Exposing Student Misconceptions about Cellular Structure: A Curriculum Topic Study Introduction Abbie Martin, M.Ed. Curriculum topic study allows teachers to investigate a specific concept in math or science by summarizing resources, such as national standards, state standards, and research-based instructional methods. In this action research study, the teacher researcher utilized the curriculum topic study approach to uncover student misconceptions in the area of cellular structure and function. The researcher utilized a formative assessment probe to find out what high school students believe about the structure of cells and macromolecules prior to teaching a cell unit. The findings identify clear misconceptions concerning the nature of macromolecules and their relationship to cellular structure. Research has shown that students have difficulty making the connection between molecular and cellular organization (Driver, et. al., 1994). Students seem to understand that both atoms and cells are made up of smaller parts, including the nucleus. However, they struggle to conceptualize the foundational principal that all matter, including cells, is made of atoms. This misunderstanding seems to perpetuate beyond differentiation between cells and atoms, and into their understanding of the structure and function of macromolecules. This action research study aims to expose these misunderstandings and identify the underlying cause for them. Curriculum Topic Study Background Research Curriculum topic study is a novel approach to pedagogy developed by Keeley (2005). The process provides teachers access to a variety of science content and curriculum development resources they can use to make pedagogical decisions with the goal of reducing student misconceptions. The teacher researcher begins by investigating the state and national benchmarks for the topic that will be studied. The learning goals set by the American Association for the Advancement of Science (1994) for the topic of cell structure and function for grades 9-12 include understanding that cell structure affects function and understanding that living cells are made of chemical elements. 31
Additionally, the Virginia Standards of Learning for Biology (2003) include understanding the structure and function of macromolecules (BIO 3.b) and learning key differences between prokaryotic and eukaryotic cells (BIO 4.a). These standards help shape the curriculum for high school biology in Virginia, and make up a continuous theme throughout the course. According to the American Association for the Advancement of Science (1994), students should experience a progression of their understanding of cell structure and function as they move through the grade levels. As elementary students, they should have an understanding that some parts of organisms must be seen through a magnifying glass, and then as they enter the upper elementary grades they should begin to form the concept of a cell as the basic unit of life. Finally, as they exit middle school students should have a clear understanding of basic cell function. By the end of the 12th grade, students should have knowledge and understanding of the nature and function of proteins and the specialization of organelles within the cell, including the cell membrane. Driver, et al. (1994), a leader in misconception research, has discovered that students often confuse the concepts of molecules and cells. Often times, students have a very general concept of molecules and cells, both of which contain a nucleus and are surrounded by other small things. This confusion seems to stay with children though the teenage years. Also, students at the high school level tend to think that larger macromolecules, such as proteins and carbohydrates, are made of cells rather than atoms. They did not understand the difference between cells and molecules. More confusion has been found in students ability to differentiate the sizes of cells and atoms. Many students at the high school level believe that cells and molecules of protein are the same size. Driver, et al. s (1994) research also found that students believe single-celled organisms contain intestines and lungs. 32
Method Action research was chosen for this project due to its ease of use and effectiveness for the classroom teacher. The researcher was able to collect data, create and teach lessons, and analyze the results from her own classroom. Qualitative and quantitative data were collected, and quasistatistics were used to identify trends within the data set. Qualitative methods of open coding were utilized to organize the data. Research Questions The researcher aims to answer the following questions: 1. What do science standards and current research say 10 th grade students should know and understand about cell structure and function? 2. What commonly held ideas and understandings do 10 th grade students in Advanced Biology at a suburban high school in southeastern Virginia have about cell structure and function? 3. What experiences have led these students to their ideas and understandings of cell structure and function? Classroom Context The students in this study were from a suburban high school in southeastern Virginia. There were 20 student participants from an Advanced Biology course. Nine student participants were 9 th graders, and the remaining 11 student participants were 10 th graders. Most students were generally highly involved in extra-curricular activities. They all had a strong background in science and were recommended to the advanced biology course by previous science teachers and guidance counselors. The class consisted of 1 African-American student, and the remaining students were Caucasian. 33
Data Collection The researcher started probing the misconceptions by administering a simple formative assessment, or probe, designed to identify student ideas and understandings of cell structure and function (Appendix A). The probe aimed to uncover misconceptions that may be held concerning the difference between molecules and cells, and the function and structure of plant and animal cells. The probe was used as a pre-assessment tool prior to the beginning of a unit on cells. The probe was designed with two columns of items containing names of organelles, molecules, organs, and elements. The students were asked to place a letter B if the items are found in both plant and animal cells, a letter A if the items are found in only animal cells, a letter P if the items are found in only plant cells, and a letter N if the items are found in neither cell type. The students were then asked to describe the process they used to sort through the items. Finally, students were asked to draw and label an example of a plant and animal cell with as many details as they were able to. From the results of the probe, the researcher was able to clearly delineate several commonly held misconceptions. These misconceptions mirrored those identified in the research by Driver, et.al. (1994). The unit plan was designed to combat these misconceptions and aid students into a clearer understanding of the structure of cells as it relates to their function and position within a multicellular organism. Results The data has been divided into three tiers. The first tier consists of data from student responses to the probe items. Students could choose from four possible answers for each item; found in both animal and plant cells, found in neither animal nor plant cells, found in plant cells 34
