1. Goal: Cell Theory: The cell theory, or cell doctrine, states that all organisms are composed of similar units of organization, called cells. The modern tenets of the Cell Theory include:
- All known living things are made up of cells.
- The cell is the structural & functional unit of all living things.
- All cells come from pre-existing cells by division.
- Cells contain hereditary information which is passed cell to cell during cell division.
- All cells are basically the same in chemical composition.
- All energy flow (metabolism & biochemistry) of life occurs within cells.
Analysis: All of the interviewees said that living things are made of cells, although when probed most (10 of 13) had difficulty in explaining what constitutes a living thing. Studies from the Missouri Department of Elementary and Secondary Education, site a common misconception among students is that living things contain cells, rather than are made up of cells. This was not observed in our interviews. Even if a student did incorrectly describe living things as containing cells, this was usually a problem in communication, rather than understanding. A follow up question in all cases of such, dictated that our interview subjects did in fact understand that living things are made up of cells. Rosalind Driver notes that students often confuse cells and molecules, another misconception we did not observe except in one student who had not had biology for several years. The knowledge of what makes a living thing alive was a large grain understanding, as represented by an answer one student gave “It has to have the ability to function.” Similarly this individual when asked what “function” meant said it had to do “something” and there was no deeper understanding. The other three individuals had a limited knowledge of processes of living things, although again this was large grain, surface only knowledge. This demonstrates the students do not have an understanding of the characteristics of living things and are therefore unable to connect these concepts to cells as living things.
When asked what a cell needs to survive, a variety of answers were given by the thirteen interviewees which included food, nutrients, proteins, air, oxygen, and shelter (“A place to reside, for example on the skin”). Driver notes the most popular attributes used, by children ages 10 to 15, to identify living things are 'eating/drinking, moving/walking, breathing, and growing.' We did not however observe any mention of growing or moving as characteristics of life. Many of the interviewees were unable to describe how these things got to a cell, although some tried to explain mechanisms, such as traveling through the blood to get to cells. As with the previous questions, the students have a limited and large grain understanding of what living things, including cells, need to survive and have very little knowledge of the processes that are carried out to ensure cells get these things.
Once again, all students (13 of 13) said that cells were different, although there was a range of answers when they were asked how cells are different. A few thought cells could be different colors and sizes (1 of 13 and 2 of 13 respectively). Eight others had an idea of cell specificity, such as hair cells and eye cells, although once again this was a large grain understanding as these individuals were unable to elaborate. All students noted there were differences between plant and animal cells and about half of the students (6 of 13) were able to describe some of these differences, such as the plant cell having a cell wall and chloroplasts. Overall though, we felt the students were just telling us the limited information they remembered and they did not fully understand these differences.
Implication: In an everyday setting, most students would probably be able to differentiate between living and non-living things, but when asked in a technical, scientific manner to describe what constitutes a living thing they are at a loss for words. We need to build on students’ life experiences and then have them build further upon these experiences to fully understand what a living thing needs to survive and be considered living. We also need to focus on more of the fine grain knowledge in this goal, such as the specific needs of living things and how these are addressed by the cell. More can be mentioned and built upon this idea in the cell structure goal when cell membranes are taught. As per cell specificity questions, we need to build on their assumptions that all cells are not the same, and expand students’ knowledge on what makes cells different and why different cells are needed in an organism.
- Develop existing ideas about what constitutes a living thing.
- Integrate existing ideas on nutrients needed for survival and cell specification to make a more complete view of each idea.
- Introduce new ideas concerning how something is deemed alive (responds to stimuli, reproduces, achieves homeostasis) and that functions keeping an organism alive originate at the cellular level.
