Guide To Success In Biology HSC

Improving answers to extended response questions in HSC Biology

This part of the Exam Café enables you to practise your exam technique by improving answers to extended questions in Biology. Highly scaffolded questions Highly scaffolded questions provide much more direction to candidates than open-ended questions. Students know what is required to gain one or two marks in a question that has a few parts.

For example:

Question 1 (6 marks)

(a) Name ONE example of a disease caused by a macro-parasite. [1]

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(b) List TWO features of viruses that distinguish them from protozoans. [2]

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(c) For a named disease you have studied, outline the life cycle of the causative pathogen. [3]

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What are the marking criteria for these questions?

In (a) students should name one example of a disease caused by a macroscopic parasite. Easy!

In (b) students list two features of viruses that make them different from protozoans.

In (c) students are required to:

Outline the life cycle of the causative pathogen. The best way to do this would be in the form of a labelled diagram.

Copyright © Pearson Australia 2010 Heinemann Biology Third Edition HSC (a division of Pearson Australia Group Pty Ltd) ISBN 978 1 4425 2819 2 Page 1 of 8 Now, attempt to answer the question in the spaces provided above. Specimen answer: 1 (a) Taeniasis or tapeworm disease.

(b) Viruses are non-living particles consisting of DNA or RNA wrapped in a protein coat whereas protozoans are eukaryotic cells. Viruses are very small (10–300 nm) whereas protozoans are 1 to 300 µm.

Question 18 (4 marks)

(a) Name a blood product extracted from donated blood and outline how it could be used to restore normal body function. [2]

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(b) Propose TWO reasons why research is needed to develop alternatives to donated blood. [2]

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Copyright © Pearson Australia 2010 Heinemann Biology Third Edition HSC (a division of Pearson Australia Group Pty Ltd) ISBN 978 1 4425 2819 2 Page 2 of 8 ______Marking criteria: (a) Name a blood product. [1]

Outline the use of the named product. [1]

(b) List two reasons why research is needed to develop alternatives to donated blood [2]

Specimen Answer: (a) blood plasma

Blood plasma is used to treat burn victims. As the skin loses its ability to contain body fluids, plasma moves from the circulation into surrounding tissues. Blood pressure drops. Plasma is given to replace blood volume and maintain blood pressure.

(b) Research to develop alternatives to donated blood is needed because:

Artificial blood does not have antigens, so won’t induce an immune response. Cross matching of blood types would not be required. This would make the process of blood donation much easier, as there would be one product for all.

Some religions like Jehovah’s witnesses will not accept donated blood, so if an alternative was available, it would mean they can have transfusions and survive operations where they would otherwise die without a transfusion.

Questions that have very little scaffolding pose greater problems for candidates because students have difficulty in knowing what the question is asking. Students also have difficulty in structuring the answer to maximise marks. Questions worth 6–8 marks require planning and in all of the examiners’ reports from 2001–2009, candidates who showed evidence of planning performed better than students who did not plan their answers.

Planning is where you create the scaffolding. Try to break down the question into parts, just like highly scaffolded questions would. Underlining the key words can help to do this. Your responses need to be focussed and succinct and, answer the question. You receive marks for logic and coherency in these questions so your responses need to be measured and have relevant examples where appropriate.

For example:

Evaluate the contributions made by both Louis Pasteur and Robert Koch to our present understanding of the causes and possible prevention of infectious diseases. [8]

Break down this question into smaller questions and allocate marks:

For example:

1. Describe Louis Pasteur’s contribution to our

(ii) prevention of disease. [2]

2. Give an example of Pasteur’s work. [1]

3. Describe Robert Koch’s contribution to our

(i) understanding of cause and

(ii) prevention of disease. [2]

4. Give an example of Koch’s work. [1]

5. Write a value statement about the contribution of both men to our understanding of disease. [2]

Organised dot points in a logical coherent order are just as good as a detailed written response. Try to avoid a stream of consciousness or a long-winded answer, where the examiner has to try to “find marks”.

Now, answer the question.

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______Specimen answer: Louis Pasteur disproved the theory of spontaneous generation, which was widely held at the time. Before Pasteur's work, people believed that maggots and fungi grew naturally from non-

Copyright © Pearson Australia 2010 Heinemann Biology Third Edition HSC (a division of Pearson Australia Group Pty Ltd) ISBN 978 1 4425 2819 2 Page 4 of 8 living material. He showed this with his famous “swan-necked flask” experiment. He showed that micro-organisms came from pre-existing micro-organisms. The germ theory became firmly established with Pasteur’s work with anthrax. Pasteur contributed to the prevention of disease by developing vaccines. In 1882, he successfully developed a vaccine for anthrax in sheep. Another major contribution was the treatment of foods with heat to kill pathogens (a process now called pasteurisation).

