Life Sciences Grade 12 IEB Paper 3 2018 Memo

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE EXAMINATION NOVEMBER 2018 LIFE SCIENCES: PAPER III MARKING GUIDELINES Time: 1½ hours 50 marks These marking guidelines are prepared for use by examiners and sub-examiners, all of whom are required to attend a standardisation meeting to ensure that the guidelines are consistently interpreted and applied in the marking of candidates' scripts. The IEB will not enter into any discussions or correspondence about any marking guidelines. It is acknowledged that there may be different views about some matters of emphasis or detail in the guidelines. It is also recognised that, without the benefit of attendance at a standardisation meeting, there may be different interpretations of the application of the marking guidelines. IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAPER III – MARKING GUIDELINES Page 2 of 6 Part A Following instructions: four test tubes are labelled 1–4 Procedural skills: appropriate syringe used (5 ml) Manipulative skills: 1 ml Solution B in syringe 1.13 Table showing the colour changes of different water samples in the presence of Activated Solution A. Water sample /tube and Colour change contents Distilled water (Tube 1) No change – remained blue-purple Sample J (Tube 2) No change – remained blue-purple Sample K (Tube 3) From blue-purple to blue-grey Sample L (Tube 4) From blue-purple to colourless /became clear Layout of table (neat with border) 1.14 Control is Test Tube 1 (distilled water). Purpose is to compare experimental results with a sample known not to contain cholera/bacteria/ prove that results are owing to cholera or independent variable and not some other variable. 1.15 Any one: • Amount/volume of Activated Solution A: each tube received 10 ml/same amount of Activated Solution A using a syringe. • Amount/volume of water sample: each tube contained 15 ml/same amount of water samples using a syringe. Do not accept – environmental conditions not relevant to this study; size of test tubes is also irrelevant to the validity of this experiment. 1.16 Qualitative. No numbers/measurable data was collected – only colour change (subjective). 1.17 Conclusion: one/two of the samples tested positive for Vibrio cholerae (tubes 3 and 4; samples K and L, respectively) as they changed colour (became colourless). Thus Sample K and L are not potable, whereas Sample J is potable. 1.18 Any one of the following: • Replicates of the water samples could be tested. • More water samples can be collected from the river (different points along the river/at different times of the year) and tested for V. cholerae. • Filter water for clarity of samples/colour change. • Rinse kebab stick/stirring rods between samples. IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAPER III – MARKING GUIDELINES Page 3 of 6 1.19 Lab precaution: any one of the following: • Wear gloves during testing • Do not drink the water samples • Wash hands after handling water samples • Clean the equipment used for testing with bleach • Do not discard the samples down the drain (Accept other suitable safety precautions) 1.20 Sample L  Point A (city)/Point B (village). High populations therefore high amounts of faeces; more human activity; no waterborne sewerage system, sewage therefore washes in river; accept other suitable reasons. 1.21 (a) Any two of the following: • Number of cases of cholera per week • Temperature (°C) • Rainfall (mm) (b) 13 (Check final printed version for accuracy) (c) The more rainfall there is, the less cholera cases there are (d) Any two or one well explained: Boiling (for a certain amount of time to kill pathogens)/addition of bleach (to a concentration of 1m/ℓ)/filtering (filtration using filter paper/other material to remove particulate matter) 1.22 (a) Measurement of scale bar = 5 mm Measured length of bacterium = 70 mm 5 mm  0,2 µm 70 mm  X µm (working) Thus real size = 3 µm / 0,003 mm / 3000 nm / 2,8 µm / 0,0028 mm / 2800 nm (must have correct unit) OR: Measurement of scale bar = 5 mm Measured length of bacterium = 65 mm 5 mm  0,2 µm 65 mm  X µm (working) Thus real size = 2,6 µm / 0,0026 mm / 2600 nm (must have correct unit) [Acceptable Range: 2,6 µm to 3,0 µm] (b) Longitudinal IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAPER III – MARKING GUIDELINES Page 4 of 6 Part B 2.1 Activated Solution A tests positive OR can be used to detect cholera at concentrations less than 100 cells/ml (statement) 2.2 To determine if Activated Solution A can be used to detect cholera at a concentration of lower than 100 cells/ml 2.3 Different concentrations of cholera bacteria, /range of concentrations of cholera/bacteria 2.4 Sample method: • Label 4 test tubes 1 – 4 using a marker. • Using a syringe, place 10 ml of cholera/water sample (200 cells/ml) in test tube 1 and 5 ml into test tube 2, 2,5 ml into test tube 3 and 0 ml into test tube 4. (Control independent variable = serial or other dilution.) • Rinse syringe. • Using a syringe, add 5 ml distilled water into test tube 2, 7,5 ml into test tube 3 and 10 ml into test tube 4. • Rinse syringe. • Using a dropper, add 10 drops of Activated Solution A into each tube. • Stir each tube using a kebab stick/glass rod, rinsing the glass rod in between each tube. • Observe and record colour changes in a table for each concentration. • Samples that are colourless test positive for cholera. • Repeat the experiment to verify results. (This point is not required.) IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAPER III – MARKING GUIDELINES Page 5 of 6 Layout: Neat, numbered/listed/bulleted Aim: Must have cholera samples (at least two concentrations and at least one lower than 100 cells/ml) must use Activated Solution A Method: Original – look for cholera at different concentrations (if mention Samples J/K/L then no marks awarded). Equipment – looking for a syringe/equivalent to make a dilution of the bacterial samples; dropper or pipette used for Activated Solution A. Measuring – equal amounts of Activated Solution A added to each tube; total volumes in test tubes the same. Valid – dilution done correctly (must have different concentrations, not just different volumes) and Activated Solution A added AFTER dilution; appropriate amounts in test tubes. Measurable results – recording of colour change. IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAPER III – MARKING GUIDELINES Page 6 of 6 Method Rubric Method Rubric 5 4 3 2 1 0 Criteria L Layout – Layout meets Layout is appearance criteria untidy and of method below: neat hard to read. and tidy and OR bulleted/ Method is not numbered. formatted correctly with bullet points or numbers. A Aim – Method Method Method does method clearly tests relates to the not relate to relates to an aim that prescribed the prescribed relates to aim given, prescribed experiment the but is a little aim or prescribed confusing achieve the experiment and does not desired and achieve the result. achieves required Method given the required result. is the same result. as the given experiment. M Method – All 5 criteria given An original An original An original An original None of the this needs below are met: experiment experiment experiment experiment 5 criteria are to be 1. An original provided. provided. provided. provided. met. appropriate experiment OR and provided. Plus 3 of 5 Plus 2 of 5 Plus 1 of 5 Method a relevant to 2. Equipment is criteria are criteria are criteria is copy of the the aim, appropriate met. met. met. original, clear, and used given logical and correctly. experiment. sequential. 3. Measuring of If apparatus solutions, is given in reagents and the marking of examination equipment are paper, the explained and method this assists in should the control of resemble variables. the one 4. Instructions given in the are marking scientifically guidelines. valid and ordered. 5. Instructions are complete to produce measurable results that are recorded. Total: 50 marks IEB Copyright © 2018