, small beakers, thermometer, distilled water, syringes, stopclock, large beaker

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 temperature to keep constant. Place 1 test tube of 5cm3 casein solution into water bath alongside second tube containing 2cm3 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 solution stop clock). Repeat a further 2 times then repeat for next concn Calculations & outcome: rate = 1/time As concn of enzyme increases, rate of reaction increases until a plateau point where all enzyme has metabolised all substrate immediately.

Maintaining constant temperature Accurately making up the different

concentrations Identifying end point consistently Difficult to see the cross through the

solution

Using catalase in yeast and hydrogen peroxide

Method: using first concn 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 O2 gas produced every 10 mins until 3 readings the same. Repeat 3x for each concn of yeast solution. Calculations & outcome: rate = initial rate of reaction = gradient at steepest point from graphs of volume against time for each concn. Outcome as protease.

Attaching syringe can be slower allowing loss of gas

Inaccurate reading of gas syringe in making up dilutions

Reaction going too quickly to read





Observing Mitosis Chromosomes stained blue using orcein ethanoic stain

Garlic roots, sharp knife, 1M hydrochloric acid, Ethanoic alcohol, Orcein ethanoic stain, ice-cold distilled water, water bath @ 60˚C, 2 watch glasses, test tube, 2 pipettes, microscope slides, forceps, mounted needle, filter paper, microscope with mag x100 & x400

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 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

Resolution of microscope Human error in counting numbers of cells Enough time in the solutions to enable

successful maceration or staining.

Totipotency & Tissue Culture

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

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.

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.

The strength of plant fibres IV: source and type of fibre 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

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.

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





Investigating plant mineral deficiencies IV: minerals present DV: physical charactc of the plant

Volume of mineral solution

Species of plant Size of

container Amount of light

received

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 in 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.

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.

Effect of garlic and mint on bacterial growth IV: presence of garlic or mint DV: zone of inhibition around disc

Concn of plant material

Lawn of bacteria on petri dish

Contamination of petri dish by other microbes

Same volume of plant material on each disc

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 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.

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


As Core Practicals Handbook_2013_14

Documents

b page

core practical titlespage

alternative practical

null hypothesis

animals wrong

environment animals

effect of temperature

heart rate