Limits to cell size lab answer key

Biology Cells The Effect of Cell Size on Material Transport Background Cells are so small that their existence went unnoticed until the microscope was invented. The microscope allows scientists to examine the cellular makeup of living organisms for the first time. A question that arises is: why are cells so small? Is there a factor that limits the size of a cell? In this lab, you will investigate the possibility that diffusion of nutrients into the cell may be a limiting factor on cell size. In this lab, you will work with raw potatoes, cut into cubes to mimic a working model of a cell. You will cut the potatoes into cubes of pre-determined size and then place the cubes in a dish containing a food-coloring solution. When the food coloring diffuses into the potato, it will produce a visible stain. After incubating all potato cubes that are simulating cells in a food-coloring solution for the same time period, you will slice open each of them to determine how far the food coloring diffused. By comparing the distance that the food-coloring diffuses into each size of cell that you make, you will be able to draw conclusions about whether the rate of material transport may be one of the limiting factors on cell size. Question How does cell size affect the rate of diffusion of materials into a cell? Materials            2 raw potatoes. knife metric ruler 250 ml beaker (or medium-sized glass/metal kitchen mixing bowl) 1 cup of water 1 teaspoon of food coloring (blue, red, or green) 2 teaspoons of lemon juice paper towels cutting board potato peeler tweezers © 2014 Connections Education LLC. All rights reserved. Safety Use caution when handling the knife to cut potato cubes. Alert both your teacher and Learning Coach if you accidentally cut yourself. Wash your hands thoroughly with soap and warm water before leaving the lab. Lab Tips  When handling food coloring, be aware that it will stain surfaces, clothing, and skin. Avoid using plastic containers while conducting this lab (disposable containers are okay). Wearing an old T-shirt and plastic gloves may help avoid any unwanted clothing and skin stains. Wash your hands and any kitchen and lab tools thoroughly with soap and warm water before leaving the lab.  Potatoes without their skins will brown after being left out in open air. Do not peel or cut the potato until you are ready to place the potato cubes into the solution. If a potato is left out for an extended period of time, carefully trim the potato so it has a fresh surface.  If you need to use more than one cup of water to submerge your potatoes, there should always be one teaspoon of food coloring and two teaspoons of lemon juice per cup of water. Example: Two cups of water will require two teaspoons of food coloring and four teaspoons of lemon juice. Pre-Lab Work 1. Design an Experiment: What is the independent variable in this experiment (i.e., the variable that you manipulate)? 2. Measure: How will you determine the size of your cells? 3. Control Variables: Why will you incubate all cells in the same food coloring solution for the same length of time? © 2014 Connections Education LLC. All rights reserved. Procedures 1. Prepare your food coloring solution. Add one cup of water, one teaspoon of food coloring, and two teaspoons of lemon juice to the 250-ml beaker. Stir the solution until the food coloring and lemon juice have fully mixed with the water. Tip: It may be helpful to wear rubber gloves for this step. 2. Rinse the potato with warm water to remove any dirt that may still be present on the skin. Then pat the potato dry with a paper towel. 3. Carefully remove the skin from the raw potatoes with the potato peeler. Then cut four potato cubes out of the bodies of the potatoes. Each cube should have the same length, width, and height. For the first cube, make each side equal to 1 cm. For the second cube, make each side equal to 2 cm. For the third cube, make each side equal to 3 cm. For the fourth cube, make each side equal to 4 cm. 4. Carefully place each potato cube into the food coloring solution. Tip: It may be helpful to wear rubber gloves for this step. 5. Start a timer to allow the potato cubes to incubate undisturbed for 15 minutes. While the cubes incubate, calculate the surface area, volume, and surface area to volume ratio for each cube. Enter the values into the data table. 6. At the end of 15 minutes, remove the potato cubes from the food-coloring solution. Tip: It may be helpful to wear rubber gloves for this step. 7. Place the cubes on the cutting board and carefully slice each down the center. Measure the distance that the food-coloring solution diffused into each cell. 8. Record your observations in the data table. Data Table Cell Length of One Side Surface Area Volume Surface Area to Volume Ratio 1 2 3 4 © 2014 Connections Education LLC. All rights reserved. Distance Food Coloring Traveled Analyze and Conclude Using the information you have gathered, answer the following questions. 1. Compare and Contrast: Summarize your observations of the distance traveled by the food coloring in the four cells. 2. Analyze Results: Did the cell size affect the extent of diffusion of food coloring into the cells? 3. Infer: Do the cells have the same surface area to volume ratio? How might the surface area to volume ratio affect the ability of a cell to take in and use nutrients from its environment? 4. Apply Concepts: Which cell would be able to supply itself most efficiently with nutrients diffusing in from the outside—a large cell or a small cell? Why? © 2014 Connections Education LLC. All rights reserved. Lab: The Effect of Cell Size on Material Transport Rubric Criteria Pre-lab Questions Data and Calculations Analysis and Conclusion Questions 4 Responses to all pre-lab questions are complete and accurate. 3 Responses to 3 pre-lab questions are complete and accurate. 2 Responses to 2 pre-lab questions are complete and accurate. 1 Response to 1 pre-lab question is complete and accurate. Data and calculations for all four cells are complete, correct, contain appropriate units, and are applicable to the investigation. Data and calculations for all four cells are complete and correct, but either missing units, incorrect units, or contain some portion not completely applicable to the investigation. Responses to 3 analysis and conclusion questions are complete and accurate. Missing one or two pieces of data or calculated values; or contains one or two incorrectly calculated values. Missing more than two pieces of data or calculated values; or contains more than two incorrectly calculated values. Responses to 2 analysis and conclusion questions are complete and accurate. Response to 1 analysis and conclusion question is complete and accurate. Responses to all analysis and conclusion questions are complete and accurate. 0 Responses to all pre-lab questions are incomplete and/or inaccurate. No data recorded and/or no correctly calculated values. Points /4 /4 Responses to all analysis and conclusion questions are incomplete and/or inaccurate. /4 Total Points _____/12 Comments © 2012 Connections Education LLC. All rights reserved. ...