2. Goal: Cell Structure- Students will understand that the inside the cell is a concentrated mixture of thousands of different molecules. These molecules form a variety of specialized structures that carry out such cell functions as energy production, transport of molecules, waste disposal, synthesis of new molecules, and the storage of genetic material. The structures functions which students will be able to identify are:
- Plasma Membrane: a semi-permeable lipid bilayer
- Cytosol: the internal fluid of the cell that houses the organelles
- Structure: double membrane of an outer smooth and inner-cristae, which is folded to increase surface area
- Function: powerhouse of the cell as it is generates energy from food
- Nucleus: control center of the cell as it stores genetic material (DNA)
- Nucleus subtopics: Nucleolus (partially assembles ribosomes), Nuclear Pores, and Nuclear Envelope (double membrane)
- Endoplasmic Reticulum: passageway for transport of materials necessary for cell functions
- Rough Endoplasmic Reticulum: protein synthesis by ribosomes on RER
- Smooth Endoplasmic Reticulum: synthesize lipids
- Ribosomes: small spherical structures that synthesize proteins and can be free or on Rough Endoplasmic Reticulum
- Be familiar with DNA - stores genetic information and located in nucleus; instructions for protein formation.
- Be familiar with types of Specialized Cells:
- Nerve cells: smallest part of the nervous system; consist of a central cell with dendrites and axons; found in brain, spinal cord, and peripheral nerves of the body.
- Muscle cells: contain contractile filaments that make up muscles that are responsible of movement in the body; located all over and throughout the body.
- Red blood cells: lack nuclei; carry oxygen through circulatory system, made of hemoglobin.
Analysis: Working from the outer edge of the cell to the inner components, twelve students (of 13) were able to identify the plasma membrane as the encapsulating structure of the cell, although various terms were used in exchange for plasma membrane: membrane, cell wall, cell membrane, and one student even used the term “cell membrane lipid bilayer.” The last student thought the “stuff” in the cell was held there by “air… like a bubble”; this student was unable to further elaborate on this concept. Only one student was able to explain the structure of the membrane as a lipid bilayer, although about half (6 of 13) acknowledged they had seen a diagram similar to the one used in the interview. These six individuals had taken high school Biology already. The other seven students were completely unfamiliar with the diagram shown to them (included at the end of this document). All the students were unable to label any part of our diagram accurately, including the student who used the “lipid bilayer” terminology. From this, we can conclude that upon entering high school the students have very little to no interaction with the components of the plasma membrane. Instead their knowledge is limited to the plasma membrane as the encapsulating structure. However, since some those who have had high school Biology or higher were unable to describe the membrane appropriately, this demonstrates their knowledge, for the most part, was again on a large grain scale.
For the most part, the students understood the plasma membrane is permeable, although they had difficulty describing how things got into the cell. Many (8 or 13) said the cell “absorbs” things, but were unable to elaborate on the actual mechanism. Here there was no mention of channels or pores. Two of the interviewees were able to use the term “protein channels” and another stated “there are some kind of strips in the membrane where things can go through” but this knowledge was very limited and they could not explain a mechanism. In addition, some of the other terms that were used by the last three individuals were diffusion and osmosis; as with the previous idea, the interviewees were unable to describe actual mechanisms and it seemed as though these were terms they happened to remember and therefore decided to use. In fact, diffusion and osmosis are some of the most widely acknowledged and studied misconceptions in cell biology held by students (Odom, 1995). Overall, there was a very weak understanding of how things got into a cell and the little knowledge that was present was once again a large grain understanding. This may be linked to the lack of understanding of the plasma membrane structure that we noted previously as there was no identification of the protein channel earlier.
