• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month
Page
1. 1
1
2. 2
2
3. 3
3
4. 4
4
5. 5
5
6. 6
6
7. 7
7
8. 8
8
9. 9
9

# An Investigation to Determine the Water Potential of a potato tuber

Extracts from this document...

Introduction

An Investigation to Determine the Water Potential of a potato tuber Background This experiment involves the process of osmosis. Osmosis is the process by which water moves across a membrane is known as osmosis and is described as the diffusion of water through a selectively permeable membrane The direction and amount of movement of water is dependant on the water potential. The water potential is based on the number and concentration of water molecules a solution has. For example, distilled water has the highest water potential, as it is the purest state of water. A highly concentrated solute solution has a low water potential. The highest water potential value (which distilled water has) is 0. Any dissolved solute-solution has a negative water potential value. Water potential is measure in the units Pascal. Water moves from a region of high water potential to a region of low water potential. Therefore, it moves down the water potential gradient. In this experiment we will be trying to determine the water potential of a potato tuber. Osmosis in this respect works on a cellular level. The cells that we are looking at are large, thin-walled, and usually have a large central vacuole. They are often partially separated from each other. In areas not exposed to light, as in a potato, food storage in the form of starch grains is the main function (Where light is present, e.g. in a leaf, photosynthesis is the main function). The amount of water present in these cells results in them having certain water potentials. If we place these tissues in different concentration sucrose solution we can see the if water has gone in or out of the cells. If the environment is hypotonic (having a lower concentration of solute than the cell) the net movement of water was into the cell, it would become turgid, the cytoplasm and vacuole pushed up against the cell wall, making the cell stiffer and wider and also result in the whole cell to increase in mass. ...read more.

Middle

* The time that was spent in solution is also an important factor. The time that is spent in the solution also affects how much water has had time to enter or leave the cell which means the cell has not had time to reach the isotonic point. This factor will be taken care of by allowing the potato pieces to stay in the solutions for a few hours, which is more than enough time for them to reach their isotonic point. Any difference in time that the potato strips spend in the solutions will be held to a minimum by placing and removing them within a small space in time. * We also understand that the potatoes are not identical and have not received the same environmental factors when being grown. Since we are doing repeats in this experiment, there is not enough potato to make all of the strips so more than one potato has to be used. This factor cannot be helped except for me to choose the healthiest potatoes and makes sure they are of the same type of potato. Apparatus 1x Scalpel - used to cut the potato strips to equal length 1x Tile - used to protect the table when cutting the potato strips 1x Glass Rod - used to stir the solutions when mixing water and sucrose solution 1x 30cm Ruler - used for the approximate measure of the potato strips 1x Cork Borer - used to accurately cut out the potato strips from the potato. 2x large potatoes - used as a source of plant tissue 200ml of distilled water - used to make the solutions 8x 250ml beakers - used to contain the water and sucrose solution and the other different molar solutions 200ml of 1M sucrose solution - used to make the solutions 1x marker pen - used to mark the beakers so that the contents can be identified 2x 50ml measuring cylinders - accurately measure the amounts of liquids to make the different ...read more.

Conclusion

all gave that same answers. My conclusion of finding the water potential of the potato cell could have been helped if I had a greater range of molarities with smaller increments which would show more accurately mass changes and also allow me to plot a better graph. The amount of repeats was sufficient and I believe that any more repeats would just give the same answers. Also the potato pieces itself was not definitely from the same potato and was not exactly the same size, although I did try to cut them to 2cm each, this could have effected the amount of water gained or lost. Anomalies include that in the yellow repeat in the 0.2 molar solution. This reading is not consistent as it indicates that that potato strip has not gained or lost any mass, which is inconsistent with the other repeats which show a range of 2.58% - 3.40% mass changes. This anomaly could have been caused by the strip not being weighed correctly at the beginning of the experiment or at the end of the experiment. You'll notice that the graph that shows all the results from each experiment do not all give the same mass change. Human error may have caused this. When the potato strips were removed from the test tubes and dried I may well have dried some potato pieces more thoroughly than others may and so some would have more excess water, which would add to the mass. I think the conclusion reached is quite accurate. Although there was an anomalous result the rest lay on a smooth curve which intercepted the x-axis at a credible point. The exact value of this point may not be exactly accurate as it is calculated from a freehand curve of best fit. The best thing to do if I was to carry on this experiment would be to make a 0.24 molar solution of sucrose and place potato strips in it. If I was right then the potato strips should neither gain mass nor lose any mass. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Life Processes & Cells section.

## Found what you're looking for?

• Start learning 29% faster today
• 150,000+ documents available
• Just £6.99 a month

Not the one? Search for your essay title...
• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

# Related GCSE Life Processes & Cells essays

1. ## To determine the water potential of a potato tuber cell using varying salt solution.

5 star(s)

The water is entering the cell causing a huge amount of pressure thus causing the cell to swell and become turgid. When the cell becomes turgid the protoplast (the outer cell surface membrane, cytoplasm and the tonoplast9) starts to swell and is pushed against the cellulose cell wall because of the pressure of water entering the cell.

2. ## An Experiment to determine Water Potential in Potato Tissue.

4 star(s)

The potato was put into different concentrations of sucrose solution. In this experiment we used a number if apparatus. These included: * Boiling tubes * Boiling tubes rack * 2 ? 250 cm3 beakers * Cork borer * Scalpel * Ceramic cutting tile * Electronic balance * 10 cm3 Pipette

1. ## Water potential of potato tuber cells - the weighing method.

So the concentration of the potato cells must lie between 0.4M and 0.2M. 0.6 Molar solution carries on the pattern, the potato tuber had an average .....mass change of -26%. As the concentration of sucrose outside the tuber .....is much greater than that inside the tuber the water molecules move out of .....the tubers causing a loss in mass.

2. ## The determination of the Water Potential of Potato Tuber Cells

I would also perform the experiment in a temperature and light intensity controlled room, this would prevent changes in both of these. These changes could cause the cell work rate to rise or drop also it could cause the water and sucrose molecules to speed up movement which could effect the rate at which osmosis takes.

1. ## Investigate how osmosis affects the weight of potato strips.

~ to put the potato strips inside * Digital balance ~ to weigh the weight of the potato strips * Label ~ to label the cup with * Ruler (ascending in millimetres) ~ to measure the length of the potato strips * Rubber band ~ to hold the plastic on

2. ## Aim To determine the water potential of a potato tuber cell

For example, in this experiment, I using 2 different types of potato, one is an old potato and the other one is a new potato. The result will not be reliable as old potato's cell wall is dried out, so it's going to gain more water and the new potato will gain less.

1. ## Osmotic pressure

The readings from the experiment are represented by the green crosses, and the repeat readings are represented by the red crosses. Repeat readings were done to verify the original readings to obtain a reliable average value. From my results I can see that the iso-osmotic point on the graph lies

2. ## Osmosis is defined as 'the movement of water molecules from an area of high ...

This is where no osmosis is taking place, i.e. no water is moving in or out of the potato. The next point, 0.25 mola looses approximately 4.0g. This shows that the water potential of the salt solution in the beaker is weaker than that of the potato chip.

• Over 160,000 pieces
of student written work
• Annotated by
experienced teachers
• Ideas and feedback to