During the Activity
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Activity Sequence in Brief
Day One
Engage
Display a "Mystery Beaker" (sand and yeast). Discuss and record characteristics of life. Add nutrient solution to beaker.
Explore
Students use microscopes to observe and record plant and animal cells.
Explain
Students compare and discuss cell observations. Students examine the "Mystery Beaker" and share their observations. A Student Reader Article and related Activity Sheet are assigned for homework.
Day Two
Engage
Students examine the "Mystery Beaker" and draw some conclusions.
Explain
Students learn about cells and cell membranes. The Student Reader Article and related Activity Sheet are reviewed and discussed.
Explore
Students observe soap bubbles and learn about vesicles.
Explain
Teacher explains the relationships between soap bubbles, vesicles, and cells.
Elaborate
Students watch a video on the testing of a meteorite. They complete their Activity Sheets.
Evaluate
Students get a homework assignment.
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Day One
 EXTENSION: If your students are not yet familiar with safe and correct use of the microscope then do the Extension Activity: Microscope Skills Lab prior to Day One.
Engage (10 minutes)
- Display a "Mystery Beaker" containing a mixture of yeast and sand but do not label or state the contents. Ask students: Is this material alive? How can you tell? Distribute a sprinkling of the mixture onto students' hands or onto paper towels so students can observe more closely. You may want to distribute hand lenses as well.
- Encourage students to suggest characteristics of living things and record their ideas on chart paper titled "Characteristics of Life." (Students will probably suggest such characteristics as eating, reproducing, making waste products, dying, etc.) Draw students' attention to or add characteristics about obtaining food, reproducing, getting rid of wastes, and requiring water. Ask students for ideas as to how to test this "mystery substance" for life. (Lead them to the idea of "feeding" or "watering" it.) Ask students to predict what might happen if we add a nutrient solution to the beaker: if it does not contain living things, what would they expect to see? If it contains living things, what would they expect to see?
- Place the beaker in a shallow pan to collect any spills. Add enough warm nutrient solution to fill the beaker to three quarters, stir deeply to moisten the entire contents, and observe. Have students describe what they see. (The yeast and warm nutrient solution should slowly begin to foam, the foaming will continue throughout the class period.) Set aside in a warm place - it will be observed later in the period and again the next day.
Explore (25 minutes)
- Say that today students will look at microscopic living things that are large enough to be observed with their student microscopes. As they do today's activity, ask students to look for characteristics that the microscopic living things have in common.
- Demonstrate how to prepare an elodea slide. Demonstrate how to obtain the onion skin and how to stain it with methylene blue. Demonstrate how to obtain cheek cells and stain them with methylene blue. (The staining can be shown by putting a slide on the overhead projector. Students will be able to see the dye diffuse across the slide under the cover slip.)
- Have students form into teams of two and give an
 Observing Living Things Student Activity Sheet and a packet of colored pencils to each team. Explain that there are three samples of living things but each team will observe two of the samples. Allow two or three minutes for students to read the directions and then direct them to begin the activity. Remind students to do careful, detailed drawings, in color, using the entire space provided on the Student Activity Sheet, and to write as many observations as they can.
Explain (15 minutes)
- After student teams have finished their lab work, ask them to compare their drawings and observations with those of a team who observed different samples. Direct them to look for characteristics that all samples had in common and to write those observations down on their Observing Living Things Student Activity Sheet. Collect the activity sheets.
- After student teams have completed their observations, ask them to identify the characteristics the microscopic living things had in common. (Observations may include boundaries between distinct shapes, "things" inside the boundaries, specific shapes - round, rectangular, color, relative size differences, etc.) Mention that the shapes students observed are cells and all living things are made up of cells. This will be examined further later in the activity.
- Review the chart paper titled "Characteristics of Life" from the beginning of the activity, add "made of cells" to the list.
- Announce that it is time to take another look at the "Mystery Beaker." Show students the beaker. Solicit observations: has the appearance changed? How? Do they think there is life in the beaker? Why, or why not? How would they explain the changes? Encourage students to relate the "Characteristics of Life" to what is happening in the beaker. (At this point the yeast should have created a significant amount of foam, maybe enough to overflow the beaker. Foam could be a waste product. Bubbles, also a possible waste product, will be apparent in the sand as well as rising through the liquid, which is murky. The murky liquid could be full of growing, eating, reproducing cells. Students should suggest that cells would be visible under a microscope if the "Mystery Beaker" contains living things.)
- Assign the Student Reader Article, "Is It Alive?" for homework. Hand out the "Is It Alive?" Student Activity Sheet and tell students to complete the first section after reading the article.
Day Two
Engage (5 minutes)
- Display the "Mystery Beaker." (NOTE: handle carefully to prevent the layer of dead yeast from being disturbed.) Ask students to describe what they see. Encourage students to relate the "Characteristics of Life" to what is happening in the beaker. (At this point the liquid probably has overflowed, leaving dried up residue along the sides of the beaker. The nutrient solution should be clear, though bubbles may still be rising through it. Bubbles can probably been seen in the sand as well. There should be a layer of white residue [dead yeast cells] on the top of the sand layer. The layer of white residue and the clear liquid could mean that most of the organisms have depleted their food supply and died off.)
Explain (10 minutes)
 Show the image: Composite of Living Things. Have students compare the living things in the image to the observations of living things they made in Day One. NOTE: They can do this from memory or use their Observing Living Things Student Activity Sheet.
- A) red blood cells
- B) algae
- C) skin cells
- D) fresh water diatom
- E) colonial algae (Volvox)
- F) green algae (Scendesmu)
(All have boundaries, "things" insides the boundaries, shapes are similar - some round, some rectangular.)
