Change in mass of potatoes in different concentrations of sugar solution.

Change in mass of potatoes in different concentrations of sugar solution

Osmosis is a name given to the diffusion of water. It is when water particles are moving from a high water concentration (or low sugar concentration), to a low water concentration (or high sugar concentration) through a semi-permeable membrane. The particles will continue to diffuse until the area in which they are found reaches a state of equilibrium, meaning that the water particles are randomly distributed throughout the solution and the object, but with no area having a higher or lower concentration than any other.

Semi-permeable membranes are very thin layers of material (cell membranes are semi-permeable), which allow some things to pass through them but prevent other things from passing through. Cell membranes will allow small molecules like Oxygen, water, Carbon Dioxide, Ammonia, amino acids, etc. to pass through. Cell membranes will not allow larger molecules like Sucrose, Starch, protein, etc. to pass through. A region of high concentration of water is either a very dilute solution of something like sucrose or pure water.

Osmosis is important for living things because this is a process of transporting water without the need of energy. In root cells, the root hairs enlarge the surface area for the roots to absorb water and other mineral. The plant does not need to use energy to absorb water. The water will naturally move into the root hair from the soil through the semi-permeable membrane, because there is a lower water concentration inside the roots. After the roots have absorbed the water from the soil for a period, the roots will have the same concentration as the soil. There will still be movement of water in and out of the roots because water particles are tiny and free to move through the semi-permeable membrane, i.e. the cell membrane of the root hairs. However, the roots will have not absorbed any water from the soil, as there is no overall movement of water. Although the water particles have moved, when the concentration of roots and soil are the same, the amount of water passing in and out of the roots will also be the same.

Osmosis also occurs in amoeba, as they require the nutrients from the water. The concentration of water inside the amoeba is lower than outside therefore it allows water to move into the cell. As this carries on, it will burst because it has no cell wall. The outer layer of the cell is a very thin cell membrane, which is semi-permeable. It can be avoided as the mitochondria provide energy from respiration to the contractile vacuoles to squeeze excess water out of the cell. This process of regulating cell fluid to keep it at a constant concentration is called osmoregulation.

In the human body, there are situations that involve osmosis, like the absorbing of water in the nephrons of kidneys and in the large intestine (colon). They all involve osmosis because of the presence of difference in water concentration.

When water enters a plant cell, its cytoplasm will expand and press on the cell wall. As the cell wall is quite rigid, it prevents the expansion of the cell and water pressure builds up outside the cell. The cell is said to be turgid. The cell wall will continue to expand until the cell wall can reach no further. ...

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When water moves out of a plant cell, the pressure inside decreases. The cell becomes less turgid. Eventually, the cell membrane and cytoplasm start to shrink away from the cell wall. When this happens, the cytoplasm is no longer pressing against the cell wall and the pressure inside the cell can be said to be zero. The cell becomes soft and we describe it as flaccid. The cell is also said to be plasmolysed, i.e. the cell membrane is not touching the cell wall. As the cell becomes more flaccid when more water moves out, the cytoplasm shrinks into a small volume. The cell wall is rigid and does not shrink, so the size of the cell remains more or less the same. However, the whole plant becomes soft, and cannot support its weight – it wilts. Thus, the turgidity of cells provides support to plants. Turgid cells enable non-woody plants to stand upright. All this things rely on the process of osmosis.

I did a preliminary experiment on osmosis to see how potato would change in mass in different conditions. First, I used a knife to cut out some chips from a potato. Then I dried the cut surfaces with a tissue paper and weigh them. I put the potato chip in three different test tubes with strong sugar solution, water and air. In each of the test tube I put a bung on the top and make the test fair. After I leave them for about 35 minutes or so I take the potatoes out and quickly dried them and then weigh them. I found out that the potato in sugar solution loses mass, while the potato put in water gained mass and the one put in the air has no change in mass. I also found out that the one put in strong sugar solution became floppy and very hard to snap but the one in water became hard and brittle.

The experiment that I am doing is to test how much mass has changed in a potato chip when it is placed in different concentrations of sugar solution to find out where the isotonic point is. Potato has a selective permeable membrane which will let small molecules like water go through but it does not let large molecules such as glucose go through. Osmosis is the process where water molecules go from a region of high concentration to a low concentration of water. It is nearly the same as diffusion but osmosis is just a special name for water diffusion.

Input variables

The variable that I am going to change is the concentration of the sugar solution. I will use 25, 20, 15, 10, 5% of sugar solution and distilled water that has no sugar in it. The volume of the solution I am going to put into the petri dish is 10ml and I will be given 25% sugar solution so in order to get 5, 10, 15 and 20% sugar solution I draw a table showing how to get different concentration of the solution.

Control variables

There are some variables that I have to keep the same throughout the experiment to make a fair test. The temperature can affect the rate of osmosis. The higher the temperature, the faster the rate of osmosis because if the temperature is higher it is going to have more heat energy which will provide more kinetic energy on to the particles to move faster.

