Diffusion is the net passive movement of particles atoms, ions or molecules from a region in which they are in higher concentration to regions of lower concentration. Diffusion is important process that occurs in human body example of one of many types of diffusion which occur in the human body is gas exchange at the alveoli- oxygen from air to blood, carbon dioxide from blood to air. [5]
Osmosis is the diffusion of fluid through a semipermeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane. [1]
Diffusion and osmosis is an example of passive transport. Passive transport is a movement of substance across a permeable membrane without added energy. The difference between osmosis and diffusion is that; diffusion can take place without a membrane whereas osmosis only takes place across a semi permeable membrane. Osmosis only involves movement of water across a permeable membrane. Osmosis is much slower than the rate of diffusion. Osmosis is a passive transport of water whereas diffusion is a passive transport of solutes. [7, 8]
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A permeable membrane is a membrane that allows all types of molecules or ions to penetrate through it; it lets everything go through it such as salt. [6] Whereas a semi permeable membrane is a membrane that allows let only solvents, like water, to pass through it. It is a membrane that will only allow certain molecules through it. In general oxygen, food and water are allowed to enter; waste products are allowed to exit and harmful substances are kept out. It doesn’t let large soluble pass through it. [2, 3]
Osmosis is the main way water is transported in and out of cells in the human body. The areas of high concentration of water molecules are called hypotonic. Hypotonic solution has a low concentration of dissolved substances. Areas of low concentration of water molecules are called hypertonic. Hypertonic solution has a high concentration of dissolved substances. During osmosis, water molecules naturally travel from hypotonic areas to hypertonic areas. Water molecules travel from hypotonic areas to hypertonic areas because this process equalizes the concentrations of water and dissolved substances. [4]
This is example of osmosis in human body, Salts and minerals from water are transferred in the body through osmosis. Water flows through the plasma membrane of cells and due to osmosis concentration of water, glucose and salt is maintained inside the body. [9]
Active transport is when dissolved molecules move across a cell membrane from a lower to a higher concentration. In active transport, particles move against the concentration gradient – and therefore require an input of energy from the cell. The energy used to absorb the molecules comes from respiration.
In humans, active transport takes place during the digestion of food in the small intestine. Carbohydrates are broken down into simple sugars such as glucose. The glucose is absorbed by active transport into the villi, to be passed into the bloodstream and taken around the body. [10]
http://www.bbc.co.uk/bang/images/446×251/osmosis.jpg [11]
Diffusion[12]
http://www.phschool.com/science/biology_place/biocoach/images/biomembrane1/Tonic2.gif
[13]
Apparatus:
Potato chip: This will help me justify if osmosis is occurring. I have used potato chip to help me justify if osmosis as it is a semi-permeable cell. The length, width and mass of all the potato chip used in the experiment are to be kept same.
Scalpel and a chopping tile: The scalpel will be used to cut all the potato chip to the chosen length and width. The chopping tile will used to place the potato chip while being to reduce damages to the work area i.e. cutting of work place while cutting the chip.
Electronic scale: Electronic scale will be used in my experiment to measure the mass of potato chip during the experiment. I have decided to use Electronic scale rather than a spring balance to weigh the potato chip because using electronic scale means that my results are accurate as electronic scale has measuring units ranging from ‘grams- kilograms’. My results will also be precise as the electronic scale measures the weight of something to 2 decimal places.
The results obtained from a spring balance will not be precise; the results will also not be accurate as parallax error could occur while reading the data. The use of balance is necessary in the experiment because I will need to calculate mass of the potato ‘before and after’ during the experiment, so that I can calculate reliable percentage difference in mass.
Distilled water: This will be used to preserve the potato chip .I have decided to use distilled water rather than water because it is an isotonic solution and using distilled water to preserve the potato chip means that the potato chip won’t be affected by outside factors; therefore making my results reliable.
Ruler: Ruler will be used in my experiment to accurately measure the width and the length of the potato chip; to make sure that they are all same size. I have decided to use a ruler marked in units of cm and mm so that my results will be precise as the potato chip cutting will be even and of the same size.
Filter paper: This will be used in my experiment to blot the potato chip once it has been taken out of the sucrose solution; I will blot the potato chip in order to absorb excess water from the potato so that there is as little water molecules in the potato; doing this will help me measure the true value of the mass of the potato and make my result more accurate.
