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2012 HSC Notes from the Marking Centre – Biology

Contents

Introduction

This document has been produced for the teachers and candidates of the Stage 6 course in Biology. It contains comments on candidate responses to the 2012 Higher School Certificate examination, indicating the quality of the responses and highlighting their relative strengths and weaknesses.

This document should be read along with the relevant syllabus, the 2012 Higher School Certificate examination, the marking guidelines and other support documents developed by the Board of Studies to assist in the teaching and learning of Biology.

General comments

Teachers and candidates should be aware that examiners may ask questions that address the syllabus outcomes in a manner that requires candidates to respond by integrating their knowledge, understanding and skills developed through studying the course and including the prescribed focus areas. It is important to understand that the Preliminary course is assumed knowledge for the HSC course.

Candidates need to be aware that the marks allocated to the question and the answer space (where this is provided on the examination paper) are guides to the length of the required response. A longer response will not in itself lead to higher marks. Writing far beyond the space allocated may reduce the time available for answering other questions.

Candidates need to be familiar with the Board’s Glossary of Key Words, which contains some terms commonly used in examination questions. However, candidates should also be aware that not all questions will start with or contain one of the key words from the glossary. Questions such as ‘how?’, ‘why?’ or ‘to what extent?’ may be asked, or verbs that are not included in the glossary may be used, such as ‘design’, ‘translate’ or ‘list’.

Teachers and candidates are reminded that the mandatory skills content in Module 9.1 is examinable in both the core and option questions and that all objectives and outcomes, including the Prescribed Focus Areas, are integral to the Stage 6 Biology Course.

Candidates are required to attempt only one question in Section II and are strongly advised to answer the option they have studied in class.

Section I – Core

Part B

Question 21

  1. In better responses, candidates described the use of a microscope and minigrid to determine the field of view diameter. Cell size was then calculated by counting the number of cells observed across the field of view.

    In weaker responses, candidates did not correctly identify the equipment required to complete the investigation or failed to explain how they calculated the size of individual cells.
  2. In better responses, candidates drew clearly scaled diagrams with appropriate detail that distinguished between the two types of cells.

    In weaker responses, diagrams did not clearly distinguish between red and white blood cells or did not include a scale.

Question 22

  1. In the vast majority of responses, candidates constructed a table with headings and units and correctly transferred the identified data.

    In weaker responses, candidates could not correctly identify and transfer the data.
  2. In better responses, candidates correctly labelled the x-axis, provided a linear scale, correctly plotted the tabulated data and drew an appropriated curve of best fit as a single continuous smooth line.

    In the majority of weaker responses, candidates did not provide a correct linear scaled x-axis or correct plotting of the data points.
  3. In the vast majority of responses, candidates were unable to relate the use of a line graph to the continuous data produced in the experiment or indicate that a curve of best fit was required as the data plot was non-linear.

Question 23

  1. Most candidates answered this question well, and correctly identified data that the doctor could collect such as environmental or nutritional causes for the disease.
    1. In better responses, candidates drew clearly identifiable pedigrees using conventional symbols.

      In weaker responses, candidates used non-conventional symbols or omitted individuals or generations.
    2. In better responses, candidates correctly identified the two pieces of evidence that prove the disease was recessive and not sex-linked.

      In weaker responses, candidates often only identified a piece of evidence from the pedigree.

Question 24

  1. Most candidates identified the independent and dependent variables with temperature and enzyme activity being the most common answer. The most common error was confusing the independent with the dependent variable.
  2. In better responses, candidates clearly identified an enzyme that could be used to test the effect of temperature and explained how its activity was measured.

    In weaker responses, candidates only identified an enzyme or matched the enzyme to the incorrect experiment.
  3. In better responses, candidates explained how optimal enzyme activity varied with temperature between a narrow range for endotherms and a larger range for ectotherms. In weaker responses, candidates often only identified a difference between an endotherm and an ectotherm.

Question 25

  1. In better responses, candidates used the stimulus material to link the irradiation to the mutation of the gene responsible for the formation of the enzyme (protein) that controls the production of the amino acid, arginine. This was then correctly linked to the ‘one gene-one protein’ hypothesis.

    In weaker responses, candidates simply stated aspects of the results shown in the stimulus material.
  2. In better responses, candidates provided justification for two acceptable secondary sources. Many responses gave two or more appropriate sources without providing a justification.

Question 26

In better responses, candidates analysed the methodology by identifying strengths and weaknesses in each part of the study and supplied supporting reasons. In weaker responses, candidates only identified strengths and/or weaknesses for some parts of the study.

Question 27

In better responses, candidates identified at least two strategies that could be used to control this outbreak and provided a reason for each strategy.

In weaker responses, candidates provided strategies, or identified one strategy with an accompanying reason to control this disease outbreak.

Question 28

In better responses, the candidates linked DNA changes during replication for reproduction to changes in the gene frequencies of a population and then to evolution.

In weaker responses, candidates failed to link DNA replication and reproduction and simply identified that the favourable variants produced by mutations resulted in evolution. Many candidates wrote a brief statement about evolution and/or natural selection but failed to make any links.

Question 29

  1. In better responses, candidates recognised that crossing over had occurred and drew homologous pairs with different combinations of alleles in diagram 1 and haploid cells with appropriate chromosomes in diagram 2.

    In weaker responses, candidates incorrectly crossed over both A and B alleles.
  2. In better responses, candidates linked variation in gametes to the independent assortment of homologous chromosome pairs.

    Most candidates did not explain how chromosome segregation leads to variation in gametes. In the majority of weaker responses, candidates identified the result of random segregation as increased variation but could not explain how this occurred. In many of these responses, candidates simply re-worded the question, stating that ‘it produces a variety of gametes’.

