Seeing Inside Cells

Scene: The Tiniest Food Factories

Duration: Approximately 60 minutes

In this Science Scene, a dialogue to read aloud as a class, students are introduced to the microscopic structures of cells while playing the roles of three students Aviv, Jalen, and Xo, and one teacher: Farmer Raquel.

LEARNING OBJECTIVES

Students are introduced to the Focus Words, scientific language used throughout this unit.

Students demonstrate careful reading by identifying accurate details.

Students consider the perspectives of the characters through related questions.

Teacher Tips

• Think ahead about how you will assign the four roles (Aviv, Jalen, Xo, Farmer Raquel/Narrator), perhaps in groups or by having volunteers read in front of the class. Note that students often willingly take on roles regardless of the gender of the characters.
• While it is possible for the students to read the PDF of the script online, we suggest printing the script for the students so they can hold it in their hands and mark it as they read. Consider scaffolding the lesson for English language learners: you could let them preview the script before the lesson or read the dialogue silently once and ask questions to a partner.
• Prior to the reading the script, explain to students that they will encounter new vocabulary terms and ideas that may not be familiar. Reassure them that this lack of familiarity is okay. The reading is meant to introduce the ideas, not explain them completely.
• Review the focus words of the week. The focus word chart linked on the unit overview page should be used as a resource for students to review definitions and sample sentences.
• This activity is intended only as an introduction to the concepts.
• The roles of Aviv and Farmer Raquel/Narrator have most of the more advanced vocabulary and explanations, so you may not want to assign these roles to students who struggle with science text generally.

Materials

• Very optional props to consider having on hand for the performance(s), perhaps even enough for each small group of four (if the script is read in small groups).
  • basket
  • onion (or tennis balls / baseballs to stand in for vegetables)
  • cherry tomatoes (or marbles / table tennis balls to stand in for vegetables)
  • microscope
  • microscope slide

Teacher Tune-ups

• How do substances pass through the cell membrane on their own?
• How does the cell move large particles through the cell membrane?
• How do I teach students about microscopes?

Prompt

How would you build a machine to capture solar energy as some kind of fuel that humans can use?

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Initiate a class discussion prior to beginning the Science Scene.

Paraphrase this insightful passage from NASA:

The sun has powered almost everything on Earth since life began. The sun radiates huge amounts of electro-magnetic energy in all directions. Earth is only one small recipient of the sun's energy; the sun's rays extend far out into the solar system, illuminating all the other planets.

Ask:

How would you build a machine to capture solar energy as some kind of fuel that humans can use?

Photo Credit: NASA

Some teachers have several groups of students read at the same time. Other teachers select a few students to "perform" in front of the class. You may want to read the entire passage out loud to the class once before assigning roles to students or dividing up into groups.

The timing of 30 minutes assumes 10 minutes of the teacher reading the script to the class, 10 minutes for small groups of four students reading to one another, and 10 minutes for one selected group to perform the script in front of class.

The role of Aviv should go to a stronger reader. Farmer Raquel is a gardening teacher and uses words that may be beyond students with limited language skills.

While most of the Focus Words appear in this script, there are a few terms that appear in other activities in this unit but aren't used in the student dialogue:

• nucleus: this term is also to be explored in L5 and the M units

• fuel (compare to its use in the unit E3)
• process (compare to its use in the unit T4)

As the script is read, project the slide showing the different parts of the onion cell that the characters identify.

This dialogue touches on two topics explored in greater depth in other parts of the SciGen curriculum:

• Trophic levels and the carbon cycle in Unit L1: Populations in Balance
• Photosynthesis in E3.3 Energy Transformations and M1 Small, Smaller, and Particularly Small.

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The Script:

Setting: After classes have ended, Aviv, Jalen, and Xo are in front of their school, trying to decide what to do this afternoon.

Aviv: Hey, do you want to go visit the world’s tiniest solar-powered food factory?

Jalen: Now? Where?

Aviv: Sure…. it’s right behind the library.

Xo: What? In the school garden? Since when is there a factory there?

Aviv: Let’s go check it out. Farmer Raquel may still be there.

Narrator: The friends walk to the garden. The gardening teacher, Farmer Raquel, is nearby, collecting fallen leaves for the compost pile.

Xo: OK, I give up. Where is your tiny solar-powered food factory?

Aviv: Right here, and here, and here. All around us. Millions—maybe billions—of them!

Jalen: Yeah, right. Are you in some alternate reality, dude? I don't see anything.

