Osmosis Lab March 22, 2013 Amanda L***** Introduction Transport into and out of your cells is important because without cellular transport, the cell could not move material into or out of the cell. This would lead to its inability to survive because cells must take in oxygen and food, and expel waste material that could inhibit the cell from performing in the body. A type of cell transport in particular is passive transport.
Passive transport is a kind of transport by which ions or molecules move along a concentration gradient, which means movement from an area of higher concentration to an area of lower concentration. Passive transport does not require an output of energy. There are 4 main types of passive transport: simple diffusion, facilitated diffusion, filtration, and osmosis. In this lab, we are particularly looking at osmosis and how it affects plant and animal cells.
Osmosis is the diffusion of water molecules across a selectively permeable membrane. In part A of this lab, we submerged the eggs in vinegar overnight, followed by peeling the softened shells from the eggs carefully while trying not to break the membrane the next day. We then recorded any observations we made on the eggs including weight and appearance. Next, we recorded any observations we could make on the carrots and potatoes before we put them into their solution.
We then placed the eggs(animal cells), carrots, and potatoes(plant cells) into their solutions and let them stand in their hypotonic and hypertonic solutions overnight followed by observing any changes in weight and appearance the next day. In Part B, we observed an onion cell exposed to distilled water under a microscope, and another onion cell exposed to a saturated salt solution, and drew the two different cells comparing the differences between their exposure to the hypotonic(water) and hypertonic(salt water, corn syrup) solutions. Part A
Purpose To observe the effects of hypotonic and hypertonic solutions on plant and animal cells. Hypothesis I predict that the hypotonic solution will cause the plant and animal cells to enlarge due to the difference in concentration on the inside of the cells, and the hypertonic solutions will cause the cells to shrink due to absorption of water molecules in the cells. Materials * 400mL beakers (2) * Tap Water * Eggs (2) * Vinegar * Salt water * Carrots (2) * Corn syrup * Potato strips (2) Procedure Day 1 1. Submerge the eggs in vinegar in a beaker. May have to weigh them down) 2. Leave them undisturbed overnight. Day 2 3. Peel the softened shells from the egg carefully so as not to break the 3membrane. 4. Record any pertinent observations on the egg, carrot and potato strip. 5. Place one egg and carrot in a beaker of water. 6. Place potato strip in a test tube. 7. Place the carrot in a beaker of saturated salt water and use corn syrup for the other egg. 8. Place the second potato strip in a test tube of saturated salt water. 9. Label the beakers and test tube and place in the cupboard overnight.
Day 3 10. Record any pertinent observations. Observations Plant and Animal Cells in Hypertonic Solution: | Solution| Appearance/texture Before| Weight before(g)| Appearance/texture After| Weight After(g)| Egg 1 | Corn Syrup| -translucent-yellowish colour-soft | 77. 53| -opaque-white/yellow colour-feels firm| 51. 17| | | | | | | Carrot 1| Salt solution| -orange-sturdy| 2. 59| -orange-sturdier -appears slightly smaller| 2. 36| | | | | | | Potato 1| Salt solution| -yellowish colour-sturdy| 2. 92| -same colour-sturdier | 2. 85| | | | | | |
Plant and Animal Cells in Hypotonic Solution(Distilled Water): | Weight Before(g)| Appearance/Texture After | Weight After (g)| Egg 2| 71. 82| -opaque-orange colour| 84. 10| Carrot 2| 2. 29| -orange colour-not as sturdy| 2. 52| Potato 2 | 2. 49| -yellowish colour-not as sturdy| 2. 98| Part B Purpose To observe changes in plant cells when they are placed in a hypotonic(distilled water) solution and a hypertonic(saturated salt water) solution. Hypothesis I predict that the hypertonic solution will cause the water to leave the cell, shrinking it due to dehydration from the salt.
Materials * Microscope * Microscope slide * Coverslip * Tap water * Saturated salt water * Onion Procedure 1. Prepare a wet mount using distilled water of a thin section of onion skin on a microscope slide. 2. View to draw one to two cells. Use magnification which shows the best detail. 3. Prepare another wet mount using the saturated salt solution instead of distilled water. 4. View and draw one to two cells. Use the same magnification you used for the first drawing. Observations Refer to onion cell drawings. Analysis
My predictions were both correct in part A and in part B when I stated that the cells would shrink in the hypertonic solution and enlarge in the hypotonic solution. The reason this occurred was because when a cell is immersed into a hypertonic solution, the tendency is for water to flow out of the cell in order to balance the concentration of the solute. When a cell is immersed in a hypotonic solution, it has a tendency to balance concentrations by water flowing into the cell, causing it to enlarge because of the lower concentration of solutes in its surroundings.
None of the cells observed had the same weight when removed from their solution meaning they were not isotonic. Had they been isotonic, the solution would have no effect on the cells, therefore when placed in an isotonic solution the cells would tend to neither gain nor lose water. When observing the effects of hypotonic and hypertonic solutions on plant and animal cells, I came to the conclusion that the plant cells did not change much in weight. This is due to their cell walls which make it tougher for the cell to expand.
The pressure exerted by water inside the cell against the cell wall is known as turgor pressure. In the drawing of the onion cell exposed to a hypertonic solution, the cell membrane appeared to be shriveled up inside the cell wall due to its turgidity. Evaluation In part A, I did not experience any errors with the cells themselves, but potential sources of error could have been inaccurate measurements before and after placing the cells in their solution. Other potential sources of error could have occurred while peeling the shell off the egg, causing the membrane to break.
In part B, I added too much distilled water to the slide making it difficult to get a good view of the onion cell exposed to the hypotonic solution. When performing a similar experiment in the future, I will be sure to add less drops with the eyedropper to the slide, enabling a clearer view of the cells I am observing. Application Questions 1. If the cells of a fresh water plant are placed in salt water, they will shrivel up due to the concentration difference between the salt water and the contents of the cell (cytoplasm). The water would escape the cell through osmosis causing it to dehydrate resulting in the shrinkage of the plant cell. . The fish that is used to salt water has high solutes and the freshwater is deficient of solutes, so when you place a saltwater fish in freshwater, the freshwater will move into the cells, causing them to swell and burst. 3. Grocery stores frequently spray the vegetables because the fresh water enters the plant cells through osmosis and makes them more turgid resulting in longer lasting freshness. 4. The use of road salt in the winter kills the plants alongside the road because the salt causes the cell to enter a hypertonic state. This causes the cytoplasm to move away from cell wall eventually making the plant shrivel up and die.
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