To produce an accurate result I have cut the potato chips in long and thin because the surface area to the volume ratio would be bigger it is thin. It also lets the solution reaching the middle of the potato in a much shorter time than if it is short and thick. The length of the potato I am going to cut out is 50mm by 5mm by 5mm. When I put the potato chips and the sugar solution in the petri dish I have to make sure that the lid is closed because it is not closed the water from the sugar solution might evaporate and it will not give an accurate result. I am going to put three chips in a petri dish so in order for me to recognise which potato chip is which I will have to cut them in different shapes so I can tell which one is which.

I am going to put the potato chips for as long as possible, possibly for about two or three hours so I can make that the water has diffused I and out of the cell thoroughly.

The output variable of this experiment is the mass because this is the factor that I see if the input variable have an effect. I am going to measure using the electronic balance and I am going to measure the potatoes in grams to two decimal places. I use the electronic balance because it is more accurate than any other scales as long as I make sure that the reading is zero before I weigh the potatoes.

Apparatus

This is the list of what equipment I am going to use:

Test tubes
Ruler
Potato
Scalpel
Pipettes
Measuring cylinders
Tiles
Electronic balance
Petri dish
Sugar solution (25%)

Prediction

I predict when I put the potato chips in the petri dish, the lower the sugar concentration, the more mass it is going to gain because potato has a selective permeable membrane so water can pass through but sugar can not and because the concentration of water outside the cell is higher than the inside so water move from outside the cell to the inside by osmosis. The potato chip will gain less water as the concentration of sugar goes up until the concentration of sugar inside the cell is lower than the outside then water will start to move out of the cell and lose mass. If the placed in very high concentration of sugar the cell would so much water that it will get dehydrated and die. We say that the cell becomes plasmolysed. As the potato loses water the potato would start to get floppier and becomes hard to snap. On the other hand, if the potato chip is placed in water it will become stiff, hard and brittle because when the water move in the cell it causes to get turgid. I predict that the isotonic point is between 5 to 10% of sugar concentration.

This graph is my prediction of what the graph would look like when I plot the results on the graph.

Safety

To ensure that the experiment is safe I have to wear goggles in case some sugar solution gets into my eye. Also for people with long hair they should have their hair tied back so the hair will not distract them or getting in their way. When cutting the potato I have to make sure to cut away from me because there will be a risk of cutting towards me. I might slip and cut myself.

Method:

At the beginning of the experiment, I put on the goggles and prepare all the apparatus. After that, I should go to make different concentrations (0 to 25%) and 10ml for each one. Then I cut 18 potato chips from a potato as long and thin as possible so the sugar solutions can reach to the centre of the potato as quickly as possible. The 18 potatoes are for six for the different concentration and three for each concentration. I am going to cut the potatoes in three different shapes because when I put all three potatoes in the petri dish I have to tell the difference between them. When I finished cutting them I am going to dry them on a piece of paper in order to remove the water on the surface so I can make the test fair and weigh them in grams in two decimal places. It is important to weigh the potatoes after drying them because when I dry them the mass will be different from the beginning mass. Next, I shall pour the different sugar solutions into the six petri dishes. Then I add the potatoes in as well, closed the lid, and leave them to two to three hours.

Result:

Conclusion:

I found out that the isotonic point is about 5.5% of sugar concentration. As the concentration of sugar increases, the more mass the potatoes would lose. This is because when the potatoes are in a sugar solution which has a higher concentration of sugar than the cell sap the water would move out of the cell causing the potatoes losing mass. However, when they are in a lower sugar concentration than in their cell sap the concentration of water is higher outside the cell so water move in the cell and making the potatoes gaining mass. When the concentration of sugar solution is the same inside and outside the cell, the mass of potatoes stays the same. Although the water still move in and out of the cell as they are when they are in different concentration water move in and out of the cell at the same rate. However, in different concentration the water movement in and out of the cell is at different rate.

Evaluation:

I think my result is quite accurate and I do not think there is any anomalous result from my graph. I could have make the result more accurate if I put all the potatoes into the petri dish at the same time and then take all of them from the petri dishes out again. That means each of the potatoes would have the same time contacting the sugar solution. Also if all my potatoes have the same shape, mass and size the result would be much more accurate. However, this is impossible because I have to cut the potatoes in three shapes when I put them in a petri dish. If the potato is big and round the ratio of surface area to the volume will be much smaller than a potato which is long thin because in a round and big potato the centre of it is further to the outside then a thin potato. Next time if I do this experiment again I could reduce the gap of the sugar concentration, for example, 0,2,4,6,8 and 10% so the isotonic point that I will find will be much more accurate. I could also test the floppiness or the change in length of the potato instead of finding the change in mass. I could also see whether the isotonic point would be the same in different types of plant such as celery or carrot.