If you leave a tent pitched on the same patch of lawn, the grass underneath turns yellow and spindly. There are also some plants that have lost the power of photosynthesis altogether. The plants have no chlorophyll and get all their nutrients by parasitically attaching to the roots of nearby plants instead.
And it can react to changes that occur slowly over time — say, at sunrise — and those that happen in just seconds, for example, due to a passing cloud. Researchers agree that one key to quenching is a pigment within the LHCSR — called a carotenoid — that can take two forms: violaxanthin Vio and zeaxanthin Zea. Conversion from Vio to Zea would change various electronic properties of the carotenoids, which could explain the activation of quenching.
That type of fast change could be a direct response to the buildup of protons, which causes a difference in pH from one region of the LHCSR to another. Clarifying those photoprotection mechanisms experimentally has proved difficult.
Focusing on the LHCSR found in green algae and moss, they examined what was different about the way that stress-related proteins rich in Vio and those rich in Zea respond to light — and they did it one protein at a time. In earlier research, they had figured out how to purify the individual proteins known to play key roles in quenching. Using a highly sensitive microscope, they can then detect the fluorescence emitted in response.
Little or no energy will be left to be reemitted as fluorescence. As the fluorescence goes down, the quenching goes up. Using that technique, the MIT researchers examined the two proposed quenching mechanisms: the conversion of Vio to Zea and a direct response to a high proton concentration. To address the first mechanism, they characterized the response of the Vio-rich and Zea-rich LHCSRs to the pulsed laser light using two measures: the intensity of the fluorescence based on how many photons they detect in one millisecond and its lifetime based on the arrival time of the individual photons.
Using the measured intensities and lifetimes of responses from hundreds of individual LHCSR proteins, they generated the probability distributions shown in the figure above. In each case, the red region shows the most likely outcome based on results from all the single-molecule tests. Outcomes in the yellow region are less likely, and those in the green region are least likely.
The left figure shows the likelihood of intensity-lifetime combinations in the Vio samples, representing the behavior of the quench-off response. Moving to the Zea results in the middle figure, the population shifts to a shorter lifetime and also to a much lower-intensity state — an outcome consistent with Zea being the quench-on state.
To explore the impact of proton concentration, the researchers changed the pH of their system. The results just described came from individual proteins suspended in a solution with a pH of 7. In parallel tests, the researchers suspended the proteins in an acidic solution of pH 5, thus in the presence of abundant protons, replicating conditions that would prevail under bright sunlight.
The right figure shows results from the Vio samples. Shifting from pH 7. But it brings only a slightly shorter lifetime, not the significantly shorter lifetime observed with Zea. The dramatic decrease in intensity with the Vio-to-Zea conversion and the lowered pH suggests that both are quenching behaviors.
But the different impact on lifetime suggests that the quenching mechanisms are different. Their investigation brought one more interesting observation. According to Schlau-Cohen, the only explanation for such stability is that the responses are due to differing structures, or conformations, of the protein.
When sunlight is dim, it assumes a conformation that allows all available energy to come in. Plants need three basic things to live: sunlight, water, and carbon dioxide. Through a process called photosynthesis , the plants use the energy from the sun to convert carbon dioxide, soil nutrients, and water into food!
How do you think a seed will grow with some or partial sunlight? What do you think the plant will look like after two weeks of growth? What will be the difference between the three sunlight exposure plants? How do you think the plants will be alike? Collect a small handful of basil seeds roughly 30 seeds and sprinkle them evenly around the top of each soil cup.
Each cup should get roughly the same amount of basil seeds so that the growing conditions are consistent. Place a thin layer of soil over the seeds. Note : the science notebook should allow for a small number of notes to be taken each day during the growing process.
Notes such as: how much water was provided, sprouts that have begun to grow, leaf formation, the height of plants, etc. Provide space for each plant and for 14 days of notes.
Over the span of two weeks, track the growth of the seeds and provide water when necessary. Make sure to take notes on the growth of the basil and observations that seem important.
The growth experiment lasted 14 days. Below are the anecdotal notes and pictures that were taken throughout the plant growth. Now that we have witnessed the growth of a seed to plant and can better understand the role of sunlight in the growing process, it is important to discuss a few ideas:.
Overall, this experiment depicts just how important the sun is to the survival of plants and also humans oxygen supply. Without proper sunlight, plant growth would stop due to the lack of photosynthesis and all of the other components needed for healthy plant growth.
Once again, it is easy to see just how important the sun, a renewable resource, is to both plants and mankind. Experiment Overview: The sun is a renewable energy source that plays a pivotal role in our everyday life, from warming the earth to the water cycle, it is an essential part of our daily existence.
Experiment Process:. Step 2 Collect a small handful of basil seeds roughly 30 seeds and sprinkle them evenly around the top of each soil cup. Step 3 Place a thin layer of soil over the seeds. Step 4 Water each plant until the soil is moist and start the germination process. Step 5 Place each cup in a different growing environment. Example: a bookshelf that gets some sun indirectly from the kitchen window Place the last cup in a location that gets little to no sun.
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