Practice paper – Set. 2 A Level Biology B (Advancing Biology) H422/03 Practical skills, Exams of Biology

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Practice paper – Set. 2

A Level Biology B (Advancing Biology) H422/03 Practical skills in biology MARK SCHEME Duration: 1 hour 30 minutes

MAXIMUM MARK 60

Version 5.0 FINAL

This document consists of 19 pages MARKING INSTRUCTIONS PREPARATION FOR MARKING SCORIS

1. Make sure that you have accessed and completed the relevant training packages for on-screen marking: scoris assessor Online Training ; OCR Essential Guide to Marking.
2. Make sure that you have read and understood the mark scheme and the question paper for this unit. These are posted on the RM Cambridge Assessment Support Portal http://www.rm.com/support/ca
3. Log-in to scoris and mark the required number of practice responses (“scripts”) and the required number of standardisation responses. YOU MUST MARK 10 PRACTICE AND 10 STANDARDISATION RESPONSES BEFORE YOU CAN BE APPROVED TO MARK LIVE SCRIPTS. MARKING
4. Mark strictly to the mark scheme.
5. Marks awarded must relate directly to the marking criteria.
6. The schedule of dates is very important. It is essential that you meet the scoris 50% and 100% (traditional 50% Batch 1 and 100% Batch 2) deadlines. If you experience problems, you must contact your Team Leader (Supervisor) without delay.
7. If you are in any doubt about applying the mark scheme, consult your Team Leader by telephone, email or via the scoris messaging system.
8. Work crossed out:

Crossed Out Responses Where a candidate has crossed out a response and provided a clear alternative then the crossed out response is not marked. Where no alternative response has been provided, examiners may give candidates the benefit of the doubt and mark the crossed out response where legible. Rubric Error Responses – Optional Questions Where candidates have a choice of questions across a whole paper or a whole section and have provided more answers than required, then all responses are marked and the highest mark allowable within the rubric is given. Enter a mark for each question answered into RM assessor, which will select the highest mark from those awarded. (The underlying assumption is that the candidate has penalised themselves by attempting more questions than necessary in the time allowed.) Multiple Choice Question Responses When a multiple choice question has only a single, correct response and a candidate provides two responses (even if one of these responses is correct), then no mark should be awarded (as it is not possible to determine which was the first response selected by the candidate). When a question requires candidates to select more than one option/multiple options, then local marking arrangements need to ensure consistency of approach. Contradictory Responses When a candidate provides contradictory responses, then no mark should be awarded, even if one of the answers is correct. Short Answer Questions (requiring only a list by way of a response, usually worth only one mark per response) Where candidates are required to provide a set number of short answer responses then only the set number of responses should be marked. The response space should be marked from left to right on each line and then line by line until the required number of responses have been considered. The remaining responses should not then be marked. Examiners will have to apply judgment as to whether a ‘second response’ on a line is a development of the ‘first response’, rather than a separate, discrete response. (The underlying assumption is that the candidate is attempting to hedge their bets and therefore getting undue benefit rather than engaging with the question and giving the most relevant/correct responses.) Short Answer Questions (requiring a more developed response, worth two or more marks) If the candidates are required to provide a description of, say, three items or factors and four items or factors are provided, then mark on a similar basis – that is downwards (as it is unlikely in this situation that a candidate will provide more than one response in each section of the response space.) Longer Answer Questions (requiring a developed response) Where candidates have provided two (or more) responses to a medium or high tariff question which only required a single (developed) response and not crossed out the first response, then only the first response should be marked. Examiners will need to apply professional judgment as to whether the second (or a subsequent) response is a ‘new start’ or simply a poorly expressed continuation of the first response.

6. Always check the pages (and additional objects if present) at the end of the response in case any answers have been continued there. If the candidate has continued an answer there then add a tick to confirm that the work has been seen.
7. There is a NR (No Response) option. Award NR (No Response)
   • if there is nothing written at all in the answer space
   • OR if there is a comment which does not in any way relate to the question (e.g. ‘can’t do’, ‘don’t know’) - OR if there is a mark (e.g. a dash, a question mark) which isn’t an attempt at the question. Note: Award 0 marks – for an attempt that earns no credit (including copying out the question).
8. The scoris comments box is used by your Team Leader to explain the marking of the practice responses. Please refer to these comments when checking your practice responses. Do not use the comments box for any other reason. If you have any questions or comments for your Team Leader, use the phone, the scoris messaging system, or email.
9. Assistant Examiners will send a brief report on the performance of candidates to their Team Leader (Supervisor) via email by the end of the marking period. The report should contain notes on particular strengths displayed as well as common errors or weaknesses. Constructive criticism of the question paper/mark scheme is also appreciated.
10. For answers marked by levels of response: Read through the whole answer from start to finish, concentrating on features that make it a stronger or weaker answer using the indicative scientific content as guidance. The indicative scientific content indicates the expected parameters for candidates’ answers, but be prepared to recognise and credit unexpected approaches where they show relevance. Using a ‘best-fit’ approach based on the science content of the answer, first decide which set of level descriptors, Level 1, Level 2 or Level 3, best describes the overall quality of the answer using the guidelines described in the level descriptors in the mark scheme. Once the level is located, award the higher or lower mark. The higher mark should be awarded where the level descriptor has been evidenced and all aspects of the communication statement (in italics) have been met.

