SCIENCE
U1
THE NATURE OF SCIENCE
prepared for the course team by
Vili maka Foliaki
Unit 1 concept map This map represents the core concepts that we’ll be covering in this unit, and the relationships between them.
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Study organiser Before you begin this unit, please check through your study organiser. It shows the subtopics that we’ll be covering, the skills you need to acquire (the objectives) and the activities you’ll do to help you acquire these skills.
Subtopic
Objectives
Activities and readings
My own perceptions of science
1. Critically examine my own and my pupils’ beliefs about science.
○ Activities 1.1 and 1.2 ○ Readings 1.1 and 1.2
2. Explain how my own beliefs about science influence how I teach it. 3. Explain how my pupils’ beliefs about science influence their learning of scientific ideas. Key characteristics of science
1. Become aware that problem solving in science can involve many different behaviours that do not follow a fixed pattern.
○ Activities 1.2, 1.3, 1.4 and 1.5 ○ Readings 1.1 and 1.2
2. Develop a critical approach to descriptions of the scientific method.
Discovery of the DNA double helix: applying the nature of science to ‘real life’ science
1. Develop a variety of hands-on, minds-on activities that can help your pupils understand the nature of science.
Unit 1: The Nature of Science
○ Activities 1.3, 1.4 and 1.6 ○ Reading 1.1
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Introduction What is science? What do scientists do? What comes to mind when you hear the words science and scientist? Think about these questions for a while … Perhaps you are thinking of: a weird-looking man with glasses, a white coat, a bald head and a beard, working with glassware and chemicals? NASA, or test tubes, or doctors in an operation theatre? certain words such as laboratory, experiment, explosion, reproduction and force? These are just a few examples of a variety of mental images of science that people hold. Mental images of science reflect the different assumptions or beliefs that people have about science. For various reasons, many people think of science and scientific knowledge as dogma. That is, they perceive science as superior to other disciplines and see scientific knowledge as more trustworthy than all other kinds of knowledge. Such views are part of the distorted belief that any finding with a ‘scientific’ tag is reliable and error free; this belief has grown deep roots in society. In education, becoming aware of our own assumptions and beliefs about science is important because they shape the way we teach and learn science. As early as primary school, pupils must be made aware that science is based on several unique underlying assumptions or beliefs. So, in this unit, we will share some ideas on how you might develop this critical awareness in your pupils. Specifically, you will learn how to introduce the nature of science as a foundation for understanding science in a meaningful way. This unit will help you appreciate the interplay of various disciplines in our understanding of science and how it works. If you desire to understand the nature of science, you will transfer this same desire to your pupils. This module of ED216 aims to empower primary school teachers to teach science with confidence. This first unit is a starting point in that journey.
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1.1 What does research say about teaching the nature of science? The nature of science explains what science is and how it works. More precisely, the nature of science is: the characteristics of science as a way of knowing, or the values, assumptions and beliefs inherent in the development of scientific knowledge (adapted from Lederman and Lederman, 2004). Because it is highly relevant to a meaningful understanding of science, it has been included in the learning outcomes of many recent nationwide efforts to reform school science. Many researchers even refer to the nature of science as the ‘rules’ of the ‘game of science’ (Clough, 2000) because it is so important: to play the game of science well, we must know and follow its rules. It is common sense to include the nature of science in any preparation programme for primary science teachers. After all, to teach science effectively, science teachers must know the nature of what they are supposed to teach. Many researchers (e.g. Chiappetta and Koballa, 2004) say that teaching the nature of science provides pupils with a complete and more authentic science education. Why has teaching the nature of science been neglected? Although many science education documents state that one desired learning outcome is understanding the nature of science, research shows that it is not given adequate attention in classroom science teaching. If adequate understanding of this important element is necessary for a richer and more authentic science education, the question that remains to be answered is: ‘Why is the nature of science being neglected in most school science programmes?’ Lederman and Lederman (2004) attribute this neglect to two factors: 1. both teachers and pupils are confused about the nature of science; 2. teachers have few research-based resources available to facilitate their teaching of the nature of science. In addition, Colburn (2004) reports that because many governments emphasise high-stakes testing of pupils’ knowledge of science content, many teachers feel the pressure to neglect the nature of science in their teaching. Another major obstacle to teaching science effectively is that many pupils have a negative attitude to science. In particular, controversy over issues such as evolution has made many pupils see science as a threat to their religious beliefs. Why is it important to understand the nature of science? Understanding the nature of science offers you and your pupils these important advantages: It may improve pupils’ attitude to science and their learning in science classes. It can make them aware of how knowledge in science comes to be
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accepted, and what science can and cannot do (Clough, 2000; Clough and Olson, 2004). It may help pupils see that understanding ideas without believing that they are true can often be fruitful. The metaphor of science as a game can help to convince pupils that outside a science context (e.g. in religion) they need not adopt the rules of the game, but understanding the rules will help them understand the processes and content of science (Clough, 2000). It totally changes how we see science and scientists. As Vilashni illustrates with the example of Kekule below, when we integrate scientists’ personal thoughts with science, as we do when we teach the nature of science, we humanise science and make it ‘learner-friendly’. In addition, teaching the nature of science will help pupils to see scientists as real people – with motives, prejudices, humour and doubts (Clough and Olson, 2004). If we do not adequately address the nature of science in the classroom, pupils can maintain or develop serious misconceptions about the strengths and weaknesses of scientific knowledge. On the other hand, with an adequate understanding of the nature of science, they will relate to science easily and in turn will be better able to use the science knowledge learned in school to help them live successfully in the world at large.
