Cambridge Lower Secondary CheckpointStage 9

Science in Context

Science Stage 9 Chapter Notes

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Science in Context
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In this chapter

  1. 1Understanding the Scientific Method
  2. 2Variables and Fair Tests
  3. 3Recording and Presenting Results
  4. 4Analysing Results and Concluding
  5. 5The Impact of Science on Society

1. Understanding the Scientific Method

The scientific method is the process scientists use to explore observations and answer questions. It's a logical, step-by-step approach to investigation. It usually starts with an observation that leads to a question. The scientist then forms a hypothesis, which is a testable prediction. They design and carry out an experiment to test this hypothesis. After collecting data, they analyse it to see if it supports or refutes the hypothesis, leading to a conclusion. This conclusion might then lead to new questions, and the cycle begins again.

Key term

Hypothesis: A clear, testable statement or prediction about the expected outcome of an experiment.

Examiner insight

Examiners look for a logical flow of ideas when asking about planning an investigation, mirroring the steps of the scientific method.

Worked example 15 marks

A student observes that cress seeds grow well on her sunny windowsill but not in a dark cupboard. She wants to investigate this scientifically. How could she use the scientific method to investigate the effect of light on cress seed germination?

  1. 1

    Step 1: Formulate a Question. Based on the observation, the question is: 'Does light affect the germination of cress seeds?'

  2. 2

    Step 2: Formulate a Hypothesis. A possible hypothesis is: 'Cress seeds will germinate faster and grow taller in the presence of light compared to in the dark.'

  3. 3

    Step 3: Design an Experiment. Get two identical trays with cotton wool. Place the same number of cress seeds (e.g., 20) in each. Add the same amount of water to both. Place one tray on a sunny windowsill (light condition) and the other in a dark cupboard (dark condition).

  4. 4

    Step 4: Collect and Analyse Data. Every day for a week, count how many seeds have germinated in each tray and measure the height of the seedlings. Record the results in a table.

  5. 5

    Step 5: Draw a Conclusion. Compare the results from the two trays. If the seeds in the light grew better, the conclusion would be that the results support the hypothesis that light is needed for cress germination and growth.

Recap

  • The scientific method is a cycle: Observation -> Question -> Hypothesis -> Experiment -> Analysis -> Conclusion.
  • A hypothesis is an educated guess that you can test.
  • An experiment is designed to test the hypothesis in a controlled way.
  • The conclusion summarises what the results mean and relates back to the hypothesis.

Quick check

  1. What is the purpose of a hypothesis in a scientific investigation?1 mark

2. Variables and Fair Tests

To make sure your experiment is reliable, you must conduct a 'fair test'. This means you only change one thing at a time and see what effect it has. The things that can change in an experiment are called variables. There are three types: the Independent Variable (IV) is the one thing you deliberately change. The Dependent Variable (DV) is the thing you measure to see the effect of the change. Control Variables are all the other things you must keep exactly the same to ensure your test is fair and your results are valid.

Key term

Control Variable: A factor that is kept constant throughout an experiment to ensure that only the independent variable is affecting the dependent variable.

Examiner insight

Examiners award marks for not just identifying control variables, but also explaining why they must be controlled for a fair test.

Common pitfall

Confusing the independent variable (what you change) with the dependent variable (what you measure). Remember: the Dependent variable 'Depends' on the Independent variable.

Worked example 14 marks

A student investigates how temperature affects the time it takes for a sugar cube to dissolve in water. Identify the independent, dependent, and two control variables for this experiment.

  1. 1
    1. Independent Variable: The factor the student is changing is the temperature of the water. So, IV = Temperature of the water.
  2. 2
    1. Dependent Variable: The factor the student is measuring is the time it takes for the sugar to dissolve. So, DV = Time taken to dissolve.
  3. 3
    1. Control Variable 1: To make it a fair test, the volume of water used must be the same in each beaker. If different volumes were used, it might affect the dissolving time.
  4. 4
    1. Control Variable 2: The mass or size of the sugar cube must be the same for each test. A larger cube would naturally take longer to dissolve.

Recap

  • The independent variable is the one you change.
  • The dependent variable is the one you measure.
  • Control variables are all the factors you keep the same.
  • A fair test only has one independent variable.

