Biology IB November 26th, 2017 Frau Moll Effects of Osmosis on Living Tissue

Research Question:
What is the effect of osmosis on a slice of potato in varying salt solutions? Six different concentrations of salt water (0%, 0,4%, 0,8%, 1,2%, 1,6% and 2,0%) will be used in order to observe how the inserted potato slice changes. The length of the potato slice will be measured before and after leaving it for 24 hours in the various solutions.

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Hypothesis:
Salt solutions will be hypertonic to the potato cells thus decreasing it in size as placed in higher solutions.

Materials:
• 6 petri dishes
• Fresh potato sticks
• Ruler
• Distilled H2O, 0,4% NaCI solution, 0,8% NaCI solution, 1,2% NaCI solution, 1,6% NaCI solution, 2,0% NaCI solution

Procedure:
(Obtained from the worksheet)
1. Obtain 6 Petri dishes 0.4% NaCl; 0.8% NaCl; 1.2% NaCl; 1.6% NaCl; 2.0% NaCl.
2. Add enough of the appropriate liquids to nearly fill each of the Petri dishes.
3. Obtain six fresh potato strips. Using a razor blade, angle cut one end of each strip to a beveled point.
4. Measuring from the tapered end, carefully and precisely angle cut each strip to a length of 70 mm so that both “points” are on the same side of the strip.
5. Place one measured potato tissue strip into each of the prepared Petri dishes. Cover the dishes and leave undisturbed for 24 hours.
6. After 24 hours, remove the strips of potato, one at a time, immediately measuring the length (mm) of each.

Data Collection:
Group 1
Test Solutions (% salt) Initial Length li (mm) Final Length lf (mm) Change in Length ? l (lf – li) (mm) Rigidity of the Strip
Distilled H2O 30 mm 33 mm +3 mm Solid, Hard
0,4 30 mm 32 mm +2 mm Solid, hard
0.8 30 mm 31 mm +1 mm Flexible
1.2 31 mm 31 mm 0 mm Flexible, soft
1.6 31 mm 30 mm -1 mm Very flexible, soft
2.0 31 mm 30 mm -1 mm Very flexible, soft

Group 2
Test Solutions (% salt) Initial Length li (mm) Final Length lf (mm) Change in Length ? l (lf – li) (mm) Rigidity of the Strip
Distilled H2O 42 mm 46 mm +4 mm Hard
0,4 42 mm 44 mm +2 mm Hard
0.8 42 mm 41 mm +1 mm Flexible
1.2 42 mm 40 mm -2 mm Flexible
1.6 42 mm 39 mm -3 mm Flexible
2.0 42 mm 39 mm -3 mm Very flexible

Data Processing:
Group ? l (mm) Distilled H20 ? l (mm) 0.4% NaCl ? l (mm) 0.8% NaCl ? l (mm) 1.2% NaCl ? l (mm) 1.6% NaCl ? l (mm) 2.0% NaCl
1 +3 mm +2 mm +1 mm 0 mm -1 mm -1 mm
2 +4 mm +2 mm +1 mm -2 mm -3 mm -3 mm
Average ?l (mm) +3.5 mm +2 mm +1 mm -1 mm -2 mm -2 mm

Result:
In both groups the size of the potato increased when put into distilled H2O, 0,4% solution and 0,8 solution. From 1,2% solution and upward, the size of the potato stayed the same or decreased in both groups. One last similarity is that from 0,8% solution onwards the rigidity of the potato strip changed from hard to flexible and soft.

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