There are many historical episodes that teachers can use to influence pupils’ attitudes to science for the better. For example, before the 1860s, the scientific community had no idea about the structure of the benzene molecule. It is reported that one day in 1867, while he was on a bus, Friedrich August Kekule had a dream that he had seen the carbon and hydrogen atoms grouping together in the benzene molecule (see below). Although Kekule’s ideas were entirely speculative, his molecular structure is what all scientists today believe to be the ‘true’ structure of the benzene molecule. Kekule is reported to have said:
I have no hesitation in saying that from a philosophical point of view I do not believe in the actual existence of atoms … As a chemist, however, I regard the assumption of atoms as absolutely necessary. [bold added for emphasis] Cited in Clough and Olson (2004)
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1.2 My own perceptions of science As mentioned in the introduction, your own perceptions of science can have a major influence on your teaching and on the learning of your pupils. It could even be the most important influence, which is consistent with psychologist David Ausubel’s view of the impact of prior knowledge and experiences. Have you heard of the saying, ‘We see the world through the lens of our prior experiences’? As applied to science, it means: your prior experiences (beliefs, prior learning, etc.) influence your judgement of what science knowledge is good and what is poor or inadequate; your prior beliefs about science control what you observe (or choose not to observe) in a science activity; your prior beliefs about science lead you to decide what kind of science activities to get your pupils to do. So your perceptions of science determine what you teach and how you teach it. That means they also determine what and how your pupils learn in science. Becoming aware of your own beliefs about science is your most important first step as a responsible science teacher in an education programme. Activities 1.1 and 1.2 below offer you the opportunity to take this step and explore beliefs about science that you may often have taken for granted. As you do these activities, take time to reflect on your experiences as a teacher (as well as a student). Think of questions such as: How did I come to understand science this way? Where and how did I learn all these beliefs? How long have I been learning or teaching science? Can this course change the way I perceive science? Give these questions serious consideration. You can share your experiences with your colleagues at school, your spouse, your parents or your children at home.
To get the best results from Activities 1.1 and 1.2 (and many other activities in this module) in the classroom, we recommend that you become familiar with them by doing them yourself – and/or perhaps with colleagues – before trying them with your pupils.
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Activity 1.1 Assessing prior knowledge: what is science? OBJECTIVE
To get you (and your pupils) to start talking and thinking about your existing beliefs about science and what scientists do. WHAT YOU NEED
No special materials are required for this activity. PLEASE NOTE
You must first do Steps 1–3 on your own, either at home or when you have some free time at school. At a later date, repeat them together with the rest of the steps with your pupils (or group of colleagues). When working with your pupils in the classroom, organise them into small discussion groups of four to five pupils. Arranging the desks so that the pupils are facing each other will encourage them to discuss and share ideas. WHAT TO DO
1. Fill in the table below with your answers and those of your pupils (or colleagues). Question
Your answer
Answers of your pupils/colleagues
How do scientists do their work?
What is a scientific investigation?
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2. Study your own answers in Step 1. Using this information, briefly describe your mental image of science.
3. Explain how your mental image of science will affect your teaching of scientific ideas. Use relevant examples. (Hint: read the unit introduction.)
4. Study the answers that your pupils (or colleagues) gave in Step 1. Using this information, briefly describe their mental image(s) of science.
5. Explain how the mental images of science held by your pupils (or colleagues) will affect their learning of scientific ideas. Use relevant examples. (Hint: read the unit introduction.)
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Activity 1.2 The myths of science Source: Modified from Chiappetta, E.L. & Koballa, T.R. (2004). Quizzing students on the myths of science. The Science Teacher, 71(9), 58–61.
OBJECTIVE
To identify some incorrect beliefs (misconceptions) you have about science and how it works. WHAT YOU NEED
Reading 1.1 (see Appendix 1A) PLEASE NOTE
You do this activity on your own. You can later modify the quiz questions for use with your pupils. WHAT TO DO
1. The left column of the table below contains some statements about science. In the right column, identify whether each statement is True or False. Statement about science
True or False?
a. Science is a system of beliefs b. Most scientists are men because males are better at scientific thinking. c. Scientists rely heavily on imagination to carry out their work. d. Scientists are totally objective in their work. e. The scientific method is the accepted guide for conducting research. f. Experiments are carried out to prove cause-and-effect relationships. g. All scientific ideas are discovered and tested by controlled experiments. h. A hypothesis is an educated guess. i. When a theory has been supported by a great deal of scientific evidence, it becomes a law. j. Scientific ideas are tentative and can be modified or disproved, but never proved. k. In the history of civilisation, technology came before science. l. In time, science will be able to solve most of society’s problems.
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2. What is a scientific method?
3. Read Reading 1.1 (in Appendix 1A) by Chiappetta and Koballa (2004). This reading is about common misconceptions that pupils, teachers and the public hold about science. It offers a strategy for dealing with these misconceptions that you can use with your pupils in the classroom. 4. What are Chiappetta and Koballa’s views of the scientific method? Do you agree with them? Why or why not?
