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How light intensity affects the rate of photosynthesis
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How light intensity affects the rate of photosynthesis The aim of my experiment was to determine whether intensity of light would affect the rate of photosynthesis in a plant. To do this, I placed a piece of Canadian pondweed in varying light intensities, and observed the amount of oxygen being given off. I used Canadian pondweed because of its unusual quality of giving off bubbles of gas from a cut end, when placed in water. Introduction Photosynthesis occurs only in the presence of light, and takes place in the chloroplasts...
repeat readings and find

an average. To extend my enquiries into the rate of photosynthesis, I

could perhaps try to link in some of the other limiting factors to the

same experiment, as well as investigating them in their own right. It

could also be interesting to explore the effects of coloured lights on the

rate of photosynthesis, which could lead to the question of whether or not

other types of light, such as fluorescent lights or halogen lights, would

have a different effect on the rate of photosynthesis.

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INTRODUCTION This piece of... INTRODUCTION This piece of biology coursework is about how cells use osmosis, how, why and what affect it has on the cells in question. The example I am going to explore this in and to illustrate this is the experiment of potato chips of the same length in different concentrations of a sugar, which in this case the sugar is Sucrose. Aim: - I will investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato chips of given sizes. I will use background theory to help me make predictions and when doing the experiment I will make sure I plan to undertake a fair test and abide by any safety precautions and making sure I control all key variables. I will conduct the experiment and collect the results in a suitable table, and then I will evaluate and conclude what I have found and refer back to the theory. P.6A& P.8A BACKGROUND THEORY Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration until the concentrations are equal. The rate that diffusion happens is dependant on the difference between the two concentrations to start off. The Concentration gradient can decide how quickly diffusion happens. The bigger the difference in the concentration then there is a bigger gradient. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other. The diffusion and concentration gradient can be shown in an example from the small intestine to the blood capillaries: - This concentration gradient diagrams shows how the food can be diffused from area of high concentration in the small intestine to an area of low concentration which is the blood capillaries. The second diagram shows that the diffusion equals the concentration gradient so in the blood capillaries it increases its concentration of food. Importance of diffusion in biology can be shown in that we need diffusion to stay alive. To stay alive the cells take up oxygen because the oxygen is continually being used up in respiration, it's concentration inside the cell is lower than in the blood or tissue fluids. The concentration gradient results in oxygen molecules diffusing into cells from outside. The same applies to Carbon dioxide but in the other direction. Osmosis is the movement of water molecules across a Semi-Permeable Membrane form a region of high water concentration to a region of low water concentration. Semi permeable membrane, another name for it is a partially permeable membrane, it has small holes in it that allows only water molecules pass through other bigger molecules like glucose can not pass through. The water molecules do actually pass both ways through the membrane this is the water movement. But because there are more water molecules on one side than the other there is a steady flow into the region of fewer water molecules into the stronger solution of glucose. This causes the glucose rich region to fill up with water, the water acts like it is diluting it so the concentrations on either side are evened up or have reached equilibrium this can be explained as the water movement. Water potential: - The tendency for water to move through a partially permeable membrane is called its water potential it is at a maximum in pure water. The addition of solutes to water lowers its water potential. The amount the water potential is lowered depends on how much solute is added. This means that the more concentrated solutions have lower water potentials than more dilute solutions. Water will therefore have a greater tendency to move from pure water to any aqueous solution like and form a more dilute solution to a more concentrated one. The reason in thermodynamics terms is that the potential energy of the water molecules on the left is greater than on the right, the potential energy of the water is called the water potential, the steeper the water potential gradient then the greater the tendency for the water particles to diffuse in this direction. Therefore water potential has the capacity to be a system able to lose water. Plant cells Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become turgid when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant stand up into the sunlight and for opening guard cells. When plant cells are placed in high concentrated solutions they lose water by osmosis and become flaccid. Flaccid means the plant cells have shrunk or have become soft and floppy. This is the exact opposite of turgid. The content of the potato cells shrink and pulls away from the cell wall. These cells are