Near East College- AS Biology-Notes
UNIT 3 EDEXCEL BIOLOGY List of Core Practicals in AS Syllabus Unit 1: 1.1 The effect of caffeine on heart rate 1.2 The vitamin C content of fruit juice 2.1 The effect of temperature on membranes 2.2 Enzyme concentration and rate of reaction
Unit 2: 3.1 Observing mitosis 3.2 Totipotency and plant tissue culture 4.1 The strength of plant fibres 4.2 Investigating plant mineral deficiencies deficiencies 4.3 The antimicrobial properties of plants
Some key expressions:
Control Variable: A factor that is kept constant so that its effects on the dependent variable are consistent throughout all experiments Independent Variable: The factor that affects the dependent variable. The factor you change. Dependent Variable: The factor that is affected by the independent variable. The factor you measure. Reliability: The same results are recorded if the experiment is repeated. Standard deviation and / or standard error are excellent measures of reliability. Accuracy: There is little difference between your results and the th e recorded “true” results Validity: A combination of accuracy and reliability. Valid results are representative and can be used to make accurate predictions.
Near East College- AS Biology-Notes
Some basic rules for drawing graphs
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The independent variable should be normally on the horizontal axis and the dependent variable on the vertical axis. Each axis should be clearly labelled, including units and have a correct scale. All plotted points must be shown clearly. All graphs should be of reasonable size.
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It is advisable to join points with a straight line.
Near East College- AS Biology-Notes
Bar Charts are used when the independent variable on the horizontal axis is not a continuous scale but a distinct category. Columns do not touch each other. A bar chart is the simplest way to display two means.
Error bars
They are used to show the variability of data on graphs to enable you to analyse the data in an objective way. If the error bars show a lot of variability in a laboratory investigation in which you intended to control the variables carefully, then they may indicate a flaw in your planning.
*** A much simpler way is to use a range bar, where the bar represents the highest and lowest values above and below the mean.
Near East College- AS Biology-Notes
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.
Drawing a table
The IV ( independent variable) 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.
QUESTION 2 notes -Identifying the problem or a question
A clear statement of a precise problem or question the report is about. This problem or question must be biological but not necessarily linked to the specification There must be a description that explains exactly what the problem or question is and the biology behind it.
- Describing how the problem was solved
This section must describe clearly the work of biologists and what they are doing to solve the problem or to answer the question you have identified.
Make sure you describe the work of biologists, not just the technical details of the solutions
What is meant by implications? There are four types of implications you might consider – ethical, social, economic and environmental. Ethical Implications You must be clear what is meant by an ethical issue. You are expected to understand both what is meant by an ethical viewpoint and that different people may hold different ethical views on the same issue. Many issues are not simply “right or wrong”.
Near East College- AS Biology-Notes
Social implications Social implications are those that will have a direct effect on other human individuals or groups. Economic Implications In many cases it can be simply a question of expense and affordability on either a national scale or an individual scale
Environmental Implications Environmental Implications are concerned with the effect of the solution on other plants, animals and ecosystems. Both sides of the arguments should be discussed, not just state one fixed point.
Naming sources accurately in a bibliography – Referencing
A web- based reference will be in the following format: Authorship or Source, Year. Title of web document or web page.[type of medium] (date of update if available) Available at: include web site address/URL [Accessed date]
A scientific journal will be in the following format: Author, Initials, Year. Title of article, Full Title of Journal , Volume number (Issue/Part number), Page numbers.
Near East College- AS Biology-Notes
Practical Summary for Unit 1 Effect of caffeine on Daphnia heart rate
Independent variable: Caffeine concentration Dependent Variable: Heart rate of Daphnia Other variables to be controlled: Temperature Volume of solutions Stress of Daphnia Size of Daphnia Time of acclimatisation Other Equipment: 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 conc n of caffeine solution in place of distilled water. Carry out for 5 conc n of caffeine = 3 repeats at 3 concn . Outcome: as caffeine concn increased, heart rate increased Possible evaluation issues
Ensuring Daphnia were same size Left too long under microscope, temp e (due to lamp) = increased heart rate Ensuring enough data is collected Too high conc n of caffeine kills Daphnia Counting of heart beat can be inaccurate
Near East College- AS Biology-Notes
The Vitamin C content of fruit juice IV: Different type of fruit juices DV: the amount of fruit juice needed to decolorise DCPIP. Other variables to be controlled
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
Other Equipment 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 1cm 3 of DCPIP. Mass in sample = mass of vitamin C to decolourise 1cm3 DCPIP volume of sample required to decolourise 1cm3 DCPIP Possible Evaluation Issues:
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
Near East College- AS Biology-Notes
The effect of temperature on cell membranes IV: Temperature of water DV: % transmission of light through resulting solution Other variables to be controlled: Volume of distilled water Time left in water Size of beetroot piece Other equipment : Raw beetroot ,cork borer, white tile, knife, ruler, beaker, forceps, water baths, boiling tubes, thermometer, colorimeter and 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 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.
Possible Evaluation Issues:
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
Near East College- AS Biology-Notes
The effect of changi ng enzyme concentration on rate of reaction. IV: concentration of enzyme DV: time taken for enzyme to break down substrate
Other variables to be controlled:
Temperature Volume of enzyme Volume of substrate Concentration of substrate pH
Other Equipment: 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 O 2 gas produced every 10 mins until 3 readings the same. Repeat 3x for each conc n of yeast solution.
Possible Evaluation Issues:
Attaching syringe can be slower allowing loss of gas Inaccurate reading of gas syringe in making up dilutions Reaction going too quickly to read