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1.3 Key characteristics of science As you have learned, the nature of science refers to the characteristics of science as a way of knowing, or the values, ideals and beliefs inherent in the development of scientific knowledge. The next activities (Activities 1.3 and 1.4) reflect several of the characteristics that are unique to science. Of particular importance to you as a primary science teacher are the following. 1. Scientific knowledge is based on empirical evidence. That is, it involves the collection of information using the senses. Empirical evidence is synonymous with (virtually another name for) science. 2. Scientific knowledge is a product of both observation and inference. An observation is a descriptive statement about a phenomenon that is directly accessible to the senses (or extension of the senses). An inference is a statement about a phenomenon to which the senses do not have direct access. In other words, when we infer, we use our prior experiences to explain an observation. 3. Scientific knowledge is tentative (that is, subject to change) for two main reasons: a. There is ongoing development of technologies that improve experimentation and data collection techniques (referred to in point 2 above as ‘extension of senses’). b. As scientists gain more experience, their interpretation of sense data changes. These two factors mean that any particular aspect of scientific knowledge will not last forever. Change in knowledge is inevitable as new observations arise and challenge existing ideas. No matter how well one interpretation explains a set of observations, it is possible that another interpretation may fit just as well or better (e.g. in ‘The tracks’, Activity 1.4), or may fit a wider range of observations (e.g. ‘The cube’, Activity 1.3). Scientists are always testing, improving and occasionally rejecting old interpretations. However, any change in science is not arbitrary (i.e. not random or left to chance). A change in a scientific interpretation (such as a theory or law) is always a result of further inquiry involving rational, observational or experimental investigations. Moreover, the norm in science is to change ideas, rather than reject them outright. In this way, ideas tend to be refined and become widely accepted and survive for a long period of time. 4. Scientific knowledge is a product of creativity and imagination. From the primary school years, children must understand that science is fundamentally imaginative and creative. Many science teachers in the Pacific Islands do not encourage their pupils to be creative and use their imagination during science lessons. Rather than exploring a scientific idea and encouraging pupils to observe and interpret information for themselves, many teachers expect them to memorise the established interpretations in the textbook. To these teachers, Unit 1: The Nature of Science
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the answer in the textbook is and will always be the right one and therefore it must be committed to memory. Yet ‘The tracks’ (Activity 1.4) shows how, based on their limited experience, young children can infer in some highly creative and imaginative ways. Teachers must encourage these qualities. The popular image of the scientist as unimaginative and blindly conservative does not reflect the true nature of science. In science, brilliant and original ways of collecting and analysing data are developed, clever theories are proposed, and experiments are run imaginatively. What makes science so successful is that it blends a tireless resource of human imagination with the dedication to testing everything thoroughly against observation and the rules of reason and logic. 5. Scientific knowledge is subjective. Scientists’ beliefs, previous knowledge, training and experiences (e.g. upbringing, nationality, sex, ethnicity, age, political beliefs) influence their work. All these background factors form a mindset that affects what questions scientists investigate, how they conduct their investigations, what they observe (and do not observe!) and how they interpret their observations. This means that scientific evidence can be biased in the areas of: a. the interpretation of data – humans use their previous experiences to interpret new ones; b. recording or reporting of data, or even the choice of what data to consider in the first place. For example, in interpreting ‘The tracks’ (Activity 1.4) from a Pacific Island perspective, many of your pupils may refer to chickens, ducks or seabirds. In contrast, children from the USA interpreted the pictures in terms of dinosaurs and snowballs. 6. Science is sceptical (and scientists are always doubtful) and rejects the notion that it is possible to attain absolute truth. Scientists accept that there will always be some degree of uncertainty in the natural world. When scientists say that a hypothesis is ‘true’ and therefore they accept it, what they are actually saying is, ‘This hypothesis agrees with all available experimental evidence’. To prove a hypothesis ‘beyond doubt’ is meaningless in science. 7. Science rejects supernatural explanations for observed phenomena. Science looks for natural explanations rather than supernatural ones. 8. Scientific knowledge is socially and culturally embedded. As a human enterprise, science is practised in the context of a larger culture, and its practitioners (the scientists) are the product of that culture. It follows that science affects and is affected by the various elements of the culture in which it is embedded. As a social activity, science inevitably reflects social values and ideals. For example, up until well into the 20th century, the educational and employment opportunities of women and of people of colour were restricted, with the result that they were essentially excluded from most of science. Although a few overcame those obstacles, they then found that the scientific community dismissed or belittled their work. Today many people are disappointed with the way science has been learned and taught in our primary schools. Many also believe that a balanced solution to the problem is to give the nature of science adequate attention in our teacher Unit 1: The Nature of Science
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education programmes and school science curricula. Our children need to develop an adequate understanding of how scientific knowledge is created, and of how this process affects the status of the knowledge, because: with an understanding of the source and limits of scientific knowledge, they will be better equipped to make informed decisions about personal and societal problems; without this understanding, there is little hope that they can use their knowledge to make informed decisions.
Activity 1.3
The cube OBJECTIVE
To demonstrate how scientific knowledge is constructed. To demonstrate the importance of evidence and careful observation in science. WHAT YOU NEED
You need a cardboard cube: The cube must have a number (from 1 to 6) on each of the six sides. A template of the cube is included in Appendix 1B. Use the template to make the cube before you begin the activity. The number on one side of the cube (in this activity, number 2) has to be deliberately hidden from the pupils by placing it face downwards on the table that the cube is sitting on. PLEASE NOTE
The following instructions assume you are doing this activity with your pupils at school. However, you can also do it on your own or with a group of colleagues. To do this activity with your pupils in the classroom, put them in small discussion groups of four to five pupils. By arranging the desks so that the pupils are facing each other, you also encourage them to talk to each other and share ideas. Make it clear to your pupils, right at the beginning of the activity, that they must not try to look at the hidden number until they have completed the activity.
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WHAT TO DO
1. Draw the table below on the board. Observations
Questions arising from observation
Answers to questions
2. Tell your pupils , ‘We are about to do a very interesting science activity. You must pay attention to what I am going to ask you to do.’ 3. Place the cube on a table, with the side with the hidden number 2 facing down. 4. Tell the pupils, ‘Study the cube carefully and write down your observation in your books. You can come close to the cube, touch and feel it, and lift it up but you must not look at the bottom.’ Give them about 3–5 minutes to list their observations. This would be an excellent time to emphasise the meaning of the following terms: a. observe – to use the senses (not just sight!) to gather information about a phenomenon; b. observation – a description of what is observed. Please note that many students (even at high school and university levels) have difficulty writing observations correctly. A common mistake is to try to add an explanation (or a reason) for what was observed. Keep in mind that an observation is a description (not an explanation) – and emphasise this point while your pupils are observing and writing down their observations. 5. Ask the class for some of their observations and record them in the left-hand column of the table on the board. Examples of observations your pupils may come up with are: ‘The cube has numbers on its sides’ and ‘The cube is made of paper’. 6. Tell the pupils, ‘Based on these observations on the board, think of a list of questions about the cube that you would like an answer to.’ You can do this as a brainstorming activity. List the pupils’ questions in the middle column of the table on the board.
