REPORT ON OSMOSIS
Different concentration of solutions on potato cuboids would be examined and explore in this experiment.
All cells have two layers of lipid molecules called plasma membrane which has an outer layer, in the sense that the fat soluble within the membrane and the water-soluble parts form the inner and outer borders. Since the plasma membrane is selectively permeable, the entering and exit of substances of cells are controlled by the plasma membrane (Brown et al, 2008). There arespecialized cells that react to stimuli in the plasma membrane keeping dangerous substances away from the cell. There are other molecules that pass through the plasma membrane and its environments, I.e. ions and nutrients.
It was stated by (Faller et al 2004) that there is an ion pump which transport potassium into the cells across the cell membrane, thereby balancing the transporting ions out, which is called sodium potassium (Na+ -K+). There is a splitting enzyme called the ATP (Adenosine Triphospates) which releases the energy needed for the transport of ions. The membrane potential of the extracellular fluid therein, sodium is the main cation and cholide being the prime anion; but in the intercellular fluid potassium is the predominant cation and proteins represent the main anions. Due to difference between concentrations the potassium are normally open and both the chloride and sodium channels are shut during resting potential, therefore the potassium has the tendency to disseminate outward (Faller et al, 2004).
More so, the achievement of transport of molecules across the cell membrane is through passive and active transport.
By natural process passive transport include facilitated diffusion (glucose and amino acids inside the cells of the intestinal mucosa), free diffusion (carbon dioxide, oxygen and water), or by osmosis therefore no energy consuming transport system (ATP) is needed transport smaller molecules into the cell (Brown et al, 2008).
As stated by Taiz et al 2010, diffusion is the movement of particle molecules from an area of superior concentration to an area of inferior concentration down concentration gradients until all becomes distributed equally across the region. For example the free movement of atoms and molecules in aqueous solutions or in gas is due to their thermal kinetic energy. The molecules spread out from the higher concentration to the lower region of concentration until the concentrations are spread out evenly (Taiz et al 2010). The main power force in this process is a concentration gradient called electrochemical gradient. For instance, huge portion of transports of solids (nutrients, respiratory gases, salts) that enters and exit the cell in the intercellular depends on the processes of diffusion. On the other hand facilitated diffusion is the movement of large molecules that passes through the cell membrane by way of protein channels, consisting of sodium ions and potassium ions, down a concentrated membrane (Taiz et al, 2010).
Furthermore, osmosis, a kind of diffusion involves water molecules, and can be defined as the net diffusion of water molecules from a highly concentration (dilute solution) to a region of low concentration (concentrated solution) through a semi-permeable membrane (Kowles 2010). The process of osmosis can take place when two solutions with diverse concentrations of equal amount of solute are set apart by semi permeable membrane (Hanson, 2004). Due to osmosis, the solute cannot be able to pass through the semi permeable membrane but the solvent can pass through it easily. The water disperses through the membrane in the direction whereby there is a higher concentration of solution until the concentration has of equal balance, and the solution volume having higher concentration raises. Not only is osmosis being affected by concentrated of solute but rather by the opposition by the cell wall to movement of water in the cell. This process of resistance of movement of water by the cell wall is simply known as called turgor pressure (Dunkharse et al 2009).
The tendency of a solution to turn a cell to either benefit or lose water is known as tonicity (Dunkharse et al 2009). In hypertonic, cells that are more concentrated in solution lose water and shrink, whereas in hypotonic (less concentrated solution) rather gain water and swell. At this point the, the cell tries to take control of this process where the osmotic pressure is kept to a constant. Water will move from the cell into the hypertonic solution through the cell membrane since there is higher solute concentration but of less water potential in the hypertonic solution. The probability of water to move from one region to another by way of osmosis application is known as water potential (Hanson, 2004). Unlike the hypertonic solution, the hypotonic solution has lower solute concentration but the water potential is higher, allowing water to move from the hypotonic solution through the cell membrane into the cell (Hanson, 2004). The process, by which concentration of solutes inside the cell is of equal level as the solutes outside the cell, falls under isotonic solutions. This means that the entering and leaving of water in a cell will be constant, stressing to the fact that there would be no swelling or shrinkage of the cell. These processes are beneficial to animal cells (Hanson, 2004).
Without the energy transport consuming system provided by mitochondria, active transport cannot transport large molecules by carrier proteins to exit (exocytosis) or enter (endocytosis) through the cell membrane (Faller et al, 2004). The course at which substances are transferred through the cell membrane with the aid of energy (ATPase) which is provided by the mitochondria is called active transport. There is a conversion of energy taken from ATP into ADP (adenosine Diphosphate). Substances can be transported in this processes can happen in the same manner (co transport) or in the reverse directions (counter transport). An example of such nature can be notified within the kidney. Amino acid transported into the kidney is linked with active sodium (Na+) transport, where the manufacture of energy by the mitochondria is dependable on both the endocytosis and exocytosis (Faller et al 2004).
As plant cell the potato will lose and absorb water through osmosis. As water concentration (sucrose) passes through the potato cuboids it will increase in volume as well as in length and mass. Some of the potato will also decrease meaning that less solute will go through the cell membrane of the potato depending on the level of sucrose solution that will be used determining the type of osmosis.