The most common organelle identified as an organelle in the interviewees’ own drawings and our diagram was the nucleus (11 of 13), although most were unable to describe the function of the nucleus other than “storage.” When the students were shown our diagrams, two of these eleven were able to identify the nucleolus, but again were unable to describe the function. The mitochondrion was the next most common organelle named (6 of 13) which was drawn as well as identified in our diagram. These students knew the mitochondrion was the “power house of the cell,” although only one student was able to identify mitochondria as the site for cellular respiration. However, the interviewer was taken aback by this knowledge and forgot to ask the student what he thought cellular respiration was, so it is unknown if this was simply a remembered term or a deeper understanding of the process. Chloroplasts (not shown in our diagram), vacuoles, rough and smooth endoplasmic reticulum, and the golgi apparatus were organelles that were each discussed by three interviewees (although not by the same three interviewees). No student was able to describe the function of the chloroplasts. Two of the three students who mentioned vacuoles were able to correctly describe its function and the other was unclear; all three were not able to identify the vacuole in the diagram shown. One of the three individuals identified the difference between rough and smooth ER as “rough is the one with the dots” although these “dots” were unable to be elaborated upon. When shown our diagram, all three identified the ER although none were able to describe the function. One interviewee stated, “I know there’s one that starts with r, but I can’t think of it,” talking about ribosomes, but was unable to detail their function. The golgi apparatus was similar in that it was identified in our diagram by the three individuals but again the function was unknown. Lysosomes were mentioned by two individuals, one of whom was able to identify it in the diagram. One interviewee thought it had no function and the other said its function involved “cleaning.” The final organelle that was mentioned was the cytosol, which was termed “gooey stuff” by both students and the function was unknown. These results suggest there is a limited ability to identify organelles appropriately, even though most of the interviewees mentioned they had seen the cell diagram we used in their own textbooks. There seems to have been an emphasis on the nucleus and the mitochondria, as these were the two organelles identified most. The function of the various organelles was unknown to most of the students, and those with some knowledge demonstrated this was a superficial understanding. Similar to the previous analyses which have shown a large grain understanding of the cell, the interviewees understanding of the organelles follows suit.
Implication: This goal builds on the understanding of what is learned through our first goal. As students learn what a cell needs to survive, we will then build on this to show them what in the cell uses each of these needed nutrients. We need to work on an approach that deemphasizes the use of vocabulary terms as this appears to be the majority of what students feel they need to remember and focus more on each organelle’s function and importance to the cell. By using real world knowledge of what humans need to survive, the same knowledge can be shrunk to single-cell organism size to relate what is going on in a cell to students’ preexisting knowledge.
- Develop existing ideas of the functions involved with the nucleus and mitochondria, as well as expanding knowledge of the other organelles.
- Introduce new ideas concerning the structure and function of the plasma membrane and organelles.
3. Goal: Cellular Function with Relationship to Cell Structure (Biomolecules) Students will be able to explain, identify, and understand biomolecules as follows:
- Lipids (Fatty Acids)- functions in energy storage, structural components of cell membrane (be able to connect to lipid bilayer of plasma membrane), and signals molecules.
- Carbohydrates (Sugars) – most abundant of the four main biomolecules, serve the cell in storage, transport of energy, molecule signaling, and structural components of the cell.
- Proteins (Amino Acids) - as catalysts (enzymes), structural material, involved with signaling and regulation, and can act as carriers of cellular material. Specific proteins have ability to bind molecules tightly within the cell and assist in the cell cycle by aiding in DNA replication.
- Nucleic Acids (Nucleotides)- DNA and RNA as sources of genetic information found in the nucleus of the cell (regenerate basic shape of DNA).
- The structure of each biomolecule will be touched upon but not at a high level (No complex chemical structures)
Analysis: Most of the interviewees (12 of 13) were able to identify the genetic material that is stored in cells as DNA (deoxyribose nucleic acid). When asked to draw this structure, eight individuals drew a double helix and others mentioned genes, proteins, letters, and amino acids although all the students were unable to make the proper connections between these components. For example, there was one individual who though that one strand of the double helix came from your mother and the other strand came from your father and somehow they were connected. This suggests a limited understanding of the structure of DNA and almost no understanding of how genetic material is passed down from generation to generation. Once again, there were terms remembered but were used inappropriately or the interviewees were unable to elaborate on them. This demonstrates a limited, large grain understanding of genetic material.
