Materials:
- Scalpel or knife.
- 6 petri dishes.
- 5 boiling tubes.
- Boiling tube rack.
- 2 x 10cm or 25cm graduated pipette.
- Pye pump.
- Thermometer.
- Distilled water.
- 1M sucrose solution.
- Tile.
- 2 x 100cm beakers.
-
Six bananas picked from the same bunch.
- Labels/marker pen.
Dependent Variables - Is my quantitative data, I will be measuring the water potential, by measuring the length of each square banana segment to see whether an increase or decrease in mass has resulted in each solution to determine how ripe my bananas are.
Independent Variables - Is the method of changing the independent variable, the only variable I will be changing in this experiment is the concentrations of sucrose solution which will change the ripeness of each banana. However, apart from this variable, I will be maintaining all of the other variables constant or controlled, here are a list of my controlled variables:
- Controlled temperature of 20 C.
- Concentration of 1M sucrose solution.
- Volume of solution.
- Storage temperature of 20 C.
These controlled variables will ensure that each result is accurate and reliable.
Method:
1) Label six petri dishes appropriately, one for each of the following different molars of sucrose solution: 1.0M, 0.8M, 0.6M, 0.4M, 0.2M and distilled water. Also label five boiling tubes appropriately, again one for each of the sucrose solutions.
2) Using a graduated pipette (2 x 10cm or 25cm ), two beakers (2 x 100cm ), one beaker of distilled water and one beaker of 1M sucrose solution, make up 20cm of sucrose solution of the required concentration in each boiling tube, which are:
- 1.0M solution - 20cm of 1M sucrose solution.
- 0.8M solution - 16cm of sucrose and 4cm of distilled water.
- 0.6M solution - 12cm of sucrose and 8cm of distilled water.
- 0.4M solution - 8cm of sucrose and 12cm of distilled water.
- 0.2M solution - 4cm of sucrose and 16cm of distilled water.
- Distilled water - 20cm of distilled water.
3) Shake each of the boiling tubes to thoroughly mix the solutions.
4) Pour the mixed solutions into the appropriate labelled petri dishes. Including the 20cm of distilled water into the sixth petri dish.
5) Firstly, check the temperature of the room, ensuring it is 20 C and keep this temperature constant. Then using a scalpel or knife, cut from the middle of each banana two accurate square shaped segments, measuring 5mm thick, 1cm wide and 1cm long. It is very important to work quickly when cutting the 12 segments from the middle of the bananas because this will avoid any loss of water through evaporation as this could change the ripeness of each segment.
6) Completely immerse two segments in each petri dish.
7) Leave in covered petri dishes for ten whole days stored in a room temperature of 20 C, examine the ripeness by measuring the length every other day.
8) Once the ten days are complete, measure the lengths once again and calculate the mean percentage change in length between the two segments from each different concentration.
9) Next calculate the percentage change of each concentration, using the following calculation:
Change (cm) x 100% = Percentage Change in length (%)
Original (cm)
10) Repeat the whole experiment at least three times keeping the independent variables, dependent variables and the controlled variables the same to ensure accurate and reliable results.
From the results I will be able to determine how the water potential of bananas alters as they ripen over time. If I discover at one of the concentrations there is no change in length then the water potential of the banana hasn't changed so it is still at the same stage of ripeness as it was at the beginning of the experiment. Meaning some of the starch from the banana has not hydrolysed to form sugars. If the length of each square segment has a percentage decrease then it has ripened, which means some of the starch that the banana contains has been hydrolysed to form sugars, so therefore has become sweeter in taste.
