Distilled Water Balance Ruler Plastic wrap

Transcription

1 The following lab taken from: Background Osmosis is the process whereby water moves across a cell membrane by diffusion. Diffusion takes place when the molecules of a substance tend to move from areas of higher concentration to areas of lower concentration. The process of osmosis must be tightly controlled by cells, otherwise they will die. For example, if you place a red blood cell in pure (distilled) water, it will quickly take up water until it bursts. That is why plasma, the liquid portion of our blood is made of water with proteins and salts dissolved in it, preventing the unnecessary gain of water by our blood cells. In plants, osmosis is just as important. Plants with too little water will wilt. This happens when water moves out of the cells by osmosis. Without this water there is little pressure inside the cells and the plant can no longer support itself against the pull of gravity. However, after watering the plant, the cells become reinflated with water and the plant stands upright. The effect of water loss on plant cells is shown in the diagram below. Potato Lab In this lab activity you will observe the effects of osmosis on plant cells. You will use the masses of pieces of potato to see how much water moves in and out of cells in different salt solutions. Materials Potato Scalpel Plastic cups Salt solutions (1%, 3%, 5%) Distilled Water Balance Ruler Plastic wrap

2 Procedure 1. Label 4 containers with your group s initials, the period, and the following: distilled water, 1% salt, 3% salt, and 5% salt. 2. Using the scalpel, make 12 sticks from your potato. Trim them with a knife until they are 3 cm long. Try to make them all the same width. Caution: be very careful with the scalpel. Always cut away from yourself. Make sure there is no peel left on the core. 3. Place three sticks in each of the containers and cover them temporarily with plastic wrap. When you are ready, remove the cores and find the mass of each group of three using the balance. Find the mass all three of them together, not separately. You should find the mass to the nearest 0.1 g. Record your data in the data table. 4. Immediately return the cores to the correct container and cover them with the correct solution. Cover each container with plastic wrap and set them aside for 24 hours. 5. After 24 hours, remove each set of three cores from their containers. Briefly blot them with a paper towel to remove excess water. Quickly find the mass of each group of 3 and record the mass in the data table. 6. Find the mass of each group of three using the balance. Find the mass all three of them together, not separately. You should find the mass to the nearest 0.1 g. Record your data in the data table. 7. Make observations of the texture, color, and flexibility of the cores. Record these observations in the data table. 8. Determine the change in mass by subtracting. If the mass increased over the 24 hours, place a (+) in the data table next to the amount changed. If the mass decreased, place a (-) in the space. Data Beginning mass of the 3 cores Ending mass of the 3 cores Change in mass (give + or-) Observations Distilled Water 1% Salt 3% Salt 5% Salt

3 Graph Be sure to include a title, label your axes, and give an appropriate scale. Conclusion Please answer the following questions on a separate sheet of paper. Your answers must be given using complete sentences. The words IT, LIKE, THING, and STUFF are not to be used. Each use of one of those words will cause you to lose 1 point off the lab! 1. Which solution caused the cores to gain the most mass? Is that solution hypertonic, hypotonic, or isotonic? How can you tell? 2. Which solution caused the cores to gain the least mass (or maybe lose the most mass)? Is that solution hypertonic, hypotonic, or isotonic? How can you tell? 3. Look at your line graph. Find the point where your line crosses the 0 line. This is the point where the cores do not lose or gain any mass. Drop a straight line from that point to the x-axis. What is the concentration of salt at that point? 4. The point you found in question 3 is the general salt content of potatoes. Briefly explain what happened in your experiment to potatoes placed in concentrations lower than that content and to potatoes higher than that content. Use information from what you have learned about cell transport to help explain your answer.

4 Gummy Bear Lab In this lab activity you will observe the effects of diffusion on gummy bears. You will use the masses of gummy bears to see how much water moves in and out of cells in different types of solutions. Materials 4 Gummy Bears (all different colors) 4 Plastic cups Distilled water Salt solution Vinegar Baking soda solution Balance Plastic wrap Procedure 1. Label 4 containers with your group s initials, the period, and the following: distilled water, salt solution, vinegar, baking soda solution. 2. Find the mass of each gummy bear using the balance. You should find the mass to the nearest 0.1 g. Record your data in the data table. 3. Put one gummy bear in each container and cover them with the correct solution. Cover each container with plastic wrap and set them aside for 24 hours. 4. After 24 hours, remove each gummy bear from their containers. Briefly blot them with a paper towel to remove excess water. Quickly find the mass of each bear and record the mass in the data table. 5. Find the mass of each gummy bear using the balance. You should find the mass to the nearest 0.1 g. Record your data in the data table. 6. Make observations of the texture, color, and size of the bears. Compare your gummy bears to gummy bears that have not been soaked overnight. Record these observations in the data table. 7. Determine the change in mass by subtracting. If the mass increased over the 24 hours, place a (+) in the data table next to the amount changed. If the mass decreased, place a (-) in the space. Data Beginning Mass Ending Mass Change in mass (give + or-) Observations Distilled Water Salt solution Vinegar Baking Soda

5 Graph Be sure to include a title, label your axes, and give an appropriate scale. (A bar graph may be appropriate in this case!) Conclusion Please answer the following questions on a separate sheet of paper. Your answers must be given using complete sentences. The words IT, LIKE, THING, and STUFF are not to be used. Each use of one of those words will cause you to lose 1 point off the lab! 1. Which solution caused the bears to gain the most mass? Is that solution hypertonic, hypotonic, or isotonic? How can you tell? 2. Which solution caused the bears to gain the least mass (or maybe lose the most mass)? Is that solution hypertonic, hypotonic, or isotonic? How can you tell? 3. What information does your graph give you about the change of your gummy bears? Explain what is happening in your graph in words. 4. Briefly explain what happened in your experiment gummy bears placed in different solutions. Use information from what you have learned about cell transport to help explain your answer.