*Lab is not needed to complete this assignment* You are simply making notes based on facts as in what will happen in the situations. Answer all questions and make notes for all statements.

Background

Figure 1. Nesting Mice

Can You Pick the Best Food for Your Pet?

The processes of science give you a way to investigate the preferences of mice (Figure 1) for various food types or any other question in a scientific context. Science is a careful and methodological approach to studying the world around us. You can observe, experiment, model, and test, which yield results. You can use logic and reason to interpret the results. Others in the field must be able to repeat and verify your results. Science must be reproducible. In addition, things that are considered scientific must be testable and must be open to the possibility of being shown to be false. This is called being falsifiable.

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The scientific method is a pathway that guides the acquisition of scientific knowledge. It is a framework for critical thinking that lessens the uncertainties in discovery, especially when it is reviewed and repeated, as science always is. Though often presented as a rigid set of steps that must occur in a specific order, the scientific method may include some or all of these steps (Figure 2).

Figure 2. Five Steps of the Scientific Method

Observation

Observation involves witnessing a natural phenomenon. Perhaps you notice something that does not make intuitive sense to you. Or, you might be curious about the weather, plants, or a certain animal species. Observations that are recorded are called data (singular: datum). Data may be qualitative or quantitative. Qualitative data are descriptive. Examples of qualitative data include:

• The shape of a snake’s scales
• The pattern of remodeled bone as a result of healing after a break or in response to changes in physical activity
• The nesting behaviors of mother birds

Quantitative data include specific measurements of a particular parameter, such as time, temperature, mass, or volume. Examples of quantitative data include:

• How many triangular scales the snake has
• The increase of bone remodeling cells called osteoclasts, based on the rate of exercise
• The number of eggs a bird lays per nesting period

Question

From the observations, generate a question that you wish to answer. You might ask why or how an event happens or what outside influences affect why or how an event happens.

Hypothesis

To answer your question, formulate an educated guess, or hypothesis. The hypothesis is an answer to your question from the previous step. It describes a possible, testable outcome. The hypothesis is said to be an educated guess because formulating the hypothesis typically requires research into ideas and existing outcomes related to the hypothesis. Hypotheses can be written in terms of independent and dependent variables.

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If a hypothesis is supported through experimentation, you can share your results, allowing others to benefit from your discoveries. You can design further experiments that look at the system in greater depth.

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Note that even a negative result, one which disproves the hypothesis, is useful because it eliminates possible wrong explanations. It is important to remember that any hypothesis that can be tested experimentally is a good hypothesis, even if it is proven wrong.

Experiment

The experiment is a test of the hypothesis you formulated. It provides results that either support or disprove the hypothesis. In a controlled experiment, one parameter is varied among test groups that are otherwise treated the same. There are different types of controls.

Types of Controls

Negative control groups do not receive treatment and are compared to experimental groups that do receive treatment. For example, a researcher studying the efficacy of a new antibiotic would test an experimental group of bacteria in the presence of the new antibiotic. The negative control group of bacteria would only be treated with water.

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Positive control groups are expected to produce a positive result. A positive control might be used to compare the efficacy of the new antibiotic against an existing one that is known to be effective at killing a particular strain of bacteria.

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If the bacteria do not grow in the presence of the positive control antibiotic but do grow in the presence of the experimental antibiotic, the researcher has evidence that the new antibiotic is ineffective against that bacterial strain. If, on the other hand, the bacteria do not grow in even the presence of plain water, the researcher has evidence that something went wrong with the experiment. For example, the culture used might be dead, or the bacteria may be unable to grow under the conditions selected.

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Other types of experimental set-up may be used when a controlled experiment would be unethical or impractical. For example, scientists use a natural controlled experiment to compare two existing populations, such as smokers and nonsmokers.

Types of Variables

In controlled experiments, the parameter that is varied by the scientist is called the independent variable. Another parameter, measured during the course of the experiment, is called the dependent variable. In an experiment where the effect of caffeine on reaction time is tested, consumption of caffeine is the independent variable and reaction time is the dependent variable. The experimenter controls whether or not caffeine is consumed and how much, and the reaction time is measured.

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An experiment should only have one independent variable. To understand why this is the case, think about the bacteria experiment. If the bacteria exposed to the new experimental antibiotic were grown at 21 °C and the bacteria exposed to the positive control antibiotic were grown at 37 °C, the researcher would not know if antibiotic sensitivity was dependent upon antibiotic type or temperature.

Replicates

Experiments are often performed multiple times. Not only must experiments be properly controlled, but they must also have results that are consistent and repeatable. Any result can happen once by random chance. To show that the independent variable has an effect on the dependent variable, it should have that effect most of the time. If the results only occur in 1 out of 10 experiments, the independent variable likely does not cause that effect. However, if the results occur in 10 out of 10 experiments, the independent variable likely causes that effect. Experiments are usually performed in triplicate, or three times.

