The Effects of Osmotic Pressures on Onion and Bean Plants and the Application of Saltwater in Farming

Transcription

1 The Effects of Osmotic Pressures on Onion and Bean Plants and the Application of Matthew Bartolomei The Academy of Science, Research, and Medicine at The Paulding County High School Ninth Grade - 1 -

2 Table of Contents Title Table of Contents Abstract Introduction Methods and Materials Results Discussion/Conclusion Appendix

3 Abstract Countries all over the world are left without enough freshwater to grow the food that is necessary for survival. Saltwater cam be converted to freshwater but the process is very long and the costs are immense. Scientists have tried to use the saltwater directly for irrigation and claim that it works as an alternative. The results of this experiment will either disprove or support the standing theory. The hypothesis states that when a plant (in this case an onion cell and a bean plant) is exposed to salt water in concentrations of 5% and 10% it will shrivel up and die. In order to start the experimentation one beaker (100 ml or more), a digital scale, cotton, a red onion, a pair of tweezers, a small knife, table salt, distilled water, paper towels, spoon, paper, pencil, a microscope, three bowls, and bean plants were needed. Once all the necessary slides were prepared I used the three salt solutions, 0%(control), 5%, and 10% to finish them. Once the beans were grown I then watered them with each of the solutions. During experimentation ideas and thoughts arose like Is there some way to keep the plants from being thrown out of homeostasis? Unfortunately no way was found to test this. Onion cells were also examined. The hypothesis states that the cell will shrink when exposed to saltwater

4 Introduction The cells in our body or in any other organism are constantly required to maintain internal stability, or homoeostasis which is the organism s steady state, in order to survive. Homeostasis is achieved with many different mechanisms of regulation such as temperature regulation, waste disposal, glucose intake, and water regulation. Perhaps one of the most important methods is water regulation. Since most organisms cannot survive long at all without water, water regulation is absolutely imperative. Water regulation is important because the cells in organisms are highly sensitive something called osmotic pressures. Osmotic pressure is defined as the pressure a cell experiences from the process of diffusion of water (Osmosis, 2012). Osmotic pressures are caused by solvents and solutes. In this case the solvent would be water and the solute would be salt. Since the solutes are not able to diffuse feely through the cell membrane it is noted that water, or the solvent, always tries to diffuse through cell membranes in order to make the concentration gradient of a solute equal within the cell membrane and outside the cell membrane. What makes this problematic is that sometimes a cell will experience - 4 -

5 a change in the normal osmotic pressure and either die or become weaken by being thrown out of homeostasis. Osmotic pressures are normal when a cell is in an isotonic solution. This means the cell has a total or net movement of water of zero where the flow or diffusion of water is equal going in the cell or going out of the cell. Osmotic pressures are higher when the cell is placed in a hypotonic solution. This is where the concentration gradient of solutes within the cell is higher than the concentration gradient outside the cell. Since water diffuse to equalize water flows into the cell resulting in a net water flow into the cell and an increase in osmotic pressure which may lead to the cell expanding and ultimately bursting. Osmotic pressures are lower when the cell is placed in a hypertonic solution. In hypertonic solution the concentration gradient of solutes is lower that that of outside the cell. This causes a net flow of water outside the cell which leads to a decrease in osmotic pressure and the cell shriveling and possibly dying. One very good example of all these occurrences is the osmotic stresses in which your blood cells endure. When you body is in homeostasis the blood cells assume their natural round and slightly concave shape (How do Blood Cells Transport Oxygen?, 2012). However, when your body is low on solvents, or water, the cells are in a hypertonic solution. Your blood cells lose their structure and shrivel up when the water in the cell diffuse out of the cell in order to equalize the concentration gradient. On the flipside, when too much solvent, or water, is taken in, the cell takes in water to equalize the concentration therefore the cell expands and may burst. Not only do osmotic pressures affect individual cells, it also affects the entire organism s body as a whole (Shark Savers,2012). One of the most common examples are - 5 -

