Skills

• Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions.

Osmolarity of a solution is the total amount of solute cncentration.

• Cell walls help maintain water balance

• A plant cell in a hypotonic (Low salt) solution swells until the wall opposes uptake; the cell is now turgid (firm)

• If a plant cell and its surroundings are isotonic (same salt), there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt

• In a hypertonic (high salt) environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis (explode)

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Hypotonic solution Isotonic solution Hypertonic solution

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

Osmotic Pressure

Lab Procedure

1. Firstly, the cork borer needs to be used to cut out a piece of potato at least 4 cm in length. This allows room for trimming off untidy edges.

Lab Procedure

2. On the cutting board the cylindrical piece of potato needs to be cut to 35mm. Using a ruler, measure this as accurately as possible and cut the potato to 35mm in length using a scalpel. ( be sure to record the uncertainty of measurement)

Lab Procedure

3. Using the scaled weigh the potato and record the mass in grams. ( be sure to record the uncertainty of measurement)

Lab Procedure4. The test tube rack and test tubes need to be

assembles. Fill a syringe with exactly 10ml or sugar solution (strength 1M) and empty into a test tube. DO all sugar solutions at the same time (0.5 M, 0.25 M, 0.125M and O M)

Lab Procedure

5. Now the timing device needs to be reset and readied. An extra pair of hands to aid in the timing may be useful. This potato piece can now be placed into the test tube containing 10mL of 1M sugar solution.

6. As the potato piece is placed in the test tube, the timer should be started. After 30 minutes the potato piece needs to be removed from the test tube.

7. Dry potato on a paper towel. Then measure its mass and length.

8. Record data in data table

Make a data table to record you data

• You are recording the following data– Initial Mass (grams) & Length (cm)– Final Mass (grams) & length (cm)• 0 M Sugar • 0.5 M• 0.25 M• 0.125M• 1 M

What would happen to the potato mass if you place it in an isotonic solution?

• The mass would stay the same.

What would happen to the potato mass if you place it in an hypotonic solution?

• The mass would increase

What would happen to the potato mass if you place it in an hypertonic solution?

• The mass would decrease