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Osmosis Coursework. Investigation to determine the water potential of apple tissue and carrot tissue, and how they compare to each other.

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Investigation to determine the water potential of apple tissue and carrot tissue, and how they compare to each other. Introduction: Water potential is the potential energy of water, relative to pure water (one without any impurities, such as ions); it's basically a numeric term that describes the tendency of water to move between two areas - due to mechanics such as osmosis or gravity. Measured in kiloPascals (kPa), the maximum measure of water potential is 0kPa (achieved by distilled water) and the water potential drops into negative numbers as the water purity decreases. As such, all solutions have a negative water potential. Osmosis doesn't require any energy - it is an example of passive transport which involves the movement of water molecules from an area of high water potential to an area of a lower water potential, across a selectively-permeable membrane. Hypothesis: Apples will have a lower water potential than carrots. I believe this because apples are fruits, and as such contain more sugars and other solutes that carrots which make them sweet, which reduces the water potential. Null Hypothesis: The water potential of apples and carrots will be the same. Variables: Independent variable: I will manipulate the concentration of the sucrose solutions (which will change the water potential). The concentrations will be 0.0mol.dm-3, 0.2mol.dm-3, 0.4mol.dm-3, 0.6mol.dm-3, 0.8mol.dm-3 and 1.0mol.dm-3. Dependant variable: I will measure the mass of the plant tissue on a balance, accurate to 2 decimal places in grams. ...read more.


Confirm with a thermometer. * While the solution's temperature stabilises in the water baths, prepare the apple and carrot samples. Use a cork borer to extract 18 pieces of tissues from the apples and the carrots. Use a knife to cut each sample to the same length (3.0cm). * Use a balance to measure the mass of all 36 samples of tissue and make sure that the masses are equal. Record the mass of each piece of tissue, including details of which samples will be used for each concentration. * Whilst disturbing the water bath as little as possible, place all samples of plant tissue into the respective test tubes and start the timer. * Once precisely 40 minutes have passed, remove the test tubes from the water baths and remove the tissues from the test tubes. Use paper towels to blot each piece of tissue to remove excess solution and measure the mass of each sample, recording the results in a table. * Calculate the percentage change in mass for each sample (change in mass/original mass*100) and plot this against the concentration of solution used on a graph. * On aforementioned graph, read off the concentration for which there was no change in mass and convert it into water potential - this is the water potential of the tissue. Results: Apple data: Raw data: masses of apple samples for concentrations of sucrose solution Concentration of sucrose solution (mol.dm-3) ...read more.


samples; which is when water started to pass out of the samples and into the sucrose solution, causing a decrease in mass. The other part of my hypothesis, where I stated that the apples would have a lower water potential than carrots, appears to be supported. Since apples contain a greater number of solutes than the carrots (according to http://wiki.answers.com "all fruits contain natural sugars, especially fructose"), which lowers the water potential. Evaluation: This investigation could have been improved: * Making sure that the tissue samples are identical is nearly impossible - size, mass and surface area all affect the rate of osmosis and I only concentrated on achieving similar mass and sized samples. A machine to slice/dice the tissue into chips of the same sizes would remove the human error component of preparing the samples. * Weighing each sample after immersion allowed for different amounts of solution to remain on the samples - I patted each sample with a paper towel, but it's possible that in doing so, some water was squeezed out of the samples or that excess solution was still present on the samples. Being extremely careful with this step is very time consuming, but it would have produced slightly more valid results. * The plant tissues used should be fresh, since older tissues will lose moisture quickly, or possibly even rot - affecting the results. * The particular brand or carrots/apples used in the investigation are only representative of those brands, and not carrots/apples in general. ...read more.

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