only, or found in animal cells only. Students indicated their answer choice using the letters B, N, P, or A. The researcher found striking results in eight of the twenty-four items that are delineated in Figure 1. Figure 1. Student responses to tier 1 questioning. Both cell Neither cell Animal cells Plant cells types types only only Atoms 60% 40% 0% 0% Mitochondria 35% 0% 30% 35% Lungs 0% 60% 40% 0% Intestines 0% 45% 55% 0% Lipids 25% 0% 10% 65% Carbon 40% 45% 5% 10% DNA 60% 10% 30% 0% Water Molecule 55% 35% 5% 5% Student respondents were greatly divided in the location of lungs, intestines, water, and even atoms. As illustrated in the graph in Figure 2, there is little consensus among the Advanced Biology class about whether or not cells contain atoms, carbon, or even water. Furthermore, many students had difficulty remembering that DNA is found in both plant and animal cells. Tier 2 Questioning Tier 2 questioning requested that students describe their reasoning or rule for making the determination for each probe item. Students were able to freely respond to this question using as much or as little written response as they felt necessary. Student responses were categorized using an open coding method. This method involves creating new categories for each response 35
type and then grouping categories into broader themes to further organize the data. Figure 3 outlines the researcher s results. Figure 2. Tier 2 student responses. 9 8 7 6 5 4 3 2 1 0 Prior knowledge Guessed Remembered from middle school Thought about what each organism needed Didn t know Remembered making a model Tier 3 Questioning The third tier of responses required students to draw and label an example of a plant and animal cell. These responses ranged in detail, but were all quite similar. Most students drew a cell membrane around a nucleus for both cell types (Appendix B). Some included the cell wall for plant cells, and some did not. The general theme of all respondents drawings was their ability to remember that a cell is a container that holds smaller organelles which serve different function for different cells. The respondents, as a whole, provided this information in sufficient detail for their grade level and aptitude. Discussion Students in the advanced biology class had difficulty identifying the basic units of structure that form cells in living things. Forty percent of respondents indicated that cells do not contain atoms. This reveals a basic disconnect between their understanding of molecular structure and living systems. Carbon and water also provided students with difficulty. Thirty- 36
five percent of respondents indicated that water is not found in either cell type. Additionally, 45% of students believed that neither cell type contains carbon. Fifty-five percent of students indicated that animal cells could contain intestines. This misconception is supported by Driver s research. Students have a very hard time organizing molecular and living systems. They do not seem to understand that atoms, the smallest unit of matter, are the building blocks of macromolecules and all cells. Significance This action research has revealed a great gap in understanding of molecular and cellular structure for the studied group. Clear, direct instruction should be provided to students aimed at combating these misconceptions. In addition, students should be exposed to a variety of examples and imagery to aid them in processing and retaining the appropriate framework. It is recommended that biology teachers begin the discussion of molecular structure with a diagram or illustration comparing the size of the atom to that of a molecule, cell, organ, and organism. In addition, students may find it helpful to differentiate between the atomic nucleus and the cellular nucleus. Teachers may also find the use of interlocking blocks as a useful tool for modeling cells. Interlocking blocks can be put together in various shapes using distinct colors and patterns. Each interlocking block could be modeled like an atom, and macromolecules could be modeled out of the joining together of many blocks. Then, those model macromolecules can be placed together to simulate the formation of cell parts or whole cells. This activity may help provide a useful connection between the size and structure of atoms and the size and structure of cells. 37
Future Research Future research should be conducted to determine the starting point of this misconception. Students in lower grade levels could be interviewed and probed to find their current understanding of cellular and molecular structure. Furthermore, lessons of teachers in the lower grades could be examined to reveal possible inconsistencies. Professional development experiences may be necessary to provide elementary school teachers with effective methods of describing the relationship between atoms and cells to students. References American Association for the Advancement of Science. (1994). Benchmarks for science literacy. NY, NY: Oxford University Press. National Research Council (1996). National science education standards. Washington DC: National Academy Press. Driver, R., et. al (1994). Making sense of secondary science: Research into children's ideas. NY, NY: Routledge Press. Keeley, P. (2005). Science curriculum topic study: Bridging the gap between standards and practice. Thousand Oaks, CA: Corwin Press. Abbie Martin is a biology teacher at Jamestown High School in Williamsburg, VA. She can be reached by email at martinq@wjcc.k12.va.us 38
Appendix A Cell Type Assessment Probe Place a mark next to items you could find in a plant cell, animal cell, both, or neither. A=animal P=plant B=both N=neither Cell Membrane Vacuole Cell wall Complex carbohydrates Enzymes Lysosome Molecules of proteins Chromosome Nucleus Flagella Lungs DNA Atoms Intestines Golgi apparatus Lipids Virus Chemical compounds Chloroplasts Carbon Ribosome Mitochondria Water molecule Simple sugars 1. Explain your thinking. How did you decide if the items could be found in a plant or animal cell? 2. Now, draw and label an example of a plant and animal cell. Be as detailed as you can. 39
Appendix B 40