The lower mark should be awarded where the level descriptor has been evidenced but aspects of the communication statement (in italics) are missing. In summary:

• The science content determines the level.
• The communication statement determines the mark within a level. Level of response questions on this paper are 1(cii) and 5(a).

Mark Scheme H422/03 Practice Paper – Set 2

11. Annotations Annotation Meaning DO NOT ALLOW Answers which are not worthy of credit IGNORE Statements which are irrelevant ALLOW Answers that can be accepted ( ) Words which are not essential to gain credit __ Underlined words must be present in answer to score a mark ECF Error carried forward AW Alternative wording ORA Or reverse argument

12. Subject-specific Marking Instructions INTRODUCTION Your first task as an Examiner is to become thoroughly familiar with the material on which the examination depends. This material includes:
    • the specification, especially the assessment objectives • the question paper
    • the mark scheme. You should ensure that you have copies of these materials. You should ensure also that you are familiar with the administrative procedures related to the marking process. These are set out in the OCR booklet Instructions for Examiners. If you are examining for the first time, please read carefully Appendix 5 Introduction to Script Marking: Notes for New Examiners. Please ask for help or guidance whenever you need it. Your first point of contact is your Team Leader. Question Answer Marks Guidance 1 (a) (i) Any two from: graduated (teat) pipette  volumetric pipette  1 cm^3 / 2 cm^3 , syringe  max 1 DO NOT ALLOW unspecified size of syringe or one of greater volume DO NOT ALLOW 10 cm^3 (or smaller) measuring cylinder

(ii) (chymosin is a) mammalian enzyme  (so) active / works best , at 37oC  37 oC / optimum temperature , is in the middle (of the range chosen)  max 2 IGNORE ruminant (b) Suggestion: pH should be , controlled / the same  Reason: ensures pH is constant therefore does not , affect enzyme activity / alter enzyme structure  Suggestion: same concentration of , enzyme / chymosin  Reason: increase in enzyme concentration will , speed up the reaction / clotting process  Suggestion: same type of milk used  Reason: different types of milk may have different concentration of , protein / substrate  Suggestion: same concentration of , milk / substrate , used  Reason: increase in concentration will , speed up the reaction / clotting 4 Correct reason MUST be linked to the suggestion ALLOW chymosin works at low pH found in stomach ALLOW ORA Question Answer Marks Guidance process  ALLOW ORA

(c) (i) idea that the reaction could still continue if not enough inhibitor is used  idea that too much inhibitor could affect the quality of the final product  idea of increased cost to commercial cheese producers if more inhibitor is used than needed to stop the reaction  2 max (ii)* Summary of instructions to markers: Read through the whole answer. (Be prepared to recognise and credit unexpected approaches where they show relevance.) Using a ‘best-fit’ approach based on the science content of the answer, first decide which of the level descriptors, Level 1 , Level 2 or Level 3 , best describes the overall quality of the answer. Then, award the higher or lower mark within the level, according to the Communication Statement (shown in italics): o award the higher mark where the Communication Statement has been met. o award the lower mark where aspects of the Communication Statement have been missed.

**_- The science content determines the level.

• The Communication Statement determines the mark within a level._** Level 3 (5-6 marks) Comprehensive details of the apparatus and method used to produce reliable data. Most variables are identified and the method states how these are controlled. There is a well-developed line of reasoning which is clear and logically structured and uses scientific terminology at an appropriate level. All the information presented is relevant and forms a continuous narrative. Level 2 (3-4 marks) The apparatus and a method to provide reliable results are given although some details may be missing. Some variables are identified and the method references how variables are controlled. There is a line of reasoning presented with some structure and use of appropriate scientific language.The information presented 6 Indicative scientific points could include: Apparatus & method - test tubes - apparatus for volume measurement (e.g. pipettes, syringes, small (<50 cm^3 ) measuring cylinders) - distilled water - details of quantitative preparation of dilution series of inhibitor to include volumes and final concentration - water bath - stop clock / timer - method of determining end point Variables - independent variable = concentration of inhibitor - dependent variable = time until solution is

