What’s in This Unit?

The Light Waves unit helps students gain a deeper understanding of how light interacts with materials and how these interactions affect our world, from the colors we see to changes caused by light from the sun, such as warmth, growth, and damage.

In this unit, students investigate a specific change caused by light: skin cancer. Australia has one of the highest skin cancer rates in the world: More than half of the people who live there will be diagnosed with skin cancer in their lifetime. Scientists have investigated the factors that place Australia’s population at such an exceptionally high risk of skin cancer. They have found that less ultraviolet light is absorbed as it passes through the atmosphere above this region due to ozone depletion. They have also found that the Australian population is more susceptible to skin cancer because of the large proportion of people with light skin tones. This is because people with lighter skin tones have less melanin in their skin cells than people with darker skin tones. Melanin absorbs ultraviolet light before it damages genetic material inside skin cells, providing some protection against damage caused by light from the sun. Therefore, people with low levels of melanin in their skin cells are at a greater risk of developing skin cancer than people with higher levels of melanin in their skin cells.

Taking on the role of student spectroscopists working for the fictional Australian Health Alliance, students investigate why Australia’s cancer rate is so high, analyzing real data that scientists might consider. This problem serves as the anchor phenomenon that students focus on throughout the unit. Students use the Light Waves Simulation, conduct hands-on activities, read articles, and watch videos to gather evidence about how light interacts with materials. The Sim allows students to observe how light carries energy and how this energy causes materials to change when it is absorbed. Students can simulate manipulating the wavelength of light, observing that different types of light have different wavelengths and that different types of light can change a material in different ways. Students also learn that when energy from light is not absorbed by a material, it can be either reflected or transmitted. Students apply these ideas to construct an argument explaining the high skin cancer rate in Australia, citing both low ozone levels in the atmosphere and low levels of melanin in the population.

Why?

Students intuitively know that light can cause changes: they have felt the light from the sun warm their skin and have probably experienced sunburns. The Light Waves unit helps students draw on fundamental science ideas about how light interacts with materials to explain these observations. Focusing specifically on Australia’s skin cancer rate invites students to apply their newfound understanding of light to investigate an authentic question that scientists have studied. It allows students to arrive at a multicausal, complex explanation, taking into account how ultraviolet light interacts with different substances in the atmosphere and how ultraviolet light interacts with melanin.

The discussion of ultraviolet light in this unit provides an opportunity for students to consider a type of light that is invisible to the human eye. Unlike a unit on vision, which might marginalize the impact of invisible light in students’ lives, this unit reinforces the idea that invisible wavelengths—which make up most of the electromagnetic spectrum—have an impact on our world.

How?

The Light Waves unit begins by introducing students to their role as student spectroscopists tasked with explaining why the skin cancer rate in Australia is so high. In Chapter 1, students work to answer the question, Why does light from the sun cause skin cancer? They receive data indicating that light from the sun can cause skin cancer and that Australia’s skin cancer rate is the highest in the world. To learn about how light from the sun can cause skin cancer, students investigate how light can cause materials to change. Through a hands-on activity with solar-powered toys, liquid crystal paper, and thermometers, students gather evidence that light carries energy and conclude that energy from light can cause materials to change. Students then use the Light Waves Simulation to observe that these changes happen only when energy from light is absorbed by a material. Students apply this understanding to their investigation of skin cancer, using the Light WavesModeling Tool to show that energy carried by light from the sun is absorbed by genetic material inside skin cells, causing damage that can lead to skin cancer. At the end of the chapter, students compare the amount of sunlight Australia receives and its skin cancer rate to other countries. They observe that Brazil and Australia receive the same amount of sunlight per year. This means that something besides the amount of sunlight must be affecting the skin cancer rate in Australia.

In Chapter 2, motivated by evidence that Australia and Brazil have different rates of skin cancer even though they receive the same amount of sunlight, students investigate whether the light in Australia could be different somehow than the light in Brazil, focusing on the question, Is all light the same?Students conduct a hands-on investigation and read an article to gather evidence that different types of light can change materials in different ways. After establishing that all light is not the same, students turn their attention to investigating what makes types of light different. They create different types of light in the Sim and watch an animated video about the properties of waves to learn that different types of light have different wavelengths. Students then gather evidence that the light in Australia is different from the light in Brazil: Australia receives more ultraviolet light, the specific type of light that damages genetic material in skin cells. They also gather evidence that the there are more people with low levels of melanin in their skin cells in Australia than in Brazil. By the end of Chapter 2, students can apply what they have learned to analyze this evidence and explain how the same amount of sunlight can lead to different rates of skin cancer in the two countries.

By the beginning of Chapter 3, students know that Australia receives more ultraviolet light than Brazil, and they turn their attention to investigating why Australia receives more ultraviolet light than other parts of the world. Is it possible that something different is happening to the light as it travels from the sun to Earth’s surface in Australia? To answer this question, students investigate what can happen to light as it travels. Through investigations and Active Reading, students learn that light can be absorbed by a material, transmitted through a material, or reflected off a material. They also learn that when light is transmitted or reflected, the energy goes with the light. Next, students receive evidence about how light interacts with different substances in the atmosphere, including ozone, which absorbs ultraviolet light. Students learn that the atmosphere above Australia has less ozone than the atmosphere above Brazil, and use the Light Waves Modeling Tool to show how this allows more ultraviolet light to reach Australia. By the end of the chapter, students are ready to use the evidence about ultraviolet light, ozone levels in the atmosphere, and melanin levels in the population to write a final argument to the Australian Health Alliance about why the skin cancer rate in Australia is so high.

In Chapter 4, students apply what they have learned about how light interacts with materials to a new phenomenon: Scientists from the fictional Australian Institute of Marine Biology want to know whether a species of crab that lives near the ocean floor can see the plankton it eats. Students analyze evidence about how different types of light interact with ocean water and the dense mass of algae above where the crabs live. Students present their ideas and evidence to the whole class in the Science Seminar, and by the end of the chapter they are prepared to apply their knowledge of what happens to light as it travels and their analysis of the evidence to construct a final written argument.