2024 Biology Practical Revision PDF

Biology Practical Revision MMO (manipulation, measurement & observation) Manipulation, measurement & Observation (MMO) MMO Candidates may be asked to carry out any of the following tasks: 1. simple physiological experiments, involving tests for food substances, enzyme reactions, hydroge...

Biology Practical Revision MMO (manipulation, measurement & observation) Manipulation, measurement & Observation (MMO) MMO Candidates may be asked to carry out any of the following tasks: 1. simple physiological experiments, involving tests for food substances, enzyme reactions, hydrogencarbonate indicator solution, cobalt(II) chloride paper and so on 2. simple physiological experiments, involving the use of sharp instruments on plant or animal materials (accurate observations of these specimens will need a hand lens of not less than 6 magnification for each candidate) 3. manipulative skills in assembling apparatus, in using chemical reagents and in using such instruments as mounted needles, scalpels and razor blades, forceps and scissors 4. measurements using appropriate instruments (e.g. thermometer, syringe, measuring cylinder, ruler and so on) and simple arithmetical calculations 5. familiar and unfamiliar techniques to record observations and make deductions from them 6. recognition and observation of features of familiar and unfamiliar biological specimens, recording observations and making deductions about functions of whole specimens or their parts 7. clear line drawings of the specimens provided, indicating magnification and labelling familiar structures Physiological Experiments - Food Tests - Benedict’s test Reminders: - Any preparation required for - Iodine test sample before the food test? - Solid vs liquid sample - Ethanol emulsion test - Volume of reagents and sample required for each - Biuret test test? - Boiling/ hot water bath required? - Be precise! - iodine ≠ iodine solution - Observations? Conclusions? Iodine Test Procedure: 1. To a drop of unknown sample on white tile, add a drop of iodine solution. Observation: - If starch is present, iodine solution turns blue-black colour. - If starch is absent, the iodine solution remains yellowish-brown. Benedict’s Test Procedure: 1. To 2 cm3 of unknown solution in a test tube, add an equal volume of Benedict’s solution. 2. Shake to mix well. 3. Heat the test tube in a boiling/hot water bath for no more than 5 minutes. Observation: - If reducing sugars are present, brick-red ppt (large amount); orange/yellow ppt (moderate); green ppt (trace amount) forms - If reducing sugars are absent, the solution remains blue. Biuret Test Procedure: 1. To 2 cm3 of unknown solution in a test tube, add an equal volume of dilute sodium hydroxide solution. 2. Shake to mix well. 3. Add 1 % copper (II) sulphate solution to the mixture, dropwise. Shake well after each drop. Observation: - If proteins are present, a violet colouration will be observed. - If proteins are absent, the solution remains blue. Ethanol emulsion test Procedure: 1. To the unknown sample in a clean dry test tube, add 2 cm3 of ethanol. 2. Shake to mix well. Leave the mixture to stand. 3. Decant the ethanol into another test tube containing 2 cm3 of water to this solution. Shake to mix well. Observation: - If fats are present, a white emulsion will be observed. - If fats are absent, the solution remains clear/colourless. Physiological Experiment - Use of Visking Tubing What is the aim of this experiment? Physiological Experiments - Test for presence of starch in leaves Reminders: - Rationale for each step? - Safety precautions? Hot water Original Leaf after Leaf after for half a minute leaf ethanol iodine test treatment Physiological Experiment - Hydrogencarbonate Indicator Solution Can you state example of an experiment? Physiological Experiment - hydrogencarbonate indicator solution Indicator turns yellow Indicator turns red Indicator turns purple (acidic) (neutral) (alkaline)  What is the aim of this Physiological Experiment - experiment? Cobalt Chloride paper Cobalt chloride paper is blue when dry and turns pink in contact with water vapour  What is the aim of Physiological Experiment - this experiment? Use of vaseline/ petroleum jelly A student was provided with four leaves labelled A, B, C and D which were initially all of the same size and from the same plant. Leaves B, C and D had been left by a window in the laboratory since being picked. Leaf A had been freshly Leaf B had been picked Leaf C had been picked three Leaf D had been picked three picked and had received three days before. days before and its upper days before and its lower no treatment. surface coated