Question Answer Marks Guidance is mostly relevant. Level 1 (1–2 marks) The apparatus and an outline method are suggested but information may be missing to provide reliable results. There is limited reference to variables and how they are controlled. The information is communicated with only a little structure. Communication is hampered by the inappropriate use of technical terms. 0 marks No response or no response worthy of credit. transparent

• correct units included (mol dm-3, s)
• control variables e.g. temperature, volumes Repeatability
• repeats for dilutions of inhibitor
• reference to quantitative processing of data e.g. calculation of means Risk Assessment
• potential chemical hazards & control (enzyme / chymosin)
• potential electrical hazards & control (water bath) Communication statement guidance The method can be written as bullet or numbered points and should follow a logical sequence. For some, this will be a method with different sections e.g. apparatus, method, variables while for others it will be more similar to the method given in the question. Both are acceptable. To form a continuous narrative, all sentences or bullet/numbered points should make sense and it should be possible to read from beginning to end without having to refer to footnotes or omissions. (d) (i) non-competitive (inhibition) AND (inhibitor) binds / attaches , at , another / allosteric / 2nd, site OR changes shape of the enzyme / allosteric effect OR (causes) distortion to shape of active site 

(ii) curve / line , starts at the same point 1 ALLOW ECF from 1(d)(i) if identified as competitive inhibitor Question Answer Marks Guidance AND is the same shape as sketch graph AND curve / line , levels out / plateaus , at a lower rate of reaction than sketch graph  Total 17

Question Answer Marks Guidance 2 (a) (i) meiosis  1 DO NOT ALLOW mitosis ALLOW meiosis 1 (ii) anaphase 1  1 ALLOW telophase 1 ALLOW anaphase OR telophase if 2(a)(i) states meiosis 1 (b) X follicle cells / follicular tissue / corona radiata  Y cytoplasm / yolk  Z zona pellucida / layer of, glycoproteins / gel  3 DO NOT ALLOW ‘follicle’ (c) on photomicrograph where no sperm are present: germ layer absent  no cells close to basement membrane  lumen largely empty/proliferation of Leydig cells (purple stained cells between seminiferous tubules)  max 2 ORA throughout (d) to stain different tissues/cell types different colours  allows viewer to differentiate between, tissues/cell types  max 1 ALLOW means untrained viewer can tell cells/tissues apart OWTTE

(e) (i) x-axis labelled ‘days from start of treatment’ AND scale occupies more than 50% of paper AND scale with equidistant points AND zero/0 correctly shown  y-axis labelled ‘mean sperm count (million per cm^3 )’ AND scale occupies more than 50% of paper AND scale with equidistant points  (^4) Days from start of treatment Mean sperm count (million per cm^3 ) 0 25 30 35 60 44 90 60 120 69 Question Answer Marks Guidance all points correctly and clearly plotted  straight line of best fit (l.o.b.f.)  (ii) decrease in variability over time 1 ALLOW variability among patients decreases (with time) (iii) 3.7 x 10^5 cm-3^ day-1^  2 Correct answer with correct sig fig but wrong unit = 1 mark Correct answer with wrong sig fig but right unit = 1 mark ACCEPT answer in range 3.5 to 3.8 x 10^5 ALLOW million per cm^3 per day ALLOW correct answer not in standard form Total 15 Question Answer Marks Guidance 3 (a) (i) light dependent (reactions)  1 ALLOW Hill reaction

(ii) (it acts as an) electron acceptor  1 ALLOW reduced (iii) maintains (chemical) activity of chloroplasts  1 ALLOW references to maintaining pH in context of (chemical) activity of chloroplasts (b) (i) red  1 (ii) 3 consecutive readings of same value (in test tube E)  1 ALLOW the reaction had stopped in (test tube) E (iii) chloroplasts physically damaged during preparation of leaf extract  photosystems / chlorophyll present in supernatant  other reducing agents / AW present in supernatant  max 2 DO NOT ALLOW any suggestion of chemical damage Total 7

Question Answer Marks Guidance 4 (a) Stage 2 DNA is being denatured / 2 strands separate (by H-bonds breaking)  Stage 3 primers, anneal / bind, to complementary strands (of DNA) 

