Microbiome Lesson Brief Microscopic Evidence of Life Hands-On Flextension: Microscopic Evidence of Life Overview This hands-on activity builds on and reinforces students’ understanding of organisms and the scale of living things. Students first engage in a discussion about how they would know whether something is living or nonliving, followed by considering what the expected differences might be if they were viewing objects at the microscopic scale. Given specific objects, students then sort and discuss whether they might be living or not. Students prepare slides and observe these objects under a microscope, and that experience helps them identify characteristics of living things. Later, students bring objects from home so they can determine if there is microscopic evidence that shows whether these objects are living or nonliving. The purpose of this lesson is for students to gather evidence that living things are made of cells. You might choose to include this Flextension if you have access to microscopes and would like your students to have firsthand experience with observing cells. Recommended Placement: between Lessons 1.1 and 1.2 Suggested Time Frame: 90 minutes over two class periods (longer if students need instruction on using a microscope) Next Generation Science Standards (NGSS) Performance • MS-LS1-1: Conduct an investigation to provide evidence that Expectations living things are made of cells; either one cell or many different numbers and types of cells. Disciplinary • LS1.A: Structure and Function: Core Ideas ° All living things are made of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). (MS-LS1-1) ° Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2) Amplify Science Flextension Lesson Guide 1 © The Regents of the University of California. All rights reserved. Microbiome Lesson Brief Microscopic Evidence of Life (continued from previous page) Disciplinary • LS1.A: Structure and Function (continued) Core Ideas ° In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions. (MS-LS1-3) Science and • Practice 1: Asking Questions Engineering • Practice 3: Planning and Carrying Out Investigations Practices • Practice 8: Obtaining, Evaluating, and Communicating Information Crosscutting • Scale, Proportion, and Quantity Concepts • Structure and Function Vocabulary • cells • microscopic • organism Materials & Preparation Materials • thin fabric piece, light-colored and about 2 inches x 2 inches* For the Class • 1 feather, about 3 inches long (or • Hands-On Flextension copymaster: several smaller)* Microscopic Evidence of Life • 1 roll of paper towels* • 1 onion* • water* • 2 teaspoons of dry yeast* • 30 drops 1% methylene blue solution* • 3 teaspoons of salt* • 9 cups (plastic or similar containers, • 3½ teaspoons sugar* one for each type of object)* • several thin plant leaves (elodea, • masking tape* bamboo, or romaine lettuce)* • flat toothpicks (or small wooden • 1 sheet light-colored paper* craft sticks or cotton swabs)* 2 Amplify Science Flextension Lesson Guide © The Regents of the University of California. All rights reserved. Microbiome Lesson Brief Microscopic Evidence of Life • 2 spoons (plastic or metal)* Digital Resources for Microbiome • measuring spoon, ½ teaspoon* Lesson 1.1. Make enough copies so • measuring cup, 1 cup* each student will have all four parts. You might, however, want to hold For Each Group of Four Students off on distributing the Part 4 sheets • 1 tray* until the day you conduct the activity • 1 light microscope (at least 100X with the objects from home. magnification)* 2. Prepare dropper bottles. Add • 1 dropper bottle with water and approximately 10 mL of water to methylene blue* each small bottle. Add 3 drops of 1% • 1 dropper bottle with water* methylene blue solution to half the • 9 microscope slides* bottles; the other half should contain • 9 coverslips* only water. Label the bottles. • forceps* 3. Prepare nine different viewing For Each Student objects and place them in cups. Prepare enough objects for all • 1 copy of Hands-On Flextension: classes. The intent is to have nine Microscopic Evidence of Life student cups, each with one type of viewing sheets* object for a central materials station. • 1 pair of gloves* *teacher provided a. Onion for cup 1: Cut the onion into pieces and separate pieces into individual scales Preparation (layers). Each scale has a thin, transparent membrane on the Safety Note: Using Chemicals underside. Remove this tissue- It is recommended that students wear like outer layer with a pair of gloves when handling methylene blue forceps or your fingernail, and or iodine. Concentrated methylene blue place them in a viewing object and iodine solutions are toxic when cup. There should be at least one ingested, can irritate the eyes, and stain piece for each group. skin or