Background for Teachers
What is the scientific method?

The scientific method is a way of learning about how the world around us works. Basically, it goes like this: ask a question; think of some possible answers; decide what additional facts are required to rule out some of the possibilities; get the facts; see what the answer turns out to be. As you can see, facts are the key. Much of science is about being sure of the facts.

In this unit, your students will ask a question about the development of a baby chick, and see if they can answer it. Of course, real scientific inquiry - research - is a bit more complicated. For example, we often start by just looking at lots of data - observations - to see what questions come to mind. And the questions and possible answers may change as we go along, depending on our preliminary findings. Finally, before we start any scientific research project, it is always good to check the library to see if someone else has already answered our questions.

Using the scientific method for the MRI project

First, encourage your students to make some observations. The eye of the developing chick is very prominent after day five. The eyes are large and round. This is distinctive among birds. In some MRI views you will notice that eyes tend to have a well-defined boundary.

Now, ask the question to your students. Do the eyes of the chick grow steadily over the whole incubation period, or do they grow in spurts? (Similar questions could be asked about other chick organs too.)

Possible hypotheses you can discuss with your students (these are hypothetical as we don't have any facts yet):

  1. Growth is steady, the diameter increases by a constant amount every day.
  2. Growth is steady, the volume increases by a constant amount every day. [Ask your students how this question differs from the previous question.]
  3. Most of the growth occurs in the first week, and very little after that.
  4. Most of the growth occurs in the last week.

The required facts (or observations) by your students: Measure the size of the eyes on as many images as possible during the incubation period. Show how these measurements can be used to distinguish among the four hypotheses suggested (and any others your students come up with).

Now comes the hard part - getting the facts. A "brainstorming" session might be in order here with your students. One possibility: incubate 21 eggs. Crack an egg each day, and measure the embryo's eyes (messy and wasteful, and are all those chickens growing at the same rate?). MRI is a way of seeing into the egg without breaking it. So a new set of pictures can be made every day on the chick. And the pictures can be measured accurately through image analysis. But the pictures of MRI are "slices" - they don't show the entire egg all at once - so your students will have to be careful in analyzing and interpreting them.

Implementing the MRI project

For this activity, the images your students will work with are all side views of the egg. These images were acquired by students (from the previous Chickscope project), which are now archived in the MRI database. These images are not perfect. At the end of this unit, you may want your students to suggest a strategy for getting better data for use in the upcoming project.

As you might have guessed, the chick embryo moves a lot. Unlike humans, it cannot be told to hold still. So, often, the images will have vertical streaks or blurring. This is generally referred to as "motion artifact", and makes it hard to get a good measurement (or even to find the eye!). Furthermore, if we were to repeat the same slice over and over, it may look different each time. For example, the chick may turn its head causing you to slice through the eye at the edge rather than straight through the middle. Alas, some things even scientists just cannot control; these things must be taken into consideration by your students when they begin interpreting the data.

The first step for your students is to examine the images that you have been given for this lesson and identify the eye in those images. This may involve the students using the scientific method, too: hypothesis - this round spot is the eye; hypothesis tests - is the appearance consistent with other pictures in the series? Is the other eye visible in a reasonable location? Is the overall location consistent? (The chick tends to stay at the top of the egg, and the head tends to stay near the air cell, particularly later in development).

Your students can also work with the selected data by downloading the images to their computers and proceed with the analysis as described in the suggested Lesson plan.

Most likely, the results by your students will be inconclusive. Discuss why. Your students may wish they had better data. Ask them to think about how to get more accurate measurements, or to compensate for the expected lack of accuracy.

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