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Transcript
Course: Biology Grade Level: 9-10 Type: Informational/Explanatory Structure: Description Teaching Task 12: How does the structure of a cell membrane allow a cell to perform both active and passive transport? After reading informational texts, write an essay that defines and describes the fluid mosaic model and explains how molecules are transported through a cell membrane using various methods of active and passive transport. Support your discussion with evidence from the text(s). (L2): What conclusions or implications can you draw? Performance Level: Approaches Expectations The cell membrane is not one solid piece, it has tiny holes allowing entrance and exit to the cell. The cell membrane extends around the outside of a cell inside the cell wall. Understanding the cell membrane, passive transport, and active transport is how you gain knowledge about the structure and function of a cell membrane. Around cells there are cell membranes surrounding it. Cell membranes are selectively permeable. Which means it allows some molecules to pass through it easily and others have a harder time or can not pass. (Cellular Transport, n.d.) Size and polarity will prevent molecules from passing through the membrane. (Cellular Transport, n.d.) Vibrations of the membrane allow small water molecules to pass, and larger molecules pass less easily. (Cellular Transport, n.d.) For example, diffusion moves small particles back and forth across the membrane based on the concentration of a solutions (high to low). Cholesterol is required to help maintain the condition of a cell membrane. The cell membrane contains a lipid bilayer, carbohydrate chains, and proteins. The lipid bilayer has a hydrophilic head (water loving), and a hydrophobic tail (water fearing), which also means the lipid bilayer is amphipathic. (Cellular Transport, n.d.) Proteins and phospholipids are what make up most of the cell membrane. The proteins generally float in the bilayer. There is also a protein pump in the membrane that allows for passing of molecules. (Cellular Transport, n.d.) Carbohydrate chains act as “Identification Tags” so other cells know that it belongs there. (Cellular Transport, n.d.) The membrane is called a fluid mosaic model due to all the components that make it up. (Cellular Transport, n.d.) Part of the cell membrane is the way molecules get transported across of it through forms of passive and active transport. There are two types of transportation of molecules which are passive and active. The difference between them is that active uses energy and passive does not. During either transport there can be different concentration gradients between different solutions. (Cellular Transport, n.d.). One example of passive transport is diffusion, when molecules move from high to low concentration. (Cellular Transport, n.d.) More specifically there is facilitated diffusion that uses a protein channel that makes it easier for molecules to pass. (Cellular Transport, n.d.) Another example is osmosis which is the passing of water molecules through a cell and its membrane. Isotonic, hypotonic, and hypertonic are three different ways of comparing two solutions. (Cellular Transport, n.d.) For isotonic it means when in comparison the concentration of two solutions are exactly the same. Hypotonic is when comparing two you take the solution with a lower concentration. Hypertonic is the opposite of hypotonic where you take the one with a higher concentration. (Cellular Transport, n.d.) The other form of transport is called Active transport which moves from lower concentration to higher concentration (Miller & Levine, 2012, pgs 204213) ATP is the type of energy used in active transport. (Miller & Levine, 2012, pgs 204-213) To pass molecules through it uses a protein pump. (Miller & Levine, 2012, pgs 204-213) Endocytosis is when a cell takes in content through a vacuole. Exocytosis is when a cell releases contents through the vacuole. When a cell “eats” and takes in larger molecules it’s called phagocytosis. (Miller & Levine, 2012, pgs 204-213) Pinocytosis is the entering of liquids into a cell by small vesicles created in the membrane. Passive and active transport are important aspects of knowing about cell membranes. The cell membrane monitors what enters and exits a cell. Due to it being selectively permeable it allows molecules to move across it with passive or active transport. Understanding the structure and function of a cell membrane starts with having knowledge about the cell membrane, passive transport, and active transport. Annotation Focus 2 Reading/Research 2.5 Controlling Idea 2.5 Development 2 Organization 2 Conventions 1.5 Content Understanding 2 The essay addresses most aspects of the prompt with an uneven focus when the writer explains the cellular transport process. The details regarding the fluid mosaic model and all forms of cellular transport are weak. The writer presents limited information which relies on only two sources. Addressing the credibility of all information would strengthen the essay. The thesis generally establishes the task as related to cell membrane structure and function, but it is unevenly maintained throughout the essay: Understanding the cell membrane, passive transport, and active transport is how you gain knowledge about the structure and function of a cell membrane. The writer provides limited, appropriate details to support cell membrane structure and molecular transport but does not describe the model’s relationship to cellular transport. The writer could strengthen the development of the essay by expanding the depth of specific scientific vocabulary and integrating details into the cellular transport processes: The membrane is called a fluid mosaic model due to all the components that make it up. The essay attempts to use an appropriate organizational structure, but the flow of paragraphs is awkward. For example, the transition from explaining diffusion to the role of cholesterol in the cell membrane should be separated. The writer could create cohesion through enhanced transitions and compartmentalization of specific concepts within the topic of cellular transport. The writer demonstrates a minimal command of standard English conventions and scientific vocabulary. Sources are used without citation. The essay would benefit from academic language that reflects a formal tone (e.g., “…how you gain knowledge about…”, “…where you take the one with…”, and “…when a cell ‘eats’…”). The writer needs appropriate citations and bibliography to avoid plagiarism. The writer demonstrates a limited understanding with explanations that lack detail and insights of the biological and chemical concepts related to membrane structure, function, and transport. Minor errors exist in the explanation of cellular transport: “Passive and active transport are important are important aspects of knowing about cell membranes.” This student would benefit from feedback, discussion, and/or instruction in the following areas: • A more thorough understanding of scientific terminology relating to cell membranes and cell transport. • Complete integration of the Fluid Mosaic Model within cellular transport. • Complete development of the controlling idea to include all aspects of the prompt. • Consistent and appropriate use of parenthetical citations and bibliography is required.