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# Investigate the effect of salt concentration on the rate of water loss/gain by potato.

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Introduction

Investigate the effect of salt concentration on the rate of water loss/gain by potato. Plan: Investigate the effect of salt concentration on the rate of water loss/gain by potato. Hypothesis: I predict that the 0 M salt solution will make the potato gain weight because the water is at a higher concentration outside the potato so it moves in by osmosis. I predict that in the 0.2 M solution the potato will neither gain nor lose weight because I think that the concentrations of water in and out of the potato are the same. I predict that in the 0.4 M, 0.6 M, 0.8 M and 1.0 M solutions will lose weight because I think that the concentration outside the potato will be less concentrated than inside the potato so the water from inside the potato will move by osmosis. Background Knowledge: Osmosis - Osmosis is a special case of diffusion. Outside the cell in the animation, there is a low concentration of solute molecules and a high concentration of water molecules. Inside the cell, there is a high concentration of solute molecules and a low concentration of water molecules. The solute molecules can't diffuse out because the plasma membrane won't let them through. ...read more.

Middle

Adding solute - In fact when we add solute to water, the water molecules form a shell around each solute molecule. So this decreases the number of free water molecules that are able to exert a pressure on the membrane. Therefore, the water potential decreases. There is no solute in pure water. So pure water has the greatest water potential. Preliminary Study: Before starting this particular investigation I have conducted a similar experiment. The aim of the experiment was: To see how the mass of agar jelly affects the absorption of potassium manganate (VIII) solution. In the experiment I found that the potassium absorbed the furthest into the 0.5 cm3 cube of jelly, next into the 1 cm3 cube and last into the 2cm3 cube. Variables: VARY CONSTANT Salt concentration Control Amount of water Size of potato (length) Time (25 minutes) Temperature Type of potato Freshness of potato Apparatus Observations: I will make three repeats, recording the gain/loss in mass and length of the potato cylinders at the end and beginning of the experiment in six different salt concentrations. How I made up these concentrations is explained in the diagrams below. ...read more.

Conclusion

Mass @ start of experiment (g). Mass after (g). Mass gain/loss (g). Start length (cm). End length (cm). Length gain loss (cm). 0 2.3 2.5 0.2 3.3 3.4 0.1 0.2 2.4 2.3 -0.1 3.5 3.5 0 0.4 2.6 2.4 -0.2 3.5 3.5 0 0.6 2.4 2.1 -0.3 3.4 3.2 -0.2 0.8 2.4 2 -0.4 3.3 3.1 -0.2 1 2.2 0.7 -0.5 3.3 3 -0.3 3rd set of results: Salt concentration. Mass @ start of experiment (g). Mass after (g). Mass gain/loss (g). Start length (cm). End length (cm). Length gain loss (cm). 0 2.8 3 0.2 4.8 4.9 0.1 0.2 3.2 3.1 -0.1 4.7 4.7 0 0.4 2.8 2.5 -0.3 4.5 4.5 0 0.6 2.9 2.6 -0.3 4.7 4.6 -0.1 0.8 3 2.6 -0.4 4.7 4.6 -0.1 1 2.7 2.2 -0.5 4.8 4.6 -0.2 Average of results: Salt concentration. Mass gained/lost (g). Length gained/lost (cm). 0 0.183 0.1 0.2 -0.09 0 0.4 -0.243 0 0.6 -0.357 -0.133 0.8 -0.757 -0.133 1 -0.0497 -0.233 Analysis: From my two graphs of results I found very similar patterns, they both seem to lose length and mass mainly after the 0.2 M solution. At the first point 0 M they both gain in mass and length. They gain in mass because Evaluation: I only had one anomalous result Biology coursework. Niels Pedersen. ...read more.

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