BIO 12 UNIT 04: The Cell Membrane BCLN Rev. July, 2015

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1 Project 2: Diffusion in Gelatin Cells Lab Potential Credits: /40 Name: Project Goals: to gain and demonstrate further understanding of how cell size and shape affects the rate of diffusion across the cell membrane and into the cell Instructions: Please read through the Unit 4 Lesson, Cell Membrane Function, paying particular attention to the concepts of diffusion and osmosis and factors affecting diffusion. Please complete the cell size and diffusion lab below. Cell Size and Diffusion Lab: BACKGROUND In this lab a you will create gelatin "cells" of various sizes and shapes that contain a natural indicator and are basic. You will then place the "cells" in an acidic solution for a given amount of time. As the acidic solution diffuses into the basic gelatin "cell" it will react with the indicator and cause it to change colour (refer to Unit 1 Lesson, ph). The faster the acidic solution diffuses the greater the distance the colour change will penetrate into the "cell". Thus, this system can be used to investigate the effect of cell size and shape on the relative rates of diffusion. PURPOSE To investigate how the shape and size of a "cell" affects the rate of diffusion into the "cell". Page 1 of 11

2 MATERIALS gelatin powder such as "Knox" (found in baking or Jell-O isle of grocery store) water purple cabbage ammonia solution vinegar solution foil or glass pan at least 4 cm deep smartphone/camera various molds or cookie cutter shapes for gelatin white paper or plate measuring cup measuring spoons teaspoons knife ruler PROCEDURE 1. Please assemble all materials. 2. Prepare a vinegar solution by mixing 500 ml of vinegar with 1500 ml of water. 3. Prepare an ammonia solution by mixing 10 ml of a household ammonia-based cleaner with 190 ml of water. Please read and follow the handling precautions found on the household ammonia-based cleaner. 4. Prepare cabbage juice indicator by: i. Chop cabbage coarsely. ii. Place in 4 cups of water in a pot. iii. Boil for 10 minutes. iv. Strain cabbage keeping the now purple water. v. Add the diluted ammonia solution drop-wise to the purple cabbage water until it turns a bluish-green colour. You will now use this basic cabbage water to prepare your gelatin. 5. Prepare the gelatin according to the instructions on the package except substitute in your basic cabbage water for normal water. Precaution: Your basic cabbage water does contain a small amount of ammonia, a caustic irritant, so handle with care and do not inhale steam produced when preparing the gelatin. 6. Pour prepared gelatin into a foil or glass pan such that it is at least 3.5 cm deep and so that you have enough gelatin to cut out a total of 12 cubes (4 cubes that are 3x3 cm, 4 cubes that are 2x2 cm, and 4 cubes that are 1x1 cm). As well, pour out gelatin into various shaped molds (various spheres would be nice if you can find or create a mold for Page 2 of 11

3 this) or into a rectangular pan so that it can then be cut into various shapes by hand or using cookie cutters. 7. Place gelatin in refrigerator overnight. 8. Once gelatin is completely firm you may cut it into: i. 4 cubes that are 3x3 cm ii. 4 cubes that are 2x2 cm iii. 4 cubes that are 1x1 cm iv. 4 each of various shapes and or sizes of your choice 9. Keep one cube of each size and one of each of your various shapes and sizes aside as a control. 10. Place 3 cubes of each size and 3 of each of your various shapes and sizes in a container and then completely cover all of the gelatin shapes in the vinegar solution. 11. At 5, 20 and 45 minute intervals remove 1 block of each size and/or shape from the vinegar solution, quickly dip in water and blot on paper towel. Then cut the shape in half, take a picture, then measure the distance that the colour change has penetrated from the exterior into the interior (refer to Figure 1 below). Record both the picture and the measurements in Tables 1-3 of the results section below. Cut "cell" in half. Figure 1. Measuring the penetration of colour change within a gelatin "cell" as an indicator of the rate of diffusion. 12. For the cube shapes, calculate the surface area, volume, ratio of surface area to volume (SA:Vol) and % diffusion (distance diffused/length of cube x 100%) and record in Tables 1-3 of the results section below. Page 3 of 11

4 13. For any additional shapes or sizes simply record a picture and the distance penetrated in Table 4 and 5 (if needed) of the results section below. RESULTS (/36//////0 Table 1. The Effect of Size on Rate in Cubed Gelatin "Cells". Gelatin cubes were prepared with purple cabbage water (an indicator) that was made basic by the addition of dilute ammonia-based household cleaner such that the gelatin was a bluish-green colour. The cubes were then submerged in a dilute vinegar solution and left for 5 minutes to allow for diffusion to occur. Then a cube of each size was removed from the vinegar solution, cut in half, photographed and observed. As the vinegar diffuses into the cubed gelatin "cell" it reacts with the bluishgreen cabbage water indicator causing the gelatin to turn purplish. The distance of diffusion was determined by measuring the distance of colour change from the exterior edge to the inner edge. (/8) 5 Minutes in Vinegar Surface Area (l x w x 6) Volume (l x w x h) SA:Volume Distance of Diffusion (cm) % Diffusion (Distance of Diffusion/Length of Cube x 100%) 1x1x1 cm cube 2x2x2 cm cube 3x3x3 cm cube of Diffusion for 1x1x1 cm Cube of Diffusion for 2x2x2 cm Cube of Diffusion for 3x3x3 cm Cube Page 4 of 11