said to be plasmolysed. When the plant cells are put in a solution that has the same osmotic strength as the cells they are between turgidity and flaccidity, this can be called incipient plasmolysis. Example: - stomata cells rely on osmosis to become turgid to open pore and to become flaccid to close pore. Animal cell Animal cells do not have a cell wall and can easily burst if they are put into pure water because they take in so much water through the process of osmosis. The cell membrane in animal cells is partially permeable. An example of an animal cell bursting due to osmosis can be shown in an example of red blood cells: - The red blood cells have been placed in distilled water. Their cytoplasm is a strong solution. Water passes through into the cells by osmosis, but animals do not have a cell wall to stop them swelling up too much so they burst, this is called haemolysis. In active transport particles e.g. ions can be moved against the concentration gradient. This movement of ions or any particles against the normal concentration gradient uses a lot of energy. This type of transport is called active transport; it involves the use of energy from respiration, adenosine triphosphate ATP. Cells which that can do more active transport usually have more mitochondria than in other cells. Mitochondria are involved in aerobic respiration and the production of ATP so this is why cells with more mitochondria do more active transport. Energy is needed for active transport: - Isotonic point is the point when the potato chips is either not increasing ion mass or increasing in length, this is where no osmosis is taking place, both the potato cells and the solution have the same molar concentration. Hypertonic is where there is one thing having a higher osmotic pressure than a surrounding medium or fluid under comparison. Hypotonic is where one thing e.g. a potato cell has a lower osmotic pressure than a surrounding medium or fluid which in this case is the sugar solution. P.6A Predictions and extended theory P.8A For this particular investigation I think that when there is a lower concentration of the sugar solution sucrose in the test tube the bigger the length of the potato chip will be. The reason for this is that the water molecules pass from a high concentration, in the water itself, to a low concentration, in the potato chip. Therefore, the chips in higher water concentrations will have a bigger length than in higher sugar concentrations. I predict that the higher the concentration of sucrose sugar then there will be more length lost in the potato chips. I predict at the highest concentrations of sucrose there will be no further decreasing in size because the potato cells have plasmolysed and no more water can leave the cell. If the concentration in the solution is more concentrated than in the vacuole of the potato cell, then water passes out of the cell due to osmosis. When a solution is outside the cell is more concentrated than a vacuole of the cell water passes out due to osmosis, as cytoplasm is pulled away from the cell the entire cell becomes plasmolysed, the vacuole also shrinks. This piece of theory proves that my prediction to be true because it shows the water will pass out of the cell when there is higher concentration out of the cell than in the vacuole of the cell. I predict if a cell is surrounded by pure water or by a sugar solution whose solute concentration is lower than and water concentration is higher than that of the cells contents water will flow into the cell and the cell swells up. The external solutions is said to be HYPOTONIC to the solution in the cell. In contrast I predict that if the cells in the potato are surrounded by a sugar solution that solute concentration is higher and the water potential lower than that of the potato cells then water will flow out of the cell, the cell shrinks. In this case the external solution is said to be HYPERTONIC to the solution in the cells. If the cell has the same solute concentration and water potential as its surrounding solution then there will be no net flow of water. The external solution is said to ISOTONIC. P.4A Key variables & FAIR TEST The Independent variables the things that I am able to change: - Concentration of sugar solution: - The thing that I will be changing in this investigation into the factors affecting osmosis is the concentrations of the solution that helps me to investigate osmosis with potato tissues The different sugar sucrose concentrations will be changed to see the result of the potatoes when placed in sugar solutions placed in different molarities strengths. Dependent Variable things that I have to measure: - The things that I will be measuring in this experiment on osmosis are the initial mass and overall length change of the potatoes placed in different molarities of sugar solutions. I will record the masses in grams by using a balance and the length changes by using a ruler. Weight: - this is one of the dependant variables and so is the final length it is dependant on the rate of activity of osmosis on the tissue of the potato chips. Fixed Variables The things that I will keep the same The things that I have chosen to keep the same in each individual experiment to keep it the experiment a fair test is: - Initial length: - The initial length for all the potato chips will all be the same, this is so that this can be called a fair test and this is to keep the same sizes of each potato tissue. Temperature: - The temperature throughout the experiment will be at room temperature. The room temperature will remain constant because the experiment will be in only one room so the temperature will not fluctuate and affect the results, this will be part of a