Question 30

In better responses, candidates correctly identified the methodologies of all three scientists and linked these to the understanding of the nature and prevention of infectious disease.

In many responses, candidates did not refer to the work of MacFarlane Burnet.

Section II – Options

Question 31 – Communication

    1. Most candidates correctly identified parts A, B and C as the ear ossicles.
    2. In most responses, candidates clearly identified the functions of the ear ossicles in transferring amplified sound energy from the middle to inner ear.
    1. In most responses, candidates correctly identified three ocular structures represented in the experimental model.
    2. In better responses, candidates identified the focal length of the lens as quantitative data obtainable from the experimental setup.

      In many weaker responses, candidates had difficulty in distinguishing between quantitative and qualitative data.
    3. In better responses, candidates clearly identified similarities and/or differences between the eye and the model and related these to the process of accommodation.
    1. In better responses, candidates identified appropriate features of the eyes of two named animals and linked these to their environment.

      In weaker responses, candidates referred to one animal only or did not relate the features of the eye to the environment.
    2. In better responses, candidates referred to the source and frequency of vibrations detected by fish and insects as well as the structures and processes responsible for detecting vibrations.

      In weaker responses, candidates did not include source and frequency in their answer.
  1. In better responses, candidates identified biological problems associated with eyesight and hearing, and the appropriate technologies used to correct the problems.

    In weaker responses, candidates had difficulties in linking technologies to the identified problems and in many cases provided two separate lists.

Question 32 – Biotechnology

  1. Most candidates correctly identified two biochemical practices using yeast, the chemical bi-products produced and their purpose.

    In weaker responses, candidates referred to one practice only or did not identify named chemicals produced and/or purposes.
    1. In better responses, candidates correctly identified a transgenic organism, the source of the introduced gene and purpose of the genetic modification.

      In weaker responses, most candidates did not specify the purpose for the transplanted gene.
    2. In better responses, candidates provided a clearly linked flowchart detailing the main sequence of steps involved in recombinant DNA transfer into a transgenic organism.

      In weaker responses, candidates did not provide an appropriate sequential diagram or omitted some of the major steps in the process.
    1. The vast majority of candidates correctly identified aquaculture as manipulating a species to provide a product for humans.
    2. In better responses, candidates provided detailed information on aquaculture and agricultural biotechnologies and clearly specified the similarities and/or differences between the two processes.

      In weaker responses, candidates provided some relevant information on the two processes only.
  2. In better responses, candidates provided detailed descriptions of biotechnologies and related these to cell chemistry.

    In many weaker responses, candidates provided ample information on biotechnologies but failed to demonstrate a clear understanding of cell chemistry.

Question 33 – Genetics: The Code Broken?

  1. Most candidates correctly identified the processes used and specific examples in two types of cloning.

    In many of the weaker responses, candidates did not identify the processes involved in cloning. Others referred to one type of cloning only or did not provide examples.
    1. In the majority of responses, candidates provided a detailed model of DNA but did not identify the 3’ and 5’ ends of each of the strands indicating the direction of synthesis.
    2. In better responses, candidates clearly indicated the main processes involved in the gene expression. Many candidates confused ‘gene expression’ with the ‘regulation’ of gene expression.
    1. In better responses, candidates identified the HGP as an international collaborative responsible for the determination of base sequence and gene location of the human genome.
    2. In better responses, candidates demonstrated a clear understanding of the application of recombinant DNA technologies in determining the gene location.

      Many candidates did not describe appropriate recombinant DNA technologies. They discussed the generation of linkage maps through cross-breeding experiments.
  2. In better responses, candidates provided clear similarities and differences between the effects of both germ line mutations and transposable genetic elements on whole organisms.

    In weaker responses, candidates outlined what a mutation was and identified some similarities between germ line mutations and transposable genetic elements.

Question 34 – The Human Story

    1. In the majority of responses, candidates provided two unique skeletal features of Homo sapiens.
    2. In most responses, candidates correctly related one non-skeletal characteristic to primate evolution.
    1. In better responses, candidates referred to the maternal inheritance of mDNA in their description of the 2008 data.

      In many responses, candidates showed some understanding of the link between an isolated breeding pool and the lack of diversity in mDNA.
    2. In better responses, candidates made specific reference to the relevant 2010 data relating to migration and breeding.

      In weaker responses, candidates did not link the data to migration and breeding.
  1. In most responses, candidates demonstrated knowledge and examples of polymorphism and clinal gradations. In better responses, candidates clearly differentiated and linked these to populations and phenotype survival.
    1. In the majority of responses, candidates linked correct fossil evidence to technology and cultural development in two named hominids.
    2. In better responses, candidates related knowledge of human biological evolution to current technologies and made relevant predictions, with justifications, for future directions.

      In weaker responses, candidates discussed areas of human cultural evolution or did not make relevant links to current technologies.

Question 35 – Biochemistry

    1. In better responses, candidates correctly identified a photosynthetic product and its source.
    2. In better responses, candidates identified two non-renewable resources replaceable by photosynthetic products.
    1. In better responses, candidates provided a detailed diagram of the experimental set-up.
    2. In better responses, candidates related a measured gas volume to light intensity.
    3. In better responses, candidates described varying the level of carbon dioxide with a constant level of light intensity.
    1. In better responses, candidates identified the biological function of ATP as providing energy for biochemical reactions stored in the three phosphodiester bonds.
    2. In better responses, candidates provided detailed knowledge and understanding of the production of energy stores during photolysis.
  1. In better responses, candidates correctly related the use of identified radioactive isotopes used by named scientists in the development of biochemical pathways.
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