Cell Size Lab (Agar)

Date: March 5th, 2023 Block: A Cell Size Lab (Agar) Is Bigger Better? OR Is Smaller Smarter? Introduction: Diffusion is one of the very important processes by which substances such as nutrients, water, oxygen, and cellular wasted are transported between living cells and their environment. This activity will help you explore the relationship between diffusion and cell size by experimenting with model “cells.” In this experiment, you will use agar cubes to which the indicator phenolphthalein has been added. Phenolphthalein is an acid/base indicator that turns pink in the presence of a base such as NaOH. Thus the surface of the agar cubes will turn pink immediately when put into a NaOH solution. The NaOH will continue to diffuse through the cube and gradually turn the inside of the cube pink. *Question: (key word: diffusion, cells) Which size of the cell (cube) demonstrates the best efficiency of diffusion? Use the curiosity question to develop a hypothesis: *Your hypothesis: If 1cm cube is put into a NaOH solution, then it will have relatively greater efficiency than 2cm and 3cm cubes because 1cm cube has higher SA:V ratio. Materials: Agar A ruler 0.1M NaOH per group 200mL Knife Large beaker Spoon/Tongs Procedure: 1. Each group will cut three agar cubes: A 3cm cube, a 2cm cube, and a 1cm cube. CUT AS ACCURATELY AS POSSIBLE. 2. Pour 200mL of 0.1M sodium hydroxide solution into your 400mL beaker. 3. Immerse your 3 cubes in the sodium hydroxide solution, noting the time. 4. Let the cubes soak for approximately 10 minutes. 5. Periodically, gently stir the solution, or turn the cubes over. 6. After 10 minutes, use a spoon or tongs to remove the cubes from the sodium hydroxide solution. 7. Blot the cubes with a paper towel. 8. Promptly cut each cube in half and measure the depth to which the pink color has penetrated. Sketch each block’s cross-section. (colored pencils are available upon request) 9. Record your measurements and sketch each cube in the table found on the next page. 10. Do the following calculations for each cube and complete the following data table: Calculating % diffusion in each cube: ➢ Calculate total volume of each cube (volume = L x W x H) ➢ Calculate volume that did not turn pink. (That is, calculate total volume of the small portion of the cube that did not turn pink – use the same formula L x W x H) ➢ Calculate volume diffused = total volume – volume not pink. ➢ Calculate % diffusion = Volume diffused /total volume x 100 Calculate the surface area of each cube and the surface area to volume ratio: ➢ Calculate the surface area of a cube = L x W x # of sides ➢ Calculate surface area/volume ratio. *DATA TABLE: Cube Size Total cube volume (cm3) Total volume that was not pink (cm3) 1cm3 0.2cm3 1cm Sketch of each Cube Volume of the diffused cube (total volume – volume that was not pink) Percent Diffusion 78.4% Surface area of cube (cm2) Surface area to volume ratio 6cm2 6:1 0.8cm3 =6 3.1cm3 8cm3 4.9cm3 38.6% 24cm2 3:1 =3 2cm 5.0cm3 27cm3 22.0cm3 3cm 18.7% 54cm2 2:1 =2 *Conclusion Questions (answer in different colour!) Answer these questions on your Edublog. Be sure to post a photo of your data table with your conclusion questions. Use your own tags, in addition to #agarcubes #SAVratio. 1. In terms of maximizing diffusion, what was the most effective size cube that you tested? The most effective size cube we tested was the 1cm cube size. 2. Why was that size most effective at maximizing diffusion? What are the important factors that affect how materials diffuse into cells or tissues? Smaller objects have a greater surface area to volume ratio which allows material to diffuse throughout the cell efficiently. The most important factors are concentration gradient, membrane thickness, and temperature. 3. If a large surface area is helpful to cells, why do cells not grow to be very large? As cell size increases, volume increases more rapidly than the surface area. This makes the surface area to volume ratio smaller meaning that diffusion is less efficient than it would be in a smaller cell. Instead, they divide or reproduce to maintain good absorption. 4. You have three cubes, A, B, and C. They have surface to volume ratios of 3:1, 5:2, and 4:1 respectively. Which of these cubes is going to be the most effective at maximizing diffusion, how do you know this? Cube C with the ratio 4:1 will be the most effective at maximizing diffusion because it has the highest surface area to volume ratio. 5. How does your body adapt surface area-to-volume ratios to help exchange gases? To efficiently exchange gases, our body increases surface area-to-volume ratio by using epithelial cells specialized for absorption in organs. For gas exchanges, organs in our respiratory system are used such as the lungs. In our lungs, oxygen moves from the lungs to our bloodstream and at the same time, carbon dioxide moves from our bloodstream to our lungs to be exhaled. This process occurs between the alveoli and networks of tiny blood vessels called capillaries which are located in the walls of the alveoli. Alveoli are tin air sacs that are responsible for the oxygen and carbon dioxide exchange during the process of breathing in and breathing out. The cells become small spheres to cover as much surface area as possible. *WHICH ORGAN FOR EXCHANGING GASES? EXAMPLES? (CORRECTION COMMENT) 6. Why can’t certain cells, like bacteria, get to be the size of a small fish? Related to question 3, cells like bacteria cannot become as large as the size of a small fish because it will cause bacteria to decrease its surface area-to-volume ratio. The surface of the allows molecules to enter the cell, but large cells will not be able to absorb sufficient nutrients to support themselves. A mechanism they exhibit is called size homeostasis mechanism to maintain their size and prevent them from becoming too big. It balances stability for organisms to adjust to conditions that are best for their survival. SO WHAT MECHANISMS DO THEY POSSESS? (CORRECTION COMMENT) 7. What are the advantages of large organisms being multicellular? Large multicellular organisms have competitive advantage regarding survival because their lifespan is relatively longer than unicellular organisms. Even if individual cells die, other cells can continue living and moving. Multicellular organisms can adapt well to different environments with their increased complexity, which is permitted by its multicellularity. Organisms possess the mechanism Natural Selection which allows them to adapt to their environment easily as they continue to live there. Cell specialization allows individual cells of multicellular organisms to express fewer genes which protects the genes from the damage of mutagens. VIA WHICH MECHANISM TO GIVE THEM ADVANGES? SPECIALIZATION? (CORRECTION COMMENT)