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2010 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 2010 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 2010 Higher School Certificate examination, the marking guidelines and other support documents which have been 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 a guide to the length of the required response. A longer response will not in itself lead to higher marks. Writing in excess of 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 may be used which are not included in the glossary, such as ‘design’, ‘translate’ or ‘list’.

Teachers and candidates are reminded that 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.

In Section II, the Option question is divided into a number of parts. Candidates should clearly label each part of the question when writing in their answer booklets. Candidates are required to attempt only one question in Section II, and they are strongly advised to answer the option they have studied in class.

Section I – Core

Part B

Specific comments

Question 21

In better responses, candidates demonstrated a good understanding of Mendelian genetics, identified genotypes and phenotypes and correctly completed the punnet square.

Question 22

  1. In better responses, candidates demonstrated good graphing skills, identified dependent and independent variables, plotted points correctly and drew lines or curves of best fit. In weaker responses, candidates plotted data on the incorrect axis or used a column graph.
  2. The better responses identified the relevant human processes linked to the data and related this to the effect of a decrease in biodiversity. In weaker responses, candidates had difficulty relating the data and effect of the human process on biodiversity.

Question 23

  1. In better responses, candidates identified correct examples of hybridisation and described the desired characteristics of the hybrid. Weaker responses only provided an example or just defined the term hybridisation or confused hybridisation with examples of transgenic species.
  2. Better responses used a correctly identified transgenic species to address both the social and environmental impacts of the technology. In weaker responses, candidates did not relate the impacts to their example or did not correctly identify a transgenic species.

Question 24

In better responses, candidates identified and distinguished between independent variable, experimental control and controlled variables, and provided appropriate reasons for their chosen controlled variables. Weaker responses did not demonstrate an understanding of scientific method and/or did not provide justifications for their controlled variables.

Question 25

  1. In better responses, candidates provided a detailed diagram of xylem tissue with correctly labelled features. Weaker responses contained diagrams that lacked detail, had incorrectly or unlabelled features or included a diagram of phloem tissue.

Question 26

  1. In better responses, candidates demonstrated an understanding of the correlations and limitations of the data and made appropriate judgements related to lung cancer and increased cigarette price.

Question 27

  1. Better responses addressed the effectiveness of the quarantine regulations given.

Question 28

  1. Better responses identified label ‘Y’ as an antigen.
  2. Better responses made a judgement about the effectiveness of the model related to organ rejection. Weaker responses provided discussions on the effectiveness of the model only, without reference to organ rejection.
  3. In better responses, candidates related the role of the T lymphocyte to organ rejection. In weaker responses, candidates identified T lymphocytes but did not relate their role to organ rejection.

Question 29

  1. In better responses, candidates correctly commented on both the relevance and reliability of each article and provided judgements in each case. In weaker responses, candidates did not provide judgements, or used incorrect features to establish relevance and reliability.

Question 30

Better responses discussed more than one theory of evolution, applied the information presented in the table and related the discussion to the validation of theories. Mid-range responses discussed relevant biological practices, provided evidence for evolution and described the theory of natural selection. Weaker responses limited their discussion to natural selection, did not validate their argument and/or simply restated the data from the table.

Section II – Options

Question 31 – Communication

  1. In better responses, candidates showed a clear understanding of how to arrange information logically and correctly in a table regarding structures to detect vibrations.
  2. In better responses, candidates included two diagrams, and labelled high-pitched note and low-pitched note which clearly showed the differences in structure and location of the vocal folds in each situation.
    1. In better responses, candidates identified line Y as cone cells.
    2. In better responses, candidates identified a difference in the structure of cones and related this to differences in their location in the retina.
    3. In better responses, candidates sketched in general terms the role of rhodopsin in detecting light and producing an electrochemical impulse.
    1. In better responses, candidates provided two possible causes and described how these would result in a lack of action potential. Weaker responses only identified causes, or restated the question indicating that there would be a lack of action potential.
    2. In better responses, candidates identified that region X was associated with vision and outlined how the mammal’s behaviour would change as a result of blindness. In weaker responses, candidates did not identify that the animal would be blind or did not outline an appropriate change in behaviour.
  3. In better responses, candidates demonstrated a thorough knowledge of both the ear and the eye and linked their understanding to the technologies outlined in the stimulus material. They also provided a well-supported judgement as to how an understanding of the eye and the ear has led to the development of technologies such as those outlined. Weaker responses simply restated information from the stimulus material.

Question 32 – Biotechnology

  1. In better responses, candidates constructed a suitable table and identified an appropriate industrial fermentation process, eg fermentation of beer. They were able to link the process with the correct microorganism and product of the process.
  2. In better responses, candidates drew a well-constructed flowchart identifying all the steps in the formation of recombinant DNA. Some candidates confused the formation of recombinant DNA with DNA replication or protein synthesis.
    1. In better responses, candidates outlined selective breeding as the form of biotechnology used by the farmer.
    2. In better responses, candidates assessed the effectiveness of the selective breeding process. They used the data to show trends in the data as well as giving an indication of changes in ratios or percentages over the three generations.
    1. In better responses, candidates described the role of mRNA in protein or polypeptide synthesis. They linked this to the effect RNA interference has on protein synthesis. Many candidates also included a detailed description of protein synthesis. It was possible to have a positive or negative outcome for the process.
    2. In better responses, candidates linked both the role of DNA and RNA to a specific application of biotechnology.
  3. In better responses, candidates described a range of ethical and social issues linked to a detailed description of new biotechnologies. These issues were then well supported by relevant judgements.

