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Osmosis. Aim: To find the molarity of potato tubers cell sap. BIOLOGICAL KNOWLEDGE

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TABLE OF CONTENTS Biological Knowledge ... 3 Explanation ... 3 Types of solutions and its effects on plant cell ... 4 Factors affecting rates of osmosis ... 6 Outline Method ... 9 Apparatus ... 9 Materials ... 9 Risk Assessments ... 9 Precautions ... 9 Apparatus Diagrams ... 10 Factors to be controlled ... 11 Method ... 11 Calculations to be used ... 12 Predicted Results ... 12 Prior Test ... 13 Obtaining Evidence ... 16 Apparatus ... 16 Materials ... 16 Risk Assessments ... 16 Precautions ... 16 Method ... 17 Results obtained for Mass ... 18 Results obtained for Length ... 19 Analysis ... 21 Trends in the Bar charts ... 25 Scientific Explanation ... 25 Determination of molarity ... 28 How far I have reached my predicted results ... 30 Evaluation ... 32 Errors ... 32 Accuracy and reliability of my results ... 32 Extension work ... 33 Bibliography ... 33 INTRODUCTION Biology Coursework Aim: To find the molarity of potato tuber's cell sap. BIOLOGICAL KNOWLEDGE Osmosis is the diffusion of fluid through a semi-permeable 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. A semi-permeable membrane is a porous substance that allows unrestricted passage of water, but not solute molecules or ions. The concentration of a solution expresses the relative amounts of the substance constituting the solution. Solutions may be described as dilute, concentrated or saturated. A solution is dilute when it has little amount of solute dissolved in it. A solution is concentrated when it has solute dissolved in it to a high point. A solution is said to be saturated when no more solute can be dissolved in it. Explanation When a substance such as sugar dissolves in water, the sugar molecules attract some of the water molecules and stop them from moving freely. ...read more.


* I was careful in handling all glass apparatus as they are brittle. * I handled the electric points with care and made sure that I did not touch them with wet hands. * I kept all solutions away from the electric points in order to avoid spillage on them. * I made sure that I did not spill anything on the floor. Precautions * I chose fresh potatoes to get accurate results. * I made sure that all potato pieces were submerged in the solution. * I cleaned the Petri dishes to get rid of the dust. * I cut all the potato strips to a same length. * During measurements of water in a measuring cylinder, I checked the lower meniscus to avoid errors. * I checked the Petri dishes and beakers for cracks to avoid any leakage of the solutions. * I labelled the Petri dishes and beakers so that I did not get confused. * I covered all the Petri dishes and beakers so as to avoid the formation of fungi in the glucose solution. * I used 4 different solutions in order to get a range results. * I used 4 potato strips in each solution and took their average length and mass, for my result to be accurate and fair. Method Firstly, I prepared the glucose solutions of 0.25 molar, 0.50 molar, 0.75 molar and 1 molar solutions in labelled beakers. I did this by dissolving the right amount of glucose in 1 litre of water. Then I cut out 20 potato strips from a fresh potato using a cork borer. I resized them all into a length of 3 centimetres. I washed the Petri dishes to get rid of the dust and make them clean. I poured out the glucose solutions in the Petri dishes and labelled them respectively. I then measured the mass of the potato strips and noted them. After that I placed 4 strips in each solution, making sure that they were submerged completely. ...read more.


Since I found a lot of repeated values in my results, I think my experiment was accurate enough to be relied upon. I believe that even in a successful experiment, there is very less chance obtaining a very precise and accurate results. This may be because of human errors or apparatus variations or other factors. Extension Work Apparatus: 1. Microscope 2. Beakers 3. Measuring cylinders 4. Blade 5. Cover-slip 6. Pipette 7. Blotting Paper Materials: 1. Rhubarb Stalk 2. Glucose solutions (0.25 molar, 0.50 molar, 0.75 molar and 1 molar) Another experiment could be done by plasmolysis. I would need to peel a small piece of epidermis from a red area of a rhubarb stalk. Then I will have to place the epidermis on a slide and pour a drop of water over it with a cover-slip and pour sugar solution which consists of 0.50 molar glucose solution at one edge of the cover-slip with the help of a pipette. Then I would draw the solution under the microscope. This could be done by putting a piece of bolting paper on the other side. While doing this, I could study different cells under a microscope in order to see any change in their length using a micrometer. We could observe the effect on the size of the stalk cells by using various concentrations of glucose solution (0.25 molar, 0.50 molar, 0.75 molar and 1 molar). My prediction for this experiment is that, in case of glucose solutions the cell would shrink as water would flow out but for water there would be an increase in its size, making it turgid because of the water that will enter by osmosis. For each solution, we will note down the final length of the cell and find the difference from the initial length and calculate the percentage change. Then, plot a line graph with 'concentrations' in the x-axis and 'percentage change' in the y-axis and find out the molarity. The value of the point, the line would intersect the x-axis would give us the isotonic point and the molarity of the cell sap. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

This is a well structured and detailed report.
1. The sources of information need to be referenced.
2. There is some repetition of information that should be removed.
3. The analysis sections should be condensed down into one section.
4. The evaluation is good but needs to discuss reliability.

Marked by teacher Luke Smithen 23/07/2013

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