Please do not write on the lab handout Cell Size and Diffusion Lab

Why are cells so small? Why do they stop growing after reaching a certain size? What causes cells to stop growing and then to divide? One way to investigate these questions is to build a model. A model is often a small copy of something large. Here you will build a large model of something small. After reading the procedure, identify the independent and dependent variables and then develop a hypothesis that predicts which cell model will do the best job of moving materials in and out of the cell. Your lab report needs to include: Title, Hypothesis, Data table 1, Cube Drawings (to scale), Questions (in complete sentences) Materials: blade 0.1% NaOH spoon paper towel

metric ruler plastic cup or beaker 3cmx3xmx7cm block of phenothalein agar

Procedure: 1. Using the provided blade carefully cut the agar block into THREE CUBES – one 3 cm3, one 2 cm3 and one 1 cm3 (PLAN BEFORE YOU CUT) 2. Place the cubes in the container and cover them with 0.1% NaOH. Record the time. Use a plastic spoon to turn the cubes frequently for the next 20 minutes. 3. During the 20 minute wait period, do the necessary calculations to complete Table 1. There surface area to volume ratio is calculated as follows: For example 4 cm cube the surface area would be: (4 cm x 4 cm) x 6 sides = 96 cm2 For the same 4 cm cube the volume would be: 4 cm x 4 cm x 4 cm = 64 cm3 Surface area to volume would be: 96:64 in its simplest form the ratio would be 1.5:1 4. After 20 minutes use the plastic spoon to remove the agar cubes from the NaOH. Blot them dry. DO NOT handle the cubes until they are dry. Use your blade to slice each cube in half. Draw a SCALE diagram of each of the cut cubes and color them appropriately. Table 1: Comparison of Agar Cubes

Cube Dimensions Surface Area Volume Simplest Ratio 3 cm 2 cm 1 cm

Cube Drawings: (on your paper draw your cubes in actual size) Questions: (answer in complete sentences) 1. What qualitative evidence is there that the NaOH diffuses into the agar cube? 2. What evidence is there that the rate of diffusion is about the same for each cube? 3. List the agar cubes in order of size, from largest to smallest. 4. List the agar cubes in order of the ratios of surface area to volume from the largest ratio to the smallest ratio. How does this list compare to the list in 3 above? 5. How does periodic cell division help resolve the problems encountered by large cells? 6. What is the usual size range of eukaryotic cells? 7. How do cells that are at the upper limits of an efficient surface to volume ratio or cells that have exceeded a workable ratio modify themselves to successfully operate and survive?