Agar IB Lab DCP Practice 2015 DP

Topics: Sodium hydroxide, Molecular diffusion, Cube Zero Pages: 10 (2400 words) Published: June 4, 2015
3DIFUSSION IN AGAR CUBES – LAB REPORT
Research Question: What is the effect of surface area on volume ratio on the rate of diffusion of pigment from the agar cube measured by percentage volume of diffusion over time?

Background Research:
Diffusion is the passive movement of molecules or particles along a concentration gradient, or from high to low concentration regions. Essential towards living organism’s functions, as it describes how the nerve cells are able to communicate with each other, through electrical signals in other cells. Diffusion can also be used to describe the cells exchange of toxic gasses for life sustaining gases. Some factors that can affect diffusion are temperature, and concentration difference. As the rate of diffusion will increase along with the temperature; as well as due to a concentration difference, the higher the difference in concentration- the faster the two solutions will diffuse. As both the solution and the agar are colourless I will use agar that had before been mixed with phenolphthalein. Phenolphthalein is a solution used as an indicator often used in titration focused labs. This is because it helps identify acidic and basic solutions, as phenolphthalein will either turn pink in basic solutions or colourless in acidic solutions. This will help us observe diffusion, in our lab because the agar cubes- which have been made with phenolphthalein, and is evenly distributed through the entire agar cube. When the agar cube comes in contact with Sodium Hydroxide (NaOH) it will turn pink, and will continue to do so as diffusion occurs, and the Sodium Hydroxide solutions begins to be absorbed into the agar cubes, allowing us to later identify the distance the Sodium Hydroxide solution travelled over time. We want to examine whether ad how the rate of diffusion over time is dependent on the cubes surface area to volume ratio (SA:V). Smaller cubes have bigger SA:V than big cubes. We know that e.g. cells seek to have the biggest surface area possible and a small volume. We will therefore see, whether one of the reasons they do it is the rate of diffusion.

Hypothesis:

If the sizes of the cubes are varied, then the distance that the Sodium Hydroxide solution travels in the agar cubes after 6 minutes will vary because the rate of the diffusion over time will be dependent on the surface area to volume ratio, and will travel a greater distance in the smaller cubes than in the larger ones, as the smaller cubes will have a greater Surface area to volume ratio.

Variables:

Dependent (what is being measured):

The Distance that the NaOH solution will travel in the agar cubes after being in the solution for 6 minutes.

Independent (what are you changing):

Time (10/min)
The Sizes of the cubes; 2.4cm, 1.6cm, 0.8cm

Controlled (what is not changing):

The amount of the solution in the cup/Beaker.

Controlling the Variables:

What is being controlled?
Why and how?
Type of solution: Sodium Hydroxide (NaOH) a basic solution
As it is a basic solution the colourless agar cubes will turn pink, as they have been made with phenolphthalein. A basic solution is being used instead of an acidic solution because the colourless agar cubes will remain colourless and make it difficult to analyse data found. The solution temperature: 24.5 *C

The solution temperature is kept at a room temperature, in order to prevent the temperature to affect our data being collected. It was also kept at a room temperature, in order to keep a regular diffusion pace. As the rate of diffusion would either be too slow if the temperature was too cold, or too high if the temperature was too high and make it difficult to collect proper data. Time we keep the cubes in the solution: 6 minutes

The agar cubes were kept in the solution for an even amount of time, so that we can observe the distance the solution travelled after a constant amount of time. The agar cubes were also not kept in the solution for a long...


Bibliography: 1. Katarzyna Zaremba, „IB DIPLOMA PROGRAMME BIOLOGY SL AND HL STUDENT HANDBOOK”
2. „Writing a good biology lab report”, http://signatureibbiology.wikispaces.com/file/view/The+Perfect+Biology+Lab+Report.doc, , Web, 11.09.2014
3. „How to write a good biology lab report”, http://www.ibsurvival.com/topic/13178-how-to-write-a-good-biology-lab-report/, 21.02.2014, Web, 11.09.2014
4. „Diffusion”, http://en.wikipedia.org/wiki/Diffusion , 07.09.2014, Web, 12.09.2014
5. „Sodium hydroxide”, http://en.wikipedia.org/wiki/Sodium_hydroxide, 21.08.2014, Web, 13.09.2014
6. „What does stansard deviation show us about our data”, http://science.halleyhosting.com/sci/soph/inquiry/standdev2.htm, Web, 16.09.2014
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