6 the plants in your garden. When the plant is healthy the osmotic pressure is normal and there are no problems. However, when it is watered too little the pressure drops and the cells shrivel and die causing the plant to wilt. When the plant is watered too much the pressure increases causing the cells in the plant to burst and die. The plant eventually wilts. Another example is not one that s typically thought of like the plant scenario, but it is still very important. It is the importance and effects of osmotic pressures on animals. Take freshwater and saltwater fish. This is where we get into relative tonicities. To a freshwater fish freshwater is a slightly hypotonic solution. We will get into how it handles that environment later. Saltwater however is hypertonic solution. On the other hand saltwater is an isotonic solution to saltwater fish because the body as a whole has no net water flow. Freshwater is a hypotonic solution to the body as a whole. (see next paragraph) This means that when a freshwater fish is placed in saltwater all the solvent in the fish rushes out to equalize the concentration gradient. The fish shrivels and dies from the loss of water. When a saltwater fish is placed in freshwater the fish bloats from the water rushing in to equalize. The fish s cells burst and it dies. Organisms however have mechanisms to help keep the osmotic pressures constant and even. Plants prevent water loss, which would lead to a drop in osmotic pressures in a couple ways. In times of drought some plants fold up to decrease surface area reducing water loss. Other plants excrete an oily fluid that coats and seals the plant minimizing water loss. When rain finally does come the oil washes off. A plant s cell wall prevents the cells from bursting from an increase in osmotic pressures. The cell wall may expand a little bit but it applies pressure to the cell membrane keeping it from bursting. Animals - 6 -

7 have different ways to maintain a safe osmotic pressure. Back to the freshwater fish. The fish use osmoregulation (How Does Osmoregulation Work?,2012), Osmoregulation is the ability of an organism to maintain a constant concentration of water in its body even when its outside environment would normally cause it to lose or gain water. Freshwater and saltwater fish both use osmoregulation. The environment around a freshwater fish is slightly hypotonic. However, the fish s gills and kidney prevent an excess build up of water inside the fish s body. The kidneys in other animals provide the same function. Saltwater fish, like the bull shark, can survive in both salt and freshwater. The bull shark can survive in saltwater because of the adaptations it has. The kidneys of the shark take all the excess salt out of the shark and it is excreted through the urine. Even though compared to a single cell from the saltwater is a hypertonic solution, to the entire shark s body the water is and isotonic solution since there is no net flow of water. In freshwater however any other saltwater fish would bloat and burst. But the bull shark can live in freshwater for up to four years by adapting to the freshwater by adjusting its kidneys where it doesn t remove solutes as rapidly and to remove more water through urination (How Does Osmoregulation Work?,2012). The shark has basically reversed its osmoregulation system which allows it to maintain a safe osmotic pressure. Now that the subject of osmotic pressures has been covered the real life world connections can be discussed. All over the world, especially in third and fourth world countries, there is not enough water to go around (Why Entire Countries Face - 7 -

8 Collapse,2012). With such little water it is hard to farm the food they need to survive. Since over 90% of the water on earth is salt water why can t we put that to use and irrigate the crops with it? Now we already do use it but we take the salt out in desalination plants. Though the idea seems sound the facilities to do this are immensely expensive to operate. What if there was a way to use the actual saltwater. Scientists and farms say it is possible with a wide variety of crops even though reports show they ve only been successful with a very small variety of crops (Saltwater Farmers, 2012). The purpose of this experiment is to observe the effect of isotonic and hypertonic solution on the cells of an onion and to experiment with the idea that saltwater can be used for crops The different concentration gradients will be recorded and compared, the plants observed and the data eventually brought together to create results and ultimately to draw conclusions

9 Methods and Materials First, all the materials must be gathered before experimentation. A list of all the materials is provided. (See A-1) Once all materials are gathered prepare pots. Label one control, one 5%, and one 10%. Take the cotton and loosen it by spreading out fibers. Fill each pot with the cotton. Put all the beans in the control pot. Water with distilled water until cotton is just soaked. Water everyday to replace any water lost due to evaporation. Set aside until shoots are at least 3 in length. In the meantime start the onion cell examination. Prepare all the materials to make slides with. Take the red onion. Cut a wedge out of it with a sterile knife. Use the tweezers to peel of a thin layer of the dark purple skin. Place a drop of distilled water on the slide. Place onion skin in the water. Add a second drop of distilled water and cover with a glass slip. Lower it on at an angle so as to let all the bubbles escape. Observe under microscope. Disassemble slide and clean. Prepare the 5% salt and water solution using 100ml of distilled water and 5g of salt (not iodized). Use this solution to make the next slide. Observe. Disassemble slide and clean. Empty beaker and clean. Prepare the 10% salt and water solution by mixing 100ml of distilled water and 10g of salt. Use this solution to make next slide. Observe. Clean all materials thoroughly. Once all bean plants have grown transfer a few to the other 2 pots until all 3 pots have roughly the same number of plants. Water the 5% and 10% pots with their respective solutions. Cotton should just be soaked. Start timing once watered