ALLOW DNA is being annealed (b) (i) (Taq DNA polymerase / it) catalyses the addition of nucleotides (to the primers) to form DNA strands / polynucleotides  1 ALLOW extends the DNA from the primers (allowing for the formation of cDNA strands) ALLOW makes double stranded DNA from single stranded DNA template (ii) (Taq DNA polymerase / it is) not (thermally) denatured  by the high temperatures needed to separate the DNA strands / at 90°C 

IGNORE optimum at ~70°C (c) (i) 1 x 10^9 (a.u)  1 DO NOT ALLOW 1000 000 000 ALLOW answers in range 5x10^8 to 2.5x10^9 (ii) log(arithmic)  1 Total 7

Question Answer Marks Guidance 5 (a) Summary of instructions to markers: Read through the whole answer. (Be prepared to recognise and credit unexpected approaches where they show relevance.) Using a ‘best-fit’ approach based on the science content of the answer, first decide which of the level descriptors, Level 1 , Level 2 or Level 3 , best describes the overall quality of the answer. Then, award the higher or lower mark within the level, according to the Communication Statement (shown in italics): o award the higher mark where the Communication Statement has been met. o award the lower mark where aspects of the Communication Statement have been missed.

**_- The science content determines the level.

• The Communication Statement determines the mark within a level._**

Level 3 (5-6 marks) There is a comprehensive consideration of regions of the graph which are accurately explained in relation to stomatal aperture size. The adaptive significance of the conductance pattern is discussed in relation to transpiration and photosynthesis. There is a well-developed line of reasoning which is clear and logically structured and uses scientific terminology at an appropriate level. All the information presented is relevant and forms a continuous narrative. Level 2 (3-4 marks) There is some consideration of regions of the graph which are correctly linked to stomatal aperture size. A discussion of the adaptive significance of the conductance pattern is attempted and may consider transpiration or photosynthesis. There is a line of reasoning presented with some structure and use of appropriate scientific language. The information presented is mostly relevant. Level 1 (1–2 marks) Stomata are identified as the structures which will alter conductance values. An attempt is made to link stomatal opening with the correct times of day. There is little consideration of the adaptive significance of the patterns of conductance. 6 Indicative scientific points may include Changes in the leaf

• stomatal aperture open/wider when conductance is high
• stomatal aperture narrower when conductance is low DO NOT ALLOW stomata are closed as no conductance / value is zero
• stomata are wider during the morning
• stomata narrow from 09:
• stomata narrowest from 16:00 to 19:
• gap between guard cells forms stoma(ta) Adaptive significance
• stomata open to allow gaseous exchange
• gaseous exchange permits aerobic respiration and photosynthesis
• wider stomata increase transpiration
• stomatal aperture reduced during hottest parts of the day ensuring water loss is minimised
• stomatal aperture increased at night when it is cooler but there is no light for photosynthesis
• stomata open when evaporation is slower Technical terms Question Answer Marks Guidance The information is communicated with only a little structure. Communication is hampered by the inappropriate use of technical terms. 0 marks No response or no response worthy of credit.
• stomata
• xerophyte
• transpiration
• photosynthesis
• guard cells

(b) Advantages (up to a maximum of 2 marks) Line transect enables Spearman’s rank to be used to measure correlation  unbiased as only those plants touching the line are sampled  straightforward – no estimation of (number or area of) sub-regions  easily repeatable  Stratified sampling more representative of sub-regions  Disadvantages (up to a maximum of 2 marks) Line transect only plants touching the line should be sampled which may lead to ‘gaps’ in the data  strategy for choosing a plant nearest to the sampling point may lead to bias  Stratified sampling requires (accurate) estimation of area of sub-regions  time consuming  distance from road must be measured at each sampling point  (time consuming because) target species may be absent in randomly selected area  4 DO NOT ALLOW double marks for statements reversed for the other method ALLOW ORA for any point as long as no double marks e.g. a disadvantage of stratified sampling is that it is less easily repeatable DO NOT ALLOW any suggestion that repeats are done on the same transect Question Answer Marks Guidance

5 (c) (i) 0.7  2 ALLOW 0. If answer is incorrect or missing: ALLOW 1 mark for 0.3 OR 0.25 (not subtracting the calculated figure from 1) Species n n/N (n/N)^2 A 2 0.13 0. B 6 0.40 0. C 2 0.13 0. D 2 0.13 0. E 3 0.20 0. ∑( n/N)^2 = 0. 1 - 0.2507 = 0. 5 (c) (ii) (higher biodiversity) in the Succulent Karoo shows greater species evenness / less dominated by a few species / greater stability  (higher biodiversity) in the Succulent Karoo shows greater species richness / greater number of different species 

ALLOW ORA throughout Total 14