Biology
The photosynthesis of cyanobacteria and iron in the ocean
Author
Cécile Bardel, Charles Baudelaire
Target Group
16-17 years old students
Brief Description
The photosynthesis of cyanobacteria and iron in the ocean

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THE PHOTOSYNTHESIS OF CYANOBACTERIA AND IRON IN THE OCEAN

Topic handout (1/2)

Overview and research to carry out

It is widely considered that the first photosynthetic organisms (similar to modern-day photosyntehtic bacteria) appeared in the oceans roughly 3.5 billion years ago. Yet, the oxygen produced by this process only started to appear in the atmosphere from 2.2 billion years ago.  

Geologists put forward the hypothesis that between this period, oxygen released into the oceans couldn’t escape into the atmosphere. Indeed, banded iron formations which contain Iron(III) oxide (Fe2O3) would result in the oxidation of the iron by the oxygen, preventing oxygen accumulating in the water.

The aim is to verify that oxygen produced by photosynthetic organisms in the water could combine with an iron solution. 
Resources

Document: Sample of a banded iron formation (South Africa)

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The grey lines are made up of almost pure Fe2O3.

The brick-red lines are made up of silica, coloured pinkish red by traces of Fe2O3

Document: The different states of iron

Iron, when ferrous ions (Fe2+) are present, is soluble in water. Oxygen in the

aqueous solution is capable of oxidising this form of iron, giving Fe3+ions, which

 crystallise in the form of iron oxide (Fe2O3)

Step 1: Plan an experiment to help to resolve the problem (10 minutes maximum)

Come up with a feasible experiment which would allow you to verify that oxygen produced by photosynthetic organisms in the water could have combined with an iron solution.





THE PHOTOSYNTHESIS OF CYANOBACTERIA AND IRON IN THE OCEAN

Topic handout (2/2)

Step 2: Carry out the experiment to obtain exploitable data

Carry out the computer aided experiment in order to verify that oxygen produced by photosynthetic organisms in the water could have combined with an iron solution.


Step 3: Process the data and present your findings

In the form of your choice, process and present the raw data so that you have the necessary information to respond to the problem. 


Step 4: Used the obtained results to respond to the problem and answer the question

Process the results to verify if oxygen produced by photosynthetic organisms in the water could have combined with an iron solution.




THE PHOTOSYNTHESIS OF CYANOBACTERIA AND IRON IN THE OCEAN

Experiment protocol handout

Equipment available and protocol for using the equipment

Material:


-          Computer aided testing (CAT) with an O2 probe capable of measuring O2

-          Reaction chamber

-          agitator

-          Light source (i.e. lamp)

-          Cyanobacteria

-          Syringe or pipette to inject the cyanobacteria

-          Small 1mL syringe

-          Micro tube containing iron sulfate at 1 mol/L

to verify if oxygen produced by photosynthetic organisms in the water could have combined with an iron solution, carry out the proposed computer assisted experiment:

-       Put the cyanobacteria in the reaction chamber and in darkness

-       Start the recording for 10 minutes

-       Shine a lamp on the suspension at the two minute mark

-       Add 1ml of iron sulfate at 5 minutes



Call the teacher at the end of the experiment for verification and to eventually obtain the results

Health and Safety: Nothing to Report

Handling precautions: Ensure the absence of air bubbles in contact with the head of the probe/measuring tube

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THE PHOTOSYNTHESIS OF CYANOBACTERIA AND IRON IN THE OCEAN

Lab sheet for the teacher

Material for the student:

-          Computer aided testing (CAT) with an O2 probe capable of measuring O2

-          Reaction chamber, agitator

-          Light source (i.e. lamp)

-          Cyanobacteria

-          Syringe or pipette to inject the cyanobacteria

-          Small 1mL syringe

-          Lamp

Webography: Les fers rubanés (Banded Iron Formation) de l'Archéen de Barberton, groupe de Fig Tree (-3,26 à -3,22 Ga), Afrique du Sud http://planet-terre.ens-lyon.fr/image-de-la-semaine/Img364-2011-10-10.xml







S2 - Earth contemporary issues -  Atmosphere, hydrosphere, climate : from past to future

The Photosynthesis of Cyanobacteria and Iron in the Ocean

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Related files

expected result for the experiment 164 KB
The Photosynthesis of Cyanobacteria and Iron in the Ocean 307 KB
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