Osmosis Lab

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isThe effect of sucrose concentration on the rate of osmosis across a potato’s cell membrane submerged for 94 hours in the solutation.

Background Information:
Osmosis is the movement of solvent molecules across a partially permeable membrane. They move from a region of low concentration (hypotonic) to a region of high concentration (hypertonic). The rate of osmosis across a eukaryotic cell membrane can be affected by different factors; including temperature, concentration gradient, water potential and the surface area for osmosis to occur and pressure exerted on either side of the semi-permeable membrane. A potato (Solanum Tuberosum) contains 92% water, which is an osmotically active component. The precise osmotic potential of sweet potatoes is however unknown. The osmotic potential of sucrose is know to be at 20 oC, the osmotic potential of sucrose is 2.436 MPa2. The rate of osmosis will be calculated by measuring the percentage change in mass of a piece of potato, that has been submerged in a specific concentration of sucrose over a 94 h period.

Research Question:
What is the effect of sucrose concentration on the rate of osmosis across a potato (Solanum Tuberosum) cell membrane?

Hypothesis:
If the sweet potato cytoplasm is hypotonic relative to the sucrose solution, then water will move from the potato into the sucrose solution, resulting in a decrease in mass. If the potato cytoplasm is hypertonic relative to the sucrose solution, then water will move from the sucrose solution into the potato, resulting in an increase in mass of the sweet potato.

Variables:
Independent| Concentration of sucrose solution: 1.0 M0.8 M0.6 M0.2 M| Dependent| Rate of osmosis, indicated by change in mass of sweet potato (±0.01 g)/time (94h ±0.001h)| Controlled| Temperature Water potentialPressure exerted on either side of cell membrane| Uncontrolled| Surface area for osmosis|

Method:
1. Peel potato and cut chunks of uniform mass using a custom made potato corer. 2. Place two potato chunks on the balance and record the mass in a suitable table. 3. Put two chunks in a glass boiling tube.

4. Pour in enough 1 M sucrose solution to cover the potato. Record the concentration of sucrose used, and the initial mass of the two potato chunks, on the side of the beaker using an indelible pen. Mark the time, mark the ambient temperature recorded on the thermometer and start the stopwatch. 5. Precisely 24 h later, pour the sucrose solution off the potato chunks. 6. Dry the potato chunks carefully using a paper towel.

7. Place the potato chunks on the balance and record the mass in the raw data table. 8. Calculate change in mass and percentage change in mass (final mass – initial mass/initial mass)*100. 9. Repeat steps 1 – 8, substituting 0.2 M, 0.4 M, 0.6 M, 0.8 M sucrose for 1.0 M sucrose. 10. Repeat steps 1 – 9 four times, so that 5 sets of two potato chunks are submerged in each specific concentration of sucrose. 11. Peel potato and cut chunks of uniform mass using a custom made potato corer. 12. Place two potato chunks on the balance and record the mass in a suitable table. 13. Put two chunks in a glass boiling tube.

14. Pour in enough 1 M sucrose solution to cover the potato. Record the concentration of sucrose used, and the initial mass of the two potato chunks, on the side of the beaker using an indelible pen. Mark the time, mark the ambient temperature recorded on the thermometer and start the stopwatch. 15. Precisely 24 h later, pour the sucrose solution off the potato chunks. 16. Dry the potato chunks carefully using a paper towel.

17. Place the potato chunks on the balance and record the mass in the raw data table. 18. Calculate change in mass and percentage change in mass (final mass – initial mass/initial mass)*100. 19. Repeat steps 1 – 8, substituting 0.2 M, 0.4 M,...
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