How does varying intensity of light impact the rate of cell division of Allium fistulosum? My independent variable will be the amount of light the onions are exposed to ( 0 watts, 40 watts, 100 watts). My dependent variable will be the mitotic index of samples taken from each of the germinated onions. This will be calculated using root tip squashes.
Background Information:
Allium fistulosum, commonly called the spring onion, is an evergreen perennial. Underground bulbs are approximately the same thickness as the plant stem. They can grow to be between 2 and 3 feet tall. The end of the stalk is an umbel, a yellowish-white six-sepal flower. This plant blooms in May, requires full sun, and a medium amount of water.
The onions used in this experiment will be germinated. Germination is how a seed grows into a functioning plant. Several things are needed for germination to occur: appropriate temperature, oxygen, and water. The appropriate temperature encourages enzymatic activity, which increases the rate of reaction and thus allows for
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faster growth. Oxygen is needed for cells to carry out cellular respiration in order to produce ATP. Lastly, water is needed to keep the bulb hydrated, and is needed for the creation of ATP. It is also used in cells to transport molecules, such as glucose. Photosynthesis is the process by which plants use sunlight to create energy for nutrients.
The A. fistulosum seeds will be planted and placed with access to varying degrees of light (0 watts, 40 watts, and 100 watts). The amount of light will inhibit or encourage cells to create ATP, which they will use to synthesise organic compounds, such as glucose for energy. As the light intensity increases, the rate of photosynthesis generally increases. The more nutrients that the cells are able to produce, the more growth the seeds exhibit.
This means that there should be more growth, or cell division. This allows for me to determine the mitotic index of the bulbs. The mitotic index is a ratio of cells in a sample that are in a phase of mitosis (prophase, metaphase, anaphase, telophase, or cytokinesis) to the total amount of cells in a sample. As light intensity is a factor that affects cell growth, the mitotic index should be
impacted. Mitosis is the part of the cell cycle, following interphase (when the cell carries out life processes, and duplicate organelles and DNA) where a cell actually divides into two daughter cells. Mitosis includes 4 phases: prophase, metaphase, anaphase, and telophase. This is followed by cytokinesis, the final step in cell division. In prophase, chromatin coils into chromosomes, which become visible; the nuclear envelope disintegrates; and centrosomes move towards the opposite poles of the cell. Next is metaphase, where the chromosomes move to the center of the cell. The third phase is anaphase, where spindle fibres have split the sister chromatids, and gravitate them to opposite poles; each side of the cell now has a complete and identical set of chromosomes. Lastly, there is telophase. In this phase, chromosomes uncoil, and two new nuclear envelopes begin to redevelop around the two sets of chromosomes; the spindle fibres disappear; and the cell elongates to prepare for the final phase of cell division: cytokinesis. In plant cells, cytokinesis involves the growth of a cell plate beginning in between the two poles of the cell, and grows outward. This is because plant cells contain a cell wall. Once cytokinesis is complete, there are two identical daughter cells. Cells that are involved in a phase of cell division (i.e. are not in interphase) will be used to form the first part of the ratio in calculating the mitotic index. Hypothesis: If I allow Allium fistulosum to germinate for one week in varying light intensities, then I will find a higher mitotic index in samples germinated under a 100 watt soft white light bulb than the 40 watt soft white light bulb, or the 0. This is because plants use light to create energy, and thus the more they have available, the more the cells will be able to grow and divide.
Figure 1 indicates an increasing mortality rate (positive slope) in plants as density increases; Figure 2 shows the corresponding germination rate reflecting the exact opposite trend. Mortality remains zero until 8 seeds are planted (6% mortality), then is reduced to zero at 16 seeds then increases to 14 percent (32 seeds), 32 percent (64 seeds), and more than half (57 %--128 seeds).
Increasing the light intensity will make photosynthesis faster. Variables: In this experiment there are a few things we have to keep the same.
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The Effect of Light Intensity on the Rate of Oxygen Production in a Plant While Photosynthesis is Taking Place
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