fair test. Type of potato: - I will also be keeping the same potato through out the whole experiment to as using a different one might give me anomalous results as some might have more water in it then others. Time: - The time or duration that all the chips will be in the different solutions will be the same, it will be 2 days. The time has to be the same because each chip will have the same amount of osmosis, and it will constitute in a fair test. Amount of sugar solution: -The amount will all reach up to 40ml so it is a fair test and there are all equal parts, e.g. one part water and three part sucrose, but the solution should still reach 40 ml. For the experiment to be fair and the results to be considered reliable there has to be a fair test. A fair test can make the results be considered to be reliable and within the experiment reduce the number of errors. All the non variables will be needed to be kept as non variables so the results are not affected and so the results show how only the concentration of the sucrose affects osmosis and not any thing else. I will make sure each solution will have the correct amount of distilled water and sucrose so that each test tube has a solution that comes exactly to 40ml. The measurements for the solutions have to be perfect as to not change the out come of the experiment. I have to ensure that every time I handle the potatoes my hands are clean and dry. This is to stop any kind of contamination and make sure that I do not pass on any extra water onto the potato. If I do not keep my hands clean and dry them then this will affect the results and make my results inconclusive. I will also use the same potato in the experiment so there will less a chance of anomalous results, because of the use of different potatoes. P.2ASAFETY Safety in any experiment is always needed, because if there is no safety then the person doing the experiment and others who are not taking precautions may become injured during the experiment. In the experiment I will use some sharp pieces of equipment like scalpel, peeler, and knife; if they are misused then this could result in injuries. Whilst peeling the potato I should make sure my fingers are not in the way of the peeler or the kitchen knife as they are sharp and can cut the skin on the fingers causing deep wounds. Whilst cutting the potato, extreme care and precision had to be taken with the scalpel as it is very sharp and could easily cause a serious wound. Also I should not be holding the potato in my hand and cutting it, the potato should be put on a white tile so no damage is caused to any surfaces and the person's hands and fingers. When carrying the knife or any sharp equipment I should not run and I should face the sharp end down this could stop any injuries if I were to slip or fall. The other precautions are health ones where after the experiment the people should wash there hands as they have been in contact with any solutions or the potatoes, and if the person conducting the experiment does not wash there hands then they may have a lot of germs on their hands. P.4B APPARATUS & appropriateness of measuring equipment → Sugar solution: - the sugar that will be used in this experiment is Sucrose. → Distilled water: - used to change the molar or concentration of the sucrose. → Measuring cylinders: - measure exact amount of sucrose and distilled water. → Test tubes: - this is where the sugar solution and the potatoes will go in. → Test tube racks: - used to hold all the test tubes. → Potato → Peeler: - used to peel the skin of the potato. → Scalpel or knife: - used to cut the potato into the chips. → Clipper → cling film paper: - to cover the test tubes so no air can come into the test tubes. → Ruler: - to measure the lengths of the cut potato chips to make sure they are 3cm. → Pan balance: - an accurate electronic weighing machine to weigh the potatoes. → Masking tape and pen: - to make the labels for the different solutions. → Tile: - to cut the potato on. → Sieve: - to drain out the solution over a sink. → Paper towels: - to dry potato chips after when I take them out of the solutions. The least count for the ruler that I will use will be 0.1cm because I want to measure the cut potato chips the rulers lowest measurement is 0.1cm or 1mm so this will be the least count that I will use. METHOD P.4B To do the experiment start off by working in a group of three so each person can do a separate thing at the same time. The first person should start off by making the labels for the test tubes: - → cut out some masking tape and label each test tube from the letters A-F → then should note down what the letters solution is made up of: - A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.15 molar, 0.25 molar, 0.5 molar, 0.75 molar and 1 molar. This will be done by adding varying amounts of distilled water to varying amounts of sucrose solution: - A B C D E F SUGAR SOLUTION ml 40 ml 30 ml 20 ml 10 ml 5 ml 0 ml WATER ml 0 ml 10 ml 20 ml 30 ml 35 ml 40 ml MOLARITY molar 1.00 m 0.75 m 0.50 m 0.25 m 0.15m 0.00 m "¢ The second person will make the solutions using the Sucrose sugar and the distilled water. You should use the above table to make the solution "¢ I will do this by using the measuring cylinders and measuring the correct amount of water and sugar solution. "¢ Then I will put the correct molarities I have made into the test tubes, I will do this for one at a time so there is no confusion. The third person should be dealing with the potatoes: - "¢ Get an average sized potato. "¢ Using the knife or the peeler, peel of the skin of the potato. "¢ Then cut the potato into a block which has as all an equal width and length. "¢ Then on the tile using a sharp scalpel and ruler