The effect of osmosis on potatoes in different concentrations of sucrose solutions
Research question :
The potato chores are submerged in different sucrose concentrated solutions. Will their size decrease/increase the higher the sucrose concentration gets?
To begin with, we shall understand the term Osmosis, which is a process by which water molecules move from an area of low solute concentration to an area of high solute concentration through a semipermeable membrane in order to reach an equilibrium point between the inside and outside of the cell. Osmosis is one of the many forms of Passive transport, meaning it requires no energy (Adenosine triphosphate) to happen. In this lab experiment, we will use different sucrose concentration solutions (0.0, 0.2, 0.4, 0.6, 0.8, 1.0 mol/dm³) and compare it will distilled water solution as well to see how each solution affects the size of the potato and how high the diffusion of osmosis in each solute concentration will be in comparison to one another.
Both animal and plant cells have and use the principles of osmosis to transport water in and out of themselves and osmosis on its own is one of the fundamental bases of biology and its studies circulating areas such as Osmoregulation and how cells regulate osmotic pressure and maintain a homeostatic environment. The movement of water depends completely on the osmotic pressure, which are isotonic, hypotonic and hypertonic solutions, which manipulates the direction.
Plant cells: Osmosis is very important for the plants to be able to absorb water from the soil and thus survive. The roots are like numerous root hair cells, which increase the surface area by volume ration in order to be able to absorb more efficiently.
Animal cells: Osmosis is important for animal cells in order to keep the ion concentration balanced between the internal and external environment of a cell as well as be able to transport water molecules by osmosis through capillaries to each cell in a body to keep the cells firm, healthy and functional. A process called osmoregulation which is provided by the kidney to regulate the concentration of water and salt in the blood (the process also controlled by the hypothalamus in the brain). The regulating change differs depending on where the animal lives. If it is an animal living in a dry land/salty water have a longer osmoregulation process in order to conserve water. An example would be the kangaroo rat in a dry environment, which has adapted its body by having a long loop of Henle in the inner medulla to maximise urine concentration and conserve water. However, animals surrounded/in fresh water must conversely get rid of water as fast as possible by osmosis.
Osmosis in Plant cells:
Plant cells are usually in hypotonic environments and tend to have more concentrated fluid inside their cells then its external environment. If water molecules would be allowed to move into the cells, it would raise the turgor pressure (rigidity of cells and tissues) making the plant turgid and unable to stand upright. If the plant cells would be in a hypertonic environment, then all the water would leave the cell making it plasmolyzed. The Cytoplasm would pinch away from the cells walls and the cell would no longer function. And if the cell would be in a isotonic environment, then the cell would turn flaccid and wilt.
Osmosis in animal cells:
Animal cells in a hypotonic solution, start taking in water molecules and end up bursting. Conversely, plant cells have a rigid cell wall which prevents their cells to burst in a hypotonic solution and instead end up in a turgid state (hard and swollen). In a hypertonic solution, an animal cell starts diffusing water out of itself and shrivels, which gives the conclusion that an animal cell needs to be surrounded by a isotonic solution in order to function properly.
The size as well as the mass of a potato will decrease if submerged in a high sucrose concentrated solution as the water molecules inside of the potato chore will move out of the cell in order to create an equilibrium on both sides. However, if a potato is submerged into a distilled water beaker or a low sucrose concentrated solution, its size, as well as the mass, will increase.
This thought roots from the natural osmotic movement are solutions such as hypoosmotic, hyperosmotic and isosmotic. Considering it has been proven that water molecules move from a hyperosmotic solution (concentrated) to a hypoosmotic solution (diluted/less concentrated) in order to reach an isosmotic solution, where there is an equal amount of sucrose concentration on both sides of the semipermeable membrane creating an equilibrium.
Material and apparatus
Six beakers (no uncertainty considering they were not measuring beakers and not marked)
Plastic ruler (±0.1mm)
Prepared sucrose solutions : 0.0 mol/dm³ ⇒ Distilled water, 0.2 mol/dm³, 0.4 mol/dm³, 0.6 mol/dm³, 0.8 mol/dm³, 1.0 mol/dm³
The working area was cleared out and a cutting board was placed on the table.