Quick check

  1. In an experiment to see how the length of a ramp affects the speed a toy car rolls down it, what is the independent variable?1 mark
  2. List one variable that should be controlled in the toy car experiment.1 mark

3. Recording and Presenting Results

Collecting data is pointless unless you record it clearly and present it in a way that is easy to understand. A well-drawn table is essential for recording results during an experiment. It should have clear headings and include the units for each measurement. Once you have your data, you need to present it visually in a graph. Use a line graph to show how a continuous variable changes over time or in response to another continuous variable (e.g., temperature). Use a bar chart to compare results between different categories or groups (e.g., favourite colours). All graphs need a title, and the axes must be labelled with the quantity and its units.

Key term

Anomaly: A result that does not fit the overall pattern of the data and may be due to a measurement error or mistake.

Examiner insight

Marks are often awarded for each part of a good graph: suitable scales, correctly labelled axes with units, accurately plotted points, and a correct line of best fit.

Common pitfall

Forgetting to include units in tables and on graph axes. This is an easy mark to lose.

Worked example 14 marks

A student recorded the temperature of a beaker of water as it cooled. The results were: 0 mins, 80°C; 2 mins, 65°C; 4 mins, 54°C; 6 mins, 45°C; 8 mins, 38°C. Present this data in a suitable table and sketch the line graph you would expect to see.

  1. 1
    1. Draw a table with two columns and clear headings. The independent variable (Time) goes in the first column, and the dependent variable (Temperature) in the second. Include units in the headings.
  2. 2
    Table:Time (mins)Temperature (°C)
    080
    265
    454
    645
    838
  3. 3
    1. To sketch the graph, draw the axes. The independent variable (Time) goes on the x-axis (horizontal). The dependent variable (Temperature) goes on the y-axis (vertical).
  4. 4
    1. Label both axes with the quantity and the unit, e.g., 'Time (mins)' and 'Temperature (°C)'.
  5. 5
    1. Add a suitable scale to each axis. The x-axis could go from 0 to 8, and the y-axis from 0 to 80.
  6. 6
    1. Plot the points accurately using 'x' or a dot with a circle. The graph should show a downward-sloping curve as the water cools.

Recap

  • Always record results in a table with headings and units.
  • Use a line graph for continuous data (measurements).
  • Use a bar chart for discrete or categorical data (groups).
  • Graphs must have a title and labelled axes with units.
  • A line of best fit shows the general trend and helps to spot anomalies.

Quick check

  1. What two things must the heading of a table column or a graph axis always include?2 marks

4. Analysing Results and Concluding

Once you have your results presented in a graph, you need to analyse them. This means describing the patterns or trends you see. For a line graph, you might say 'As the temperature increases, the reaction time decreases'. You should always try to use data from your graph to support this description, for example, 'As temperature increased from 20°C to 40°C, the time taken decreased from 50s to 25s'. After describing the pattern, you must write a conclusion. A good conclusion does two things: it states what the results show and clearly says whether the evidence supports or refutes your original hypothesis.

Key term

Conclusion: A summary that explains what the results of an experiment show and how they relate to the original hypothesis.

Examiner insight

A strong conclusion not only states the finding but also uses specific data points or trends from the results to justify it. This is a key skill for higher marks.

Common pitfall

Stating a conclusion without referring to the data as evidence. A conclusion like 'My hypothesis was right' will not get any marks.

Worked example 13 marks

A student's graph shows that as the concentration of an acid increases, the time taken for magnesium to react decreases. The original hypothesis was 'A higher concentration of acid will make the reaction with magnesium faster'. Write a suitable conclusion for this experiment.

  1. 1
    1. Start by stating the main finding, describing the relationship between the variables. 'The results show that as the concentration of the acid increases, the time taken for the reaction decreases.'
  2. 2
    1. This means the reaction gets faster. Rephrase this to be more direct. 'This shows that a higher acid concentration leads to a faster reaction rate.'
  3. 3
    1. Link the finding back to the original hypothesis. 'This supports the original hypothesis that a higher concentration of acid will make the reaction with magnesium faster.'
  4. 4
    1. (For top marks) Quote some data. 'For example, at a concentration of 1 mol/dm³, the reaction took 60 seconds, but at 2 mol/dm³, it only took 30 seconds.'

