Lesson: Measuring Tears

Launch the slideshow “Studying Tears” and zoom in on the image of the first slide so that students can’t see the text. Ask students to describe the photograph and have them guess what it shows, keeping the description hidden. Then tell students the photo is a close-up image of caiman tears. Click through the slideshow to view the tears of other animals. Select volunteers to share their observations for each photograph.

Have students read the article independently. As they read, ask them to take brief notes about different adaptations each animals’ tears provide and which paragraph they found the information in. Then have volunteers share what they learned. For example: Tears allow animals to blink less, so they avoid attracting predators with movement.

• Why are graphs important? What is the point of displaying data in a graph? (Graphs help tell stories about data. They make the data easier to understand. You can organize or compare information, or you can spot trends.)
• When you make a graph, what is important to include? (You must include a title, axis labels, and scales.)
• What types of graphs were mentioned in the video? What type of data can each graph be used to show? (A line graph displays data changes over time. Bar graphs compare different groups of data. Circle graphs show how different parts make up the total, or the whole.)

Have volunteers read aloud the introduction and examples of the “Displaying Data” box on page 7. Then ask students to find key words in each description that will help identify which graph is best for a particular problem. For a line graph, key words might be “change in data over time”; For a bar graph, “compare data by category”; And for a circle graph, “compare data as parts of a whole.” Encourage students to highlight or underline these phrases. Then work though the “Your Turn” questions as a class. Choose students to explain their reasoning for why they chose each graph type. 

Teach students how to construct a circle graph with proportional reasoning to determine sector sizes by using the skills sheet “Drawing a Circle Graph.”

The “Your Turn” questions provide examples of controlled experiments. Teach students about independent variables (a factor changed by the scientist), dependent variables (a factor that’s measured and tested), and controls (a part of the experiment that acts as a standard and does not change, that scientists can compare their results against) in scientific experiments. Read through “Your Turn” questions 1 and 3. For each question, ask students to identify the independent variable, the dependent variable, and any controlled variables.

Have students collect sets of data around their homes and then determine which graph types would best represent these data sets. If students have difficulty brainstorming data sets, provide them with some ideas to get started: Measure lengths of pencils; count different items in their refrigerator; track how many paper towels are used over the course of a week.