Labels: To make sure that the experiment run smoothly, each agar plate that is being utilised in the experiment will be labelled. Labels will be used in my experiment so that the potato chip in a solution can be easily identified. Labels will help me find the concentration of a particular solution. Labelling the agar plates will prevent confusion, and reduce anomalous results.
Sucrose solution: I will need a sufficient number of concentrations. This is so that I can easily show anomalies and trends in my results in order to draw an accurate conclusion. Sucrose solution will be used in my experiment as this will help me to figure out if osmosis is occurring. The aim of my investigation is to see how the rate of osmosis is affected by the concentration of the sucrose solution so I will be using different concentration of sucrose solution.
Measuring cylinder: Cylinder will be used in my experiment to measure the amount of sucrose solution. I have decided to use a measuring cylinder rather than a beaker to measure the amount of sucrose solution because it is made to +0.5ml or -0.5ml where as a beaker is made to +3ml or -3ml. Using measuring cylinder will mean that there will be a high level of accuracy in my results. Using cylinder will mean the amount of concentration on each is accurate.
Agar Plate (6): Agar plate will be used in my experiment to hold the sucrose solution and the potato chips. The agar plates will be labelled to prevent confusion and this will reduce chances of anomalous results. For e.g. If I were to add a sucrose solution with a concentration of 0.1 on to a agar plate but believed I had picked a sucrose solution with a concentration of 0.2, the results produced would contain error and would be anomalous.
I have also decided to use an agar plate. Using a test tube could possibly result in potato chips leaning on the sides and decreasing the chip’s surface area. Therefore, I have decided to an agar plate rather than a test tube to carry out the experiment
Stop watch: Stopwatch will be used in my experiment to record the amount of time the potato chip has been placed in the solution. Stopwatch watch will be used so that the timings of the experiment are accurately followed, and that the potato is removed from solution at the correct time. This way, the experiment remains fair.
Health and Safety:
Healthy and safety procedures are very important while carrying out the experiment:
Scribe: Scribes will be used in the experiment to cut the potato chips, but could cause fatal injury if treated carelessly. Scribes are dangerous; they are sharp and could cause wounds. You should not walk in the lab carrying a scribe. Scribe shouldn’t be placed at edge of the table which could result in injury if it falls off.
Wear goggles- It is important to wear goggles to protect our eyes from any spills that could happen. In case of sucrose solution getting into your eyes, immediately flush eyes with water.
It is also recommended to wear latex gloves as they are thin, see through and will not create difficulty for you while doing the experiment. Latex gloves will create a barrier between the substances and your hand. Wearing gloves protects our hand form the irritation which could be caused by sucrose solution.
Wearing goggles and latex gloves will mean that there is maximum skin protection and minimises chances of irritation from substances coming in contact with the skin. People with sensitive skin are more likely to be affected if the solution gets spilled on their skin.
Hands should also be washed after doing the experiment.
Carry out the experiment standing- It is important to carry out the experiment standing, so that there is less chance of injury happening to you. If something happens, i.e. Sucrose solution spills, you can quickly move from the area.
Positioning of equipment- Acids and Alkalis should be kept in a position where they are not likely to fall or spill. It shouldn’t be kept at edge of the table. Equipment such as measuring cylinder which is made out of glass could fall and break easily if placed inappropriately, i.e. edge of the table. Broken pieces of glasses are hazard, it could easily cut someone. It is also important to put the beaker which contains the concentration of solution accordingly so that there are no spills; spills in the work area is an hazard, people could easily slip.
Work area: Working area must be kept clear, there should be no baggage lying on the floor which could cause people to trip over, it is a hazard. Hazards in work place could lead to injury. It is also important not to run around while carrying equipment, equipment such as scribe could cause injury to yourself.
Factors:
Independent variable:
The independent variable in the experiment is the concentration of sucrose solution. I will be changing the concentration of the sucrose solution to see how it affects osmosis.
Dependent variable:
The dependent variable in the experiment is the mass of the potato. I will be measuring the mass of the potato before placing it in the solution and after they have been placed in the solution.
The mass of the potato after they have been placed in a solution is a continuous variable.
Controlled variable:
The controlled variable in the experiment are:
Experimental room: The temperature affects the rate of a reaction because the greater the temperature, the greater the heat. There will be a higher rate of osmosis in the cell membrane because particles in the solution will be moving quickly due to temperature change. Water molecules will gain kinetic energy which increase osmosis. Higher temperature could also cause the cell membrane to denature, the water molecules in the solution could also evaporate. The temperature at which the experiment is carried out must remain constant in order for an experiment to be a fair test and my results to be reliable. I would conduct the experiment in the same room to make this factor constant.
