Investigating to find the concentration of potato cells using osmosis

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Biology GCSE Coursework

Investigating to find the concentration of potato cells using osmosis

Introduction

Osmosis is the net movement of water molecules from a low concentration (high concentration of water) to a high concentration, (low concentration of water) through a semi permeable membrane. For example2, potato cells in a sugar solution.

Aim

To find out the concentration of potato cells using osmosis, by putting potato cells in different amounts of sugar solution and seeing by a graph when there is no change as the concentration of the solution is the same as the potato.

Factors that effect osmosis

Temperature and light - The molecules will get more kinetic energy and so more osmosis will take place, and also a higher temperature would make the water evaporate, increasing the concentration of the solution

Amount of solution - The larger the surface area, the more osmosis will happen

Size of potato - More solution might also increase the rate of osmosis by increasing the surface area

Type of potato - Different potato cells might change the rate of osmosis

Things that will change with experiment:

Length of potato

Weight of potato

I have decided to look at the difference in mass to find the concentration of potato cells, by seeing when the mass stays the same.

Preliminary Experiment

Apparatus

* 50ml measuring cylinder in 0.5ml steps - to measure accurately

* One large potato - so it is fair and only one potato is used

* Three medium sized test tubes - to put the solution in

* Rack - to hold three test tubes

* Balance that can measure to 0.01 of a gram - to be accurate

* Medium sized corker borer - to cut pieces out of potato which are all the same size

* Scalpel - to cut the pieces to same length

* Ruler in millimetres to measure potato - to be accurate

* Ceramic tile to place potatoes on - to be neat and safe

* Kitchen paper to clot wet potatoes - to be accurate and have each one as dry as each other

* Tap water - to make the solution

* Sugar solution - to make the solution

* Goggles, lab coat - for safety

Method

- Three potato cylinders were cut using a cork borer out of the same potato

- They were measured in mm and cut with the scalpel so they were the same length

- They were each weighed to the nearest 0.01g

- Three test tubes were put in a rack and filled with 1: 10cm3 sugar solution, 2: 10cm3 water and 3: 0.1cm3 sugar solution and 0.9cm3 tap water

- One potato was put in each of the test tubes and a bung put on top to stop evaporation

- The test tubes were left for 30mins

- The potatoes were blotted with kitchen paper and weighed again to the nearest 0.01g

- Results were taken and are in the table below

Results

The sugar concentration % (m)

Mass of potato before (g)

Mass of potato after (g)

Change in mass (g)

0.0

0.1

.0

.43

.45

.44

.46

.43

.24

+ 0.03

- 0.02

- 0.2

Conclusion

The results show that the more sugar solution there is, the mass gets less. There is a dramatic change between 0.1 and 1.0m. For my investigation I will use the range 0.0 to 0.3 going up in 0.05m steps. I have chosen this range because the preliminary results show that somewhere between 0.0 and 0.1 the potato will be at the same concentration as the sugar solution.

Planning

Prediction

I think that the concentration of the potato will be between 0.0 and 0.1m of sugar concentration. My preliminary experiment showed that 0.0m made the change in mass a positive number, while 0.1 made a negative number.
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According to the scientific introduction, when water moves out the potato cell it means the potato had a higher concentration of water inside, and when water moves in, the potato has a lower concentration of water.

Therefore, there is a point where the concentration is the same, and water moves in and out from either side, which is called when they are at equilibrium. Half way between +0.03 and -0.02 is +0.05. I think the concentration of the potato will be at that, so in my method I will use the range going up in 0.05m.
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