Aviv: Just because you can't see them, doesn't mean that they're not there. They're so small, they're microscopic. What we need is a microscope and a… uh… specimen.

Jalen: Why do we need a spaceman?

Xo: (laughing) Sheesh, Jalen. Aviv said SPEHS-uh-mun. Specimen. A sample. But of what?

Aviv: (picking up a small onion from the basket held by Raquel, who came over to see what was happening) How about this? We can use a thin layer of onion, just the skin.

Xo: Oh, I get it! You're talking about plants! I never thought of plants like that, but you're right—plants really are solar energy plants, solar energy factories.

Jalen: This is confusing! Plants are…energy plants? Huh?

Aviv: Well, actually, I don’t mean the whole plant. The real factories are the millions of cells that make up each plant. Each cell is like a tiny machine that uses sunlight to change air and water into fuel.

Jalen: Fuel? Do you mean biodiesel?

Aviv: Kind of, sort of. Fuel like food. Plants have been doing this as long as they've been around. Is that about right Farmer Raquel?

Raquel: Absolutely! Plants make their own food. They convert the sun’s energy into sugars—something that they can store and access later as an energy source. Plant cells power themselves, using energy from the sun—solar power. So a plant cell really is a tiny solar-powered food factory. Humans have never invented any kind of nanomachine as cool as the cell, the basic unit of all life. Here, let’s take that onion into the shed to take a closer look.

Farmer Raquel helps the three friends mount a thin piece of onion skin onto a slide and then look at it through the microscope.

Raquel: Look closely. What do you see?

Xo: It looks like a strange brick wall.

Raquel: Each “brick” is a cell. They look flat, but just like bricks they are totally 3-D. And you're right that there are walls in there. Those thick lines around each plant cell are cell walls. Just inside each walled-off space, there are membranes for each cell, too thin to see.

Jalen: The cells have some kind of brains?

Raquel: Oh, no, not brains but membranes. A very thin boundary between the inside and outside of any cell. It's like a wall, but thinner and more wiggly.

Aviv: Oooh! I see dark dots. Looks like there's one on each cell.

Raquel: Those are the nuclei. Each dot is the nucleus of one onion skin cell. It's the closest thing the cell has to a brain. The nucleus is the control center, and it has the cell's DNA.

When finished with the Science Scene, ask students to answer these four questions.

You may opt to assign single questions, rather than having all the students answer all the questions. Students can discuss with their partners and try to reach an agreement about their answers to the questions. This activity is an opportunity for students to practice using scientific language as they discuss the questions.

Possible answers:

• Both definitions overlap with Aviv's meaning in different ways. Cells are the place of some kind of production (sugar production).
• Each cell uses sunlight to change air and water into fuel.
• Sugars are something that plants can store and access later as an energy source.
• Some of the differences between plant and animal cells mentioned in the script:
• Animal cells don’t use sunlight for energy the way that plant cells do. Animal cells require energy that animals get from plants. Human cells have cell membranes but not cell walls. Plant cells have chloroplasts.
• Consumers consume, while producers produce food for themselves and others.

Comprehension Questions

Respond in writing to the questions, then compare and discuss your answers with someone else.

The Merriam-Webster Dictionary defines "factory" as

1. a building or set of buildings with facilities for manufacturing
2. the seat of some kind of production

What meaning do you think more closely overlaps with the way Aviv uses "factory" to define a cell?

Draw a simple sketch of some of the parts the students see in the cell when they put the onion specimen under the microscope.

What do plant cells use sunlight to do?

How does Raquel describe plants' use of sugars?

What are some differences between plant and animal cells? What are some similarities? Use complete sentences OR a Venn diagram to record your answers.

What's the difference between consumers and producers? How is that difference reflected on a cellular level?

Writing

Your teacher will assign you one or more of these writing prompts. After writing your response, share your answers with a neighbor, then be ready to share what you talked about with the rest of the class.

Many people believe that trees get all they need from the soil around them. It is a common misconception: a way that people think about the world that doesn't match scientific fact.

List some ideas about cells and plants that you know are true. Then list some ideas that are ideas that are false but believable: misconceptions you think your friends may have, or misconceptions you used to have. Read them in a random order to your neighbors and see if they can tell which ones you meant to be true.

Explain how the world's largest tree, the General Sherman giant sequoia, grew from a seed about 5 mm (0.25 inch) long, to a tree nearly 95 meters (311 feet) tall, a base of 103 feet (31 meters) around, weighing over 2,000 tons.