immediately surface coated immediately with with petroleum jelly. petroleum jelly. Biological Drawing Biological Drawing Biological Drawing - example A student was provided with a leaf stalk from a different plant that had been left to stand in a liquid stain for several hours. Fig. 1.1 shows the leaf stalk cut across its width. Make a large labelled diagram of the cut surface. What is the aim of this experiment? Biological Drawing - example Marking points: - large, clear drawing, - correct shape and proportion, ridges on upper side - Labels: vascular bundles; xylem; epidermis - Magnification Remember! Magnification of drawing = Length of drawing / Length of specimen Precision to 1 d.p Biological Drawing - example Biological Drawing - example Biological Drawing - example Biological Drawing - example Precision of instrument Precision of instrument - ½ of the smallest division (except for measuring cylinder, where there are 2 points of uncertainty) PDO (presentation of data and observations) Presentation of Data & Observations (PDO) Table Characteristics of a good table: 1. Neatly ruled table 2. The independent (changed) variable should be in the leftmost column of the table, with following subsequent columns showing the dependent (measured) variables 3. The heading of each column must include both the quantity being measured and the units in which the measurement is made. 4. The unit should be written in solidus (backslash) notation, e.g., the length of string is written as L/cm 5. The body of the table should not contain units 6. Readings recorded must have correct precision. Calculations Examples of common calculations: ○ Taking the mean or average ○ Difference between initial and final readings ○ Percentages ○ Reciprocal of a certain value e.g. 1/t Calculations Show calculations in full and working should be explicit and easy to follow. Calculated values should not be more accurate than raw data than the data used to obtain it. Calculated data are consistent (e.g. no. of decimal places) Decrease in length indicated as negative value (-) while increase in length, as positive value (+) so that graph plotted is correct. Table - example +2.0 -2.0 -4.0 +4.0  Table - example Iodine test Benedict’s test Biuret test Ethanol emulsion test Sample Observation Conclusion Observation Conclusion Observation Conclusion Observation Conclusion X Iodine Starch is Solution Reducing Violet Protein is Solution Fats is solution absent remained sugar is colouration present remains absent remained blue absent formed clear yellowish- brown Y Iodine Starch is Brick-red Reducing Solution Protein is White Fats is solution present ppt formed sugar is remained absent emulsion present turned blue- present blue formed black Note: - Correct recording of observation - Correct conclusion made based on observation Graphs Graphs are used to show relationships in data. Examples of types of graphs in Biology ○ Line graphs ○ Histogram ○ Bar charts Graphs Line graphs (straight lines and curves): ○ appropriate for data from an investigation where the independent variable has been manipulated by the investigator and a causal relationship with the dependent variable is established. Graphs SLAP S: scale is appropriate L: line of best fit A: axes labelled with units P: plotted points are correct Graphs Histograms: ○ both axes involves variables that lie on a numbered scale and the independent variable has been grouped into ranges. - bars placed accurately and drawn neatly touching each other - class size positioned centrally under each column  Graphs Bar charts: ○ independent variable is grouped in distinct categories (e.g. tongue roller and non-tongue roller) and the dependent variable is continuous. - columns should be of equal width with an equal space between the columns - shading of the columns is unnecessary Let’s try...histogram or bar chart? Seeds of legumes are known to contain higher levels of protein than any other food plants. Table 2.2 shows the approximate masses of protein found in 100 g masses of some fruits and vegetables. Let’s try...histogram or bar chart? A group of students investigated the rate of transpiration from four leaves. They covered different surfaces of the leaves with petroleum jelly. They then measured the mass of each leaf. The leaves were left hanging from a piece of string in a warm place for 24 hours. The students then measured the mass of each leaf again. Table 2.1 shows their results. Let’s try...histogram or bar chart? This fruit is composed of many small fruits (fruitlets) joined together. 