Life Sciences Grade 12 IEB Paper 3 2019 Memo

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE EXAMINATION NOVEMBER 2019 LIFE SCIENCES: PRACTICAL ASSESSMENT TASK MARKING GUIDELINES Time: 1½ hours 50 marks These marking guidelines are prepared 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 © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAT – MARKING GUIDELINES Page 2 of 7 Part 1 Following instructions: five holes made as instructed; A, B, C, D written on paper in correct orientation; well E made in the centre of the petri dish. Procedural skills: appropriate syringe used (10 ml) Manipulative skills: 10 ml solution correctly drawn up in syringe 1.5 Diameter of well E (in line with pen tube diameter) (4–10 mm) 1.17 Table showing the presence of a yellow halo around the well/ colour change of gel at 20 minutes for different concentrations of PVSA solutions. Well Concentration of Presence of yellow halo PVSA solution (%) around well after 20 minutes (yes or no) A 0,16 Yes/ No B 0,8 Yes/ No C 4 Yes/ No D 20 Yes E 100 Yes 1.18 (a) (Letter) E (b) Reasonable diameter between 8 and 20 mm 1.19 Any one: • Well size: each well was made the same way (same diameter/ same distance from edge e.g. 15 mm) using a pen tube/ straw/ glass tube/ ruler • Amount/ volume of PVSA solution/ total liquid (do not accept "saline"): each well contained 1–3 drops (same amount) using a pipette or dropper. • Total volume of liquid/ solution left in beaker was 40 ml controlled using a syringe (Do not accept volume of PVSA or volume of saline or concentration). • Time: each of the solutions in the wells was left for the same amount of time (20 minutes) (or put in at the same time / recorded at the same time ) using clock or watch • Gel in petri dish: the same gel/ same concentration of snake venom/ same depth in the same petri dish was used in the experiment. Do not accept: environmental conditions (e.g. temperature/ humidity), use of syringe, beakers as these are not relevant to this study. IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAT – MARKING GUIDELINES Page 3 of 7 1.20 Conclusion: Halo size / colour change; specific reference to concentration / dilution / well identified and effectiveness of antiserum E.g. diluting the PVSA reduced the effectiveness of the antiserum; halos around wells became smaller with each dilution, but was still effective at lower concentrations. E.g. Halos around wells C, D and E were present, therefore diluting the antiserum means it was still effective/ active/ neutralised the venom E.g. There were no halos/ colour changes around wells B and A, therefore at low concentrations the antiserum is not effective/ active/ does not neutralise the venom. Refer back to the candidate's table in 1.17. 1.21 Measure the diameter/ size of (all) the halos / halos for each dilution using a ruler or compare it to the 100% concentrated PVSA; time taken for the halo to develop/ yellow colour to develop for each well. 1.22 Lab precaution: any one of the following: • Wear gloves/ masks/ goggles/ eye protection during testing • Do not consume venom or antivenom • Wash hands after handling venom or antivenom samples • Do not discard the samples down the drain / dispose of them correctly (Accept other suitable safety precautions) 1.23 (L) Drawing is larger than the original (P) Drawing is in pencil (G) Groove correctly labelled (Do not accept arrow-heads.) (S) Shape and proportion (length and width proportions must be correct) (C) No colouring or shading No marks are awarded for the heading. However, it is best practice to encourage candidates to include a heading. Please use the codes in brackets when assigning marks. IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAT – MARKING GUIDELINES Page 4 of 7 1.24 Correct key provided (█ = PAN AFRICA CLEAR (PAC); ▲ = PROVALENT and X = VIPERA) Time (hours) on the x-axis Snake venom concentration (µg/ L) on the y-axis Two points (12 and 18 hours) correctly plotted for all three antisera AND points joined correctly to produce three lines (one for each antiserum) and all lines must end on zero at 36 hours. No marks are awarded for the heading although encourage candidates to include headings. 