Student-generated model for animal cells. 

Contexts in source publication

Context 1

... provides a “drafting” approach while having a designated area for student, name of cell, and teacher approval. The graphing format of the DesignGrid paper (as shown at the product website) gave the students a sense of order and layout that preempted poor planning. However, large graph paper or posterboard could be substituted. Students deciphered structures and functions of a particular organisms cell to determine the specific cell assigned to each group (Table 2). Four organisms were selected and divided evenly over eight table groups. Presently, I use cell types from the following organisms for the projects model: strawberry plant, salmonella bacteria, human cells, and hydra. In Table 2, the teacher circles specific properties ahead of class that serve as clues about which of an organisms cells a particular table group will study. This method of determining the organisms cell, rather than being told from the outset, fosters guided inquiry, group decision-making, and participation. It reinforces knowledge of each cells properties by using prior knowledge, notes, textbooks, and group decision making. For this reason, group scores and participation were allocated, even though some school districts are moving away from this type of grading. Once the organism and cell type were agreed upon by each member, the group sought out their “matching” cell type among the other table groups of four students each. This required students to walk from one table to the next, comparing results from their cellular clues, until the matching cell was found. These matching- cell-type tables then had to communicate with one another to obtain chemical compounds needed by organelles. This ensured that each group of students was up and communicating with its matching cell. The next step was experimenting on how best to draw the cell and its membrane while allowing for the passage of compounds. Membrane permeability and chemical exchange required special attention to make them tangible to students. Even though the membrane was described as a “gatekeeper” or, more specifically, a fluid mosaic structure, what this means chemically and how such things work remained a mystery for many learners. Therefore, I asked that they construct “channels” for molecular exchanges in their models. Students visualized channels in the membrane by erasing four small areas of the membrane drawn in pencil. By erasing these bits of the membrane, they could see how channels permeate the membrane and how chemical compounds and waste can be exchanged. This way, by the time students enter high school, they are familiar with the permeability of membranes, what type of compounds pass through it, and how it serves as a gatekeeper. While not explaining the details of protein channels and transport proteins that they learn in high school, this model provides the first step in preparation for later AP Biology studies (see College Board, 2011). In subsequent modifications, membrane permeability will stress that water enters through channels, whereas carbon dioxide, oxygen, and lipids diffuse directly through the membranes. Sugars, amino acids, nucleotides, and proteins will use other transport mechanisms, as appropriate for seventh grade. The structure and function of key organelles were reinforced by the project, as were connections between cellular processes and their functions in a whole cell system. For this reason, the drawing had to be large enough to accommodate eight organelles, to affix appropriate compounds to the organelles, or to depict compounds entering the cell through the membrane. For each cell model, compounds were lined up to enter or leave the cell, or to be used by particular organelles. This exchange was accomplished by table groups working with their “cellular” partner table. Because the compounds and other cellular needs came from their matching cell, students got up and carried out the process of cellular exchange and communication to obtain and use required compounds. The molecules or compounds included in the project were sugar, protein, amino acid, oxygen, lipids, water, carbon dioxide, and nucleotides. These compounds were included to reinforce prior lessons on chemical reactions that were now related to the organelles in which they take place. Waste is included in the model as it is removed from the cell by the lysosomes and made ready by intracel- lular digestion to be released back into the cell in the form of vesicles. Sunlight is included for the chloroplast and enzymes as necessary for many reactions. Symbols were compiled representing each compound listed above. Students obtained compounds from their matching cell table, cut these out, determined where they entered the