The Effect of Cell Size on Material Transport

Question: How does cell size affect the rate of diffusion of materials into a cell? Background information Cells are so small that their existence went unnoticed until the microscope was invented. The microscope allowed scientists to examine the cellular make up 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 potato cut into cubes as a working model of a cell. You will cut the potato into cubes of pre-determined size and then place the cubes in a dish containing an iodine solution. Iodine is a stain that reacts with starch molecules to make a black product. As iodine diffuses into the potato, it will produce a visible black stain. After incubating all “cells” in iodine solution for the same time period, you will slice open each “cell” to determine how far the iodine diffused. By comparing the distance that the iodine diffuses into each size “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. Materials: • 2 raw potatoes • Knife • Metric ruler • Iodine solution • 250-mL beaker • Tweezers • Paper towels • Cutting board • Potato peeler Safety Wear safety goggles and plastic gloves when handling iodine solutions. Rinse off any solution that spills on your skin or clothing. Use caution when handling the knife to cut potato cubes. Alert your teacher if you accidentally cut yourself. Wash your hands thoroughly with soap and warm water before leaving the lab.  ©2012 Connections Education LLC. All rights reserved. Biology A Cells and Energy Unit 4 Lesson 4 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 iodine solution for the same length of time? Procedure 1. Put on your safety goggles. 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 0.5 cm. For the second cube, make each side equal to 1.0 cm. For the third cube, make each side equal to 2.0 cm. For the fourth cube, make each side equal to 3.0 cm. 2. Put on your plastic gloves. Pour the iodine solution into the beaker so …