Approximately 4-5 potatoes with a medium size (not too small) were placed on the cutting board.
With a ruler, sides of the chosen potatoes were measured and reached the length of 4 cm.
With a knife, sides of the potatoes were cut and turned into rectangularly shaped potatoes.
0.5 cm width and thickness was marked with a scalpel first and then slowly and precisely cut throughout, making a smaller rectangle.
Step 3-6 was repeated until 30 potato chores were made.
6 beakers were placed beside the potato chores on the table.
A piece of tape was put on each beakers side and with a pen, each was labeled on the tape according to what concentrated sucrose solution they were going to contain.
After each tag on the beakers, the written sucrose solution on the beakers was poured until they all were half full.
5 potato chores were then placed in each and altogether put in a box.
After 24 hours the potato chores were brought out of the solutes and then the final lengths were measured.
The potatoes were generally :
Kind of bendable
Similar in size and shape
The potato chores were out of being submerged in different sucrose solutions for 44 hours and were soggy and soft.
The higher the sucrose solution, the smaller the potato chores were ⇒ leading to the conclusion that the solution had made the potatoes shrink.
The lower the sucrose solution was, especially with the distilled water, the larger the potato chores were ⇒ leading to the conclusion that the solution had made the potatoes grow in size.
As the results show, the hypothesis given was correct and the potato chores did grow in low sucrose concentration/distilled water and did shrink in high sucrose concentration. This also gives another fact that if the potatoes were to be measured in weight, we would then see that the mass would decrease in a high sucrose concentration and decrease in a low sucrose concentration/distilled water.
The largest % average size change was between the sucrose solution 0.6 and 0.8 from -11% to 14.5%, which is a point of which we can see that the potato chore simply shrunk and got more affected from 0.8 mol/dm³ and down. In distilled water, the percentage average change from the initial size was 8%, which supports the hypothesis even more with the fact that the lower the sucrose concentration is, the more water will move inside the potato.
The average size change between sucrose concentration 0.2 and 0.4 mol/dm³ was not so much in comparison to all the others, giving the conclusion that the potato chores original sucrose concentration must have been between those two values. As told above in section “Introduction” we explained who osmosis is the net movement of water molecules moving from a low solute concentration to a high solute concentration, meaning that between those two sucrose solutions, we probably hit very close to a isotonic solution (not exactly but still).
A further consolidation of the hypothesis, results, and the background information is how the potato chores in distilled water and in the sucrose solution 0.2 mol/dm³ were indeed turgid and the potato chores in 0.8 mol/dm³ and higher were flaccid as well as felt a bit squishy.
A wide range of errors can be kept in consideration when it comes to the measurement of temperature, potato chores and the fact that we manually kept on touching the potatoes with our hands which could have defected the sugar distribution across the potatoes surface and altering the osmosis results. Another error factor would also be the fact that more than one potato was required in the experiment to get the 30 potato chores, thus us having several different sucrose sources and by the fact that each potato has different levels of nutrition, the results might have a deficiency inaccuracy in this area.
Erika Steele. Osmotic pressure : Definition&formula (Available online): http://study.com/academy/lesson/osmotic-pressure-definition-formula-quiz.html (Accessed 23/9-17)
BBC. Diffusion and Osmosis (Available online): http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/green_world/diffusionrev4.shtml (Accesses 23/9-17)
Elysia Northall. Explaining why osmosis is important in animal and plant cells (Available online): https://getrevising.co.uk/resources/explaining_why_osmosis_is_important_in_animal_and_plant_cells (Accessed 23/9-17)
Etomica. The effects of osmosis (Available online): http://www.etomica.org/app/modules/sites/Osmosis_old/Background1.html (Accesses 23/9-17)
Yahoo. Why is osmosis important in animal cells (Available online): https://uk.answers.yahoo.com/question/index?qid=20090326094148AAgsYGx (Accesses 23/9-17)
Biology Junction. Osmosis lab example 2 (Available online): http://www.biologyjunction.com/osmosis_lab_example_2.htm (Accesses 23/9-17)