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Examples of questions your pupils may come up with are: ‘Is the cube solid or hollow?’ and ‘Is the cube heavy?’ Emphasise that in science, new knowledge is constructed after scientists come up with questions, based on careful observation, that they want to investigate and find answers to. So you and your pupils are scientists! 7. Check that you have the question ‘What is the number at the bottom?’ in your list on the board. If it is not there, add it to the list, telling the class, ‘This is an important question and it must be included’. 8. Tell the pupils, ‘Copy the table into your books. Then use the observations in the first column to answer each of the questions in the middle column. List your answers in the right-hand column.’ 9. It is possible that your class may come up with many answers to a single question. Emphasise that the best scientific answer is the one that has observations to support it. For example, possible answers to ‘Is the cube solid or hollow?’ are shown below. Question: Is the cube solid or hollow? Possible answers: 1.
There is nothing in the cube because it is light.
Supporting observations are shaded. 2.
There is nothing is the cube because it didn’t make any sound when I shook it.
10. Encourage the pupils to present their answers to each question in the format below. Tell them, ‘You must cross out the answers that are not supported by observation because scientific answers are supported by evidence.’ Observations
Questions arising from observation
Answers to questions
The cube is very light.
Is the cube solid or hollow?
The cube is hollow because it is soft when I touched it.
11. Draw the pupil’s attention to the question, ‘What is the number at the bottom?’ and ask the pupils to use the observation list to answer it. Give them 5–10 minutes to do this. Your pupils may find that they do not have enough observations on their list to work out a scientific answer to this question. If so: – ask them to observe the cube again;
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– emphasise the importance of careful and complete observation in science: ‘Because the construction of scientific knowledge is based on observation, it is very important that you observe carefully and completely.’ Examples of observations your pupils may come up with are: ‘It is a sequence of numbers beginning at 1 and going up to 6 but with 2 missing from it’ or ‘Numbers on opposite sides add up to 7’. Using these observations, they should come up with answers like the following. Question: What is the number at the bottom? Possible answers: 1. Two (2) is the number at the bottom because opposite numbers add up to 7 and because 5 is the number on the top, 2 must be the number at the bottom.
Supporting observations are shaded. 2. Two (2) is the number at the bottom because it is the missing number from the sequence 1, 3, 4, 5, 6.
Emphasise that in science, an answer becomes stronger (that is, less likely to be proved wrong) when a lot of evidence supports it. For example, two observations in the above example support the idea that 2 is the number on the bottom. 12. Ask the pupils, ‘What are the important characteristics of science that you learned from this activity?’ Give them 3–5 minutes to discuss their ideas and write their answers in their books. 13. In the space below, write a reflective paragraph (of no more than 100 words) on your experiences with your pupils in regard to learning about science in this activity.
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Activity 1.4 The tracks OBJECTIVE
To further develop your understanding of the important characteristics of science as a way of knowing. WHAT YOU NEED
Photocopies or an overhead projector transparency of the three tracks templates (see Figures 1 to 3 in Appendix 1B) Photocopies or an overhead projector (OHP) transparency of the interpretations of tracks (see Appendix 1B) A group of school pupils or friends PLEASE NOTE
Do this activity on your own or with a group of colleagues before you try it out with your pupils. Divide your pupils into working groups of four or five. When doing this activity with your pupils, it is important that they can see the tracks clearly. Therefore, in preparing for this activity, photocopy the tracks (and the interpretations) on either: – A4 sized paper and hand out the copies to each of your pupils; or – a transparency for a class presentation on an OHP. WHAT TO DO
1. Tell your pupils, ‘Working in your groups, observe Figure 1 carefully and then write down your observations in your books.’ Give them three to five minutes for this. 2. Tell them, ‘Put Figure 1 away and study Figure 2 carefully. Write down your observations again.’ Give them three to five minutes for this. 3. Tell your pupils, ‘Write a short story (5–10 lines) about what you think may have happened to make these tracks, based on your observations of Figures 1 and 2.’ Give them three to five minutes for this. The pupils’ stories represent their interpretations of the available data (that is, the tracks). Remind them, ‘Careful observation and evidence are important in science. This means that your interpretations must be well supported with evidence from your observations.’ 4. After writing their stories, the pupils put away Figure 2 and study Figure 3 carefully then write down their observations. Give them three to five minutes for this.
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5. Ask your pupils, ‘Add a final part to your story (as started in Step 3 above), saying what happened based on your observation of Figure 3.’ Give them three to five minutes for this. 6. While your pupils are completing their stories, draw the following table on the board. Inference
Supporting observations
1. 2. 3. 4. 5.
7. Ask a volunteer, ‘Please read out your story to the class.’ While the pupil is doing so, identify the inferences in the story, and list them in the table on the board. 8. Discuss the following terms with the class: Infer means to use our prior experiences to explain an observation. An inference is a description of what is inferred. For example, suppose a police officer is at your school looking for one of your pupils. From previous experience, you know that police officers usually look for people who have committed crimes. So it is reasonable for you to infer that one of your pupils has done something wrong. This inference makes sense but the police officer could be looking for your pupil for some other reason – perhaps she is your pupil’s mum! Emphasise that the ability to make good and sensible inferences is very important in science. 9. With reference to the table on the board, hold a class discussion on the question, ‘Which inferences are consistent with the three pictures?’ Cross out those inferences that are not well supported by observation, making sure that the pupils understand the reason for doing so in each case. 10. Collect the pupils’ books and comment on their stories overnight. 11. Show the pupils Interpretations 1 to 4 (Appendix 1B), either handing out photocopies or presenting them on an OHP. These interpretations were made by some primary school children in the USA. Ask for comments, prompting with questions such as: ‘What do you think of these interpretations? Are the interpretations believable?’ Write your pupils’ responses and your own in the table below. Unit 1: The Nature of Science
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Interpretation
Your view
Your pupils’ view(s)
1.
