Set up the experiment

1. 1. Get four 8 oz. cups from the lab kit. Place a piece of tape on each cup or glass. Using a pen or marker, label the tape on each cup with one of the following percentages: 0%, 1.75%, 3.5%, and 7%.
   2. Using the graduated cylinder, measure out 100 mL of distilled water. Pour the water into the fifth, unlabeled cup.
   3. Measure out 1.5 level teaspoons of salt and add it to the unlabeled cup containing 100 mL of distilled water. Mix completely. This is the 7% salt solution.
   4. Using the graduated cylinder, measure out 50 mL of this mixture and pour it from the graduated cylinder into the cup labeled 7%.
   5. Add distilled water up to the 100 mL mark of the graduated cylinder to make the next dilution. Adding 50 mL distilled water to 50 mL of a 7% solution will result in 100 mL of a 3.5% solution.
   6. Using the graduated cylinder, measure out 50 mL of the 3.5% solution and pour it from the graduated cylinder into the cup labeled 3.5%.
   7. Add distilled water up to the 100 mL mark of the solution in the graduated cylinder to make the next dilution. Adding 50 mL of distilled water to the 50 mL of the 3.5% solution will result in 100 mL of a 1.75% solution.
   8. Using the graduated cylinder, measure out 50 mL of the 1.75% solution and pour it from the graduated cylinder into the cup labeled 1.75%.
   9. Empty the remaining 1.75% solution down the drain of the sink and rinse out the graduated cylinder with tap water.
   10. Using a sharp steak or kitchen knife, slice eight pieces of potato exactly 10 mm x 10 mm x 40 mm (1 cm x 1 cm x 4 cm). It is critically important that these potato core pieces are cut as precisely as possible; they need to all start out having the same volume. A single- edge razor blade may work better than a knife.
   11. Determine the volume of the potato cores. The volume, is calculated by multiplying the width x height x length. Therefore, each core starts out with a volume of 4,000 cubic millimeters or 4 cubic centimeters. Measure the cores with both the mm ruler and the calipers. Measuring with the calipers to the nearest millimeter will be good enough for this lab. Create a data table like the one below to record the beginning and ending volumes.

   Table 1. Potato core measurements

   	0% salt solution	1.75% salt solution	3.5% salt solution	7% salt solution
   Beginning average volume (cu mm)
   Ending average volume (cu mm)
   Percent difference

   12. Place two measured cores into each solution overnight, or for at least 8 hours. That time period is not critical to the results; it can be longer.
   13. Remove the cores from one of the cups and pat them dry with a paper towel. The solution may now be discarded down the drain of a sink.
   14. Using the caliper, measure the height, width, and length of the cores, and then determine the volume of each core. Average the measurements for the two cores and record in the data table above. The cores can now be discarded.
   15. Repeat Steps 13 – 14 three more times: one time for each cup.
1. Illustration of the Importance of Surface-to-Volume Ratios
   1. Calculate the surface-to-volume ratio of the following potato cubes:
      1. CUBE 1: Length, width, and height are all 5 mm
      2. CUBE 2: Length, width, and height are all 3 mm
   2. Effect of cell size on diffusion rate
      1. With clean hands, cutting board, and knife, cut the skin off of the potato.
      2. Using the knife, cut two cubes of potato with dimensions of 1 cm x 1 cm x 1 cm.
      3. Using the knife, cut two cubes of potato with dimensions 1.5 cm x 1.5 cm x 1.5 cm.
      4. Using the knife, cut two cubes of potato with dimension of 2 cm x 2 cm x 2 cm.
      5. Place distilled water into a cup or glass. Add the vial of food coloring to the water until a dark color is achieved.
      6. Carefully place the potato cubes in the solution. The cubes must be completely submerged in the water. Let them stand in the solution for 2 to 4 hours.
      7. After 2 to 4 hours, remove the cubes. Using the knife, cut each cube in half.
      8. Using the ruler, measure how far the solution has diffused into each potato cube.
      9. Record the results. A sample data table is included below that may be used to organize and record the results.
      10. Complete the following calculations to determine the rate of diffusion and record the results.

   Rate of Diffusion (cm/min)= Distance of diffusion ÷ time.

   Cube	Distance of Diffusion	Rate of Diffusion
   1 cm cubed
   1 cm cubed
   1.5 cm cubed
   1.5 cm cubed
   2 cm cubed
   2 cm cubed
   	Average Rate of Diff.