cut ten chips all the same length of 3cm on the white tile. "¢ This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. "¢ Then I would weigh the chips individually on the pan balance and record the weight of the chips and make sure the difference is no more than +0.5 "¢ After this I would then place two potatoes in each of the test tubes. "¢ The top of the test tubes will be covered with cling film paper. "¢ Then I would put the test tubes in the test tube rack. I would leave them for 2 days as this will allow sufficient time for osmosis to happen and the experiment to take place. After these 2 days I will have to take out the chips to measure them: - "¢ First I will do test tube A "¢ I will drain out the solution from the test tube over the sink using a sieve. "¢ Then I will dry out the chips on the paper towels and then measure the chips and then make a note of the results when the chips are dry. "¢ I will put the result as test tube-A results, chip 1, and chip 2, recording the results of the lengths. "¢ I then will do this same procedure for the rest of the test tubes and taking down the results. "¢ I will do it one by one because there will be less chance of any mistakes or errors within the experiment and the recording of the results. P.6B NUMBER OF READINGS & APPROPIATE RANGE The table format that I will show my results in: - Sucrose Solution A-E m=molar Volume of sugar ml Volume of water ml Initial length of chip cm To 1.d. Final Length of chip cm to 1.d.p Change in length of chip 1dp + - cm % change in length of chip to 2.d.p no unit Average % change in length of chip no unit to 1.d.p 1 2 1 2 1 2 1 2 A 1.00 m B 0.75 m C 0.50 m D 0.25 m E 0.15 m F 0.00 m This is the table format I have chosen. The table shows that I have appropriate range because I have used 2 readings for each concentration so I can have reliable results. The 2 readings per concentration can give me an average so I can get a group of reliable results. Each column has the correct heading and the correct measurement unit; it also has the decimal point the numbers will consistently and appropriately be rounded to. I have got a sufficient amount of readings as I have chose 6 different molars concentrations this will make it have a wide and suitable range. P.8b PRELIMINARY WORK secondary sources of info Previous studies and work have shown that the predictions I have made are true. These secondary results show what the percentage of mass change in potato chips in different concentrations molars. Bibliography: - Britannica encyclopaedia 2001 CD-ROM edition. Percentage change in accordance to the varying solutions Concentration Average % change in mass 0.00m +4.9 0.25m -2.1 0.50m -5.2 0.75m -7.9 1.00m -9.7 These results show that the varying concentration of the solution gives a gain or loss of % of mass. The results suggest to me that as the molar or concentration is high then the more mass has been lost. It also shows that the lower the concentration of sucrose the less % of mass lost and when the solution has no sucrose 0 molar then the potato chips actually gain mass. A graph to show the preliminary results: - The result from the graph can explain part of my theory. For example on 0 molar concentration of sucrose which is all water the mass has increased to as my theory states as the higher water concentration the bigger the mass will be and the potato cells have become turgid. The graph shows as my theory states that the higher the concentration of the sugar solution then the potato chip will have a lower mass and flaccid. The graph shows that at 1.00 molar of sucrose the potato cells have plasmolysed and no more water can leave the cell, this is shown because this is were the graph shows that there is no more decreasing in mass. This agrees with my theory and predictions but it proves it about the mass and to some extent a link with the length, but I want to know if this applies to the length so I will conduct my experiment, but this has made me understand and given me an overall impression. OBSERVATIONS O2A, O4A, O4B, O6A, O6B, O8A General observations from the experiment: - After I had taken out the potato chips out of the test tubes I had realized some of the potato chips had swelled up while others had shrunk, this is all due to osmosis. The test tube-E potato chips had volume of water of 40 ml and I could see that the chips in this test tube swelled up and increased its length. In test tube-A there was 40 ml of sugar and I noticed that the potato chips in this test tube had shrunk in length. RESULTS TABLE: - Sucrose Solution A-E m=molar Volume of sugar ml Volume of water ml Initial length of chip cm to 1.d.p Final Length of chip cm to 1.d.p Change in length of chip 1d.p + - cm % change in length of chip to 2.d.p no unit Average % change in length of chip to 1.d.p no unit 1 2 1 2 1 2 1 2 A 1.00 m 40 0 3.0 3.0 2.8 2.7 -0.2 -0.3 6.66 % 10.00 % -8.3 % B 0.75 m 30 10 3.0 3.0 2.7 2.9 -0.3 -0.1 10.00 % 3.33 % -6.6 % C 0.50 m 20 20 3.0 3.0 3.0 2.8 0.0 -0.2 0.00 % 6.66 % -3.3 % D 0.25 m 10 30 3.0 3.0 3.2 3.1 +0.2 +0.1 6.66 % 3.33% +5.0 % E 0.15 m 5 35 3.0 3.0 3.3 3.3 +0.3 +0.3 10.00 % 10.00 % +10.0 % F 0.00 m 0 40 3.0 3.0 3.5 * 3.5 +0.5 +0.5 16.66 % 16.66 % +16.6 % The results table shows that there are hardly any anomalous results which make the results reliable. In each column I have used the same decimal place to make it consistent and to keep the data in an accurate record. There was one unreliable reading and it was changed to a suitable one the reading marked with * shows that it has been changed to a suitable reading. The reading to begin with could have been unreliable because of slight human error which is within experimental error. All the lengths are written