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Gcse Biology Assessment - Osmosis

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Introduction

GCSE BIOLOGY ASSESSMENT - OSMOSIS Planning of Experimental Procedures Background Knowledge: Osmosis is the diffusion of water over a membrane; it takes place due to differences in the concentration of water surrounding an object such as a plant or animal cell whose surface is comprised of a membrane, to the concentration inside the object. The rate at which osmosis takes place, which is what the assessment is investigating, is affected by a number of factors, of which one must be investigated and the others controlled in order to make the experiment a fair test. The following factors affect the rate of osmosis; one of these factors must be chosen for investigation in the experiment: 1: The temperature of the water in which the experiment is conducted. 2: The size of the water concentration gradient; i.e. the difference in the concentration of water between the solution surrounding the object and inside the object itself. 3: The size of the pores in the membrane; i.e. the type and properties of the plant or animal cell used in the investigation, in this case the type of potato used. 4: The surface area of the membrane; i.e. the number of pores there are for water to diffuse through. The experiment is to be conducted using potato chips as the cellular object, the potato chip could be weighed before and after placing in sucrose solutions in different conditions to find the rate of osmosis. ...read more.

Middle

I predict that the rate of osmosis in the potato chips will decrease from pure water to 0.1M solution (the concentration at which the chips are stored before the experiment) after this the rate will increase to the highest concentration of sugar solution, where water will be moving by osmosis out of the potato chips the quickest due to the much stronger concentration of sucrose (less water) in the most concentrated solution (1M) The rate of osmosis increases as the concentration gradient between the object and its surroundings increases, this increase is a steady increase, which would be displayed on a graph of rate against solution concentration as a straight line increasing from 0.1M, the solution which the potato chips were stored in. It can be said therefore, that the rate of osmosis is directly proportional to the concentration of the solution of sucrose. GCSE BIOLOGY ASSESSMENT - OSMOSIS Obtaining Evidence The experiment was carried out as suggested in the method, and the results for each part were similar, no anomalous results were found and the results were shown to be precise as the results for each of the two experiments were close. Results: Concentration of sugar solution Weight of Potato chip before Weight of Potato chip after 0.0M 1.58 1.60 0.1M 1.84 1.84 0.2M 1.65 1.63 0.4M 1.73 1.68 0.8M 1.66 1.55 1M 1.72 1.59 Experiment 2 0.0M 1.69 1.71 0.1M 1.76 1.76 0.2M 1.79 1.78 ...read more.

Conclusion

as much water can move from the side with a higher concentration of water than from the side with a lower concentration of water, as twice as many water particles move through the pores from the side with the higher concentration of water than from the side with the lower concentration of water due to the random movement of particles, or Brownian motion. All the results from the experiment supported the prediction that I had made, and neither of the experiments showed any anomalous results, although not all of the results were absolutely precise, although this could have been due to slightly different timing for different parts of the experiment or due to not drying the chips well enough prior to weighing at the start or at the end. I made the experiment as fair as possible by using percentage change of weight instead of weight change, as this catered for the slight differences in weight of the potato chips, although I think that a preliminary experiment which would find out how long to leave the chips in, by finding out how quickly osmosis slows down over time would have been useful, as the parts of the experiment using very small gradients may have equalled out their concentration gradients very quickly, in much less than ten minutes, which would make the rate seem slower as the chips possibly sat in the solution doing nothing for a while. ...read more.

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3 star(s)

***
Although the author has a good understanding of osmosis there is quite a lot of poorly used scientific terminology and a lack of attention to detail.

Marked by teacher Adam Roberts 01/05/2013

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