48 of these fruits were collected and, for each fruit, the number of fruitlets was counted. The results were recorded as shown below. Plot a graph to show the number of fruitlets per fruit. Let’s try...histogram or bar chart? This fruit is composed of many small fruits (fruitlets) joined together. 48 of these fruits were collected and, for each fruit, the number of fruitlets was counted. The results were recorded as shown below. Plot a graph to show the number of fruitlets per fruit. Number of Tally Number fruitlets per fruits 50 - 59 III I 6 60 - 69 11 70 - 79 14 80 - 89 10 90 - 99 6 100 - 109 1 ACE (analysis, conclusion and evaluation ) Analysis, Conclusions & Evaluation (ACE) Analysis of data Data presented in graphical forms can be analysed in a variety of ways: 1. reading values directly from graph 2. finding gradient 3. finding intercepts Analysis of data 1) Reading values from a graph ○ draw dotted perpendicular lines to connect the data point to both the horizontal and the vertical axes, for ease of reading. ○ data values should be read to an accuracy within ½ of one of the smallest squares on the grid. Analysis of data 2) Finding gradient: choose two points on the line that are far apart, minimally spanning across ½ the length of the line of best fit. ○ This will reduce the percentage uncertainty in the calculation of gradient. draw a right-angled triangle on the graph with the two chosen points forming the hypotenuse of the triangle. Gradient can be calculated either from the ratio of rise (∆y) to run (∆x) Analysis of data Gradient of straight line Gradient of curve  Source of error Error: Difference between measured value and ‘true’ value. When assessing sources of error, think about what features of the experiment are important in gaining accurate results. Source of error Source of error: ○ What causes this difference? Some examples… Lack of precision in the equipment Problems in experimental procedure Inconsistencies of biological specimens Interference from external environmental factors (e.g. wind, humidity, temperature) Source of error - example Measurements that were difficult to observe and record accurately - An experiment may require students to record time taken for a complete reaction by observing the exact moment where a colour change occur. - E.g. time taken for solution to turn yellow (recall: lipase experiment) - The time measure may be inaccurate as there is a time lapse between seeing the colour change, and stopping the stopwatch - E.g. time taken for iodine solution to turn blue-black - colour change is subjective, thus difficult to determine end- point Source of error - examples Other than the measured variables, what other factors could have affected the results? - sometimes impossible to ensure that all control variables are kept constant in an experiment. - e.g. in an experiment that investigates the rate of heat loss of a liquid over a period of time, the room temperature may vary during the experiment due to changing weather condition. - presence of wind may also affect the rate of cooling. All these factors could all potentially affect the rate of cooling. P (planning ) Planning Requirements Planning Requirements Planning Requirements Planning Requirements Required to describe an experimental procedure to investigate the problem ○ procedure must be clear and anyone can follow it to conduct the experiment ○ Use verb; state apparatus & quantity e.g. use a scalpel to cut the potato into 10 discs, each 2mm ○ encouraged to include diagrams to help in describing procedure Procedure should also include how the data should be used in order to reach a conclusion Refer to textbook examples on examples of well-written procedure. Plan before you start! Refer to planning template next slide.  Planning Requirements 1. Aim of experiment refer to task 2. Changed variable How to change? What is a suitable range and interval? 3. Measured variable How to measure? Use what apparatus? 4. Constant variables What are the constant variables? E.g. duration of incubation, temperature 5. Control Do i need a control set-up? What is a suitable control set-up? Purpose of control set-up? 6. Results How should i interpret the data? i.e. how to use results to answer aim of experiment Any calculations required? e.g. find average What is the best way to present my findings? e.g. record results in table? Plot a graph? 7. Risk(s) and Any safety concerns? precaution(s) E.g. alcohol is flammable and no open flame should be used; use a hot water bath to heat the alcohol instead E.g. handle the sharp scalpel with care to prevent cutting your fingers Resources Practical worksheets Textbook ○ Investigations Aim of experiment? Predicted results? Conclusion? Source of error and how do they affect results? How to overcome?