membrane, and affixed some of these compounds to organelles for chemical reactions. For example, four symbols for amino acids were cut out, with two flowing through the membrane and two others placed on the ribo- some, where they were used to build proteins (see Figure 1). To demonstrate cell-to-cell communication, recognition, and signaling, students matched unique cell-surface receptor sites with the correct signal molecule. The paper cutouts for the receptors came from one table, but the matching signal molecules had to come from the cells companion table, indicating that the students had “acted out” cell communication. Each table groups scale model had to have four sites, with the correct signal placed on them. Once applied, these were easily seen and graded to ensure that “cell communica- tion” occurred. “A Cellular Encounter” became the culminating project for our unit on cells, requiring three full 90-minute classes. Grading of the project was based on the following assessment tools: 1. a group score for the final scale model drawing using a project rubric 2. an individual grade for the project packet, and 3. a grade provided by the teacher for observations of group decision making and individual participation. The rubric used to grade student knowledge, performance, and the accuracy of the model is shown in Table 3. The total score for this part of the assessment is 50 points. The second 50 points come from individual responses to the final, open-ended questions, with points awarded for use of evidence in the answer and completeness of response. An example of one version of the animal cell model is presented in Figure 1. The range of organelles selected is clear, as are the channels through the membrane. Requisite compound symbols are attached to each organelle or in transit through the membrane. As noted above, further specificity can be added to capture exactly what type of mechanism is used by each specific compound to enter or leave the cell. As for the nucleus, symbols for nucleic acid molecules were correctly located; however, no further activity with the nucleus was planned for this version of the model. These nucleic acids can be seen attached to the nucleus of the animal cell. This cell model also notes the ATP production occurring from the mitochondrion. There is clearly a place where other symbols could be inserted in the nucleus, such as mRNA molecules making their way to the ribosomes, or DNA itself, and copies to show how and where it is replicated. Although these extra symbols were not included, students were familiar with the nucleus as the cells information and control center and were thus able to consider how protein synthesis might occur and how these proteins would be packaged to leave the cell. The project was undertaken by 141 students in five periods. This required 35 table groups with an average of four students per group. I rated the groups on their participation, supportive work habits, and whether or not one or two students were carrying out the work of others. Approximately 50% of the groups had a score of 5 for participation. The other groups, despite warnings and encouragement, worked consistently with less-than-full participation or with full participation only at limited times. Despite the other 50% working at less-than-optimal participation, all cell drawings were completed and turned in for grading. Students were initially presented with two concluding essays. The first asked, “What can cells tell us about life?” The second asked the students to choose one particular organelle, describe its function in a cell, and tell what would happen if the cell did not have this particular organelle. The first question proved much harder to answer than the second. The students had numerous queries, including what is a good answer, what does the question mean, and where should they look for answers. Because I had experienced these questions before, a number of topics were included for them to consider: • Six characteristics of life • Functions and properties of the particular cell type they studied • How and why cells communicate with each other • Use of facts and observations from the project as supporting evidence. Unfortunately, many students just began listing these things without ever addressing or coming back to the actual question. For many students, my comment was that “they had not answered the question.” Even though we studied how and why cells are the fundamental cor- nerstone of life, for many students, answers to this question were not able to provide an adequate parallel between cells and life. Those who succeeded with the first essay question did so by connecting many of the themes of cells and life that we had studied or that were brought out in this project. For example, one student wrote ...