2.
3.
4.
12. Brainstorm the different characteristics of science that have been reflected in this activity. Copy pupils’ ideas on the board under the heading ‘Characteristics of science reflected in this activity’. 13. Use the tracks and the best stories (interpretations) to make a chart for your class in the following format.
14. Write a short essay (a paragraph or two) yourself to explain what you understand by the above chart. Paste this essay at the bottom of the chart.
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1.4 Discovery of the DNA helix: applying the nature of science to ‘real life’ science After working through Activities 1.1 to 1.4, you and your pupils will be aware of key ideas underpinning the nature of science. This next activity (Activity 1.5) gives you the opportunity to consider what these ideas mean in practice, with a We use a lot of technical terms in this historical example of how scientific section but don’t worry! You don’t need to knowledge can be developed. To make Activity 1.5 more meaningful, we’ll first cover some background information about DNA, its structure and its functions.
memorise all of them. Instead, aim to grasp the main ideas behind the terms. If you need to, you can refer back to this section when you are doing Activity 1.5.
DNA is the abbreviation for deoxyribose nucleic acid. DNA is a very important molecule in all living things. It is found in the nucleus of a cell. DNA is commonly referred to in science as a macromolecule (very big molecule) because it is made of smaller molecules. It is through this molecule that characteristics of living things are passed on to the next generation. Current science states that: DNA is made of two strands of molecules; these two strands are made of smaller molecules called nucleotides (see diagram below);
each nucleotide is made from three different kinds of even smaller molecules – phosphate group, a deoxyribose sugar and a nitrogenous base (commonly called simply a base); there are four kinds of bases: adenine and guanine (sometimes called the purines) and thymine and cytosine (sometimes called the pyrimidines).
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The nucleotide molecules are linked to each other at the phosphate and sugar groups, resulting in a very long single strand of DNA (see diagram on the right). Do you remember that DNA is made of two strands? The complete doublestranded DNA is formed when two single strands are linked at their bases. Because of the structure and chemical nature of the bases, the double-stranded DNA is twisted into a helix. It is believed that this structure was ‘discovered’ by two scientists, James D. Watson and Francis Crick, in 1953. Activity 1.5 is about this discovery. Other well-known scientists who were eager to find out about DNA in the 1940s were Edwin Chargaff, Maurice Wilkens, Rosalind Franklin and Linus Pauling. In 1950 Chargaff found that the amount of adenine was equal to the amount of thymine and the amount of cytosine was equal that of guanine. Rosalind Franklin was a hard-working scientist and an expert in using X-ray to study molecules. In 1953 she presented her research report which included the helical structure of DNA. Perhaps because she was a woman, most scientists ignored her findings. Watson and Crick did not do any experiments on DNA. However, after reading about the research findings of other scientists and secretly using Rosalind Franklin’s X-ray data, they were able to build a model of DNA that was consistent with all known facts. In this way, Watson and Crick won the DNA discovery race. They published their findings in Nature in 1953, in an article that made them famous: ever since then, they have been recognised as the discoverers of DNA structure.
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Activity 1.5
The DNA story Source: Adapted from: Clough, M.P. & Olson, J.K. (2004). Nature of science: Always part of the science story. The Science Teacher, 71(9), 28–31.
OBJECTIVE
To enable you to use the knowledge gained from Activities 1.1 to 1.4 to identify important aspects of the nature of science in a historical short story. WHAT YOU NEED
Reading 1.2 (see Appendix 1A) PLEASE NOTE
You do this activity on your own or with a group of colleagues. Before you do this activity, you must read the pages above on the discovery of the DNA helix. You must also read Reading 1.2 in Appendix 1A, which highlights the key developments that led to Watson and Crick’s discovery. It also describes some odd behaviours of scientists and the conflicts and injustices that many science textbooks don’t mention. WHAT TO DO
Work through this activity, reading an extract (there are three in total, all from Clough and Olson, 2004) and then answering the questions that follow it. Extract 1 In the 1940s, most scientists thought that the genetic material would be made up of protein. Several reasons supported this contention … However, work by Avery, MacLeod, and McCarty in 1944 was interpreted by many scientists to mean that deoxyribonucleic acid (DNA), not protein, was the genetic material … Not all scientists agreed with this interpretation of the evidence. Of course there were scientists who thought the evidence favoring DNA was inconclusive and preferred to believe that genes were protein molecules. Francis (Crick) however, did not worry about these skeptics. Many were cantankerous fools who unfailingly backed the wrong horses. One could not be a successful scientist without realizing that, in contrast to the popular conceptions supported by newspapers and mothers of scientists, a goodly number of scientists are not only narrowminded and dull, but also just stupid. (Watson 1968, 13) However Watson admitted that further experimental work was needed to show that all genes are composed of DNA. Additional evidence for DNA being the genetic material was reported by Hersey and Chase in 1952 … However, Watson and Crick (and other scientists) were already engaged in efforts to determine the structure of DNA before this work was reported, confident it was the genetic material.
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1. Extract 1 describes a disagreement between scientists. Who are these scientists and what did they disagree on?