in accordance to the least count of the measuring devise. For the lengths of the chips all are to 1.dp because the ruler I used had a least count of 1mm or 0.1cm. The final column I put to 1 decimal place 1.d.p because this will be the most suitable to plot on a graph paper. ANALYSIS A.2A: - From the results of this experiment I have found out that the higher the concentration of the sucrose sugar solution then the bigger the % increase in length of the potato chips. I have also found out that the lower the concentration of the sugar sucrose the more % length of chips is lost in relation to initial length. A.4A A.6A: - graph and line of best fit A.4B: - Pattern in readings: - From the readings results we can get a certain idea of what pattern there is. In the readings of 0.00 molar which is 100 % water this is the point where the maximum amount of water was taken in through osmosis and therefore as the reading shows us the potato chips in this solution had the biggest % increase in length it was + 16.6 %. From the table of readings we can also see that at 1.00 molar of the sucrose solution this is the concentration where the potato chips had lost the most % amount of length it was at "“ 8.3 %. From the readings we can see that results do not double so we know this relationship is not directly proportional. Pattern on graph: - The shape of the graph is a one of a curve, going from + y to - y and in the + x. On the y axis the value go from + 16.6 to "“ 8.0. The graph shows the y-axis is inversely proportional to the x-axis so this indicates to us that the % change in length of the potato chip is inversely proportional to the concentration of the sucrose sugar solution. The patterns on the graph show that as the higher the concentration of the sucrose solution the more % of length is lost, but only to a point. On the graph this point is 0.90 molar, after this point on the graph till 1.00 molar the % change in length stays at "“ 8 %, this point is where the potato cells in the chips have fully plasmolysed so no more mass is lost and the cell stops shrinking in length. At low concentrations of sugar or high concentrations of water the graph gets steeper, for example at the points of 0.1 molar and 0.2 molar on the graph, they show a very steep gradient suggesting the lower the concentration of sugar the higher the % gain in length. Also at the point where there is all water 0.00 molar of sucrose this are where most % gain of length is and the maximum point of the cells in the amount of water they can take in through osmosis. The gradient does change in my graph, it is not consistent this show it is inversely proportional. It gets less steep as x-axis gets bigger or the molar/concentration gets stronger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in length of each molar concentration is becoming closer and closer together. A.6B: - EXPLANATION OF RESULTS WITH THEORY & A.8A: -EXPLANATION OF RESULTS WITH DETAILED THEORY Explanation of readings results and patterns: - At the concentration point of 0.00 molar the % change in length was + 16.6 % this result shows that the most water taken up by osmosis is in a solution which is 100 % water and the potato cells became turgid so the length has increased. It did this because in osmosis the water tries to create equilibrium to go from one high water concentration which was the 0.00 molar solution of sucrose to a low concentration which is the cells of the potato. At 0.00 molar there is high water potential because in pure water this is the maximum. As the results in the table show when the addition to solutes which in this case is sugar sucrose it lowers the water potential which means there is less water moving across the solution to the potato. This is why in the results as it shows that as the concentration of the sugar increases the less water is taken into the cells of the potato from the solution. From the results of the table of reading you can see that at strong concentrations of sucrose sugar at 1.00 molar this is the point concentration were most % of length has been lost. The reason for this is as my theory and predictions state that when plant cells are placed in high concentrations of sugar solution they lose water through osmosis because the concentration gradient makes the water from the cells to go to dilute the sugar solution, this makes the potato cells become flaccid means that they have shrunk in size and they are called plasmolysed cells. The diagrams below show the gradient at which the water from the cell goes to dilute the strong concentration of sucrose sugar by the process of osmosis: - First stage: - the original state. Second stage: - the osmosis makes the loss of water in the potato so the potato shrinks in size as it becomes flaccid. The sugar solution has know been diluted. Explanation of graph results and patterns: - The results from the graph are similar to the ones from the readings table. The reason why the graph gets steeper as the molar increases is because as the concentration is increased in the solution the water in the cell is more than in the solution so the water net movement is from the cell to the solution to dilute the solution. The potato chip becomes flaccid but as much as it can because there is a limit so this I why the points become closer together. There is a limit to how flaccid the potato chip cells become because this I the isotonic point were there is hardly any more increase or decrease the cells in the potato and in length as no osmosis is taking place because the solution and cells in the potato have the same molar concentration. The graph results show that as the higher the concentration of the sucrose solution the more % of length is lost but