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International Baccaulaureate Organization
Diploma Programme
San Ignacio de Recalde School
Biology Lab Report-Photosynthetic activity

Candidate Name: Camila Loyola Ochoa
Biology-Standard Level
Diploma Session: November 2012

Photosynthesis is the process by which plants obtain energy from sunlight to transform it to chemical energy. It is converted intosugar and then, by cellular respiration, into ATP.
In this lab report my objective is to detect the photosynthesis performance of an aquatic plant by measuring the color variation in a bromothymol blue solution. This substance is an indicator that changes color as pH of a solution changes. In acidic ones it is yellow and in basic it is blue. The plant we used in this experiment is called Elodea. Itlives in lakes, ponds and rivers. It is common in Brazil, Canada, U.S.A (Washington), and other countries.
Apart from detecting the photosynthesis performance, we also want to reach the original absorbance of the solution by giving more minutes of photosynthesis.

Research question
Is fixation of CO2 evidenced by the bromothymol blue reaction directly proportional to the photosyntheticactivity on a plant?

The fixation of CO2 is going to be directly proportional to the photosynthetic activity on the plant because while the fixation increases the photosynthesis too. And when there is too many CO2 the molecules are going to get saturated so the photosynthetic rate will not continue. That is going to happen with the bromothymol blue reaction. While more minutes we leavethe plant in the solution the photosynthetic absorbance will be reducing to its original absorbance.

* Dependent: Absorbance that evidences CO2fixation
* Independent: photosynthetic activity
* Controlled:
Light intensity and distance from the bulb to the plant sample solution
Time the solution takes staying under the light

* Spectrophotomer UV&VIS(±0.0005A)
* Light bulb
* Bromothymol blue solution
* 1 Elodea plant sample (5.3 cm)
* 25 ml graduated cylinder
* 15 ml test tube
* Straw
* 2 beakers of 25 ml
* 2 spectrophotometry cuvettes
* Dropper
* Towel paper
* Chronometer (±0.005 min⁡)
* Test tube rack

In first place, 20 drops of bromothymol blue solution were put in a 50 ml beaker and10 ml of current water were added. The absorbance of this substance was read at 430 nm.
Then the CO2solution was prepared. The prepared solution was passed to a clean beaker. With a straw inside the solution we blew through it for 20 seconds. Notes were taken and the absorbance was read at 430 nm.
After this, we put the elodea plant sample in the bromothymol blue/CO2solution. All the solutionwas taken to a small test tube. So a small piece of the Elodea plant sample, approximately 5 cm, was introduced into the test tube.
Moreover, the light bulb was turned on and it stayed 10 cm away from the test tube that contained the Elodea sample. This step was kept for 15 minutes and the absorbance of this solution was read at 430 nm too.
Finally the results of the spectrophotometricreading of the different solutions were compared.

Data gathering
First solution (original) table:
In the following table we present the absorbance and the physical characteristics of the first solution we made which is the original solution. We describe it when it was pure and when it contained CO2.
Table 1
Solution | Absorbance(430nm) | Observations |
Number 1(original) | 0.322 | Blue color|
Number 1 with CO2 | 0.829 | Green color |

Elodea Bromothymol/CO2 solution tables:
The next tables present the time the elodea sample stayed inside the solution plus the observations that are the physical characteristics too.
Table 2
Time(±0.005min) | Observations |
At 2min | Little bubbles |
At 4 min | Increasing of bubbles |
Rest of the 15 min | Little bubbles |

And in...
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