5 Table 2. The Effect of Size on Rate in Cubed Gelatin "Cells". Gelatin cubes were prepared with purple cabbage water (an indicator) that was made basic by the addition of dilute ammonia-based household cleaner such that the gelatin was a bluish-green colour. The cubes were then submerged in a dilute vinegar solution and left for 20 minutes to allow for diffusion to occur. Then a cube of each size was removed from the vinegar solution, cut in half, photographed and observed. As the vinegar diffuses into the cubed gelatin "cell" it reacts with the bluishgreen cabbage water indicator causing the gelatin to turn purplish. The distance of diffusion was determined by measuring the distance of colour change from the exterior edge to the inner edge. (/8) 20 Minutes in Vinegar Surface Area (l x w x 6) Volume (l x w x h) SA:Volume Distance of Diffusion (cm) % Diffusion (Distance of Diffusion/Length of Cube x 100%) 1x1x1 cm cube 2x2x2 cm cube 3x3x3 cm cube of Diffusion for 1x1x1 cm Cube of Diffusion for 2x2x2 cm Cube of Diffusion for 3x3x3 cm Cube Page 5 of 11

6 Table 3. The Effect of Size on Rate in Cubed Gelatin "Cells". Gelatin cubes were prepared with purple cabbage water (an indicator) that was made basic by the addition of dilute ammonia-based household cleaner such that the gelatin was a bluish-green colour. The cubes were then submerged in a dilute vinegar solution and left for 45 minutes to allow for diffusion to occur. Then a cube of each size was removed from the vinegar solution, cut in half, photographed and observed. As the vinegar diffuses into the cubed gelatin "cell" it reacts with the bluishgreen cabbage water indicator causing the gelatin to turn purplish. The distance of diffusion was determined by measuring the distance of colour change from the exterior edge to the inner edge. (/8) 45 Minutes in Vinegar Surface Area (l x w x 6) Volume (l x w x h) SA:Volume Distance of Diffusion (cm) % Diffusion (Distance of Diffusion/Length of Cube x 100%) 1x1x1 cm cube 2x2x2 cm cube 3x3x3 cm cube of Diffusion for 1x1x1 cm Cube of Diffusion for 2x2x2 cm Cube of Diffusion for 3x3x3 cm Cube Page 6 of 11

7 Table 4. The Effect of Shape and/or Size on Rate in Gelatin "Cells". Gelatin blocks of various shapes and sizes were prepared with purple cabbage water (an indicator) that was made basic by the addition of dilute ammonia-based household cleaner such that the gelatin was a bluish-green colour. The blocks were then submerged in a dilute vinegar solution and left for 10, 20 or 45 minute intervals to allow for diffusion to occur. Then a block of each shape and/or size was removed from the vinegar solution, cut in half, photographed and observed. As the vinegar diffuses into the cubed gelatin "cell" it reacts with the bluish-green cabbage water indicator causing the gelatin to turn purplish. The distance of diffusion was determined by measuring the distance of colour change from the exterior edge to the inner edge. (/9) Shape/Size 5 Minutes in Vinegar 20 Minutes in Vinegar 45 minutes in Vinegar Page 7 of 11

8 Table 5. The Effect of Shape and/or Size on Rate in Cubed Gelatin "Cells". Gelatin blocks of various shapes and sizes were prepared with purple cabbage water (an indicator) that was made basic by the addition of dilute ammonia-based household cleaner such that the gelatin was a bluish-green colour. The blocks were then submerged in a dilute vinegar solution and left for 10, 20 or 45 minute intervals to allow for diffusion to occur. Then a block of each shape and/or size was removed from the vinegar solution, cut in half, photographed and observed. As the vinegar diffuses into the cubed gelatin "cell" it reacts with the bluish-green cabbage water indicator causing the gelatin to turn purplish. The distance of diffusion was determined by measuring the distance of colour change from the exterior edge to the inner edge. Shape/Size 5 Minutes in Vinegar 20 Minutes in Vinegar 45 minutes in Vinegar Page 8 of 11

9 DISCUSSION (/7) 1. Based on your cubed gelatin "cell" data in Tables 1-3, how does SA;Volume ratio relate to the percent diffusion? State the relationship in a format such as "when X increases then Y decreases" but specifically for your findings. (/1) 2. Based on your data and your Unit 4 readings, please explain why cells cannot be infinitely large? (/1) Page 9 of 11

10 3. Based on various shaped gelatin "cell" data is Table 4 and 5, how do different shapes appear to affect the degree of diffusion? (/1) 4. Based on your data and Unit 4 readings, how can a particularly large volumed cell maximize its SA:Vol ratio so that it can survive? (2) Page 10 of 11

11 5. Please list at least 2 other factors that can influence diffusion rates in cells (/2) Marking Guide: Results /33 Discussion /7 Total = /40 Page 11 of 11