When making a biosphere you should realise that nature (and thus your biosphere) is all about cycles and balances. Because your biosphere will be a closed ecosystem, you have to make very sure that there is no cycle that is broken. Only light and heat are capable of going in/out of your biosphere, so all the other essential elements have to be present and available.
One example is the CO2/O2 cycle. Plants use CO2 and produce O2 in sunlight, animals use O2 and produce CO2. This way the cycle is complete and they are in balance. If you make a biosphere with just animals, they slowly consume all the O2 and eventually die from suffocation.
Another cycle you should consider is the food chain. It always starts with a plant or alga, which may be eaten by an animal, which in turn may be eaten by another animal etc. Plants or alga should therefore always be included in your biosphere.You shouldn't forget that all animals and plants eventually die and (as well as the animal-droppings) have to be decomposed for the cycle to be complete. This is done by bacteria, so your biosphere should also include a healthy population of different species of bacteria.
Below are 4 types of organisms that you should at least include:
1. Plants. These are necessary for photosynthesis. This is the production of sugars and oxygen from carbon dioxide, water and light energy. In stead of plants you can also use green algae.
2. Animals. They breath oxygen en produce carbon dioxide.
3. Food for the animals. Preferably a food source that will not run out, so it must replenish itself. Alga is very suitable for this, because most small animals will eat this, and it grows so it will not easily run out.
4. Bacteria. Some bacteria will decompose dead organisms and animal droppings. (Bacteria can also serve as food for the animals.)
Take a few minutes a week to record the changes in your biosphere. This could be very helpful later. See this example.
· Maybe it would be good to let the bottle 'get to rest' before you seal it. This is important because the water and organisms in your bottle come straight from the pond, where the temperature and light intensity are very different from in your house. So, just keep the bottle open for a few weeks to let gases diffuse in and out, and to let the animals and plants/alga find a balance. This sounds like a step which impatient people will 'forget' easily, but I believe it could be a very important step. Also, it is less boring than it sounds to look at an open bottle; you will certainly see life change in these few weeks.
· See if the water fleas will reproduce. If they do, your biosphere could in theory last forever… (Read carefully: in theory :) )
biopshere for a frog