to a point, this point on the graph is 0.90 molar, after this point on the graph till 1.00 molar the % change in length stays at "“ 8 %, this point is where the potato cells in the chips have fully plasmolysed so no more mass is lost and the cell stops shrinking in length, this is why the graph towards the end of the x-axis straightens out horizontally. The reason why the cells in the chips have fully plasmolysed is because the concentrations of the water or sucrose have both reached an equilibrium point or the isotonic point. Therefore from the results and explanation the isotonic point on the graph is 0.9 molars of sucrose solution. At the point on the graph were there is high concentration of sugar solution the results on the graph show there is a lot of % loss of length of the potato chips. The detailed reason behind this is that if there is a solution that is more concentrated than a vacuole of the cells of potato, water passes out due to osmosis. As the cytoplasm is pulled away from the cell the entire cell becomes plasmolysed and the vacuole shrinks. As the vacuole shrinks, so does the cell and therefore the potato chip decreases in length. In this case the solution is said to be hypertonic. On the graph at low concentrations of sugar the graph gets steeper for example from the concentrations of 0.15 to 0.37, it suggests that lower the concentration of sugar the higher the % gain in length. The reason behind this is that because the potato is surrounded by a sugar solution whose solute concentration is lower than and the water potential is higher than that of the cells contents, then water will flow into the cell and the cells swell up so the potato chips increase in length. The external solution is said to be hypotonic to the solution of the cells. This can be shown on the graph of the results of 0.00 molar, where there is the most % gain in length this is also the maximum point of water the cells of the potato can take up. The points on the graph which show a % gain in length are 0.00 molar to 0.37 molar. A.8A: - My predictions were correct as the theory within my prediction was verified by the results that were obtained from this experiment. The results were backed up by my theory and stated the same ideas and principles that my predictions did. Throughout the analysis of my results I have found results from both the readings and the graph match and this has led me to an overall conclusion of the analysis of results which backs up my original prediction and theory. Therefore the statements I made in the analysis have already been proven by theory and the results from both the readings and the graph; this proves my predictions are correct. The evidence that shows my predictions are correct: - In my prediction I said "I think that when there is a lower concentration of the sugar solution sucrose in the test tube the bigger the length of the potato chip will be." This prediction is supported by my result that is "At the concentration point of 0.00 molar the % change in length was + 16.6 % this result shows that the most water taken up by osmosis in the lowest concentration of sucrose sugar." Another prediction that I made was "the higher the concentration of sucrose sugar then there will be more length lost in the potato chips." This is supported by my results which can be seen from this passage, "From the results of the table of reading you can see that at strong concentrations of sucrose sugar at 1.00 molar this is the point concentration were most % of length has been lost." Another prediction I made was "I predict at the highest concentrations of sucrose there will be no further decreasing in size because the potato cells have plasmolysed and no more water can leave the cell." The results that proved this correct were "The graph results show that as the higher the concentration of the sucrose solution the more % of length is lost but to a point, this point on the graph is 0.90 molar, after this point on the graph till 1.00 molar the % change in length stays at "“ 8 %, this point is where the potato cells in the chips have fully plasmolysed so no more mass is lost and the cell stops shrinking in length, this is why the graph towards the end of the x-axis straightens out horizontally." In my prediction I also said, "If the cell has the same solute concentration and water potential as its surrounding solution then there will be no net flow of water. The external solution is said to ISOTONIC." The result that proved this is "The reason why the cells in the chips have fully plasmolysed is because the concentrations of the water or sucrose have both reached an equilibrium point or the isotonic point. Therefore from the results and explanation the isotonic point on the graph is 0.9 molars of sucrose solution." In my prediction I said "I predict that if the cells in the potato are surrounded by a sugar solution that solute concentration is higher and the water potential lower than that of the potato cells then water will flow out of the cell, the cell shrinks. In this case the external solution is said to be HYPERTONIC to the solution in the cells." This is proven by the results: - "On the graph at low concentrations of sugar the graph gets steeper for example from the concentrations of 0.15 to 0.37, it suggests that lower the concentration of sugar the higher the % gain in length." The predictions that I have made have been supported and been proven by my results, therefore with all this conclusive evidence it can be concluded that my predictions were correct. EVALUATION E-2A The experiment and procedure that I undertook was quite interesting and enjoyable to carry out. It was interesting and enjoyable to do the experiment because the