- Say that the living things they observed under the microscope yesterday, and the living things pictured here, are called cells. The boundary at the edge of a cell is a membrane called the cell membrane. Return to the image: Composite of Living Things. Ask students to point out which are cells and explain how they know. (All are cells. All have cell membranes.)
- Explain that all living things are made up of cells. Write this preliminary description for cell on the board: "Cells are the basic units of life; all living things today are made of cells or are the products of cells." (NOTE: products of cells include: hair, nails, tendons [animal cell products], and xylem, sugars, etc. [plant products].)
- Ask students if they have ideas about what function the cell membrane serves. (To keep some things in, keep some things out of the cell. To give the cell its shape. To define the cell from its environment.) Record the definition of cell membrane on the board. Cell membrane: The outer barrier of a cell. Separates a cell from its environment, and is typically composed of phospholipids. Allows for the selective passage of some molecules.
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 emind students that the cells they observed under the microscope and the cells in the image: Composite of Living Things were seen in cross section or in a limited depth of view. This is akin to taking a slice from a hard boiled egg, the slice is what was observed but the whole egg represents the entire cell. Show the image: Whole Cells to reinforce the 3-D nature of cells.
- Tell students that the substance which made the "Mystery Beaker" foam is a single-celled organism described in the student reader article. Have students explain what they think the substance is and what happened in the beaker. (Yeast, in a state of suspended animation, was present in the sand. When the nutrient solution, sugar and water, was mixed in the yeast began to eat, grow, and reproduce. The rising bubbles are the byproducts of the yeast metabolism [carbon dioxide]. When the food supply was depleted the yeast died off. The layer of white residue on top of the sand is dead yeast cells.)
- Have students take out their "Is It Alive?" Student Activity Sheet and the Student Reader. Review and discuss the "Is It Alive?" article and student activity sheet using the "Is It Alive?" Teacher Answer Key. Be sure students add the definitions of cell and cell membrane that were recorded on the board. Other definitions will follow.
Explore (10 minutes)
- Put some soap solution in a shallow, flat-bottomed glass dish. Position the dish for display on the overhead projector. Turn on the projector. Using a straw, gently blow just below the surface of the liquid to create a collection of soap bubbles. Gently pierce a bubble with the wet straw - it should not break. Wiggle the dish - the bubbles should wiggle, too. Ask students for observations about the bubbles.
 (They should notice size, shape, ability to move and return to original shape, ability to be pierced and to self-repair, etc.) OPTIONAL: If you have time, provide straws and a petri dish with soap solution to each pair of students. Have them conduct their own experiments and make observations.
- Show the video: Vesicles. Ask students what cells and vesicles have in common. (Membranes that separate what is inside from what is outside.)
Explain (10 minutes)
- Explain that soap bubbles are also similar to vesicles, and similar to cells. Soap molecules are composed mostly of long chains of carbon atoms, and carbon atoms are also linked to hydrogen atoms. Say that molecules made up of only carbon and hydrogen atoms are called hydrocarbons. (Motor oil and gasoline are other examples of hydrocarbons.)
- Remind students of Wenonah Vercoutere's (Dr. Deamer's graduate student) explanation of the hydrophilic/hydrophobic characteristic of vesicles. This is also true of soap bubbles - at one end of the hydrocarbon chain in the soap molecule there is a part of the molecule that likes to be in water: it is hydrophilic, or water-loving. The rest of the chain avoids water: it is hydrophobic, or water-hating. Since the water-avoiding end of the molecule does not want to be in contact with the water the soap molecule is mixed with, it turns inward. When many molecules turn inward like this a sphere is produced: in this case, the sphere is a soap bubble.
- Say that soap molecules self-assemble into bubbles that resemble the microscopic appearance of living things: they resemble cells. In addition, soap bubbles can also behave like cell membranes.
Elaborate (10 minutes)
- Ask: If vesicles were precursors to cell membranes, where might the first vesicles on Earth have come from? Tell students that they are going to watch a video that shows the examination and testing of a meteorite. Tell them that as they watch the video, they should think about the questions: What steps does Dr. Deamer perform to analyze the meteorite. What does Dr. Deamer hope to simulate by following these steps?
- Before showing the video, write on the board:
- Vesicle: a membranous and usually fluid-filled sac.
- Organic molecule: molecules containing carbon, usually associated with living things.
- Examples of organic molecules found in the tested meteorite: hydrocarbons, amino acids, fatty acids, and proteins. (These will be covered in greater depth in future activities.)
These are terms students will find useful in understanding the video. Leave this information on the board for future student use.
 Show the video: Investigating a Meteorite.
- After the video ask the following questions: What does Dr. Deamer hope to simulate by following his procedure? (He is trying to simulate the conditions on early Earth.) What did Dr. Deamer find in the ancient meteorite? (Vesicle-forming molecules.) Ask students to speculate why Dr. Deamer and other scientists are so excited about this discovery? (It provides evidence that vesicles may have been the early precursors to cells. It also shows that vesicles can be made with certain materials from space in early Earth-like conditions.)
- Have students return to their "Is It Alive?"
 Student Activity Sheets and complete using the definitions written on the board.
Evaluate (5 minutes)
- Display the image: Living Things Homework Assignment and have students copy onto their own paper.
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NOTE: All Teacher CD-ROMs in the complete Voyages Through Time curriculum (not this SAMPLE) provide both MS WORD and PDF versions of items such as student activity sheets and tests. In the complete VTT curriculum, teachers may use MS WORD (or other word processor) to modify any of the printable items if they wish to do so.