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G. Carboni, November 2004
Translation edited by John G. Davies





Figure 1 - Small bottle with pond water that has been kept closed for about 3 years. Inside it, you can see green clumps of photosynthetic organisms. For comparison, a 10 € cent coin is shown.





Two or three years ago, I put some pond water in a little medicine bottle and I closed it with a plastic plug. I forgot about it till, some days ago, I happened to notice it and I saw greenish clots in the water it contained. I was amazed to see this and, while I was thinking they were algae, I wondered how it was possible that some forms of life were able to survive with so little of water, air and without any exchange of materials with the outside.


By examining the green clots from the little bottle close up, I noticed that some of them had a green-yellow color and the other blue-green. Through the microscope, the green-yellow heaps n showed themselves to be green algae. Green algae are a rather heterogeneous group of eukaryotic algae. They are advanced cells like those of protists and multicellular organisms. Many species are unicellular or colonial, other are multicellular and all are aquatic . The blue-green heaps n showed themselves to be made up of blue-green algae or cyanobacteria. The blue-green algae include a lot of species of unicellular algae, with prokaryotic cells. They are primitive cells, similar to bacteria. Both these groups are photosynthetic.. Their differing colors come from the different composition of their photosynthesis pigments.

Most of the green algae I saw were gathered in heaps of cells like those of figure 2. Other organisms were isolated or in groups of two or four cells. The identification of these algae is not easy because there are many species that look similar. Because of the characteristic of forming groups of four cells placed side by side, Scenedesmus make an exception.

Most of blue-green algae I saw, were filamentous, like those of figure 3 and 10. These filaments appear segmented with a cell corresponding to each segment. These organisms are not considered to be multicellular because their cells are not differentiated. There were also spherical blue-green algae. They were rarer and some times they were made of just two or four individuals that had not separated after cell division (figure 5 and 6). Probably, they belong to the genus Chroococcus.

In order to take these photos I used an Optech Biostar B5 microscope with a Nikon Coolpix 800 digital camera that takes 1600x1200 px pictures. To put them in this article, I reduced them to 400x300 px. So, the definition of these reduced pictures is lesser than the original ones, but it is sufficient to describe the forms of life that survived in that bottle.


Figure 2 - Green Algae. 650X.

Figure 3 - Blue-green filamentous Algae and green Algae. 650X.

Figure 4 - Filamentous blue-green Alga and green Algae. 650X.

Figure 5 - Globular blue-green Alga, probably belonging
to the species of Chroococcus limneticus. 400 X.

Figure 6 - Chroococcus turgidus (blue-green alga)
and Scenedesmus (4 aligned cells ). 400 X.

Figure 7 - Amoeba. 400 X.

Figure 8 - Green Algae and blue-green Algae
which seem to be in troubles. 400X.

Figure 9 - Green Algae and shells of Thecamoeba. 250X.

Figure 10 - Filamentous Blue-green Algae
and shell of Thecamoeba. 250X.

Figure 11 - Shell of Thecamoeba. 400X.

Figure 12 - Empty cells. 400X.

Figure 13 - Green Alga of an unidentified species. 650X.


Among the life forms present in this microscopic world of three or four cubic centimeters of water and a similar amount of air, there were some Amoeba and also some rare bacteria. I wasn’t actually looking for rod-shaped bacteria, but I noticed bacteria that were swimming in a spiral path with a steeper pitch than the Spirochaetes that usually are present in pond water. I saw one of these bacteria rotating as it tried to perforate the membrane of an alga. The Amoeba and these bacteria were the only non-photosynthetic organisms I saw in the observed sample. So, it seems the Amoeba was the only consumer in the bottle.

Besides the living organisms, there was a remarkable amount of dead algae, most of which consisted of empty oval bodies about 18 µm long. Probably, they were the cell walls of Green Algae like that in figure 13. There were also a lot of shells of the Thecamoeba species, Centropyxis aculeata, but I didn’t see any living specimens.

Altogether, this micro-world was populated by at least 10 living species, 3 Green Algae species, 4 Cyanobacteria, 1 species of Amoeba and 2 species of bacteria. It is likely the number of species would increase on closer examination.


Inside the algal cell the chlorophyll absorbs sunlight and, using carbon dioxide and water as raw materials, it photosynthesises producing starch and releasing oxygen. Blue-green algae are also able to fix nitrogen and can transform sugars into protein. Other living things feed on plant material. The waste from all these organisms and the dead material decomposes and returns the carbon dioxide into the system. In its turn, oxygen is used by the organisms in the respiratory process, here the energy stored during photosynthesis is made available to the processes of the cell, which include movement. Some other elements such as phosphorous, potassium and iron that make up part of nucleic acids and other compounds are essential to living organisms. Carbon, oxygen and nitrogen are continuously recycled, passing incessantly from the gaseous state into organic molecules and back again.