Model Organisms

Not all organisms can be studied in depth. So, several animal species are designated as model organisms. Model organisms are chosen to represent classifications of organisms. For example, E. coli is a model for bacterial studies. Model organisms are used to learn about that specific organism, about genes or proteins that many organisms share, or about humans who are not usually experimented on. Model organisms have been widely studied, are easily cared for in laboratory environments, and have particular experimental advantages. Some experimental advantages are having a genome that is completely mapped, being robust, and being easily manipulated during an experiment. Mice, fruit flies, the nematode C. elegans, and E. coli are examples of model organisms.

Evaluation

Results must be evaluated to ensure that the experiments were conducted properly and that conclusions are valid. The evaluation process in science also includes review of conclusions by the greater scientific community and reproduction of results by other researchers.

About This Lab

In this lab, you will investigate the question of the best food source for an upcoming mouse metabolism study. You will test multiple food sources. Mice are omnivores and eat a variety of foods. You will then determine which food source will be best for the study based on the fact that it generated the most weight gain. After concluding which of the options will be best for the study, you will repeat your experiment in triplicate, or with three different mice, to confirm your result.

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Assume that previous researchers have used one unit of cooked pasta for mouse metabolism studies and that mice do indeed gain weight eating a diet of cooked pasta. In your experiment, please use cooked pasta as a positive control. For the negative control, you should not feed the mouse any food items. When working with real live mice, this type of experiment would be heavily regulated. Mice can only survive without food for so long and you would not be allowed to perform an experiment in which a mouse starved to death. Be mindful of this when planning your experiment. Your virtual mouse can also die if not fed, which would be a failure in your experiment. You cannot compare a dead mouse as a negative control to your living experimental mice.

Experiments

Open the simulation by clicking on the virtual lab icon below. The simulation will launch in a new window.

You may need to move or resize the window in order to view both the Procedure and the simulation at the same time.

Follow the instructions in the Procedure to complete each part of the simulation. When instructed to record your observations, record data, or complete calculations, record them for your own records in order to use them later to complete the post-lab assignment.

Procedures

Experiment 1: Find the Best Mouse Diet for Weight Gain

1. Develop a hypothesis about the best food source for mouse weight gain. Record the hypothesis to reference later.
2. Take a light box and a balance from the Instruments shelf and place them onto the workbench.
3. Take a mouse cage from the Containers shelf and place it onto the workbench.
4. Move the mouse cage onto the balance. The value you see displayed is the mass of the cage, a full water bottle, and the other materials inside the cage.
5. Press the ZERO button on the balance with the mouse cage on it. The balance should now read 0.000 g.
6. Take a mouse from the Materials shelf and place it into the cage.
7. If the balance has been appropriately zeroed, the reading on the balance should reflect the mass of the mouse alone. Record the mass and move the mouse cage back to the workbench.
8. Take a Petri dish from the Containers shelf and place it onto the workbench.
9. Take cooked macaroni from the Materials shelf and add it to the Petri dish. (One unit of food is added automatically). Cooked macaroni is the positive control for this experiment.
10. Place the Petri dish of food into the mouse cage.
11. Move the cage into the light box.
12. Use the up and down arrows on the light box to adjust the number of days. Run the light box for 1 day.
13. Press the blue Start button to begin. You will notice a light turn on in the light box. Note: Time passing in the light box has been sped up for you in the virtual lab.
14. Remove the cage once the display for the number of days reads “0”. In the virtual lab, you can assume the cage is cleaned, the water bottle is washed and refilled, and the balance is re-zeroed for the cage each time you take the cage out of the light box. You do not need to perform these cleaning steps.
15. Remove the dish of food from the cage.
16. Put the cage on the balance and measure the mass again. This is the mass of the mouse after one day of the food source. Record the results.
17. Empty the cage and the dish of food into the waste bin, then place them in the sink.
18. Repeat steps 3 – 17 for each of the other food sources and for no food (negative control).

Experiment 2: Replicate the Experiment

1. Identify the food source from Experiment 1 that led to the most weight gain. Record this food source to reference later. You will now try to confirm that the food caused weight gain, as you saw in the first experiment.
2. Repeat Experiment 1, steps 3 – 17 for five new mice as follows:
   1. Positive control
   2. Negative control
   3. Experimental group, trial 1
   4. Experimental group, trial 2
   5. Experimental group, trial 3

Be sure to use the same type of food for each of the three experimental food trials.

1. Clear the bench of all materials, containers, and instruments, then return to your course page to complete any assignment for this lab.