To review cell structures and investigate how the components of a cell operate as a system.
This lesson is the second of a two-part series on cells. At this grade level, research suggests that understanding of systems can now be made more explicit. Students can engage in the analysis of parts, subsystems, interactions, and matching. The descriptions of parts and their interaction are more important than just calling everything a system. (Benchmarks for Science Literacy, p. 265.) In addition, studies of student thinking indicate that they tend to interpret phenomena by noting the qualities of separate objects rather than by seeing the interactions between the parts of a system. (Benchmarks for Science Literacy, p. 355.) In the context of cells, students should be encouraged to look at the cell as both a system and subsystem and to develop an understanding of how the parts of a cell interact with one another, i.e., how they help to do the "work" of the cell.
In Cells 1: Make a Model Cell, students compared a plant and animal cell and then made a model of a cell.
Cells 2: The Cell as a System encourages students to view the cell as a system. Students will begin to understand the cell as a system by exploring a more familiar and tangible example of a system-a factory. Throughout the lesson, students will compare the factory to a cell, beginning to understand how both can be thought of as a system.
Preview the Cells: A Busy Factory resource used in this lesson. As you'll see, the site contains introductory as well as rather in-depth information. Determine what level of information is appropriate for your students.
Students will read seven pages of online material in this lesson. They can do this reading online, or you can print the text for them ahead of time.
Begin by reviewing the organelles included on the Science NetLinks student sheet, Inside of a Cell.
Once you're comfortable with students' understanding of basic cell structures and functions, tell them they're going to switch gears for a moment and think about systems.
Ask students these questions:
- With what systems are you familiar?
- What makes these things systems? That is, how would you define a system?
- (Examples are school system; the solar system; the digestive system.)
- (Responses will vary, but may include terms such as parts, whole, inputs, and outputs.)
Next, focus the discussion on factories by asking these questions:
- With what types of factories are you familiar?
- Do you consider these systems? Why or why not?
- (Responses will vary.)
- Responses will vary, but may include terms like products, input, output, parts, and whole.)
Let students know that in this lesson they will compare a factory and cell, considering how each can be thought of as a system.
Divide the class into small groups of two or three. Students should use their The Cell as a System student esheet to go to Cells: A Busy Factory, which has been adapted from Beyond Books.
When students arrive at the site, have them pay close attention to the picture of the cell/factory and read the first four paragraphs (stopping when they reach the section labeled, Cell Structure: An Overview).
Then ask this question:
- As stated on this site, a cell is a factory that produces what? (It produces proteins.)
Next, distribute a copy of the Comparing a Cell to a Factory student sheet to each student, and have students work in their groups to complete it. They can find the answers by reading the rest of the resource.
Note: You can find sample answers to the student sheet on the Comparing a Cell to a Factory: Answer Key.
Discuss answers to the student sheet in class, and then ask these questions:
- What is the ultimate energy source for the cell? Remember that a cell needs energy to produce proteins.
- Why is the cell membrane explained in terms of a "fluid mosaic model?"
- What organelle contains the "blueprints" for the production of proteins?
- Three types of what do most of the work in the cell? For example, identify the cell to other cells; move materials in and out of the cell; allow the cell to interact with other cells?
- Where does most of the cell's work take place?
- What is the basic difference between rough endoplasmic reticulum (ER) and smooth ER?
- What are some things that can happen to proteins, once they leave the golgi apparatus and enter the cytoplasm?
- (The sun.)
- (Because the phospholipids and proteins that make it up are not fixed in a rigid pattern; they are just floating around in the membrane.)
- (The nucleus.)
- (In the cytoplasm.)
- (Rough ER contains ribosomes, smooth ER does not.)
- (They can become plasma membrane proteins; stay in the cytoplasm for use by the cell; or be stored in vesicles until needed for transport.)
Students should be able to clearly state why the factory, and more importantly the cell, can be thought of as systems. They should also be able to explain how the individual parts of the cell system operate within the larger context of the cell, and that the processes necessary for life take place within each cell.
Ask the following questions to assess this understanding, telling students to think about the cell as a system:
- When this system is working, what does it do?
- For this system to work, must it receive any input?
- What, if any, output does this system produce?
- Identify at least four parts of this system. Describe what each part does, and tell how each part contributes to the system as a whole. Can any one part of the system do what the whole system does? Justify your response.
- Identify at least two parts of this system that must interact if the system is to function. Describe how these parts interact.
- Can you identify any subsystems within the whole system?
- Describe how the functioning of this system would change if one of the parts wears out.
- In what ways is it useful to think of the cell as a system?
- (It produces proteins.)
- (Yes; for example, energy ultimately from the sun.)
- (It produces proteins.)
- (Answers will vary. Students should realize that the organelles need to work together to produce proteins.)
- (Answers will vary.)
- (Answers will vary, but students should be able to describe at least one subsystem.)
- (Answers will vary.)
- (In general, thinking about a cell as a system helps in understanding individual cell organelle functions, and how they operate within the larger context of the cell.)
The Science NetLinks lesson, Mitosis, introduces cell division. In this lesson, students create a physical representation of mitosis on posterboard, and perform a skit to show the process of mitosis.
For another lesson on systems, see the Science NetLinks lesson entitled The Bicycle as a System, in which students identify the properties of the various subsystems of a bicycle and examine how they relate to the whole.
Students could create a travel brochure for a tour through the cell. Instructions are available in an activity called Travel Brochure for a Cell, on the Access Excellence website.