1. What were the percent differences between the volumes of the potatoes in the osmosis experiment for each salt solution? (8 points)
   1. 0%
   2. 1.75%
   3. 3.5%
   4. 7%
2. What extraneous variables might have affected how the results came out in the osmosis experiment? Describe three. (6 points)
3. In osmosis, which direction does water move with respect to solute concentration? (2 points)
4. Answer the following questions:
   1. Explain what would happen to a freshwater unicellular organism if it were suddenly released into a saltwater environment. Use the terms isotonic, hypotonic and hypertonic in the answer. (3 points)
   2. What would happen if a marine organism were placed in freshwater? (3 points)
5. A student purchases and weighs 5 pounds of carrots from a local grocery store. She notices that the grocery store constantly sprays its produce with distilled water. After returning home, she weighs the carrots again and discovers that they weigh only 4.2 lbs. They also no longer seem as crisp and taut. Provide a possible explanation for why the carrots weighed more at the store, based on the information learned in this lab. (5 points)
6. People always say that leeches can be removed from the body by pouring salt on them. Based on what the student learned about osmosis, provide an explanation that supports or refutes this information. (5 points)
7. What is the surface-to-volume ratio and rate of diffusion for each potato cube from Procedure 3b? (6 points)
   1. Cube 1 surface-to-volume ratio
   2. Cube 1 rate of diffusion
   3. Cube 2 surface-to-volume ratio
   4. Cube 2 rate of diffusion
   5. Cube 3 surface-to-volume ratio
   6. Cube 3 rate of diffusion
8. Assume the potato cubes are cells. Which cube would be most efficient at moving materials into and out of the cube? Briefly explain the answer. (4 points)
9. From what was observed in the potato procedure, how do the rate of diffusion and surface-to-volume ratio limit cell size? (5 points)
10. One night, Hans decides to cook a hamburger and spaghetti with meatballs. To test ideas of surface-to-volume ratios, he makes a quarter pound hamburger and a quarter pound meatball and cooks them at the same temperature. Which food item will cook the fastest and why? (5 points)
11. While watching a special on animals, Brianna discovers that hares tend to lose heat through their ears. Based on this and what is known about surface-to-volume ratios, propose an explanation as to why hares that live in hot climates (such as the desert) have large, extended ears. (5 points)

1. In the Spirogyra cells observed on the virtual microscope, about how many circular green chloroplasts were seen in a single cell at 40X magnification? (2 points)
2. What were the percent differences between the volumes of the potatoes in the osmosis experiment for each salt solution? (8 points)
   1. 0%
   2. 1.75%
   3. 3.5%
   4. 7%
3. What extraneous variables might have affected how the results came out in the osmosis experiment? Describe three. (6 points)
4. In osmosis, which direction does water move with respect to solute concentration? (2 points)
5. Answer the following questions:
   1. Explain what would happen to a freshwater unicellular organism if it were suddenly released into a saltwater environment. Use the terms isotonic, hypotonic and hypertonic in the answer. (3 points)
   2. What would happen if a marine organism were placed in freshwater? (3 points)
6. A student purchases and weighs 5 pounds of carrots from a local grocery store. She notices that the grocery store constantly sprays its produce with distilled water. After returning home, she weighs the carrots again and discovers that they weigh only 4.2 lbs. They also no longer seem as crisp and taut. Provide a possible explanation for why the carrots weighed more at the store, based on the information learned in this lab. (5 points)
7. People always say that leeches can be removed from the body by pouring salt on them. Based on what the student learned about osmosis, provide an explanation that supports or refutes this information. (5 points)
8. What is the surface-to-volume ratio and rate of diffusion for each potato cube from Procedure 3b? (6 points)
   1. Cube 1 surface-to-volume ratio
   2. Cube 1 rate of diffusion
   3. Cube 2 surface-to-volume ratio
   4. Cube 2 rate of diffusion
   5. Cube 3 surface-to-volume ratio
   6. Cube 3 rate of diffusion
9. Assume the potato cubes are cells. Which cube would be most efficient at moving materials into and out of the cube? Briefly explain the answer. (4 points)
10. From what was observed in the potato procedure, how do the rate of diffusion and surface-to-volume ratio limit cell size? (5 points)
11. One night, Hans decides to cook a hamburger and spaghetti with meatballs. To test ideas of surface-to-volume ratios, he makes a quarter pound hamburger and a quarter pound meatball and cooks them at the same temperature. Which food item will cook the fastest and why? (5 points)
12. While watching a special on animals, Brianna discovers that hares tend to lose heat through their ears. Based on this and what is known about surface-to-volume ratios, propose an explanation as to why hares that live in hot climates (such as the desert) have large, extended ears. (5 points)

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