Knife or razor blade
Sucrose solutions (0.0M, 0.2M, 0.4M, 0.6M, 0.8M, 1.0M)
Before the beginning of the practical lesson a lab coat was worn and a risk assessment form was filled out. All equipment and items such as: balance or scale, knife, forceps, chopping board, beakers, ruler, potato, filter paper, tray and sucrose solution were all set up.
A potato was peeled and was cut into six cuboids with the measurement of (length: 2 cm, width:1 cm and height: 1 cm.)
Each potato cuboid was associated with concentration (M of solution that was introduced.) The letters B and A was used in the experiment where B stood for ” Before” and A was used to represent ” After.”
Firstly, the balance was switched on and was set in grams (g), the potato cuboids was then weighed making sure the scale or balance was not moved whilst it was in use.
A filter paper was then placed onto the balance’s pan. The TARE or ZERO KEY on the balance was then zeroed on the mass.
The potato cuboid was then transferred into each solution of the beaker with the use of a forceps. The stop clock was then pressed using the green button.
After 40 minutes approximately, (the time was recorded) each potato chip was removed at a time. All excess solution on the potato cuboids was drained without it being squeezed. The filter paper was then placed onto the balance’s pan and was zeroed on the balance. The potato chip was then placed on it, weighed and recorded after osmosis had taken effect.
The data obtained from the practical experiment showed no isotonic process and had a value of R2=1. Also, the data from the graph gave an indication of Y=-39.814 x + 14.29 and R2 being 0.9795 meaning that Y= mx + b with x being stable and showing the isotonic level of 0.385 where the fittest line crosses the x axis and the water potential of (kPa) on the chart.
TABLE OF RESULTS
Sucrose solution of mass (x axis)
Percentage of mass (y axis)
The observed potatoes that was submerged into the sucrose solution of 0.0M and 0.2M had a weight gain from 3.2g and 3.0g to 3.6g and 3.3g with a percentage change of mass 12.5 and 10. The rest of the potatoes decreased from 3.6g, 3.2g, 2.6g and 3.3g to 3.5g, 2.9g, 2.1g and 2.5g respectively in the sucrose solution of 0.4M to 1.0M. This gave an indication that the remaining four potatoes shrank by losing water whilst the first two potatoes swelled up by gaining more water. Hence hypertonic and hypotonic process occurred and the osmolarity of the sucrose solution within the potato was between 0.2M and 0.4M. With the data collected from the practical experiment an isotonic solution will have 0.3485M. The hypotonic concentration will set from 0.0M to 0.3484M while the hypertonic solution will set from 0.3486M or above. Six beakers of concentrated (sucrose) solution was used for the experimenttherefore giving different measurement anddetermine the type of osmosis that has occurred. On the first concentrated (sucrose) solution which was identified as: 0.0 the results showed that the solution was hypotonic because before it weighed 3.82g and after it was soaked in the (sucrose) solution it weighed 4.48 g meaning that it had more water potential than solute. It also gained a percentage mass of 17.3%. The second solution that was 0.2 also showed the same result as hypotonic as it was 3.79g and after it had been soaked showed 4.03g with a percentage change of 6.3%. The third solution which was also identified as 0.4 showed a different type of osmosis which was isotonic whereby it weighed 3.58g before and after showed 3.77g with a percentage change of mass as 5.3%.
It was noted that when the last four potatoes were placed in hypertonic solutions, there was a decrease in the mass of the potatoes. This decrease might be as an outcome of the osmotic loss of water from the cell of the potato and the interstitial space between the cells. This could be as a result of two possible reasons:
Firstly, as water leaves the potato cells, the osmotic gradient across the cell membrane reduced and the solutes in the solution were very much diluted. Secondly, it reached a point whereby almost all the water from the potato cells had vanished due to diffusion and cannot lose any more of the water.
There were restrictions applied to this experiment since the significance of R2 was not equivalent to 1. This might be because the potato was blotted too much with paper towel or careful considerations was not taken when the scale was tarred to 0.0g before the potatoes being weighed after soaking.
If the surface area to volume ratio was low, then the result obtained would have been dissimilar since the osmosis will have little effect to take place as surface area will not be adequate and only diminutive transformations would have been identified. It was evident that osmosis took place in both hypertonic and hypotonic but not isotonic since there was different concentrations. This could be proven from the results as some of the concentrations bear too many solutes and little water potential or the solute inside the cell of the potato cuboids being higher than the solution in the beaker.
If the potato cylinders were left for more than the 40 minutes allocated time, it would have enabled me to look at the point whereby there would be no more water entering or leaving the potato cuboids. The cutting of potato discs raises the surface area and may result in an improved quality of data. The micrometer used to determine the potato cylinder could another area of improvement to the experiment since it was tricky in measuring the length of the potato cylinder with a ruler, although the disparities of figures using the ruler were very diminutive.
Keeping the potatoes in the solutions for the same time, it allows the potatoes to have the same effect of osmosis to happen and also maintaining the same potato shows that there will be the same amount of sugar concentration in the potato. Other ways to determine the movement of substances across membranes could be used such as the use of salt and cassava solutions to study if the end result of salt solution has osmosis on the cassava.
To conclude, because the trends of the results were clear and the calculation of concentrations of sugars inside the potato from the graph was achieved, it shows all the scientific ideas proven about osmosis.