Diffusion & Cell Size

Names ______Period ______Date ______Diffusion & Cell Size (Why are cells so small?)

Diffusion: How do different things move in, out of, and between cells? This activity models the process of diffusion. Diffusion is the process by which molecules move from an area of higher concentration to an are of lower concentration. In this activity you will watch sodium hydroxide (NaOH) diffuse into different sized blocks of phenolphthalein agar. The phenolphthalein agar cubes turn pink in the presence of NaOH, which is a base. When you place the cubes into the NaOH solution, the base will diffuse into the cubes, causing the cubes to become pink. You will be able to see how far the base was able to diffuse into the cubes by measuring the width of the "PINK ZONE".

Safety: Put on goggles. Handle all glassware carefully. Always use caution when working with laboratory chemicals. NaOH is the base chemical for Dranoand it may irritate skin. Phenolphthalein is the active ingredient in most laxatives. Due to the possibility of accidental exposure to lab chemicals, eating or drinking is strictly forbidden during lab activities.

Vocabulary: Diffusion-

Phenolphthalein:

Investigative Question(s): In this activity you will address two Investigative Questions: a) How does the size of the cube affect the rate at which diffusion can occur? b) How does the surface area to volume ratio affect the rate of diffusion?

Hypothesis: Write a hypothesis for each of the above questions. Remember to use both a manipulated variable and a responding variable in the hypothesis. a) Hypothesis #1:

b) Hypothesis #2

Materials: Agar cubes Plastic knife Beaker or glass equivalent 0.4% solution NaOH Names ______Period ______Date ______Procedure: 1. Obtain a piece of phenolphthalein agar from your teacher. 2. With your plastic knife cut the agar into three cubes. (3 cm3, 2 cm3, & 1 cm3) Measure carefully and trim away excess agar.

1 cm3 2 cm3

3. Place the cubes in the beaker. Pour 100mL of the NaOH solution into the beaker. This should be enough to cover the cubes completely. 4. After 10 minuters remove the agar cubes with a plastic spoon. 5. Place the agar cubes on a paper towel and gently blot them dry. 6. Cut each block in half. Make sure to dry your plastic knife between each cut!!! 7. Measure the distance from the outside edge of the cube to the point at which the color diffused in millimeters on each side of the the cube. Record the average distance traveled.

8. Measure the distance from from the edge of the pink color to the middle of the cube that remains unchanged in color. Record the average. Names ______Period ______Date ______

9. When you have finished taking your measurements, clean up you lab area: a) Place the agar cubes in the garbage. b) Dump the NaOH down the drain. c) Rinse the beaker and dry it completely with paper towels. d) Return goggles to bin and throw away gloves if used.

Data & Graphs: Construct your data tables here! You will need two. Get Mr. Winkley's initials to approve your data table.______

Construct your graphs here! You will need two. Names ______Period ______Date ______Analysis: 1. When writing your analysis you should address the following questions. o Is there a relationship between the size of the cube and the rate of diffusion? o Is there a relationship between the surface area of a cube and the rate of diffusion? o If the cubes were cells, which would be the most efficient at letting materials to enter and exit the cell? Why? o Which would be the least effective? Why?

Conclusion:  Restate your hypotheses.  Is there evidence to support your hypotheses.  Summarize your procedure and your results.  What could be some sources of errors.  What could be your next investigative question & hypothesis?