Recap

  • Describe the pattern or trend shown in your results.
  • Use the words 'As X increases/decreases, Y increases/decreases'.
  • A good conclusion must refer back to the original hypothesis.
  • Use specific data from your results to support your conclusion.
  • Always consider evaluating your method and suggesting improvements.

Quick check

  1. What is the difference between describing results and writing a conclusion?2 marks

5. The Impact of Science on Society

Science is not just about experiments in a lab; it has a huge impact on our daily lives, society, and the environment. Scientific discoveries have given us medicines, computers, electricity, and ways to grow more food. These are huge benefits. However, some scientific developments also have negative consequences or create difficult choices. For example, burning fossil fuels provides energy but also causes climate change. The invention of plastic was revolutionary, but plastic pollution is now a major environmental problem. When we consider these issues, we are thinking about ethics – the moral principles that help us decide if a scientific application is right or wrong, and who it might help or harm.

Key term

Ethics: Moral principles that guide scientific research and decision-making, considering what is right and wrong and the potential impact on people and the environment.

Fun fact

The development of fertilisers from the Haber-Bosch process, a chemical reaction, is estimated to support food for about half of the world's population. It is one of the most significant scientific applications of the 20th century.

Worked example 12 marks

The use of fossil fuels for energy has many benefits but also significant drawbacks. Discuss one benefit and one drawback of using fossil fuels.

  1. 1
    1. Identify a clear benefit. 'A major benefit of using fossil fuels like coal, oil, and gas is that they are a very reliable and concentrated source of energy. Power stations can be run 24/7 to provide the electricity we need for our homes, schools, and hospitals.'
  2. 2
    1. Identify a clear drawback. 'A significant drawback is that burning fossil fuels releases large amounts of carbon dioxide, a greenhouse gas. This gas traps heat in the atmosphere, leading to global warming and climate change, which can cause extreme weather and rising sea levels.'

Worked example 22 marks

Scientists can now use genetic modification to create crops that are resistant to disease. Suggest one ethical argument in favour of this technology and one against it.

  1. 1
    1. Argument in favour: 'An ethical argument for genetically modified (GM) crops is that they can increase food security. By making crops resistant to disease or drought, we can grow more food, which could help to reduce hunger and famine in parts of the world.'
  2. 2
    1. Argument against: 'An ethical argument against GM crops is the potential for unknown long-term effects on the environment and human health. Some people are concerned that introducing new genes into an ecosystem could have unforeseen negative consequences for other organisms, like insects or wild plants.'

Recap

  • Scientific developments can have both positive and negative impacts on society.
  • Ethics in science involves considering the moral implications of research and its applications.
  • Many modern issues, like climate change and pollution, require scientific understanding to solve.
  • Decisions about science and technology often involve weighing up benefits against risks and costs.

Quick check

  1. State one positive and one negative impact of the invention of plastic.2 marks

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. A student wants to investigate if the surface area of a potato piece affects the rate of osmosis. Identify the independent variable, the dependent variable, and one variable that must be controlled.3 marks
  2. Explain the difference between a hypothesis and a conclusion in a scientific investigation.2 marks
  3. A scientist is testing a new fertiliser. They grow ten plants with the fertiliser and ten plants without it. All plants are given the same amount of water, light, and are grown in the same type of soil. After 3 weeks, they measure the height of the plants. Why was it important to have a group of plants with no fertiliser?2 marks
  4. The results of an experiment measuring the extension of a spring with different masses are: 100g, 2cm; 200g, 4cm; 300g, 7cm; 400g, 8cm. Identify the anomalous result and explain your choice.2 marks
  5. Describe how you would present the results of an investigation into the favourite sports of students in your class. Name the type of chart you would use and explain your choice.3 marks
  6. A student concludes, 'The experiment worked'. Explain why this is a poor conclusion and what they should have written instead.3 marks
  7. The use of electric cars is increasing. Discuss one advantage and one disadvantage of replacing petrol cars with electric cars for the environment.4 marks
  8. A company claims its new washing powder works better at low temperatures. Design an experiment you could carry out to test this claim. You must state your hypothesis and identify your key variables.5 marks
  9. A graph shows that as exercise intensity increases, a person's heart rate also increases. The line on the graph is a straight line going up. Describe the pattern and relationship shown in this graph.2 marks
  10. The development of antibiotics has saved millions of lives. However, their overuse has led to antibiotic resistance. Explain what this means and why it is a major problem for society.4 marks

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