Investigating Osmosis in Plant Tissue
GCSE
Investigating Osmosis in Plant Tissue
Aim
To investigate factors which affect the rate of osmosis.
The main factors which affect osmosis are:
Pressure
Temperature
Surface area
Solute Concentration
Plant Tissue
We will be investigating solute concentration as this is the easiest factor to measure and will give us the most accurate results. We will mainly investigate the different rate of osmosis when potato cells are placed in solution with different solute concentrations. We are going to use potatoes as they have homologues cells (all their cells are the same).
Preliminary work
We investigated the rate of osmosis of potato cylinders left in different solute concentrations.
Our hypothesis was that Rate of osmosis is proportional to the difference in water potential inside and outside the cell.
Water potential(?) indicates which way water will move in a system. Water will always move from a high ? to a low ?. ? can be measured in Kilopascals (kPa). Pure water has a ? of 0 kPa. As solute is added, ? is reduced (it becomes a negative number.)
e.g.
This is useful because you can add pressure to the equation.
If a pressure of 400 kPa is added to B (due to squeezing), the equation is
-1000 + 400 = -600
?-600 = -600
Now that the forces are equal, there will be no water movement.
We will measure ? using Molar Concentration which has a concentration of 0 - 1. Pure water has a ? of 0M.
Using 'Biology, a functional approach' by MBV ROBERTS, we deduced that the ? of a potato cell ? 0.27M.
The water potential inside the cell is 0.27 M. I predict that there will be the lowest rate of osmosis at this point and it will get higher as the solute concentration levels move further away from 0.27M. The rate of osmosis will be higher when there is a greater difference in water potential.
We used cork borers to produce potato cylinders from an estima (general purpose potato. All the cylinders were from the same potato. We made 9 cylinders. They all had a similar shape, weight and size. We split these into three groups of three and labelled the cylinders in a group, 1, 2 and 3. We took three beakers and filled one with a 0M sucrose solution, one with a 0.6M sucrose solution and one with a 1M sucrose solution and labelled them, each beaker was filled with 25ml of solution. We assigned each one of these cylinder groups ...
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We used cork borers to produce potato cylinders from an estima (general purpose potato. All the cylinders were from the same potato. We made 9 cylinders. They all had a similar shape, weight and size. We split these into three groups of three and labelled the cylinders in a group, 1, 2 and 3. We took three beakers and filled one with a 0M sucrose solution, one with a 0.6M sucrose solution and one with a 1M sucrose solution and labelled them, each beaker was filled with 25ml of solution. We assigned each one of these cylinder groups to a beaker. We then weighed each cylinder and recorded the results in a table.
We used a stopwatch to time the experiment. We placed the cylinder groups into the beakers at ten minute intervals( ten minutes is enough time take out, dry of any excess surface moisture and weigh one number group of cylinders. At 0:00 on the stop watch, we put the 1's in their respective beakers, at 10:00 we put the 2;s in and at 20:00 we put the 3's in. We planned to leave each cylinder in for an hour. So we scheduled the 1's to come out at 60:00, the 2's to come out at 70:00, and the 3's to come out at 80:00. In between these times, we weighed the cylinders and entered the results into a table.
To keep the test fair, we put 3 cylinders into each beaker so we could work out an average % mass change.
To keep the test fair we used cylinders that were the same shape so the surface area factor would be under control. The same size so the results could all have the same level of accuracy and the same weight so that the results could be accurately compared to each other and a proper % mass change could be worked out.
To keep the test fair, we dried all the cylinders the same way, trying to avoid under and over drying.
% Mass Change
The results supported my hypothesis. The % mass change increases as you get further away from 0.27M.
We can conclude from this that the bigger the difference in water potential, the higher the rate of osmosis.
Hypothesis
I predict that Rate of osmosis is proportional to the difference in water potential inside and outside the cell..
Explanation
Water potential(?) indicates which way water will move in a system. Water will always move from a high ? to a low ?. ? can be measured in Kilopascals (kPa). Pure water has a ? of 0 kPa. As solute is added, ? is reduced (it becomes a negative number.)
e.g.
This is useful because you can add pressure to the equation.
If a pressure of 400 kPa is added to B (due to squeezing), the equation is
-1000 + 400 = -600
?-600 = -600
Now that the forces are equal, there will be no water movement.
We will measure ? using Molar Concentration which has a concentration of 0 - 1. Pure water has a ? of 0M.
Using 'Biology, a functional approach' by MBV ROBERTS, we deduced that the ? of a potato cell ? 0.27M.
The water potential inside the cell is 0.27 M. I predict that there will be the lowest rate of osmosis at this point and it will get higher as the solute concentration levels move further away from 0.27M. The rate of osmosis will be higher when there is a greater difference in water potential.
This is what I expect to see for the % mass change per concentration. I expect to see the lowest % change at 0.27M.
Method
The equipment we used was as follows.
A cork borer
A large estima potato
Forceps
A scalpel
Dishes
Beakers
Sucrose solutions
A stopwatch
We used cork borers to produce potato cylinders from an estima (general purpose potato. This is because potato cells are homologues and these were the same type of potatoes used in our previous experiment All the cylinders were from the same potato and we made 18 cylinders. That was enough cylinders for us to repeat the experiment 3 times for reliability and accuracy. They all had a similar shape, weight and size. We split these into six groups of three and labelled the cylinders in a group, 1, 2 and 3. We took six beakers and filled one with a 0M sucrose solution, one with a 0.2M sucrose solution, one with a 0.4M sucrose solution one with a 0.6M sucrose solution, one with a 0.8M sucrose solution and one with a 1M sucrose solution and labelled them all, each beaker was filled with 25ml of solution. This range was used to give a broad and accurate set of results and to coincide with the 0.27M concentration. We assigned each one of these cylinder groups to a beaker. We then weighed each cylinder and recorded the results in a table.
We used a stopwatch to time the experiment. We placed the cylinder groups into the beakers at ten minute intervals( ten minutes is enough time take out, dry of any excess surface moisture and weigh one number group of cylinders. At 0:00 on the stop watch, we put the 1's in their respective beakers, at 10:00 we put the 2;s in and at 20:00 we put the 3's in. We planned to leave each cylinder in for an hour. So we scheduled the 1's to come out at 60:00, the 2's to come out at 70:00, and the 3's to come out at 80:00. In between these times, we weighed the cylinders and entered the results into a table.
We then converted the measurements to mass change in %. This is done because the potato cylinders have different weights and only a percentage would show the true rate of osmosis.
To keep the test fair, we put 3 cylinders into each beaker so we could work out an average % mass change. We used cylinders that were the same shape so the surface area factor would be under control, the same size so the results could all have the same level of accuracy and the same weight so that the results could be accurately compared to each other and a proper % mass change could be worked out. We dried all the cylinders the same way, trying to avoid under and over drying.
We did the experiment all on the same day so the potato cells would remain homologous. We took all our samples from the same potato and used the same cork borer to make all our potato cylinders.
Results
This is the raw data table.
This is a brief summary table. (In three parts)
