BIOLOGY OSMOSIS LAB REPORT
1. Research Question/ Aim
How do the different sodium chloride concentrations of solutions affect the length (measured in mm) and mass (measured in grams) of potato cores placed in them overnight (approximately 10 hours)?
Alternative hypothesis: As the concentration of sodium chloride in the solution increases, the mass of the potato cores will decrease. If the solution they are in has a lower water potential than the potato cores, there will be net movement of water out of the potato cores. If the solution has a higher water potential than the potato cores, there will be net movement of water into the potato pieces. Therefore, potato cores in less concentrated solutions will gain more weight than the potato cores in more concentrated solutions.
Null hypothesis: Different sodium chloride concentrations in solutions have no effects on the mass of the potato cores.
3. Analysis of Variables
Type of Variable
Notes on how variable is manipulated / measured / controlled Independent (manipulated)
Sodium concentration of the solutions
Different amount of salt (sodium chloride) is put in the solvent (water) to make 0.34M, 0.67M, 1M, 1.34M, 1.67M solutions. Dependent (responding)
Final mass of potato pieces
Measured at the end of the experiment with a ruler (in mm) and an electronic balance (in gram).
Volume of solutions
Each solution is mixed with 300 cm3 of solvent (water) and then divided into two beakers with 150 cm3 in each.
All beakers are kept in the same room, so that they all experience the same conditions.
Type of potato
All the potato pieces come from potatoes bought at a store, packaged together.
Initial sizes of potato pieces
Measured before putting the pieces into the solutions with a ruler (in mm) and an electronic balance (in gram).
Temperature of the solutions
All the beakers were kept in the same place, so the solutions experienced the same conditions.
Size and material of the beakers
The 500 ml beakers were made of glass.
Duration of time the potato is left in the solutions
The potato pieces were left in the solutions overnight, approximately 10 hours.
4. Background Information
Osmosis can be defined as the movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration. The semi-permeable membrane allows small particles through it but does not allow large particles such as sodium chloride. Osmosis will continue until a state of equilibrium is reached i.e. there is no area with a higher or lower concentration than another area.
To land plants, water and osmosis are vital as they play leading roles in the structural support of a plant, they facilitate transport of materials, etc. Lack of water will lead to a plant wilting and possibly dying.
When a cell is in a hypotonic solution (more solute concentration than the cell), water will move from the hypertonic solution (less concentrated) to the hypotonic solution via the process of osmosis.
In this experiment, the movement of water in and out of potato cells left in sodium chloride solution will be investigated. The sodium chloride molecule is too large to be passively transported across the cell membrane, so only net movement of water will happen without any input of energy.
2 x potatoes
1 x bag of salt (sodium chloride)
10 x 500 ml glass beakers
1500 cm3 of water
500 ml measuring cylinders
30 cm plastic ruler
A. Preparation of solutions
1. The molar mass of sodium chloride is 58.44 g/mol.
Molar concentration = moles of solute/ volume of solution in liters
1M sodium chloride solution = 58.44g sodium chloride in 1 liter of water.
0.34M sodium chloride solution = 19.87g sodium...
Bibliography: Campbell , N. A., J. B. Reece, et al. AP Edition Biology. Eighth edition. San Francisco: Pearson Education Inc., 2008. Print.
Davala, Steve. Simple Science Experiment: Osmosis with Potato Slices. Apr 2013. Web. 7 Feb 2014.
Siebrits, Tessa. How to write a good lab report. 2014. Web. 3 Feb 2014
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