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The aim of this investigation is to find out how the concentration of the solution a plant is in affects the rate of osmosis in the plant.

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Kirsty McIver GCSE Biology Coursework Osmosis Osmosis Aim The aim of this investigation is to find out how the concentration of the solution a plant is in affects the rate of osmosis in the plant. I am going to do this by placing potato tubes in 3 different concentrations (levels of sugar) solutions and measuring the change in their length and weight (the amount of osmosis that has occurred. Osmosis Theory The definition of osmosis; Osmosis is the movement of water molecules across a partially permeable membrane from an area of high water concentration to an area of low water concentration. In other words, water moves from cell to cell in a plant by osmosis. Dilute solution Concentrated solution Cell membrane - partially permeable The dilute solution is the solution containing the more water and less sugars, the concentrated solution is the solution containing less water and more sugars. The water moves through the cell membrane, which contains holes so small that only water molecules can pass through them, in both directions, but the biggest movement of water is from the dilute solution to the more concentrated solution, and this is called osmosis. Osmosis enables plants to move water from the soil into the roots and up through plant cells. This is because it works in a long chain, as when the water moves from the dilute solution to the more concentrated solution, it makes the cell with the more concentrated solution dilute and it fills up with water. As the cell is now dilute, the cell on the other side of it is likely to be more concentrated than it, so osmosis occurs between these two cells, and so on. Osmosis is a continuous process because the cell losing water gains concentration and so can gain water again by performing osmosis with a cell with a dilute solution. When a plant cell fills with water, it swells, or becomes TURGID, giving a lot of support to the plant, making the leaves stand towards sunlight. ...read more.


* The temperature at which the experiments will occur, because on a hotter day, the rate of transpiration (water loss) from a plant is higher, so more water is taken into the plant by osmosis, so if one group was put into hotter conditions the rate of osmosis would be higher and make the results inaccurate. Therefore, the whole experiment will occur at the same time in the same room temperature in the same amount of sunlight with the same cold water in each solution. * The amount of solution each group of potato tubes is in, because if there was 75ml of solution for one group and 20ml for another, the 75ml group would have more chance to take water in (i.e. perform osmosis), so the results would be inaccurate. Therefore there will be 75ml of each solution in its beaker. * The ruler/scales used to measure the lengths/weigh the potato tubes, because different rulers/scales have different degrees of accuracy - for example some rulers may not use millimetres, which are essential to get accurate lengths and some scales may be broken, meaning the changes in the lengths and weights would be impossible to work out accurately. * The units measured/weighed in, because although it would be possible to work out the equivalent in the correct unit, that would be a waste of time and could lead to error. Therefore, the lengths will be measured in cm and to 0.1cm and the weights in g and to 0.01g, so there is the same degree of accuracy. * The potato used, because, depending on the conditions it has been kept in, different potatoes could contain different concentrations of solution, and this would change the rate, or even direction of osmosis, because if there was a 1M concentration of sugar in one potato and 2M in the other, there would be more likely to be osmosis out of the 1M and into the 2M. ...read more.


and therefore 5 different weights into beakers with the same amount of the same concentration of water and sugar solution for the same amount of time. I would then measure how much the lengths and weights had changed to see how size affects the rate and direction of osmosis. * Temperature, I am not sure exactly what plant I would do this with as the reason osmosis occurs more in higher temperatures is due to a higher rate of transpiration from the leaves which results in more water needing to be drawn up the plant by osmosis in the cells, and potato tubes have no leaves. However, I would put (plant) of the same length and weight if possible into beakers with the same concentration of the same amount of sugar and water solution for the same amount of time in 5 different water baths (10�c, 20�c, 30�c, 40�c, 50�c). I am also not sure how I would measure the changes in the cells, but I would like to do this experiment as it would be interesting to see how the whole plant works together to alter the rate of osmosis. I would like to do the experiments comparing different types of plants, for example potato and carrot, that grow in the same way, to see if one carries out osmosis quicker, or which loses most water in high temperatures, or which contains the most sugar. Temperature would be especially interesting with tropical or desert plants compared to British plants, as tropical or desert plants are in higher temperatures where more water could be lost from leaves, but often are adapted for this by having high water stores, whereas British plants are used to cooler conditions and don't have these features. I think this experiment has a lot of scope, but the one I carried out went well and proved that osmosis always occurs from a solution of high water/low sugar concentration to a solution of low water/high sugar concentration. Kirsty McIver GCSE Biology Coursework 01/05/2007 Cator Park School Centre no. 14221 Candidate no. 3918 ...read more.

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A thorough account of an osmosis investigation but greater attention to detail and less repetition of some points would have helped gain 5 stars.

Marked by teacher Adam Roberts 01/05/2013

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