Question 33 – Genetics: the code broken?

  1. In better responses, candidates correctly identified the effect of the mutations on chromosome number and tabulated this information with appropriate headings.
  2. Better responses showed a diploid cell with two pairs of homologous chromosomes. The drawings showed similarities and differences between the chromosomes appropriate to the cell drawn. In such responses, candidates indicated that only one of each homologous pair of chromosomes was donated to the haploid cell, thus correctly reducing the diploid number from four in the diploid cell to two in the haploid cell.
    1. In better responses, candidates provided a prediction for each gene, ie limb and vision defects.
    2. In better responses, candidates gave genotypes for both parents 9 and 10 for vision and limb defects and then provided working and phenotypic ratios for the offspring of these two parents if the genes were on the same chromosome. They provided correct phenotypes for offspring from the linked cross and then subsequently repeated the process for the scenario where the genes were not linked.
    1. Mid-range responses detailed crossing over, recombination and positioning of linked genes on the chromosome but did not identify ‘cross breeding’ as the means of collecting the relevant data. Weaker responses identified the collection and analysis of data in a general way.
    2. In better responses, candidates correctly described three reasons why studying linkage maps alone cannot be used for determining a genome.
  3. In the better responses, candidates clearly distinguished between gene and whole organism cloning. Many responses failed to give supported judgements about how this understanding affected the development of these technologies. Weaker responses demonstrated a basic understanding of gene cloning, gene cascades and some associated technologies.

Question 34 – The human story

  1. In better responses, candidates organised their answers into a table and identified the characteristics that classify humans as mammals, and identified the characteristics that classify humans as chordates and animals.
  2. In better responses, candidates correctly labelled corresponding features on their drawings to highlight the differences including the opposability of the big toe, the length of the digits and/or the arch in the foot.
    1. In better responses, candidates correctly identified both the pattern of maternal inheritance of mtDNA and the ancestral inheritance of nuclear DNA.
    2. In better responses, candidates provided a judgement about the extensive use of mtDNA in developing ideas about evolutionary pathways. These were supported by descriptions of mtDNA with respect to a greater quantity in samples, increased mutation rate and no recombination. They compared this with nuclear DNA where recombinations and crossing-over occurs, small sample sizes and unpredictable mutation rates making the direct tracing of an evolutionary pathway more difficult.
    1. In better responses, candidates identified that the collection of the data was reliable because of the use of reputable scientific journals, averaging of a significant number of skulls and using only adult skulls to make the measurements. They also justified the presentation of the data indicating that it allowed a clear visual representation so that a relationship could be made between the average size of the skull and the age of the fossil.
    2. In better responses, candidates identified point ‘A’ to be either Australopithecus afarensis or A. africanus found in Africa OR at point ‘B’, Homo erectus found in Africa and/or Asia.
  3. In better responses, candidates correctly identified examples of cultural development including the use of tools and technology, communication methods, use of modern medicine and genetic engineering, and compared similarities and differences between primates and humans in a table. These comparisons were then linked to possible impacts on future evolution. They made reference to the impact on human evolution of reducing natural selective pressures including food availability, protection from temperature extremes and diseases as well as identifying the potential impact of reducing the diversity of the gene pool and the failure to eliminate deleterious genes.

Question 35 – Biochemistry

  1. In better responses, candidates provided a table identifying the contributions of Hales, Priestley and Ingen Housz.
  2. In better responses, candidates correctly named an isotope used in plant research, and used a flow chart to map its use to identify biochemical pathways.
    1. In better responses, candidates identified the x axis as wavelength and y axis as percentage absorption.
    2. Better responses described how chromatography is used to separate plant pigments and how these can be purified. Then, by using other named technologies, they described other features of the plant pigments such as absorption spectrum. The use of isotopes to tag the pigments for further investigation was also identified.
  3. In better responses, candidates identified that ‘Observation 1772’ did not recognise that there was a light dependent and a light independent phase of photosynthesis, but identified the reactants and products of photosynthesis. ‘Observation 1905’ led to identification that a photosynthetic phase was light dependent and a phase that was CO2 dependent and light independent. ‘Observation 1939’ provided evidence that oxygen was produced in a phase that was not dependent on CO2.
  4. In better responses, candidates communicated a thorough understanding of photosynthetic process and correctly linked the use of carbon dioxide in photosynthesis to the problems posed by climate change. These responses identified technologies such as genetic engineering, and the development of enzyme systems similar to those in plants for photosynthesis, as a means of reducing climate change caused by increased CO2 emissions.

20110266

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