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| Research Question | Would flipping the petri dish in which the plant is upside down every day affect seed germination? We came up with this question because we are interested in gravitropism, which is how the pull of gravity affects which direction the seeds grow. We wanted to know that if the direction that 'up' was changed every day, if the direction that the stem or the root was going would change every day, as well. |
| Predictions | If we flipped our petri dish over every day, then the plant might grow a different direction each day because because it would want to grow up, but which direction ‘up’ is would change each day. It would look somewhat like a zig-zag, because the stem would go one direction the first day, then the opposite direction the next day, etc. |
| Experimental Design | Seeds: Pisum sativum - or peas. These are the seeds that we will be using in our lab. Data/control groups/experiment: We will be collecting data on which way the stem is growing and if the control or experimental plant has grown more than the other one. Also, we will collect data on texture, shape, color, and size. The variables that we will keep constant are the type of seed, the amount of water, the temperature, the light, the amount of seeds in one dish (3), and the location. The variable we will be changing is change gravity, or which direction ‘up’ and ‘down’ are by flipping the petri dish over each day. It will look like this: the seeds are in a petri dish that is sitting on a table/flat surface (not moving or being flipped), and get watered (we’re not sure when or how much yet, but it will probably whatever planting instructions come with the seed), in some amount of light that the plant would normally grow in.Our independent variable is gravity. We will have 2 groups - one experimental group, with a petri dish that gets flipped over every day, but not on weekends, and one control group, with a petri dish that stays still. This will show us if there is a difference in how many plants get germinated, and in what the plants look like. Our negative control group is the petri dish that we don’t flip. We will leave this dish alone, and just water and observe it. Procedure: Procedure for Petri dish one: 1. Get 2 nasturtium seeds 2. Observe seeds and record data 3. Soak the seeds overnight in a container with 2-3 cm of water a. Observe seeds and record data 4. Place seeds on a moist paper towel in a petri dish and place in a controlled environment a. Take observations and record data b. Moisten paper towel 2-3 times per week c. Flip petri dish over every day - leave it like that for the night, then flip it over the other way the next day. If it isn’t possible to flip every day, then do it every possible day. Procedure for Petri dish two: 1. Get 2 nasturtium seeds 2. Observe seeds and record data 3. Soak the seeds overnight in a container with 2-3 cm of water a. Observe seeds and record data 4. Place seeds on a moist paper towel in a petri dish and place in a controlled environment a. Take observations and record data b. Moisten paper towel 2-3 times per week Research: • The reason plants know which way to grow in response to gravity is due to amyloplasts in the plants. Amyloplasts (also known as statoliths) are specialized plastids that contain starch granules and settle downward in response to gravity. Amyloplasts are found in shoots and in specialized cells of the root cap. When a plant is tilted, the statoliths drop to the new bottom cell wall. A few hours later, the shoot or root will show growth in the new vertical direction . • A plant laid on its side in the dark will send shoots upward when given enough time. • Plant shoots grow away from gravity, toward sunlight, while plant roots grow into the soil in the direction of gravity. My comment on this: the lightsource isn't always upwards - I wonder how this would turn out. Is it always that the shoots grow away from gravity, or is it always that the shoots grow towards light? It would be interesting to figure out which one is the major influencer on the shoot - gravity or light? • Definition of ‘tropism’: a response in a plant’s growth to something - this something could be weather, touch, time, gravity, and/or light. A positive response is when the plant grows in the direction of the stimulant, and a negative response is when the plant grows away from the stimulant. Gravitropism also causes the roots to move into the soil. • Gravitropism, then, is a negative response, because the stem grows away from gravity. • If you were to place a plant sideways, it would still grow upwards - this is mainly because of a hormone called auxin, that concentrates on the side of the stem where gravity pulls it down, then causing the plant to grow upwards, and elongate in the direction opposite to gravity. • The plant will respond to gravity’s pull, no matter what direction the plant is facing, or what how the seed is laid down. • This means that our experiment will most likely end up like our hypothesis, because the auxin would change would change which direction the plant grows each day that we flip it. • A chemical called auxin in plants allows them to turn direction by having it collect at the bottom part of the stem so the cells on one side elongate, forcing the stem to grow up. Resources for Research: • https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/plant-sensory-systems-and-responses-184/plant-responses-to-gravity-703-11928/ • http://www.bioedonline.org/lessons-and-more/lessons-by-topic/plants-form-function/how-does-gravity-affect-root-growth/ • https://www.youtube.com/watch?v=eDA8rmUP5ZM • http://herbarium.desu.edu/pfk/page8/page9/page9.html |