As mentioned under the analysis of the plasma membrane, only one individual understood lipids make up the plasma membrane. Lipids were described as “a circle with tails” and once again, the individual was able to describe the structure more in depth. Similar to the previous analysis, it appears there has been very little discussion of the plasma membrane and its components and therefore there is a very small number of students who can identify it and even these have a large grain understanding of the structure.
There were a variety of descriptions about proteins. About half (6 of 13) of the interviewees knew proteins came from food but had difficulty linking this to cells. Some of these and a few others (6 total of 13) thought proteins were external sources of food for cells and somehow traveled to the cell and was absorbed by it. One individual identified the protein in our membrane diagram as being made of proteins, which represents an idea that things can be made of proteins. Another individual who had used the term protein channels earlier when describing the membrane stated upon seeing the figure we provided, “Maybe all the small circles are proteins [the lipids] but I don’t know what those are” referring to the actual proteins. Yet another individual was able to say there was a relationship between proteins, amino acids, and DNA but they were unable to identify what this relationship was. There were six students who were completely unclear about what a protein was. We can gather that the limited knowledge of proteins may be a result of the common knowledge of protein as a food source and the link between our cells and protein is therefore unclear.
Carbohydrates were explained in a similar fashion to the proteins. Ten individuals identified carbohydrates as a source of energy and of these ten, six said carbohydrates were obtained through food. Similar to the proteins, about half (6 of 13) thought carbohydrates were external sources of food for cells and describe the process of getting the food to the cell as previously stated. There were three individuals who linked carbohydrates to sugar, one even mentioning glucose, but once again this link was unstable as they could not elaborate. When we pointed to the carbohydrate on the image of the plasma membrane, two individuals thought it was a “feeler” or for movement. None of the interviewees identified this structure as a carbohydrate. Once again, we can hypothesize the knowledge is limited to everyday understandings of carbohydrates. The students attempted to make connections between their understanding and the cell, but just as previously shown, this was a very large grain understanding.
Implications: There are two major areas that need to be built up in this goal, one specifically about DNA and the other about other biomolecules in the cell and their functions therein. A connection between the genetic material that was taught in the cell unit and DNA in the genetics unit needs to be organized so students can understand that everything they are learning about heredity and gene functions occurs inside the cell and helps to determine how each cell functions. Proteins and their multiple functions in a cell need to be clarified as well as their origin and synthesis. Knowledge gained from diet fads and media outlets needs to either be completely removed or clarified scientifically so misconceptions due to them do not persist.
For other biomolecules such as carbohydrates, a similar approach may need to be taken since they are mentioned so much in the media. Their uses and where they are found in the cell need to be emphasized, such as how exactly they are used for energy, and in comparison to fats (lipids). This again should be able to be comprehended better by students if the first two goals are being accomplished effectively, as carbohydrates will be known as a substance needed for cells to survive, are used by organelles to form ATP, and then their other functions can be expanded upon in this goal using previous knowledge as a base.
- Develop existing ideas of the genetic material to include that what is learned in genetics units applies to cellular function.
- Differentiate exiting ideas concerning carbohydrates and protein from what is learned about them nutritionally to where they are found and how they are used on the cellular level.
- Integrate existing ideas that DNA located in the nucleus controls cell function to the fact that DNA synthesizes protein and works with other organelles in the cell to survive.
- Introduce new ideas about biomolecules, where they are found in the cell and what functions they perform.
1. Missouri Department of elementary and secondary education. 2005. Misconceptions in Science. dese.mo.gov/divimprove/curriculum/science/SciMisconc11.05.pdf
2. Driver, R. 1994. Making sense of secondary science: research into students ideas. pg. 17-26
3. Odom, A. L. (1995, October). Secondary & college biology students' misconceptions about diffusion & osmosis. "American Biology Teacher", 57 (7), 409-15. [EJ 518 917]