clothing. b. Yeast for cup 2: In another viewing 1. Print Hands-On Flextension object cup, mix 2 teaspoons (one copymaster: Microscopic packet) of yeast with about ½ Evidence of Life. Locate the teaspoon of sugar and ¼ cup of Hands-On Flextension copymaster: warm water. Mix gently. Microscopic Evidence of Life in Amplify Science Flextension Lesson Guide 3 © The Regents of the University of California. All rights reserved. Microbiome Lesson Brief Microscopic Evidence of Life c. Fabric, paper, leaves, feathers • 4 sets of gloves for cups 3–6: Cut or tear these • 12-inch piece of masking tape objects into tiny pieces that will fit 6. Create Living and Nonliving under a coverslip. Place objects T-chart. Make a T-chart on the by type into viewing object cups. board with the headers “Living” and d. Sugar, salt, toothpicks for cups “Nonliving.” You will add to this chart 7–9: Place these items in the throughout class. Remember to remaining three cups: erase entries between class periods. • 3 teaspoons of sugar and one 7. Optional: Prepare and examine plastic spoon in cup 7 a set of slides before class. In • 3 teaspoons of salt and one order to support your students as plastic spoon in cup 8 they work, it is helpful to anticipate the student experience and view • toothpicks or craft sticks in these objects under a microscope cup 9 beforehand. Prepare a sample set 4. Set up central materials station. of slides with the nine objects and Place the nine filled viewing make your own observations. object cups in a central location so students can easily obtain the 8. Immediately before the lesson, objects they need. have on hand the following materials: 5. Prepare microscope stations and • student sheets trays. Set up microscopes around • microscope stations with trays of the classroom, one microscope slide preparation materials for each group of four students. If • filled viewing object cups in a you have additional microscopes, central location students can work in smaller groups. Prepare one tray of slide preparation 9. Between classes, clean and materials for each microscope. Place replenish microscope tray the following items on each tray: materials. Clean slides, coverslips, and forceps; replenish materials. • 9 microscope slides During Part 4 (another day), each • 9 coverslips group will prepare slides for the • 1 dropper bottle with methylene objects brought from home. blue and water Students will again need the • 1 dropper bottle with water microscopes and slide preparation • 1 pair of forceps materials trays. 4 Amplify Science Flextension Lesson Guide © The Regents of the University of California. All rights reserved. Microbiome Lesson Brief Microscopic Evidence of Life Notes Methylene Blue Substitute Iodine solution can work in place of methylene blue. Typical Lugol’s iodine stock solution should be diluted with a 1:5 dilution ratio before use. Obtaining Plant Leaves Elodea or a similar aquatic plant can usually be obtained from an aquarium store. In certain areas, you may be able to acquire bamboo from a park or someone’s yard. Bamboo plants can also be purchased from some stores. Romaine lettuce is another easily obtainable option, but the cells are not as well defined. Science Background Cells are the basic unit of structure and reproduction in all living things. Some tiny organisms are made of only one cell, and this single cell carries out all the functions of life. Bacteria are one type of single-celled organism. Other examples include unicellular algae and unicellular fungi. Multicellular organisms are made of many cells. In multicellular organisms, cells are specialized to serve particular functions—for example, the cell types in mammals include skin cells, muscle cells, neurons, and blood cells. In nearly all cases, individual cells are too small to be seen with the naked eye. Tools, such as microscopes, are needed to see cells clearly and are especially necessary to view any details of cellular structure. (There are a few types of cells that are visible to the unaided human eye, including the human egg cell.) Although cells vary in size, they are typically on the scale of micrometers (1 micrometer = 1 millionth of 1 meter). Molecules are more than 1,000 times smaller, most of them less than a nanometer in size (1 nanometer = 1 billionth of 1 meter). Amplify Science Flextension Lesson Guide 5 © The Regents of the University of California. All rights reserved. Teacher Microbiome Reference Microscopic Evidence of Life Teacher Reference Preparing a Wet-Mount Microscope Slide forceps object slide 1. Place the object on the 2. Squeeze one drop of water or slide near the center. diluted methylene blue on top of the object. coverslip small piece of paper towel or blotting paper 3. Place the edge of a coverslip on the slide so it touches the edge of the liquid.