10 Record how much time it takes for the first brown wilt spot to appear. (Note- plants will have shrunk long before that.) Results At the end of the experimentation and examination all the data was recorded. There was a problem with onion cell examination however. There was no way to collect quantitative data for the examinations. There was no way available to measure the amount of shrinkage from the micrographs. So a ranking system was devised in order to assign quantitative data to an otherwise immeasurable result. The ranking works as follows 1- No shrinking whatsoever. Perfectly normal, happy cell in homeostasis. 2- Slight shrinking. A normal amount of shriveling of shrinking associated with forgetting to water a plant for a day. Reversible (meaning can be returned back to homeostasis by adding water) 3- Moderate shrinking. Cell membrane has pulled away from the cell wall. Associated with a plant beginning to wilt from water loss. Reversible. 4- Heavy shrinking. Cell membrane has pulled back a considerable distance from cell wall. Associated with a plant on the verge of dying from water loss. At this point it is reversible but unlikely to see positive results. 5- Severe shrinking. Cell membrane and the contents within are no longer distinguishable. All that s left is the cell wall skeleton. Associated with a plant that is long dead and crunchy. Like an autumn leaf

11 Each of the solutions, 0%, 5%, and 10%, were tested five times. For the 0% solution, or the distilled water control, each trial resulted in a ranking of 1. (Note- to avoid biased responses multiple views from different people were collected and averaged out) The 5% solution got an average of 2.4 meaning that they were all at least slightly shriveled. The 10% solution got an average rating of 3.6 meaning the cells weren t doing so well and shrunk considerably. The hypothesis that stated that the onion cells would shrink was proven to be correct. There were three beans in each pot. All the beans grew and the beans that were watered with the 5% salt solutions remained brown spot free for an average of 40 hours. The plants began to shrivel within an hour however. The bean plants that were watered with the 10% solution remained brown spot free for 18 hours. The hypothesis that stated that the plants would shrivel and die was proven to be correct. However the effects were delayed longer than was predicted. Onion Cell Exam Results 0% Distilled control 5% Saltwater solution 10% Saltwater solution Trial Trial Trial Trial Trial Average Bean Plant Results Bean plant Bean plant Bean plant Average (Hours) % Distilled control Infinite* Infinite* Infinite* Infinite* 5% Saltwater solution % Saltwater solution *-limited only by the life of the plant

12 Onion Cell Examination Trial 1 Trial 2 Trial 3 Trial 4 10% Saltwater solution 5% Saltwater solution 0% Distilled (control) 0% Distilled (control) 5% Saltwater solution 10% Saltwater solution Bean Plant Farming % Distilled (control) Bean plant 1 Bean plant 2 Bean plant 3 10% Saltwater solution2 5% Saltwater solution 0% Distilled (control) 5% Saltwater solution 10% Saltwater solution2-12

13 Discussion/Conclusion At the end of my experimentation and analysis, my hypotheses were proven to be correct. I also disproved the scientists theory. My hypotheses stated that the onion cells would shrivel up and possibly die when exposed to saltwater and that the bean plants would also shrivel up and die when exposed to saltwater. When I exposed the onion cells to 5% and 10% saltwater solutions they did in fact shrink and shrivel. When I began to water the already mature bean plants with 5% and 10% saltwater solutions they shriveled and died just as expected. This was due to osmotic pressures. When the concentration gradient of solute outside of the cell is higher than that of the inside of the cell, water rushes out to equalize. The cell undergoes negative osmotic pressures and shrinks. The onion or the bean plant also doesn t have an osmoregulatory system. I must note that the effects did take much longer than I predicted. I predicted that the bean plants would negative effects within no more than five minutes. I came to this premature conclusion because of what I observed with the onion cells. It took no more than five seconds for the onion cells to show negative effects. However since an entire bean plant is comprised of many more cells than a thin slice of onion it takes considerably more time to show the negative effects of saltwater