experiment is important and think it has a real relevance as I know what importance osmosis has in biology. The procedure was suitable in this investigation because it was fair and it had all the requirements like the correct equipment and method to find the particular results that were needed. E-4A EVALUATION OF ACCURACY AND ANOMALOUS RESULTS From the graphs line and the plotted points from the results table there is some difference as the graphs line may not go exactly straight through the point. The points are mainly on the graph line but a few are not, these points are not anomalous because they are not far away from the graph line of best fit. This shows that my results are accurate and reliable. Some of the results that were off the line of best fit could have been down to human error in the procedure or little problems in the method. The results just of the line of best fit show some experimental error and the results that I obtained are not anomalous. If you look back on page 13 on the graph you can see I have indicated the points which have shown an error but an error within experimental error and not an anomalous result. On the graph the result points that are off the line of best fit are not very far away from the line of the graph they are in fact quite close, this shows that there are no anomalous results as the results from the readings and results from the graph are the same or similar. E-4B EVALUATION OF METHOD If I were to do this experiment again there would be some definite changes that I would make to make sure that there is as little experimental error and human error as possible so that this will not come up in the results. In the method I would have changed the way I cut the potatoes, next time I should use a machine or device that can cut the potato into an equal square shape where all the dimensions and weight are equal. I would also use another device that cuts the chips into the same length and width, as having chips with the same dimensions will not affect the surface area and affect the rate of osmosis, when I did it I used a knife and scalpel and the dimensions of the chips were not 100 % the same this is due to my human error, this could had affected the results. If I were to do the experiment again I would use a wider range of concentrations, for example I would do 0.0 molar, 0.1 molar, 0.2 molar, 0.3 molar, 0.4 molar, 0.5 molar, 0.6 molar, 0.7 molar, 0.8 molar, 0.9 molar and 1.0 molar. This is a complete range of concentrations of the sucrose solution. This will give me even more reliable results and will back up my predictions more so as the results will be to every 0.1 molar which is very accurate and will allow me to find the isotonic point far more accurately. The other things I will change in the method is I will reconsider the time I allow the potato chips to be in the solution, I will decide the time when I know what the saturation point of the potato chips are so I can decide the appropriate duration the chips should be in the concentration. I could also improved the method by changing the way I measured the different liquids to make the solution and also by changing the way I dried the chips. Some of the small indifferences in the results could have been down to me not drying the chips for the same time and the same way, so if I were to do it again I would find another way to do this. The way I could next time measure the solutions could be with a burette or a pipette, this is so I could measure the amount of fluids accurately, so no mistakes are made on my behalf. E-6A RELIABILTY OF RESULTS Detailed comment on accuracy Concentration Of Sucrose. % From Experiment 1.d.p % From Graph 1.d.p % ERROR 1.d.p 0.00 molar + 16.6 % + 16.6 % 0.0 ÷ 16.6 × 100 = 0.0 % error 0.15 molar + 10.0 % + 9.6 % 0.4 ÷ 9.6 × 100 = 4.1 % error 0.25 molar + 5.0 % + 5.0 % 0.0 ÷ 5.0 × 100 = 0.0 % error 0.50 molar - 3.3 % - 3.2 % 0.1 ÷ 3.2 ×100 = 3.1 % error 0.75 molar - 6.6 % - 6.6 % 0.0 ÷ 6.6 × 100 = 0.0 % error 1.00 molar - 8.3 % - 8.0 % 0.3 ÷ 8.0 × 100 3.7 % error Average % error = 1.8 % The table show that my results are within the acceptable 5 % of experimental error, therefore this proves that my results are reliable and are accurate. Many of my results had no errors and my average % error is only 1.8 % this is small and well inside the 5% accepted experimental error, so there are no anomalous results in context. This tells us that my results in general were accurate and reliable. E-6B FUTHER WORK In this investigation and experiment that I undertook I looked at how the varying concentrations of the sugar sucrose affects osmotic activity in the solution and cell, but more importantly how it affects the length of the potato chips. For further work I would go along this line but investigate some different things. The things that I would investigate are looking into how the varying concentrations of sugar solution affect the % change in mass. I could use the same sugar or I could use a different one like glucose. The other things that I would also change the potato and use a soft fruit like a strawberries or a peach. Other further work which I could under take is an experiment with visking tubing; it will involve a beaker full of pure water and visking tubing containing a sugar solution, there is also a tube there and as the water enters the visking tubing the water rises up the tube. These are just some of the things that I can do to extend my investigation in this area.   

INTRODUCTION This piece of biology coursework is about how cells use osmosis, how, why and what affect it has on the cells in question. The example I am going to explore this in and to illustrate this is the experiment of potato chips of the same length in...

