Practice Biology Ia: Diffusion

Topics: Standard deviation, Transport phenomena, Molecular diffusion Pages: 10 (2399 words) Published: May 3, 2013
Practice Internal Assessment Report
Christine Zhu
St Pauls Grammar School
Biology HL
Trial 1 & 2: 8/4/13
Trial 3 & 4: 10/4/13
Photo credits: Smarties by Andrew Dean, copyright Rebecca Douglas, retrieved 9/4/13 Smarties Diffusion Experiment


How does changing the colour of smarties affect the extent of its passive diffusion?


Passive diffusion, also known as simple diffusion, is used to describe the exergonic reaction of a substance where the substance passes in the direction of the concentration gradient. Most of the molecules move from the area of high concentration, inside the membrane of a cell, to the outside where there is a lower concentration. No expenditure of energy is used during the transportation; the molecules are moved by their innate kinetic energy. The purpose of the experiment was to model and investigate simple diffusion. This particular investigation was chosen because it is a simple demonstration of the processes of passive diffusion. The variables of concentration and spread are easy to work with; the experiment is also familiar because it has been conducted in year 7. The concentration is an important factor in diffusion. It is expected that a bigger concentration will have a greater concentration gradient and thus more diffusion. In comparison, the smaller concentration will have a smaller gradient and hence less diffusion. Therefore, it is predicted that darker colours will spread better because of the more colour concentration.


Table 1 - Risk assessment and control measures
Risk| Control Measures|
Filter paper- flammable.| Do not expose to flame. After use, dispose of residue appropriately| Pipette Filler - possibility of ingestion of liquid if pipette filler is not used. Organic solvents may cause swelling of the surface layer of plastic, causing cracking.| Properly fitting pipette filler needs to be provided with every pipette.Do not use with organic solvents or clean with organic solvents.| Ruler - Long rulers can be used as swords. Wooden and plastic rulers burn if placed in Bunsen flame.| Do not use inappropriately, do not place near flame.| Water (ice, steam, distilled water, deionised water) H2O: steam may cause severe heat burns. Fingers may stick to surface of ice at low temperatures, causing skin to rip off when finger pulled away. Risk of chemical contamination from ingestion of laboratory water.| Do not drink laboratory water.| Smarties – risk of choking| Do not ingest/attempt to ingest.| Wash bottle – May cause bodily harm| Keep away from eyes, use appropriately|


Table 2.1 - Independent and Dependent Variables
Type| Variable|
Independent| Colour of smarties: * Blue * Orange * Purple * Red| Dependent| Extent of diffusion, measured in centimetres using a ruler|

Table 2.2 - Controlled Variables
Controlled variables| Control measures|
Weight/size of smarties| * The size of a smartie is approximately 1.5cm in diameter and weighs roughly 1.3 grams. * The smarties look similar in size and should weigh about the same| Amount of water| * The amount of water should be the same for each smartie * If amount is different, the extent of diffusion will be inaccurate| Size of filter paper| * The size of the filter paper should be the same for all trials * Four smarties of each colour should go on one filter paper| Position of smartie | * The four smarties on every filter paper should be positioned equidistant from each other and the centre| Time| * The time taken for every trial should be the same for every trial|


* 3x box of smarties
* 11x large filter paper
* 200 ml distilled water
* 1x plastic pipette
* 1x 30cm ruler
* 1x pencil
* 1x wash bottle


Trials 1 & 2
1. Using a ruler and...
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