14 My data was relatively spot-on and consistent despite the fact that during my experimentation I encountered several problems. All but one of them were easily fixed. The problems encountered we troublesome but relatively simple like not being able to see the onion under the microscope. This problem was thought to have been fixed by staining the cells with iodine. This remedy did not work as only the nucleus absorbed the dye and the cytoplasm absorbed none of it. I then found that if I peel the dark purple skin of a red onion versus any other onion, the cytoplasm was a nice vivid purple and very easily visible under the microscope. I also had problems with introducing the solutions into the slides. I wanted to be able to watch the cell shrink so I placed a drop of the solution I wanted to introduce on one side of the slide. I then took a small piece of paper towel and used to absorb some of the distilled water on the other side. This led to the distilled water being sucked up and the saltwater solution rushing in to take its place. The procedure worked great but since the microscope is very sensitive to bumps and movements, the actions I was making to carry out that process caused the view to be distorted and so I resorted to making fresh slides each time. The major problem I had though was that I had no way to measure my shrunken cells. My microscope didn t have a built in scale and I didn t have a hand-held scale. However it was recommended to me that I use a ranking system as a way to assign quantitative data to my qualitative data. The data is still qualitative since it s not a legitimate measurement but it works as a way to express the data in a way that can be read and understood. This problem could be fixed by either purchasing a microscope with a scale built in to the ocular or a hand-held scale that is held under the objective with your specimen

15 Despite these complications my data, overall, did not comply with previous research on this topic. They did say that some plants are not capable of handling of saltwater irrigation techniques but one plant they did say, the bean, was able to be watered with salt water. Perhaps the bean they used was not the same as mine and there may very well be bean plants that have adapted to salty environments but this was not that bean. I tried to the author of the article saying that saltwater farming is possible but received no reply. I feel like my experimentation was limited. I would ve liked to use more crops and experimented with those. I was limited by my budget unfortunately

16 A-1 Appendix Materials (onion examination) One beaker (100 ml or more) digital scale red onion tweezers small knife table salt (not idodized) distilled water (grocery store) paper towels spoon paper and pencil (to record data) Materials (bean plant experiment) Celestron LCD Digital Microscope (or any other light microscope preferably one that goes up to 600x magnification) 3 small garden pots (bowls are fine) Cotton (enough to cover bottom of bowls) bean plants (any bean out of the cupboard will work too pinto beans were used for this experiment) light source

17 paper and pencil (to record data) A-2 Procedures 1. Gather materials needed for your plant cell science project experiment. 2. Use the knife (with adult supervision) to cut the red onion into small wedge shaped pieces. 3. Use the eye dropper to place a drop of distilled water in the center of a microscope slide. 4. Use the tweezers to peel a thin layer of skin tissue from the thick part of the red onion wedge and place it in the center of the microscope slide. 5. Add a drop of distilled water. 6. Carefully and gently lower a cover glass slip at an angle over the stained tissue, allowing air bubbles to escape. 7. Examine the prepared slide under the Celestron LCD Digital Microscope at 100X magnification. (increase magnification if needed) 8. Draw and identify observed structures. 9. Prepare a 5% salt solution by adding 5 grams of salt (measure with digital scale) per 100 ml of distilled water in a beaker. Gently shake or stir until dissolved. 10. Grab the dropper and fill with 5% solution. Use the dropper to add a drop of 5% solution to the slide. Repeat step Add a drop of 5% solution. Repeat steps 7 and Empty the beaker. Rinse thoroughly then fill with 100ml of distilled water. Prepare a 10% solution by adding 10 grams of salt to the distilled water. 14. Grab the dropper and fill with 10% solution. Use the dropper to add a drop of 10% solution to the slide. Repeat step

18 15. Add a drop of 10% solution. Repeat steps 7 and 8. A-3 Bean Farming procedures 1. Prepare three pots by labeling them control, 5%, and 10% 2. Loosen cotton by stretching and pulling apart fibers. Do not rip. 3. Place cotton on bottom of pots. 4. Place all 12 beans in control. 5. Water with distilled water until cotton is just soaked. 6. Water daily by just soaking the cotton. Wait until all shoots are 3 long. 7. Take 3 plants and put them in each of the other pots. Each pot should have 3 plants. 8. Water each pot with their respective solutions and start timing. 9. Record time when plant develops first brown spot