The light energy needed for these processes is the only external part of the system. As mentioned, sunlight provides the energy necessary to fix the carbon atoms on to sugar molecules. In a subsequent phase, these molecules are broken down in order to recover the energy for the different processes of the cell. At the end of the cycle, the energy is converted into heat that is dispersed. So, the energy used to fix carbon in the plant tissues is the same that organisms use for their metabolism and movement, coming entirely from Sunlight. In the end, the light energy that the Earth receives from the Sun is returned into Space as infrared radiation. In the case of our little bottle, heat is dispersed through its walls. In this way, the system’s energy equilibrium is maintained.

On our planet, the Carbon Cycle is a more complex than in our little bottle, but it is essentially the same. In fact, the primitive atmosphere was rich on carbon dioxide, most of which was absorbed by the oceans. It combined with calcium and magnesium precipitating on the bottom forming carbonate rocks. Another part was absorbed by the algae and plants that formed fossil deposits of coal and oil. Because of these processes, the content of carbon dioxide in the atmosphere went down to very low values of 260 ppm (parts per million). This gas would completely disappear from the Earth’s atmosphere, with the consequence that the life on the Earth would be extinct, if it was not continuously put back in circulation by volcanoes. In fact, carbonate rocks and the coal and oil deposits are carried toward the mantle by the movements of the Earth's crust. Because of the high temperatures of the mantle, these materials decompose and the carbon is freed in the atmosphere as carbon dioxide.

In its turn, oxygen is in equilibrium between two "pumps" which act in opposite directions. The first one is formed by the photosynthetic organisms that produce oxygen as waste; the second one is formed by the rocks that erosion exposes to the air and become oxidized (so they absorb oxygen). The Earth’s primitive atmosphere was devoid of oxygen, but around 4 billion years ago Cyanobacteria started to release oxygen, which however was removed by many oxidizing processes. With the blue-green algae spreading throughout the oceans, the oxygen production increased and about 2,3 billion years ago, the atmosphere started to have a little oxygen. This content kept on increasing until it attained a peak around 30% during the Carboniferous era, about 300 million years ago. Later, the atmosphere’s oxygen content dropped, reaching about 21%, today’s level.

The different speed of the carbon cycle compared with that of oxygen inside our little container might have altered the content of these substances compared with the initial values, which must have been very close to the atmosphere. It would have been nice to have measured the gas composition in that little bottle before opening its cap. How much oxygen? And how much carbon dioxide? What was the pH of the water? What was the energy flow and how did the elements move in this miniature world? Probably, from the intensity of the illumination, from the size of the heaps of algae and from the efficiency of the photosynthesis in those organisms it might be possible to assess the energy flux that characterizes that system.

Nevertheless, by observing those living organisms, I noticed that none of them wasted energy in fast movements. There were some motionless species, the filamentous ones that oscillate slowly, amoeba too were sliding without hurry. There were no fast moving ciliate, flagellate and other protozoa.


Collect water samples from different places and put them into different bottles. Seal them and put them in a quiet place near a window, so they receive light (avoid the direct sunlight). The differing samples you collect will ensure that you obtain microworlds with populations different from each other. At intervals of months or years, you can open these bottles to examine the little world which is formed in them with a microscope. Try to identify the species that are in it and establish what equilibrium has been reached.

Minor elements are very useful for the metabolism of the microorganisms. If you want to enrich your microworlds with trace elements, prepare the following solution and add a few drops. Put some tap water in a small container with a few of grains of soil. Boil it to help the minerals dissolve and to sterilize them. Leave this liquid overnight so the atmospheric gases dissolve in it. Finally, put some drops of it in the bottle. To enrich the microworlds with the carbon dioxide that the algae require, add a few drops of sparkling mineral water. An interesting experiment would be to put identical specimens of water in conditions with varying amounts of air. Controlling the variables would be interesting too. This type of experiment fits well with the requirements for a science fair, but it is necessary to prepare it well in advance.

I think you know the ecospheres, those transparent spheres almost full of water and sealed, which contain some algae and little crustaceans. These spheres hold several liters of water and some hundreds of cubic centimeters of air. Inside them, crustaceans and algae are able to live for years. For the microscopist, the microworlds that can be formed in bottles with a volume of a few cubic centimeters are the equivalent of the ecospheres. Instead of crustaceans, we will have unicellular algae, protozoa and bacteria. Even if the life forms that inhabit these small worlds are microscopic, they prove life is able to continue even in a very limited space.

Ecospheres and Microworlds are models of our planet, which for billions of years has not exchanged substances with the outside, but simply receives light from the Sun and returns infrared radiations into Space. After all, the microworld held in the little glass bottle is a model of the Earth... and of its fragility.

BIBLIOGRAPHY  The Varieties of Algae  A Webserver for Cyanobacterial Research  Chlorophyta the “Green Algae”  Methods in Plant Hystology  Classification and description of the living beings  Division Green Algae  University of Toronto Culture Collection of Algae and Cyanobacteria  Protozoa and all I know about it!!!  Ciliates in the Classroom  Droplet, Amateur Microscopy of the Protozoa

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