Type of cell: Permeability of potatoes can differ, if I use potato chips with different level of permeability, the amount of solution going through will not be the same. I will be using potatoes with same level of permeability.
Surface area of the chips: It is important to keep the surface area of each potato the same in the experiment. Potato chips with higher surface will mean that osmosis occurs faster, because more of the potato is available for reaction.
Time: In order to find out how concentration affects osmosis. The amount of time which the potato will be left in a solution should remain constant. Having a potato chip in a solution for longer time will mean that it will have a greater chance to carry out osmosis than the other chips. This will mean that my experiment will become an unfair test; I will be using a stopwatch to keep this factor constant.
Volume of concentration used: The volume of concentration used in the experiment needs to remain constant to make my experiment a fair test. If this factor wasn’t kept constant then the amount of water molecules on the agar plate would be different and will be varying the rate of osmosis because there will be higher probability of water molecule diffusing through the permeable membrane. I will be keeping this factor constant by using a measuring cylinder which has a measuring accuracy of +0.5ml or -0.5ml.
Hypothesis:
I also believe that when the chip is placed in a dilute concentration of sucrose solution, it will gain mass and become rigid. The concentration of sucrose solution will have more water than the inside of the chip. This will result in water moving from the solution to the chip. The chip will gain mass as water goes in to the cell. The chip will become turgid and strong.
I also believe that there will be a stage in the experiment where the potato will neither gain nor lose any mass. This will occur because the potato chips will be in an isotonic solution. The concentration inside and outside of the potato will be the same so no osmosis will be occurring.
I believe as the concentration of the sucrose solution increases, the mass of the potato will decrease. During osmosis substances move from an area of high pressure to an area of low pressure. Therefore, when a chip is placed in a concentrated sucrose solution, it will lose mass because the chip has a higher concentration of water than the sucrose solution. The sucrose solution in which the potato is kept will have will be concentrated and will not have much water. Water will move out from the chip and the cell becomes flaccid.
Sugar molecules in the sucrose solution are too large to go through a semi-permeable membrane so water moves out during osmosis. The permeable membrane only allows solvent through it, the solute (sugar molecules) can’t go through it.
Preliminary test
I have also carried out a preliminary test to see if there were any changes to be made in the final experiment.
Preliminary method:
I collected all the equipment needed for experiment.
I made sure that I labelled the six agar plates that I used in my experiment to reduce confusion and minimise any chances of anomalous results.
I measured the length of the potato; the width of each potato chip was same. The width of each potato chip to be used in the experiment was same. I measured the length of each potato chip using a ruler to make sure it was equal.
Using potato chips with same length and width will result in all chips having mass but I measured mass of each chip rather than assuming the mass to be the same. If the mass had been different due to inaccurate measuring of length and width, I would change the length and width and measure the mass again.
Then, I measured the mass of the potato using an electric scale. I also blotted the chip before measuring it to get an accurate value. I also waited 5 seconds after placing it on the scale to ensure that the figure displayed on the scale was not fluctuating.
I poured … m3 of a particular concentration of the sucrose solution into the agar plate using a measuring cylinder. Then, I placed the chip in a labelled agar plate with the correct concentration for 5 mins.
I then took out the chip from the solution and blotted the chip with tissue paper to absorb any excess solution off the potato. I measured the mass of the potato after it was placed in the solution to figure out if it gained or lost mass.
I carried out three repeats for each concentration to make sure that my results were reliable
Then, I repeated step 3-7 for all the concentrations to be used in the experiment.
Graph Analysis:
During the experiment, I placed a potato chip on different concentrations of sucrose solution.
We can see that as the concentration increases the mass decreases.
During 0.5.
Mass is acquired this cud be due to inaccurate measuring.
From the graphs it is clear that there is coherent negative correlation the independent variable and the dependant variable. As the concentration increases, the percentage difference decreases. As the concentration increases from 0 – 100 the percentage change in massdecreases from …….
My results are reliable and accurate; it shows a strong negative correlation.
All the concentrations have small range bars, indicating that the results are accurate and can be relied upon.
However, results: 0.1m, 0.9m, and 1.0m all have large range bars suggesting they are unreliable.
Ultimately, there is a connection between the concentration and the percentage change in mass
Evaluation:
I used an electronic scale to measure the mass of the potato during the experiment. The results given by the scale were precise but while measuring the chip during the experiment, there was a zero error. The scale showed mass of 0.04g when there was nothing placed on it. The scale was also free of water or any solution which could have caused the scale to show mass. The zero error present on the scale could have been the cause for anomalous results in the preliminary experiment.
