Biology lab report of osmosis
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In this experiment the length of the potato cylinders is affected by osmosis. As the water moves in or out of the potatoes, the potatoes swell or shrink, thereby reducing or increasing in size or length. From the graph it can be inferred that the there is a negatively linear relation between the concentration of the solution and the percentage change in length of the potato cylinders. This indicates that as the concentration of the solution increases the osmosis in the potato cells decreases. This is supported by:- The linear best fit line that passes through most data points. The R2 (0.9938) coefficient of determination which indicates that the change in one variable affects the changes in the other variable. From this the correlation coefficient R which is 0.9969 can be determined. This also establishes that both the variables have a strong positive correlation. The concentration of sucrose in the potato cylinders can be determined to be 45g dm-3 as at this concentration of sucrose, the percentage change is 0.5%. EVALUATION:
Sources of errors:
The best fit line passes through most of the data points, it doesn’t pass through the 3rd and the 5th data points. This indicates that there were random errors in my 3rd and 5th readings. This random error could have been caused due to many reasons. The piece of potato might have had less or more surface area, since a parallax error might have occurred while measuring the length of the cylinders using a ruler and cutting them into pieces of equal and desired length. Here the knife used to cut the cylinders might not have been perpendicular to the ground and this might have resulted in uneven surface area. When the different concentrations of the solutions were made, water was directly poured into the beakers and filled to the 40ml marking on the beaker, without being measured through burettes or measuring cylinders.
This could have led to imprecise readings in the concentration of solution. When the sucrose powder was weighed on the weighing machine after being placed on a filter paper, some of the powder might have flown away from the filter paper before being transferred into the beakers or some powder might have been stuck to the filter paper itself. This could have again led to imprecise readings in the concentration of solution. There might have been systematic errors caused due variations in the external temperature and humidity of the environment in which the experiment was conducted. As the setup was left for 5h for osmosis to take place, the temperature and humidity changed considerably over the day. Hence these changes would have affected the osmosis in the setup and caused inaccurate readings. Suggestions for improvement:
A protractor could have been used to check if the knife is cutting the cylinders in a perpendicular manner and another person could have been made to see if the appropriate reading on the ruler is measured so that there is no parallax error. The water should have been taken from a burette so as to take precise readings of volumes and the some excess amount of 0.01g of sucrose from the weighing machine as due to some of the powder not getting transferred into the beakers, the amount of powder mixed will now give more precise values for the solutions. The beakers should have been covered with aluminium foils. This would also make the experimental setup be impervious to humidity and its variations. After this all the beakers should have been placed inside a thermocol ice box which is resistant to temperature changes. This would make the experimental setup impervious to temperature changes.