Osmosis

Osmosis.

Introduction:

Osmosis is a net diffusion of water between two solutions that differ in

solute concentration and that are separated by a selectively permeable

membrane.

Hypertonic solution – higher solute concentration outside the cell.

Hypotonic solution – lower solute concentration outside the cell.

Isotonic solution have the same solute concentration outside and inside the

cell.

Hypothesis:

Potato cells in 0% solution of salt will swell up. Potato will gain weight,

because net movement of water will be into the cells. Water moves down the

concentration gradient.

Potato cells in 2% and 3% solutions will shrink. Water moves out of the

cells to regions of greater solute concentration.

Potato cells in 1% solution will change little in cell size or shape. The

difference between solution concentration and potato concentration is

small. So there is no big movement of water.

Materials: Knife, potato, 4 salt solutions ( 0%, 1%, 2%, 3%), paper, razor

blade.

Method:

Cut 12 plugs from similar potatoes. Remove the ends of each plug and skin.

Make up four solutions of salt ( 0%, 1%, 2%, 3%). Weight the plug sets.

Place plug sets into each solution and continue to measure or weight them

at specified time intervals. Report mean values only fo measurements or

weights. Determine the percent change in lenght or weight for the potato in

each solution. Calculate the exact percent of salt in the potato cell from

the graphed data.

|Salt |Initial |Weight of plug sets after some |Mean |

|Solution|weight |time: |percentage |

|s |(g) | |change in |

| | | |weight |

| | |12 min.|22 min.|40 min.|52 min.| |

|0% |5.61 |5.87 |6.01 |6.13 |6.25 |11.4% |

|1% |8.84 |8.85 |8.87 |8.90 |8.86 |0.22% |

|2% |10.02 |9.61 |6.51 |9.20 |8.99 |-10.3% |

|3% |6.64 |6.01 |5.77 |5.48 |5.31 |-20% |

[pic]

We can’t compare the changes in weight using grams, because each plug set

had different initial weight before placing them into salt solutions.

Conclusion and evaluation:

From the graphed data the percent of salt in the potato cell is 1.1%. The

original potato cell concentration is 0.9%. The error could be, because the

water outside potato has influence on weight and not accurate measurement

of mass by not exact scales, which showed only one decimal place.

If the concentration of water is not equal across a potato cell membrane

(concentration of water outside the sell is more or less than [pic]0.9%),

osmosis tends to occur. Water will move osmotically to regions of greater

solute concentration (from hypotonic to hypertonic solutions). If water

concentration outside and inside the cell is equal, water shows no net

osmotic movement from one to the other – isotonic solutions.

The experiment can be improved: Firstly, by drying potato from water

outside the potato. Secondly, by using scales, which have more accuracy.