2. What does this disagreement tell us about interpretation of experimental data?
3. What does Extract 1 illustrate about how science works?
Extract 2 Watson spent considerable time trying to make a like-with-like (i.e., cytosine paired with cytosine, guanine with guanine, thymine with thymine, and adenine with adenine) double stranded DNA structure work. However, he acknowledged that the difference in sizes between the pyrimidines and purines meant the sugar phosphate backbone would be quite irregular in width. Crick also noted that Watson’s like-with-like idea did not account for Chargaff’s rule (the amount of adenine in an organism equals the amount of thymine, and the amount of cytosine equals the amount of guanine). Interestingly, Watson professed not to have much faith in Chargaff’s experimental work (Watson 1968, 112). Although Watson continued to work with his like-with like idea, he eventually began entertaining other possibilities.
4. What important characteristic of science and scientists is reflected in Extract 2?
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5. Although there was evidence against Watson’s ‘like-with-like’ structure of the DNA, he was unwilling to admit he might be wrong. What might explain his attitude, or a similar unwillingness in any scientist to admit to mistakes?
6. There is a belief that scientists are objective people. That is, they deal only with ‘facts’ and are not influenced by personal feelings or opinions. Do you agree with this belief? Please explain your view.
7. What does Extract 2 illustrate about the objectivity of an individual scientist?
Extract 3 Later while trying different arrangements of the purine and pyrimidine base pairs, Watson became aware that an adenine-thymine pair was identical in shape to a guanine-cytosine pair. He writes, “my morale skyrocketed, for I suspected that we now had the answer to the riddle of why the number of purine residues exactly equaled the number of pyrimidine residues. Chargaff’s rule then suddenly stood out as a consequence of a doublehelical structure for DNA” (Watson 1968, 114).
8. In Extract 2, Watson spoke negatively of scientists who did not accept the evidence indicating that DNA is the genetic material – yet he was not willing to accept Chargaff’s experimental evidence. Why do you think Watson changed his mind about Chargaff’s work, as Extract 3 shows?
Once you have finished: feedback on this activity is provided in Section 1.5.
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1.5 Final reflections This final activity (Activity 1.6) asks you to look back and reflect on what you learned in this unit as a whole. Then I offer some ideas on answering Activity 1.5. You will find final reflections of this kind in every unit of this module. Use them to check and develop your understanding of the topic, and to evaluate your teaching and learning.
Activity 1.6 Self-reflection OBJECTIVES
To help you consolidate your ideas. To make you a critical evaluator of your own teaching and learning. WHAT TO DO
Take some time to reflect carefully on your experience with all the activities in this unit (both those designed for you individually and those recommended for you and your pupils) and to record your evaluations. Your experiences in completing this unit
1. What was the most important learning experience for you?
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2. What would you change in some (or all) of the activities to use them well with your pupils in the classroom?
3. What concerns do you have about using any of the activities with your pupils in the classroom?
4. What did you learn about your pupils by doing the activities in this unit?
5. What did you learn about yourself as a teacher from the activities?
6. What are some important issues arising from these activities that you would like to discuss with colleagues and workmates?
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Feedback on selected activities
Remember that, to get the most from this activity, you should try it yourself first. This feedback will make much more sense after you’ve thought about the issues yourself. And, if you’ve thought about it, you may find that you disagree with some of these ideas. If so, great! It will make your discussions in tutorials richer and will deepen your learning.
Feedback on Activity 1.5 Here are my thoughts on how to answer Activity 1.5. Are yours similar? Discuss your ideas in your tutorial session with your tutor and colleagues. 1. The disagreement was about whether the genetic material, containing the genes, is some kind of protein. In the 1940s, most scientists interpreted the research data available as showing that the genetic material is made up of proteins. Although this view was widely accepted, some people (e.g. Watson, Crick, Hersey and Chase) interpreted the same data differently: in their view, the genetic material is made of DNA. 2. This disagreement tells us that interpretation of data in science is subjective – i.e. largely based on prior knowledge, not on definite concrete evidence. Previous experience and learning have a huge impact on our interpretation of data. This extract also shows how scientists’ need to interpret data can become a major cause of disagreement among different scientists. It is this need to interpret data that makes science an inventive discipline. 3. Extract 1 shows that science is a process of inquiry that everyone uses to make sense of information about the natural world. It also shows that scientific work does not end with a list of conclusions about natural phenomena; instead it is a continuous process of finding meaningful and logical explanations. The scepticism of scientists and the tentative nature of scientific knowledge are clearly reflected in this extract. Although there was already a widely accepted perception of the structure of DNA, the scepticism of some scientists and their willingness to test their doubts by experiments kept science alive and changed traditional beliefs.
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4. The characteristic that stands out most here is that Science is sceptical and scientists are always doubtful. For example, although Chargaff’s rule was already widely accepted, Watson said that he did not have much faith in it. Watson was determined to test his ‘like-with-like’ double-stranded DNA model against observation. He imagined what DNA would look like with his ‘like-with-like’ idea but he was not willing to accept Chargaff’s ideas until he tried out his own theory first and observed the inconsistencies for himself. 5. Again, Watson may have taken this attitude because, like many scientists, he tended to doubt and question other people’s ideas. Perhaps he found that Chargaff’s ideas were not convincing. His unwillingness to admit his mistakes also shows that scientists are real people, just like you and me – for all of us, it is often difficult to admit we may be wrong. Perhaps he was blind to alternative explanations, without realising it, because of his determination to look for evidence to support his ideas. 6. No, I strongly disagree with the statement, because scientists’ beliefs, ambition, culture, prior learning, etc., influence their work so there is no way that they can interpret data in a way that is free of biases and prejudices. Moreover, science is a human enterprise so it is often influenced by ordinary human passions of ambition, pride and greed. 7. The extract shows that scientists are attached to their work and are determined to look for evidence to support their favoured ideas, sometimes overlooking or even rejecting ideas that are different from theirs. 8. I guess Watson changed his mind because he found something that other scientists (even Chargaff) were not able to see. Perhaps he was unwilling to accept Chargaff’s ideas because they were not meaningful to him. But when he realised that the adenine–thymine pair was identical in shape to a guanine– cytosine pair, he realised that not only had he ‘discovered’ the structure of DNA but he had also found an explanation for Chargaff’s findings.