500 Snake venom concentration (µg/L)  450 400 350 300 250  200   150 100 50  0 0 6 12  18 24 30 36 Time (hours)  PAN AFRICA CLEAR PROVALENT VIPERA  (a) VIPERA (b) Not all three of the antisera started out at the same concentration of snake venom OR VIPERA started at 450 µg/ L and not 400 µg/ L OR VIPERA was (50 µg/ L) higher than the other antisera; OR PAN AFRICA CLEAR and PROVALENT were 50 µg/ L lower than VIPERA; OR The starting/ initial concentration of snake venom for each antiserum was not the same OR: Omission of 30 hours from table/ graph means that PROVALENT neutralisation time cannot be determined. (NOTE: "30 hours was skipped/ left out" / "no value for 30 hours" without "PROVALENT" is not acceptable). IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAT – MARKING GUIDELINES Page 5 of 7 Part 2 2.1 Statement / one sentence – do not award statement mark if reasons given in hypothesis (e.g. "because of …") do not award mark if aim is given. Need to mention one or more specific antiserum (do not accept PVSA). Need to mention neutralisation or colour change of gel from blue to yellow / halo forming. E.g. Antiserum "W/ X/ Y/ Z" will neutralise the cobra venom. OR Antiserum "W/ X/ Y/ Z" will produce a yellow halo in the blue gel. OR Antiserum W and Z will neutralise the venom whereas Y and X will not. 2.2 Antisera W, X, Y and Z; types of antisera; different antisera; do NOT accept concentration of antisera. 2.3 colour change; neutralisation of venom; size/ diameter of halo; blue to yellow gel; yellow halo 2.4 Sample method: • Place the petri dish in the middle of the sheet of white paper. • Using a marker, make a mark at the "12 o'clock", "3 o'clock", "6 o'clock" and "9 o'clock" positions. Use the petri dish as the clock face. On the paper, write "W", "X", "Y" and "Z". • Using the pen tube/ straw/ glass tube, pierce five holes in the gel as shown in Figure B on your information sheet. • Use the dissecting needle or forceps to remove the five "plugs" from the five "wells" you have created above. Discard the plugs. • Using a pipette, place 1–3 drops of antiserum W into well W, antiserum X into well X, antiserum Y into well Y and antiserum Z into well Z. • Leave the petri dish undisturbed for 20 minutes. • Record the colour changes and/ or presence of yellow halos around the wells. IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAT – MARKING GUIDELINES Page 6 of 7 Layout (L): Neat, numbered/ listed/ bulleted. Aim (A): needs to make use of antisera W, X, Y and Z AND involve a colour change/ neutralisation in the infused blue gel. Method (M): 1. Original – must make use of W, X, Y and Z; no marks awarded if dilutions made with saline nor if PVSA is used as in Part 1 (look for solutions "W" to "Z" rather than "A" to "E"). 2. Equipment – must make use of petri dish with infused blue gel (can make use of wells punched with tube, or cut cubes from the dish using knife) 3. Measuring – same amount of solutions W, X, Y and Z (must be undiluted) used AND wells made the same way/ cubes of gel cut from the petri dish are the same size. 4. Valid – order of instructions makes sense AND W, X, Y and Z (must be undiluted) come into contact with the blue gel for the same amount of time. 5. Measurable results – recording of colour change/ neutralisation/ halo formation in the blue gel (either yellow halo or cube of gel changes from blue to yellow. (This mark cannot be awarded if W, X, Y and Z not used). Do not accept "record the results" with no indication of what is being measured and recorded. The rubric has been interpreted in this way for this experimental design. Please do not attach a copy of the rubric. Use the following key when marking. e.g. L A M 12345 OR L A M  12345 Do NOT place any other ticks in the method. IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: LIFE SCIENCES: PAT – MARKING GUIDELINES Page 7 of 7 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 does prescribed confusing not achieve experiment and does not the 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 © 2019