I also placed the chip in the solution for 5 minutes; I believe the time isn’t long enough for osmosis to take place.
Changes made from preliminary
In my preliminary, I used five different concentration of sucrose solution, to find out if concentration affects osmosis. I have now decided to use nine different concentration of sucrose solution, ranging from 0% to 100%. I have done this to make sure that there will be a range of results which I can draw a conclusion from.
I also placed the chip in the solution for 5 minutes; I believe the time isn’t long enough for osmosis to take place. I believe perhaps a longer time would enable osmosis to take more effect. I will be putting the chip in the solution for 10 mins in my final experiment to increase the osmotic activity.
Final experiment method:
Final experiment results:
*All data in the results are given correctly to two decimal places.
*The difference in mass is worked out by the increase/decrease in mass, divided by the original mass and then, X 100.
For example,
The difference in mass for the concentration 0% is worked out by:
(1.81-1.71) X 100
1.75
This is 3.43%.
Graph analysis:
The graph depicts a negative correlation. As the sucrose concentration increases (the independent variable), the change in mass of the plant tissue (the dependant variable) decreases.
Evaluation:
I would pick the chip from the distilled water by tweezers rather than hand. I will tweezers to pick it because this will mean that the potato chip doesn’t make contact with skin, and no moisture will be absorbed by the chip form the potato. Moisture from skin could affect the mass of the potato. However, using tweezers to pick the potato, I could be damaging the chips cell which will have an effect on the results.
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I also used an electronic scale to measure the mass of the potato chip during the experiment; the use of electronic scale to measure the potato chip meant that my results obtained are precise as it gave figures to two decimal places. I think my result were also accurate because using an electronic scale meant that no parallax error occurred. If I were to use a spring balance to measure the chip of the potato, parallax error could occur. However, using an electronic scale could have resulted in systematic and zero error which could change my results significantly.
I have also made sure that while measuring the chip, there was no zero error occurring. Zero error could have been the possible reason for anomalous results in the preliminary experiment. I have made sure that the scale displayed 0.00, in order to get an accurate value of the chip and to make my results reliable.
It was also very hard in my experiment to make sure that each chip had a same surface area. The chips could possibly have different surface area. Although, we too care while measuring the length and width to make sure the difference of surface area between chips was minimal. I would also like to use a ruler with even smaller increments, such as tenth of millimetres to make sure that the length and width of the chip is very accurate.
Despite the fact the chips could have different surface area; other controlled variables were kept the same throughout the experiment so my experiment can be considered reliable. I also carried the experiment three times for each concentration, doing this improves the reliability of the experiment. Doing three repeats for each concentration also increases reliability of the results.
I also used concentration of solution ranging from 0%-100%, I believe I have used sufficient amount of concentrations to draw a conclusion. If I were to repeat the experiment, I would change the concentration in the experiment by 5% rather than 10%, this will allow me to work with a range of results.
There could also be a human error in my experiment. For instance, I could have blotted one of the chips with filter paper more than the other; this would have resulted in a lower mass of the chip while weighing it. Human error could have been the reason for anomalous results. Other reasons for anomalous results could have been due to:
Inaccurate measurements of the sucrose solution
Systematic/ zero error while weighing the chip
Pipette
I also waited 5 seconds after I place the chip on the scale to measure it, so that the figure was settled. I also used an agar plate to ensure that potato chips were not touching the sides.
The range of concentrations I used in the experiment are sufficient enough to
Even though, I chose 10 mins prior to 5 mins for my real experiment, I would still like to change the time, I would make the time to 30 mins. This time would allow the process of osmosis to occur fully. Therefore, allowing me to collect clear data which shows the true difference made by each concentration.
I would also consider using a precise, accurate and better weighing scale to measure the mass of the potato. Even though, the scale was accurate and precise. The weighing scale was constantly fluctuating which didn’t allow me to get an accurate reading. I would like to use a scale which doesn’t fluctuate and has higher level of precision- it should be able to measure to 3dp. This would also make my experiment and the results obtained reliable.
Conclusion:
Error bars
The error bars have quite a small range. This means that my experiment is reliable. The error bars are not far apart; this implies that the results have been recorded in a similar way. This also tells us that the controlled variables such as, ‘type of cell’ have been maintained throughout the experiment.
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