An investigation to find out the concentration of the cell sap of potato tuber cells.

Authors Avatar

Laura Sainsbury -Yr 10 Biology Coursework

AN INVESTIGATION TO FIND OUT THE CONCENTRATION OF THE CELL SAP OF POTATO TUBER CELLS

PLAN –An Investigation To Find Out The Concentration Of The Cell Sap Of Potato Tuber Cells

This experiment is based on the scientific theory of osmosis. 

Background Information

Osmosis is the passive (requires no energy) net movement of water molecules down a concentration gradient across a semi-permeable membrane.  The process makes plants swell up to make them turgid and is useful for giving support to green plants and for opening stomatal guard cells so photosynthesis can occur.  When plant cells are placed in water or very weak sugar solutions they gain mass.  This is because the plant cells have a higher concentration of sugar than their surroundings so the water molecules in the surrounding solution, move down a concentration gradient into the plant cells.  However, when plant cells are placed in solutions of the same concentration as the cell sap nothing happens.  This is because the concentration of sugar in each is the same, so the water molecules do not need to move down a concentration gradient to become isotonic (they have the same concentration of sucrose molecules).  If the plant cells (for example a potato tuber) are placed in solutions of higher concentration than the cell sap then water will move out of the cells and they will lose mass.

Preliminary Experiment

To aid my hypothesis and test my method I did a preliminary experiment to see how mass changes in different solutions of sucrose.

Method: 3 potato sections were measured by a ruler and cut by a scalpel to an equal length of 3.5 cm and they were then weighed individually on a balance.  The weights of the sections were recorded and the sections were put in three separate plastic dishes, which contained different concentrations of sucrose solution (0.2 molar, 1 molar and 2 molar).  Each dish contained 50 ml of sucrose solution.  They were then left in the solutions for 15 minutes.  When 15 minutes (timed by a clock) had passed each potato section was taken out of the sucrose solution and weighed individually on a balance.  They were then put back in the same dishes as before.  This process was repeated after 30 minutes.  Safety was kept to a high standard throughout the prelim with overalls being worn, hair tied up and the beakers were placed far from the edge so contents would not be spilled easily.

Results:                                                         NB. all results to 2 d.p

Conclusion

The results show that the higher the concentration in which the cylinder is placed, the quicker it decreased in mass.  This is because the concentration gradient is steeper (the concentration of sucrose in the cell sap will be the same for all the cylinders but the concentration of sucrose in the solution varies).

Join now!

Hypothesis

Based on my preliminary experiment and background research I have done, I predict that as the concentration of the sucrose solution increases, the loss in mass of the potato cylinder will increase.  When the concentration of sucrose solution is the same as the concentration of the cell sap the potato segment will neither gain nor lose mass.  By using a range of sucrose concentrations I will be able to deduce the isotonic solution and therefore the concentration of the cell sap.

Equipment

Ceramic Tile

Scalpel

12 Potato Sections

150 ml sucrose solution

150 ml of ...

This is a preview of the whole essay