2019 Year 12 IB Extended Essays

wheatgrass sprouts move into the external solution, causing the plant to wilt. A similar phenomenon occurs with the plants grown in the nitrate solution. Graph 2 demonstrates that as the concentration of NaNO3 is increased, the difference between the height of the plant at most of the concentrations decrease. This is expressed in the difference in height between the plants grown in 0M and 0.0068M NaNO3 and those grown in 0.4381M and 0.1095M NaNO3 with a difference in height of 3.16cm and 0.24cm respectively. The heights of these plants didn’t constantly increase as the Nitrate concentration was increased because of osmosis, with the water in the plant entering the soil. But while nitrates are beneficial for plant growth, excessive amounts of nutrient don’t serve any purpose as the plant only requires certain quantities of nitrates and supplying higher levels could have a negative impact on the growth of plant, leading to the plant taking on a burnt look due to dehydration. Excess levels of both nitrates and NaCl also affects the growth of the roots of the plant although this was only demonstrated by the plant grown in 0.1095M NaCl solution. It was found that that while the endodermis filters out substances, only allowing certain materials to enter the vascular core, it also restricts roots from growing into regions that could potentially be dangerous for the plant. It accomplishes this by releasing a stress hormone called Abscisic Acid which inhibits root growth in a particular direction (Carnegiescience, 2013). In a natural setting, as the root is growing, when it enters a harmful region in the soil, Abscisic Acid is released, causing the roots to change direction. But in my experiment, as the seeds were grown in solutions with the salt and nitrates evenly dissolved in the solution, the roots came in contact with the same concentrations regardless of the direction of the root growth. This is the reason why the roots of the plants grown in 0.1095M NaCl solution had significantly smaller roots than the other plants.

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