The work of Robert Koch provided the proof that microscopic pathogens cause disease. His first experiments were with the disease anthrax in sheep.

First Koch found bacteria in sheep infected with anthrax. Then, he placed the bacteria on agar plates in Petri dishes so that many colonies of the bacteria were produced. He used bacteria from these colonies to infect healthy sheep and found that they became infected.

After his experiments with anthrax, Koch was able to state a series of steps that are needed to identify the micro-organism responsible for a particular disease. These steps are called Koch's postulates.

• Step 1: All infected hosts must contain the suspect organism.

• Step 2: A pure culture of the suspect organism must be obtained.

• Step 3: A healthy organism infected with the pure culture must have the same symptoms as the original host.

• Step 4: The suspect organism must be isolated from the second host, grown in pure culture and prove to be identical to the first culture.

Koch's postulates can be used to identify the causative organism of an infectious disease. Koch found the causative agents for diphtheria, typhoid, tetanus, cholera and tuberculosis. One of his major contributions for prevention of disease was a paper on the epidemics of water-borne diseases and how they can largely be prevented by filtering drinking water.

Koch and Pasteur contributed significantly to our understanding of the cause and prevention of disease. Their work has resulted in improved health and well-being of generations of animals and humans as well as decreased death rates from infectious diseases.

Answer adapted from: http://www.hsc.csu.edu.au/biology/core/better_health/9_4_3/943net.html#net2

Instead of writing questions, it is just as effective to write a plan for an answer. Think about the scaffold questions that could be asked to help you to write your plan. Also think about the allocated marks and structure your answer accordingly.

In 1962 James Watson, Francis Crick and Maurice Wilkins were awarded the Nobel Prize in medicine for identifying the structure of DNA. Using examples, evaluate the impact of this discovery on current genetic technology. [8]

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Suggested plan:

1. Outline the structure of DNA. [1]

2. Draw a diagram of the DNA molecule. [2]

3. Describe one example of gene technology – DNA fingerprinting. [2]

4. Describe another example of gene technology – gene cloning, insulin production [2]

5. Write a value statement about the impact on society of the discovery of the structure of DNA. [1]

Marking criteria:

1. Identify the structure of DNA. [2]

2. Describe two examples of gene technology [4 (2 each)]

4. Write a value statement about the impact of the discovery of the structure of DNA. [1]

Answer______

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______Specimen answer: Deoxyribonucleic acid is a molecule consisting of 4 bases, a sugar (deoxyribose) and a phosphate. A diagram of DNA is drawn below.

The discovery of the structure of the molecule has meant humans can begin to understand the sequence of DNA and the proteins for which it codes. This knowledge allows us to manipulate segments of DNA for specific purposes, like gene cloning and DNA fingerprinting.

Gene cloning involves genetic engineers identifying and splicing certain segments of DNA with enzymes. These segments are called genes and code for specific proteins. The scientists then insert the gene into a plasmid in a bacterial cell. The bacteria reproduce and reproduce the inserted gene also. The gene functions in the bacterial cell to produce the desired protein, such as insulin.

The DNA in some chromosomes consists of varying lengths of base sequences that are repeated. These hypervariable regions are useful in producing a unique profile of a person from a source containing body cells, for example from blood or semen. There are two types of variable DNA used in forensics: VNTRs variable number of tandem repeats) and STRs (short tandem repeats). The repeat might be catcatcatcat, etc.

Copyright © Pearson Australia 2010 Heinemann Biology Third Edition HSC (a division of Pearson Australia Group Pty Ltd) ISBN 978 1 4425 2819 2 Page 7 of 8 Each individual has two numbers of STRs per locus (a specific area on the chromosome), as there are two homologous chromosomes. The DNA “fingerprints” of individuals are unique. By using four locus probes the chance of misidentification is more than six million to one. Use in forensics involves matching profiles from cells found at the crime scene with the profiles from the cells of suspects.

By understanding the structure of DNA, therefore, scientists can help sufferers of diseases such as diabetes in obtaining a source of insulin. They can also help police to catch criminals and release innocent suspects from crimes through the use of DNA fingerprinting.