| Conclusion | The question that my group, The Scientific Specimens, is researching is: Would flipping the petri dish, in which the plant is in, upside down every day affect seed germination? We chose this question because we were interested in gravitropism, and we wanted to know how a plant's growing and germination would react to the plant being flipped over every day, because gravitropism leads the root to grow downwards and the stem to grow upwards. We wanted to see what would happen if ‘up’ and ‘down’ changed every day. The seeds we were using for trial 3 were nasturtium seeds (Tropaeolum majus) , but they take too long to germinate and since our experiment is mostly about looking at the sprout after it’s started, we decided to use other seeds instead. We decided to use pea seeds because they seemed to germinate very quickly (the group next to use had peas, and their seeds germinated on the first day). Our hypothesis was if we flipped our petri dish over every day, then the plant root might grow a different direction each day, because gravitropism would force it to grow down. The direction that ‘down’ is, though, would change each day. Therefore, we hypothesize that it would look somewhat like a zig-zag, because the stem would go one direction the first day, then the opposite direction the next day, etc. I think that our data did support our hypothesis - especially with trial 2. In trial 2, the experimental batch of pea seeds grew up and down in a zigzag pattern, exactly as we expected them to. The control plants grew straight upwards, as we expected them to, as well. Trial 2’s plants got very tall, because they were peas, which germinate quicker than nasturtium seeds. From our research, we learned that if you were to place a plant sideways, it would still grow upwards - this is mainly because of a hormone called auxin, that concentrates on the side of the stem where gravity pulls it down, then causing the plant to grow upwards, and elongate in the direction opposite to gravity. Even if you placed a plant sideways in the dark, it would end up growing upwards - so it is not the sun that tells the plant which way to go up or down, but something else. This ‘something else’ is a chemical called auxin. The auxin gathers on one side of the plant, pulled by gravity, and forces the stem to grow upwards. So, if we kept on flipping the petri dish, then the auxin would force it to continue to change direction. My graph is showing the angle of the zigzags in our plants - this one shows trial 2’s different pea plants. I took the angles of each curve with a protractor, and then found the average of each. Then I put this data on my chart. I think that trial 2 showed the most results for sure, because it was the batch that grew the most (trial 1, nasturtium seeds, take a really long time to germinate; trial 3 is newer and only two seeds germinated, the other ones got moldy). That is why I am showing the trial 2 graph here. A quantitative observation that we had was that it took about 10 days for one of our nasturtium seeds to germinate! This is why we chose a different seed for trials 2 and 3. When, on March 22nd, we finally saw a little sprout poking through, we were very relieved. But even after we had waited for another 4-5 days, we still saw no sign of the other seeds germinating - so we had to give up on trial one. I’m still wondering that if we waited a little longer, if those seeds would then have sprouted. But our scientist, Allison, said that maybe we should have soaked the nasturtiums for a few more days, so maybe this is why most of our nasturtiums did not grow. We noticed a smell being emitted from the nasturtium seeds after we soaked them - it smelled sort of like smoked salmon, with a peppery smell too. This was odd; we didn’t expect to be taking observations about the smell of a seed! Near the end of trial 1, we noticed that the smell had changed - especially in the seed that had sprouted - to a sort of spicy smell. It was exactly what you would taste when you bite into a nasturtium petal! I wonder why it smelled so different at the beginning. In between the beginning and the end, there were a variety of smells - from almost moldy to smelling like and actual nasturtium. The peas also smelled once they had sprouted, and they smelled of peas! Exactly what you taste when you bite into a pea - that was what the peas smelled like. The moldy ones, though, didn’t smell so nice. My last qualitative observation is about the sprouts of the seeds, and how our flipping of the petri dish affected them. Instead of seeing if our seeds actually germinated and when they did, our experiment was about which direction the seeds germinated in. We expected to see a zigzag pattern, and we did actually see one - though the zigzag itself actually was slightly flattened every time, as the plant grew in a new direction and then forced the whole stem to come with it in that direction, so the former zigzags were slightly dampened every time. But there were still zigzags, so I think that our hypothesis was supported. |
| Investigation Theme | WOS |
| Grade Level | Middle School Students (grades 6,7,8) |
| School Name | San Francisco Friends School |
| Session | Spring 2017 |
