# Biology Lab Report Ib Hl Osmosis

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• Published : April 21, 2013

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Biology Lab Report 2
Investigating the phenomenon of Osmosis in plant tissues:
Potato in different concentrations of NaCl

Tutor: Maria Tsaousidou
By Marina Gkritzioudi
Biology Lab Report 2
Investigating the phenomenon of Osmosis in plant tissues:
Potato in different concentrations of NaCl

Tutor: Maria Tsaousidou
By Marina Gkritzioudi

Investigating the phenomenon of Osmosis in plant tissues:
Potato in different concentrations of NaCl

Introduction:
Osmosis is the movement of water molecules through a semipermeable membrane from low concentration to high concentration. Research Question:
How does the concentration of salt (NaCl) affect the mass of a potato soaked in water (H2O) with different concentrations of NaCl over the course of 30 minutes? Hypothesis:
It is expected that the solution with the highest concentration of salt will cause more mass loss to the pieces of potato. The pieces that will be placed in the solution with the lowest concentration of salt will have small weight loss. Finally, the pieces that will be placed in water (NaCl concentration 0) will gain weight. This is expected because of the phenomenon of osmosis which was examined in a previous lab. Variables:

Independent: concentration (%) of salt (NaCl)
Dependent: mass (g) change
Controlled:
* shape and material of the beakers
* size and weight of the potato pieces
* volume of the aqueous solution
The beakers need to be of the same size, of the same shape and of the same material, either plastic or glass. The size of the potato pieces needs to be the same in order for the surface to volume ratio to be the same and the initial weight of the pieces should also be the same so that the mass change can be compared. Since this is not always possible, we calculate percentages and make the pieces approximately the same. Lastly, the volume of the water solutions should be the same in all beakers so that the osmotic effect will only depend on the concentration dissolved in the solution. Materials:

5 beakers sized: 250cm3 (±0.5cm3)
Tap Water
Potato
Knife
Weigh balance (±0.01g)
Salt (NaCl)
Watch glass
Spatula
Timer (±0.1sec)
Volumetric cylinder
Procedure:
Step 1: Line up the five beakers and with the help of a volumetric cylinder add 100cm3 of water (H2O) in all of them. Step 2: Place the watch glass on the weigh balance and after zeroing it, measure four different concentrations of salt by adding it with the spatula. Start by measuring 0.5% of NaCl, then 1%, then 3%, and finally 5% and add each one in a different beaker. Step 3: Stir the solutions using the spatula in order for the salt to dissolve. Step 4: Take a potato and after peeling it with the knife, cut it into 10 same size small pieces. Step 5: Measure each one of the 10 pieces and in order to equalize their mass chop, or scrape off some of the piece if needed. Step 6: Record the initial mass of the potato pieces and place 2 potatoes in each beaker. Step 7: After 15min take each of the pieces out of the beakers and measure its weight and record it. Step 8: Repeat Step 7 after 30min and after 35min in order to get the rate at which the mass changes. Data Collection:

Table 1: Mass measurements of the potato pieces in solutions with different NaCl concentrations over the course of 35min | Time in min| Mass(g)(±0.01) in 0.5% NaCl concentration| Mass(g)(±0.01) in 1% NaCl concentration| Mass(g)(±0.01) in 3% NaCl concentration| Mass(g)(±0.01) in 5% NaCl concentration | Mass(g)(±0.01) in 0% NaCl concentration| | Trial 1| Trial 2| Trial 1| Trial 2| Trial 1| Trial 2| Trial 1| Trial 2| Trial 1| Trial 2| 0| 1.76| 1.76| 1.76| 1.76| 1.76| 1.76| 1.76| 1.76| 1.76| 1.76| 15| 1.80| 1.80| 1.63| 1.63| 1.57| 1.57| 1.58| 1.58| 1.95| 1.95| 30| 1.80| 1.80| 1.54| 1.54| 1.50| 1.50| 1.51| 1.51| 1.97| 1.97| 35| 1.79| 1.79| 1.52| 1.45| 1.49| 1.42| 1.48| 1.45| 1.98| 1.98|

Data Processing:
In...