How does your hair know how long to grow?

Overview / Objectives

Overview

Hairs don't have nerves or eyes, but if they aren't cut they will always grow out to the same length. Each kind of hair grows to its own length. How do hairs "know" when to stop growing? In this exercise the students are introduced to the observed growth rates and lengths of phases in the hair growth cycle. Using computer models they compare these factors to develop a theory to explain how hairs "know" when to stop growing.

As they work through the process they are introduced to the scientific concepts of verification and validation. As scientists, we need to verify that we have followed the directions correctly, i.e., did we put the right numbers into the equation? Scientists also need to validate their conclusions: "Is the answer reasonable? Did I use the correct equation?"

Objectives

The students will learn the process that regulates the length that hairs grow. They will be able to explain why some people can grow long hair while other people can only grow shoulder- length hair. They will learn the value of computational models in the exploration of scientific questions. They will understand the importance of verification and validation in the scientific process. They will learn that the answers to scientific inquiry are opportunities for further inquiry.

General discussion: This lesson is designed to help the students view questions like scientists. Scientists ask a lot of questions. They don't ask questions to put people on the spot. Questioning is the way they think. It helps discipline their thoughts so they are careful not to miss things. Questioning also opens up new areas to explore. As you encourage your students to question everything, help them appreciate the honesty and respect that this approach requires.

This lesson is designed to help the students discover that science is cumulative. We start with a question. We look around to learn what others have discovered about the issue and then make models and experiments to expand our understanding. Our models and experiments answer some of our questions but if we are doing good science they really give us more questions. At the core, science is an exploration. It isn't a set of answers. Reading a science book or journal is like reading a history book. It helps us learn what explorers have learned and how they went about it. Science, on the other hand, is pushing the envelope. With the right attitude and tools we can be scientists and explorers. The nice thing about science is that we don't have to go to uncharted worlds to be explorers. We can explore the hairs on our own heads.

National standards addressed:

Unifying concepts and processes: Evidence, models, and explanation; change, constancy, and measurement.

Science as inquiry: An appreciation of "how we know" what we know in science. Understanding of the nature of science.

Life Science: 5-8 Regulation and Behavior

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How does your hair know how long to grow?

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