Investigation into the effects of osmosis on Potato cells

Apparatus

* Cork borer Vernier calliper

* 6 specimen bottles 1 large potato

* Labels Approx. 80ml of glucose solution (0.5M)

* One-sided blade Approx. 100ml of distilled water

* Filter paper Measuring cylinders - 10ml & 25ml

Method

* Label the specimen bottles: 0M through to 0.5M

* Pour the glucose solution into their respective bottles (20ml). See table.

* Using the cork borer cut out several cylinders of potato and obtain 12 cylinders of approx. length 3cm (not less than).

* Trim with the blade.

* Measure the exact the length of the cylinders with the vernier callipers (2 d.p.)

* Record the length of the cylinder in your table.

* Immerse two cylinders in each of the six tubes (must be approx. the same length).

* Put the lids on the tubes and leave for 24hrs.

After 24hrs

* Remove the cylinders of potato from the first tube (0M - distilled water).

* Dry quickly on filter paper and measure the length with the callipers.

* Record the lengths in you table.

* Repeat with each of the other tubes in order (0M...0.5M).

* Calculate the % change in length for each concentration=

% change in length = x(final - original) length *100

x original length

* Record these results in your table.

Safety

* Make sure to take extra care when using blade to cut potato cylinders, as it is very shape.

* Take extra care when using vernier calliper and they have a pointed end, which could inflict injury.

* If a specimen bottle breaks, be careful not to cut yourself on the broken glass.

How I got my precise results

To get my results I had to use accurate instruments such as the vernier callipers, which are precise to 0.01cm so I could get the length of the potato cylinders at, start and finish of the experiment. Other instruments which were the measuring cylinders - 10 ml & 25ml that are accurate to *-0.1ml & *-0.5ml respectively. This helped when I had to measure out glucose solution and distilled water. This all helped to get accurate results & a successful experiment.

Strategy for results

For my results for the experiment, I will make a table with concentrations down the left side and lengths of potato cells along the top. Then the percentage change in length down the right side. The title will be - -Investigation into the effects of osmosis on potato cells: Results. The graph that I will plot my results will have Concentration of glucose (M) on the X-axis and % change in length on the Y-axis. On this I will draw a best-fit line. Above the X-axis, the results are Hypotonic and below the X-axis the results are Hypertonic. But if the results are on the X-axis line, the result is isotonic meaning the concentration inside equals' concentration outside.

Table and graph overleaf

To find the percentage change in length, I had to use the following formula: final length - original length

original length * 100

(1) 0M; 3.12 - 2.96

2.96 * 100 = 5.405%

(2) 0.1M; 3.14 - 2.98

2.98 * 100 = 5.369%

(3) 0.2M; 3.09 - 2.99

2.99 * 100 = 3.344%

(4) 0.3M; 2.985 - 3.02

3.02 * 100 = -1.159%

(5) 0.4M; 3.00 - 3.03

3.03 * 100 = -0.99%

(6) 0.5M; 2.62 - 2.95

2.95 *100 = -11.186%

INTERPRETATION

Conclusion

* Hypotonic concentrations are 0M, 0.1M and 0.2M because the movement of water moving in is greater than the amount of water moving out.

* Hypertonic concentrations are 0.3M, 0.4M and 0.5M because the amount of water moving out is greater than the amount of water moving in.

* Isotonic concentration is 0.25M because the concentration inside equals the concentration outside.

See leaflet overleaf to see diagrams of movement of water.

Description of a Potato cell

* Cell wall is totally permeable which means it will allow anything to pass through it. It is rigid and strong and maintains the shape of the plant cell so that the cell will increase in size, but there is a limit that the wall will not allow further stretching.

* Cell membrane is partially permeable as it selects what passes through it.

* Vacuole solutes-Is cell sap and can continue dissolving glucose and other sugars.

Gradient of the graph

To work out he gradient of the graph I will

Y2 - Y1 (=) -4 - 4.2 = -8.2 = -43.2% change in L/M

X2 - X1 0.34 - 0.15 0.19

Do my results support my prediction?

I do think my results support my prediction in my first section. As the experiment was carried out properly and once I plotted my results on the graph, all produced pattern in a negative fashion.

Are your results reliable?

Yes, because of the apparatus used be my group in the experiment. For example the measuring cylinders are accurate to *-0.1ml and *-0.5ml plus the vernier callipers are accurate to 0.01cm so my results should be pretty accurate.

Any anomalous results?

Yes, there is one result that doesn't really follow the pattern of the rest of the results. This could be because with the results I got, Conc. 04M, there was very little change between the starting length and the length at the end. This might be anomalous because maybe the volumes measured inaccurately or the vernier callipers were read slightly wrong. This means if there was a mistake it was because of human error.

How suitable was my procedure?

I feel my procedure was well suited to this investigation, because 0.25M (isotonic) fell in between 0.2M and 0.3M, meaning a perfect experiment. Also the apparatus was good enough for a successful experiment.

Any changes to improve?

I fell that there are many changes I could do to improve my experiment to get more accurate results. And they are:

. Be more accurate when cutting the cylinders, try to be as close to 3.00cm as possible. If we had two different starting lengths e.g. 3.02cm and 3.12cm it would not be fair because 3.03cm chip has a greater SA: VOL giving it an advantage in terms of osmosis.

2. A third potato cylinder could be cut and put into the specimen bottle to increase accuracy in getting results.

3. A burrette could be used. These are accurate to 0.1ml, which would help when we are measuring out our solutions.

4. Also Digital Vernier callipers would be useful as we could just read off the measurement and possibly eliminate human error when measuring.

Does the evidence support a firm conclusion?

Yes, because 0.25M (isotonic result) corresponds with book value so this is encouraging. Five of my plotted values follow the pattern and only one is anomalous.