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Summary In this unit you learned that science is essentially about understanding what is happening in the natural world. It is not about having the content knowledge of science. It is a process of inquiry that involves gathering sense data from our environment and making good inferences and hypotheses based on those data. Through learning about the nature of science, you learned that scientific ideas are not facts but tentative, logical explanations of natural phenomena. As a human enterprise, science relies largely on people’s imagination and inventiveness to extend its boundaries. In science, people also work cooperatively to understand a particular problem.
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Glossary It’s important that you have a strong understanding of the key terms that will be used throughout this course. Start to develop your own glossary by completing the following table: fill in the term from the list below that fits each definition. Key term
Definition The understanding that a person has before education The characteristics of science as a way of knowing Cytosine and thymine Small molecules making up DNA Sense data collected in an experiment Information collected using the senses An idea or belief that represents what we see as science Deoxyribose nucleic acid Not certain or definite A description of a phenomenon based on sense data The four kinds of bases of nucleotides (thymine, cytosine, guanine and adenine) A process of finding answers to natural phenomena Adenine and guanine A shape that is like a spiral or a twisted ladder Using prior knowledge to explain an observation The discoverers of the DNA helix
Choose from these key terms Nitrogenous bases Helix The nature of science Purines Nucleotides Empirical evidence Inferring Observation Metal image (or perception) of science James Watson and Francis Crick
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References American Association for the Advancement of Science. (1993). Benchmarks for science literacy: Project 2061. New York: Oxford University Press. Benbow, A. & Mably, C. (2002). Science education for elementary teachers: An investigation-based approach. Canada: Wadsworth. Chiappetta, E.L. & Koballa, T.R. (2004). Quizzing students on the myths of science. The Science Teacher, 71(9), 58–61. Clough, M.P. (2000). The nature of science: Understanding how the game of science is played. The Clearing House, 74(1), 13–17. Clough, M.P. & Olson, J.K. (2004). Nature of science: Always part of the science story. The Science Teacher, 71(9), 28–31. Colburn, A. (2004). Focusing labs on the nature of science. The Science Teacher, 71(9), 32–35. Lederman, N. (2002). The nature of science. In J.M. Peters and P.C. Gega, Science in elementary education, 9th edition (pp. 31–47). New Jersey: Pierson Education. Lederman, N.G. & Lederman, J.S. (2004). Revising instruction to teach the nature of science. The Science Teacher, 71(9), 36–39. Martin, D.J. (2003). Elementary science methods: A constructivist approach (3rd ed.). California: Wadsworth. McComas, W.F. (2004). Keys to teaching the nature of science. The Science Teacher, 71(9), 24–27. Michaels, E. & Bell, R.L. (2003). The nature of science & perceptual frameworks: Emphasizing a more balanced approach to science instruction. The Science Teacher, 70(8), 36–39. Ramig, J.E., Bailer, J. & Ramsey, J.M. (1995). Teaching science process skills. Michigan: McGraw-Hill. Watson, J.D. & Crick, F.H.C. (1953). Molecular structure of nucleic acids: A structure for deoxyribose nucleic acid. Nature, 171, 737–738.
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Appendix 1A: Readings Reading 1.1 Chiappetta, E.L. & Koballa, T. R. (2004). Quizzing students on the myths of science. The Science Teacher, 71(9), 58–61.
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Reading 1.2 Online Ethics Centre for Engineering and Science at Case Western Reserve University (2005). The search for the structure of DNA. Available online at: [http://www.onlineethics.org/]
The Search for the Structure of DNA In 1953, an article was published in the British science journal, Nature, by James Watson and Francis Crick on the structure of DNA. Like most important scientific discoveries, this result was based on the work done by a large number of investigators over many years. It has become known as the Watson-Crick model and has laid the foundation for the tremendous advances made in genetics and molecular biology in the ensuing decades. The double helix structure of DNA and the genetic code it incorporates is regarded as one of the most important scientific discoveries of the century. On the basis of this work, the 1962 Nobel Prize for Medicine and Physiology was awarded to Watson, Crick and Maurice Wilkins. High school and college biology students throughout the world learn about the Watson-Crick model. In 1968 James Watson published a book entitled The Double Helix (New York: Atheneum, 1968) giving his own account of the events leading to the solution of the DNA structure. The Norton Critical Edition of this book edited by G.S. Stent in 1980 contains the six original published articles, as well as 13 reviews of the book that appeared in journals. These reviews express the viewpoints of other scientists regarding the discovery of the structure of DNA and Watson’s account of the work. Watson’s portrayal of the personal lives of the people involved and the events leading to the discovery proved to be highly controversial. Harvard University Press refused to publish this book, considering its style and content to be irreverent of the scientific research process. In 1975 Anne Sayre’s book entitled Rosalind Franklin and DNA (Norton) appeared and presented a different perspective on the discovery by describing Rosalind Franklin’s outstanding X-ray diffraction studies on DNA and making the case that the Watson-Crick model would not have been postulated by them without access to Franklin’s data, which they obtained by rather devious means. Anne Sayre was a personal friend of Dr. Franklin and was unable to recognize the “Rosy” that Watson described as the Rosalind she knew. An amusing 1987 made-for-TV film, “The Race for the Double Helix,”, is loosely based on Watson’s book and illustrates the concerns raised by Ms. Sayre. By the early 1940’s it was known that genes were the chemical constituents of plant and animal cells that carried the hereditary information. What was not known was their chemical identity and structure. The many researchers who were avidly seeking the answer were divided among those who thought that genes were specific types of proteins and those who thought evidence made it more likely that they were nucleic acids (e.g., DNA). While some scientists thought it unreasonable to understand the complexities of genetics in terms of the structures of “lifeless” chemicals, others believed that the molecular structure of the genes carried by the chromosomes held the key to understanding how genetic information is inherited and expressed. It seemed logical to consider proteins as the carriers of genetic information due to their greater complexity than DNA, which contains only four different nucleotide bases. In the 1920’s DNA was found by staining to be concentrated in the chromosomes, but was commonly thought to play an auxiliary role in hereditary. Although DNA was isolated in 1869 by Miescher, there was not much interest in it for several decades. Levene subsequently determined correctly that each nitrogenous base was attached to a sugar molecule and phosphate group. However, he postulated that they existed as a tetranucleotide cluster which repeated over and over to form the DNA molecule. Such a simple, monotonous structure could not be envisioned to carry genetic information, and since Levene’s theory was given great weight by his renown as a biochemist, scientists looked to proteins for many years. It wasn’t until 1950 that Erwin Chargaff published results indicating that the bases were not present in equal proportions. He found a correlation between the amount of adenine to thymine and
