Exercises: The steps of the scientific method

These steps of the scientific method are in the wrong order: (a) analyse data, (b) formulate a hypothesis, (c) experiment, (d) observe a striking fact, (e) draw conclusions. Put them in the correct order and write one sentence explaining what is done in each step.

Explain in your own words what a hypothesis is and write a possible hypothesis for this observation: the plants on a classroom windowsill grow leaning towards the window.

The diagram shows the steps of the scientific method, but one of them is hidden behind a question mark. Identify the missing step and explain what it involves.

Explain in your own words what a scientific observation is and give an example of an observation made only with the senses and another made with the help of an instrument, such as a magnifying glass or a thermometer.

Of these two questions, only one can be investigated with an experiment in the school laboratory: (a) "why are plants green?" and (b) "does the amount of daily water affect the growth of a bean plant?". State which one and explain what makes it investigable.

Describe what is done in the experimentation stage and explain why it is so important to note down in the laboratory notebook everything that happens, even the results we were not expecting.

In the conclusions of an experiment only two things can happen to the hypothesis. What are they? Explain what the scientist does in each case.

In the experiment "we water two pots with different amounts of water to see whether they grow differently", state what we change on purpose (independent variable) and what we measure (dependent variable).

A group of students observes that bread goes mouldy faster in the kitchen than in the larder. Write an investigable question about this observation, formulate a hypothesis, and express it as an "if..., then..." prediction.

To test whether light affects growth, two identical pots are prepared with the same plant, the same soil, and the same watering: one is left in the sun and the other inside a dark cupboard. Identify the independent variable, the dependent variable, and two control variables (variables kept constant), and explain what role the plant in the cupboard plays.

Explain in your own words the difference between a hypothesis, a scientific law, and a theory, and give an example of each related to falling objects.

Read this hypothesis: "lentils germinate sooner if they are soaked in warm water the night before". Write it as an "if..., then..." prediction, point out the independent and the dependent variable, and describe which group would act as the control.

A team plants a single seed in each condition and draws conclusions from what happens to it. Explain why this design is not reliable and reason how many seeds you would use in each pot.

"On Tuesday the maximum temperature was $23\ ^\circ\text{C}$" and "Tuesday was hot because the classroom air conditioning was broken": one of these sentences is a piece of data and the other an interpretation. Tell which is which and explain the difference between data and interpretation.

The data from an experiment do not support the researcher's hypothesis. Explain what options she has (checking the procedure, repeating the measurements, reformulating the hypothesis) and why fiddling the data so they "come out right" is never an option in science.

María suspects that plants grow worse if they are watered with salt water. Describe in four steps the experiment that would let her test this: which pots she prepares, what she changes between them, what she keeps the same, and what she measures.

Fewer tadpoles have been spotted in a park pond since a fountain that stirs up the water was installed. Design an experiment to test whether water movement affects tadpole development: write the hypothesis, the experimental set-up, the control group, and what you would measure.

A laboratory repeats the same experiment ten times and gets the expected result on only one occasion. Explain why the hypothesis cannot be considered proven and what the team should do next.

To prove that its new fertiliser is "the best", a company fertilises fifty pots with its product and, after a month, announces that all the plants have grown. Point out at least three flaws in the experimental design and describe how it should be done correctly.

Design a home experiment to test whether sugar dissolves faster in hot water than in cold water: write the hypothesis, the materials needed, the procedure, the variables you will keep constant, and how you will make sure the result is reliable.

To test the theory of spontaneous generation, as Francesco Redi did in the 17th century, three jars are prepared with identical pieces of meat: jar A is left completely open; jar B is hermetically sealed; and jar C is covered with fine gauze that allows air to enter, but prevents flies from passing through. Days later, fly larvae only appear inside jar A and on the outside of the gauze of jar C.

1. a) A critic of Redi claimed that maggots did not hatch in jar B because "vital fresh air" was missing. Justify how the results of jar C prove that this claim was false.
2. b) Predict what would have happened in jars B and C if the spontaneous generation hypothesis had been correct.
3. c) Identify the independent variable and the dependent variable in this investigation.

You want to know whether adding salt to water changes the time it takes to freeze. Design the experiment with household materials: hypothesis, glasses and amounts, what you will measure at regular intervals, what you will keep constant, and how you will organise the results.

For a week you will observe which foods the ants in the playground prefer. Draw up the complete investigation plan: question, hypothesis, which foods you will offer, when and for how long you will observe each day, what you will note down in each session, and how you will draw conclusions. State also how you will make the observations without harming the animals.

A friend claims: "My cat always sits on my notebook when I study; therefore, it is a scientific fact that cats detect when we work and want to keep us company."

1. a) Justify why your friend's observation is an anecdote and not valid scientific evidence, pointing out at least two possible flaws or biases in their conclusion (for example, sample size or confirmation bias).
2. b) Propose two alternative hypotheses that explain the cat's behavior without requiring the animal to know whether you are studying.
3. c) Design a controlled experiment to test which of the hypotheses is correct. Indicate what you will do in the experimental group, in the control group, and which variables you will keep constant to ensure the test is rigorous.