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Aim I am going to...Aim I am going to investigate the effect that different concentrations of sugar solution have on the amount on osmotic activity between the solution and potato chips of a given size. Scientific theory and diagrams For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from a high concentration i.e. in the water itself, to a low concentration i.e. the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in the higher sugar concentration. As a result of this the potato will decrease in mass because there are less water particles in the potato cell than there is outside. In this instance the potato will go flaccid. I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from a high concentration i.e. the water itself, to a low concentration i.e. in the potato chip. Therefore, the chips in the higher water concentrations will have a larger mass than in the higher sugar concentrations "“ this is referred to as being turgid. Water molecule Movement. Semi permeable Membrane. This is an example of Osmosis. The water particles move through the partly permeable membrane from the region of high concentration to the region of low concentration. The diagram on the right is the potato chip. Equipment I will need: Core borers Ruler Knife Sugar solution diluted to 5 different strengths Balance ½ a large potato. Access to boiling equipment e.g. boiling tubes. Method Firstly I got ½ a small potato and used a core borer to remove the pieces of the potato. Once I had got 15 pieces of potato I cut them and obtained their mass in gram. Through careful and precise cutting and boring techniques I attempted to obtain potato samples that were nearly identical in mass in the region of 0.65g. I then got 5 test tubes and filled them with the correct solution here are the 5 solutions:- · 20ml water 0M · 15ml water 5ml sucrose 0.25M · 10ml water 10ml sucrose 0.5M · 5ml water 15ml sucrose 0.75M · 20ml sucrose 1M Then I put 3 pieces of potato in each test tube and labelled the tubes so I knew which one was which. I left them for 24 hours and then weighed them again and plotted a table of results. Diagram of the experiment Was it a fair test? I tried to make it a fair test by trying to make all the pieces of potato the same size and put the same number in each test tube. I used electric scales so they were more accurate and made sure I left them all for exactly the same amount of time. When I weighed them at the end I made sure they were all dry so it would be a fair test. To create a fair test certain aspects of the experiment will have to be kept the same with only one key variable to be changed. They variable that will be changed in my experiment will be the concentration of the sugar solution. By doing this I will obtain a varied set of results from which I hope to draw my conclusion. If any of the following non "“ variables are not kept constant my experiment would not be a fair test. · Length of potato samples to be constant thereby preventing variation in surface area. · I am going to carry out the experiment at a constant room temperature. · I shall treat the potato in the same way e.g. have all been cored without being washed or peeled. · I will the same set of electronic scales and measure in grams to 2 decimal places. · I will measure the potato samples before it is put in the solution and after. · The volume of the solution will be the same in each test tube. Number and range of results I bored 15 pieces of potato using the corer and measured them so they were nearly all the same weight. I put 3 in each test tube so I could get a better set of results. This gave me a wider range of results to work with so I could give a better explanation. My results will be accurate because I have got a lot of results and I have used electric scales so my results are more accurate and reliable. I repeated my results 3 times so they were accurate. I have tabulated and graphed the results on the following pages. Preliminary work Before I did this coursework I did nearly the same experiment but with sultanas, I did not measure the results when I used sultanas I just did it as a trial coursework so I had some experience in what to do. Final prediction and plan I knew roughly what would happen because I knew that one would swell up and that one would go down so I had a plan really because I did some work in class. Safety procedures v Be careful with core borers to prevent injury. v Wear safety goggles to protect the eye from food products and the solutions. v Be careful carrying glass around the room. v Make sure there is no electricity near water. v I washed my hands every time I handled the potatoes to make sure they were clean and dry to prevent contamination of any kind. I thoroughly to make sure I did not pass on extra water onto the next potato sample. What I found out I found out that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. This is demonstrated clearly in my results with an average percentage change of -27.3% at 1 molar concentration and a 56.5% increase at 0 molar concentration. My results also match with my initial predictions. Evaluation The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create an informative graph. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen and possibly find out the saturation point of the chips. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on. This way would have allowed me to also find out the isotonic point far more accurately. Obtaining the same size sample of the potatoes was the most difficult part of the experiment because even though I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to obtain precise sample sizes to ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. I could have used a burette or dropper pipette. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g. There were not any results that were wildly out of the ordinary. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. Despite this I think that the experiment was successful and I was very pleased with the complete comparison of my results with my initial prediction. Table to show the results of the experiment and the difference in mass of the potatoes. This table shows the weight before the potato was put in the solution, the weight after the potato was in the solution for 24hours, and the difference between the weight before and the weight after and the concentration in molars. There are 3 results in each table because I put 3 pieces of potato in each test tube. There are not really any odd results they are all fairly accurate. I have recorded my results to 2 decimal places for accuracy and consistency. Mass before sample 1 Mass before sample 2 Mass before sample 3 Mass after sample 1 Mass after sample 2 Mass after sample 3 Difference sample 1 Difference sample 2 Difference sample 3 % change sample 1 % change sample 2 % change sample 3 Average % change 20ml sucrose 0.68 0.65 0.64 0.49 0.47 0.47 -0.19 -0.18 -0.17 -27.94 -27.69 -26.56 -27.40 15ml suc 5ml water 0.62 0.63 0.63 0.58 0.51 0.57 -0.04 -0.12 -0.06 -6.45 -19.05 -9.52 -11.67 10ml suc 10ml water 0.63 0.65 0.67 0.63 0.61 0.67 0 -0.04 0 0.00 -6.15 0.00 -2.05 5ml suc 15ml water 0.62 0.63 0.63 0.66 0.69 0.69 0.04 0.06 0.06 6.45 9.52 9.52 8.50 20ml water 0.68 0.64 0.67 0.77 0.72 0.83 0.09 0.08 0.16 13.24 12.50 23.88 16.54   

Aim I am going to investigate the effect that different concentrations of sugar solution have on the amount on osmotic activity between the solution and potato chips of a given size. Scientific theory and diagrams For this particular investigation I think that the lower the concentration...

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