Context 2

... table groups of four students each. This required students to walk from one table to the next, comparing results from their cellular clues, until the matching cell was found. These matching- cell-type tables then had to communicate with one another to obtain chemical compounds needed by organelles. This ensured that each group of students was up and communicating with its matching cell. The next step was experimenting on how best to draw the cell and its membrane while allowing for the passage of compounds. Membrane permeability and chemical exchange required special attention to make them tangible to students. Even though the membrane was described as a “gatekeeper” or, more specifically, a fluid mosaic structure, what this means chemically and how such things work remained a mystery for many learners. Therefore, I asked that they construct “channels” for molecular exchanges in their models. Students visualized channels in the membrane by erasing four small areas of the membrane drawn in pencil. By erasing these bits of the membrane, they could see how channels permeate the membrane and how chemical compounds and waste can be exchanged. This way, by the time students enter high school, they are familiar with the permeability of membranes, what type of compounds pass through it, and how it serves as a gatekeeper. While not explaining the details of protein channels and transport proteins that they learn in high school, this model provides the first step in preparation for later AP Biology studies (see College Board, 2011). In subsequent modifications, membrane permeability will stress that water enters through channels, whereas carbon dioxide, oxygen, and lipids diffuse directly through the membranes. Sugars, amino acids, nucleotides, and proteins will use other transport mechanisms, as appropriate for seventh grade. The structure and function of key organelles were reinforced by the project, as were connections between cellular processes and their functions in a whole cell system. For this reason, the drawing had to be large enough to accommodate eight organelles, to affix appropriate compounds to the organelles, or to depict compounds entering the cell through the membrane. For each cell model, compounds were lined up to enter or leave the cell, or to be used by particular organelles. This exchange was accomplished by table groups working with their “cellular” partner table. Because the compounds and other cellular needs came from their matching cell, students got up and carried out the process of cellular exchange and communication to obtain and use required compounds. The molecules or compounds included in the project were sugar, protein, amino acid, oxygen, lipids, water, carbon dioxide, and nucleotides. These compounds were included to reinforce prior lessons on chemical reactions that were now related to the organelles in which they take place. Waste is included in the model as it is removed from the cell by the lysosomes and made ready by intracel- lular digestion to be released back into the cell in the form of vesicles. Sunlight is included for the chloroplast and enzymes as necessary for many reactions. Symbols were compiled representing each compound listed above. Students obtained compounds from their matching cell table, cut these out, determined where they entered the membrane, and affixed some of these compounds to organelles for chemical reactions. For example, four symbols for amino acids were cut out, with two flowing through the membrane and two others placed on the ribo- some, where they were used to build proteins (see Figure 1). To demonstrate cell-to-cell communication, recognition, and signaling, students matched unique cell-surface receptor sites with the correct signal molecule. The paper cutouts for the receptors came from one table, but the matching signal molecules had to come from the cells companion table, indicating that the students had “acted out” cell communication. Each table groups scale model had to have four sites, with the correct signal placed on them. Once applied, these were easily seen and graded to ensure that “cell communica- tion” occurred. “A Cellular Encounter” became the culminating project for our unit on cells, requiring three full 90-minute classes. Grading of the project was based on the following assessment tools: 1. a group score for the final scale model drawing using a project rubric 2. an individual grade for the project packet, and 3. a grade provided by the teacher for observations of group decision making and individual participation. The rubric used to grade student knowledge, performance, and the accuracy of the model is shown in Table 3. The total score for this part of the assessment is 50 points. The second 50 points come from individual responses to the final, open-ended questions, with points awarded for use of evidence in the answer and completeness of response. An example of one version of the animal cell model is presented in Figure 1. The range of organelles selected is clear, as are the channels through the membrane. Requisite compound symbols are attached to each organelle or in transit through the membrane. As noted above, further specificity can be added to capture exactly what type of mechanism is used by each specific compound to enter or leave the cell. As for the nucleus, symbols for nucleic acid molecules were correctly located; however, no further activity with the nucleus was planned for this version of the model. These nucleic acids can be seen attached to the nucleus of the animal cell. This cell model also notes the ATP production occurring from the mitochondrion. There is clearly a place where other symbols could be inserted in the nucleus, such as mRNA molecules making their way to the ribosomes, or DNA itself, and copies to show how and where it is replicated. Although these extra symbols were not included, students were familiar with the nucleus as the cells information and control center and were thus able to consider how protein synthesis might occur and how these proteins would be packaged to leave the cell. The project was undertaken by 141 students in five periods. This required 35 table groups with an average of four students per group. I rated the groups on their participation, supportive work habits, and whether or not one or two students were carrying out the work of others. Approximately 50% of the groups had a score of 5 for participation. The other groups, despite warnings and encouragement, worked consistently with less-than-full participation or with full participation only at limited times. Despite the other 50% working at less-than-optimal participation, all cell drawings were completed and turned in for grading. Students were initially presented with two concluding essays. The first asked, “What can cells tell us about life?” The second asked the students to choose one particular organelle, describe its function in a cell, and tell what would happen if the cell did not have this particular organelle. The first question proved much harder to answer than the second. The students had numerous queries, including what is a good answer, what does the question mean, and where should they look for answers. Because I had experienced these questions before, a number of topics were included for them to consider: • Six characteristics of life • Functions and properties of the particular cell type they studied • How and why cells communicate with each other • Use of facts and observations from the project as supporting evidence. Unfortunately, many students just began listing these things without ever addressing or coming back to the actual question. For many students, my comment was that “they had not answered the question.” Even though we studied how and why cells are the fundamental cor- nerstone of life, for many students, answers to this question were not able to provide an adequate parallel between cells and life. Those who succeeded with the first essay question did so by connecting many of the themes of cells and life that we had studied or that were brought out in this project. For example, one student wrote ...