To review and compare plant and animal cells, and then build a model of an animal cell.
This lesson is the first of 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 a 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 will compare a plant and animal cell and then make a model of a cell. They will select items to represent various cell structures and justify their choices by describing how the items they have chosen represent the actual parts of a cell. Prior to this lesson, students should have at least been introduced to cells, including the basic differences between plant and animal cells.
In Cells 2: The Cell as a System, students will review cell structures and investigate how the components of a cell operate as a system.
Review all websites used in the lesson, paying close attention to the background information on the Inside a Cell Teachers Guide from the Genetic Science Learning Center.
Just before the lesson, gather the materials and place them on a large table so that students can select the items they will use for the cell model at the appropriate time. Note: You may want to have students bring in some materials from home.
This activity is intended to review the basic structures of an animal and plant cell. Refer students to Eucaryotic Cell Interactive Animation, on the Cells Alive website, where they can look at the picture of an animal cell. Once students are to the main animation page, they should choose "Animal Cell."
Ask these questions:
- What are the parts inside the cell? (For example, the nucleus, endoplasmic reticulum, mitochondrion.)
- What part of a cell keeps it intact? (The cell membrane on the outside and the cytosol on inside.)
- What do you think some of these cell parts do? (Answers will vary.)
Have students click on the organelles in the picture to see an enlarged view and description of each. Do not focus on the terms used so much as on the big idea that the cell has many parts and each has a job to do. Emphasize that this is a model of an animal cell and that it doesn't represent any cell in particular.
Next, have students go back to the Eucaryotic Cell Interactive Animation page of the Cells Alive website and choose "Plant Cell" to see an image of a plant cell. Again, have students click on the organelles in the picture to see descriptions and enlarged views. Remember, focus on big ideas here rather than specific terms.
- What structures indicate that this is a plant cell, rather than an animal cell? (The cell wall and chloroplast.)
- What do these structures do? (The cell wall provides and maintains cell shape and serves as a protective barrier. The chloroplast contains chlorophyll and provides a plant's green color.)
Again, emphasize that this is a model of a plant cell and that it doesn't represent any cell in particular.
Distribute the Inside of a Cell student sheet and have students complete the first two columns. Have them indicate whether each structure is part of a plant cell, animal cell, or both by placing a check in the appropriate column(s). For example, a cell wall is only part of a plant cell, so only the plant box should be checked. Whereas a cell membrane is part of both a plant and animal cell, so there should be two checks.
When you are comfortable that students understand the basic differences between a plant and animal cell, let them know that they will work in pairs to build a model of an animal cell, choosing materials from a variety of items that you provide.
Refer students to the Inside a Cell page. This page features an interactive presentation of the inside of a cell. After going through the different parts of a cell, student pairs should discuss briefly the types of items they could use to represent the cell structures listed on the student sheet. Then they should gather their materials (from the collection you prepared ahead of time) and make the cells.
Model Making Tips:
- Students should work in pairs, though each can make his/her own model cell depending on the amount of materials available. Working in pairs is important because the Karo syrup can be messy and students will need to work together to pour it into the plastic baggie.
- Students should put the items representing the various cell parts into the baggies before they pour in the syrup, so that they can promptly seal the bag once the syrup is poured.
- Once the "cell structures" are in the baggie, have students add the syrup. Have them pour the syrup into a measuring cup that has a spout for easy pouring. One student should carefully hold the baggie with both hands as the other pours in the syrup.
While making their models, students should continue working on the student sheet. On this sheet, they should record the function of each structure, using information from the Cells Alive website used in the Motivation, as well as the Inside a Cell page.
In addition, they should record the material they chose to represent each cell structure, as well as the reason for doing so (i.e., indicate how the material is representative of the particular structure).
Note: The student sheet contains two structures found only in plant cells (cell wall and chloroplasts). Because students are making models of animal cells, have them mark N/A in the "Materials Used" and "Why Used" boxes for these structures.
After students have made their model cells, allow students to compare their models and discuss the similarities and differences.
Then, ask these questions:
- Why do we often depend on models? Why are models useful when discussing cells?
- How is your model like a real cell?
- How is it different?
- What are some limitations of models in general?
- What could we do to make this a model of a plant cell?
Students should understand the basic functions of the cell structures highlighted in this lesson, as well as have a better understanding of the usefulness and limitations of models. Assess students on their answers to the student sheet as well on their participation in class discussions.
Follow this lesson with the second lesson in the cells series: Cells 2: The Cell as a System.
The Science NetLinks lesson Mitosis introduces cell division. In this lesson, students create a physical representation of mitosis on posterboard, and then write and perform a skit to show the process of mitosis.
The following activities from the Access Excellence website can be used to extend this lesson:
- The Cell can be used to reinforce or reteach the concepts covered in this lesson. In this activity, student groups investigate individual cell structures for both plant and animal cells. Each group is responsible for creating a model of a specific structure that will be used to create class models of plant and animal cells.
- Cell Project is a cooperative learning activity in which students also construct a giant cell model.
- Cell Observation is a guided lab for students to examine cells under a microscope.
- Cell Organelles can be used as an alternate assessment. It requires students to collect electron micrographs of cells.