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cytosine to guanine providing the important clue to the coupling of these pairs of bases in the DNA structure. It was correctly anticipated that if DNA was the carrier of genetic information, determination of its three-dimensional structure would provide answers to how it functioned. X-ray crystal-lography is a technique uniquely suited to this task. However, by mid-twentieth century scientists had only just begun to apply it to large biological molecules. For many of these it was difficult to obtain suitable crystals. Although today macromolecular structures are routinely solved with the aid of fast computers, in the 1950s the determination was mathematically very tedious. Rosalind Franklin was brought to Kings College, London in 1951 to set up and be in charge of an X-ray diffraction laboratory. She came with considerable experience, particularly in working with macromolecular materials that do not readily form crystals, and which give diffraction patterns that are difficult to interpret. She set to the task of determining the structure of DNA by X-ray diffraction of DNA fibers. In March of 1953 she presented a research report that included the following key results based on her experimental evidence: that DNA contained two polymeric strands arranged in a coaxial helical structure with a type of symmetry described as “C2,” and that the phosphates were on the outside of the helix. She had also determined the number of molecules of water per structural unit, the molecular diameter and repeat distance, and the number of nucleotides per turn of the helix. The important missing piece of information was precisely how the nucleotide bases fit into the structure. Watson and Crick collaborated at Cambridge to work on determining the structure of DNA. Each of them had been assigned to work on another problem, but recognizing its key importance, they talked about and worked on the DNA problem extensively at the expense of their official responsibilities. They did not actually perform experiments, but based their theorizing on bits of information published in the literature, as well as on Dr. Franklin’s results, which they obtained, without her knowledge, from an unpublished report she had written for her research director. They relied on the relatively new technique of using physical models incorporating approximate distances and angles of atomic groupings from known molecular structures. By guessing the correct position and structural pairing of the nucleotide bases, they were able to construct a model that was consistent with the known facts and that could account for the biological role of DNA. This was the structure that Watson and Crick published in their famous 1953 paper, which resulted in their receiving worldwide recognition as the discoverers of the DNA structure, and ultimately led to the Nobel prize. No mention of Franklin’s key contribution appears in their paper. Franklin’s coworker, physicist Maurice Wilkens (whom Watson mistakenly refers to as Franklin’s boss in his book), did share the Nobel Prize with Watson and Crick. Franklin died of cancer before the awarding of the Prize, which can not be received posthumously, so it cannot be assumed that the Nobel Committee considered Wilkens’ work more important than Franklin’s. If she had lived, they could not both have been honored because Nobel stipulated that no more than three people can share the prize. What is unquestionably true is that little recognition is accorded to Franklin’s important role in most descriptions of the quest for the DNA structure, and her name does not appear in most high school or college biology texts in association with the discovery. Anne Sayre’s book stresses the difficulties faced by a woman scientist in England during the period in question. The small female minority were not even allowed into the lounges in scientific research institutions, where many of the important discussions among male scientists took place. The influence that contemporary attitudes toward women had on Watson’s (and subsequently on the scientific world’s) evaluation of Franklin’s contribution to the DNA work warrants serious consideration.
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Appendix 1B: Resources to support activities Cube template for Activity 1.3
Cut through the solid lines and fold along the dotted lines.
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Tracks templates for Activity 1.4
Figure 1
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Figure 2
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Figure 3
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Interpretations of tracks for Activity 1.4 INTERPRETATIONS BY SOME PRIMARY SCHOOL CHILDREN IN THE USA Source: Adapted from Martin, D.J. (2003). Elementary science methods: A constructivist approach. California: Wadsworth.
Interpretation 1 A small monster was walking down a hill, minding its own business, when all of a sudden it saw a huge monster walking down from the opposite direction. At just that moment, a gigantic snowball rolled down from the top of the hill, and both monsters panicked. The snowball killed the little monster, but the big monster managed to get away. Tired, confused, and still breathing heavily from its successful attempt to avoid being killed by the huge snowball, the big monster walked away.
Interpretation 2 The two animals were walking. They came together and hit heads because they weren’t looking where they were going. They got dizzy and were walking around in circles. Then the dizziness went away. Then they saw each other and started fighting. The bigger one killed the smaller one and carried him off in his mouth.
Interpretation 3 The Dance. One night the Gleep and the Glorg were walking through the grasslands and they met each other and fell in love. Then the Gleep and the Glorg had a romantic weird dance together. After that the Gleep jumped on the Glorg’s back and walked off in the night and got a free ride on his back.
Interpretation 4 There was this dinosaur and a bird that were walking in the same direction, and the dinosaur saw the bird. He tried to get away by taking big steps. The bird saw the dinosaur, ran to him, and they got into a fight. The bird scratched and the dinosaur stomped. The fight finally ended and the dinosaur won. However, he didn’t eat meat so he walked away.
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