2019 Year 12 IB Extended Essays

Discussion: It is clear from Graph 1 and Graph 2 that the plants grown in the Nitrate solution grew more that the plants grown in the Salt solution. While the plants grown in 0.04381M NaNO3 solution reached a height of 19.02cm on Day 20, the tallest plants in the NaCl solution were those grown in the lowest concentration of 0.0068M NaCl, reaching a height of 12.3cm which was only 0.18cm taller than the plants grown in 0M of NaCl. This addresses the question whether nitrates have a better impact on plant growth when compared to salinity. The plants grown in the 0.04381M NaNO3 solution grew to their respective heights because plants require the nitrogen to produce proteins. The reason it had a significant impact on the growth of the plant however is because plants use this nitrogen to produce chlorophyll which plays a major role in photosynthesis, enabling the plant to grow taller (Bbc.com, n.d) (Cropnutrition.com, n.d). This was one of the reasons for the stunted growth of the plants grown in the 0M and NaCl solutions as the plant didn’t have access to sufficient levels of nitrogen. This is further supported by the change in the colour of the leaves of the Wheatgrass from green to yellow as the plant couldn’t produce the green chlorophyll required to give the plant its colour. The reason for the size of the plant grown in the 0.0068M NaCl solution being 0.18cm taller than the plant grown in the 0M solution is because Chloride is a necessary micronutrient for plants. It plays an important role in balancing out the potassium ions that increase in the guard cells as the stomata open and close. It also plays a role in photosynthesis, aiding in the water splitting system and also stimulates the biosynthesis of chlorophyll through the activation of specific enzymes (Tetrachemicals.com, n.d). (Ma, Q, 2011) However, Graph 1 also shows that the plants that were grown in the 0.04381M NaCl solution grew to a size of 0.4cm over a period of 20 days. This is because the although NaCl serves a beneficial purpose in photosynthesis, excess levels of salt such as the one in the 0.04381M solution has a detrimental impact on the growth of the plant. Plants rely significantly on osmosis for extracting water using their roots because there is a higher solute concentration within the plant than in the soil and hence the water moves from a region of low to high solute concentration. As in this case the external solution has a higher concentration of NaCl when compared to concentration within the plant, the water in the

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