This is a wonderful activity in which students build a self-sustaining ecosystem containing primary producers (microscopic algae), primary consumers (brine shrimps) and decomposers (micro-organisms) inside a lemonade or coke bottle.
So long as you leave the bottle ecosystem on a sunny windowsill, the brine shrimps never require feeding and never run out of oxygen because the photosynthesising algae on which they feed, multiply by asexual reproduction. In turn, the algae never runs out of carbon dioxide, water or mineral salts because they are all recycled.
A book produced by Stephen Tomkins and Michael Dockery entitled ‘Brine Shrimp Ecology – a classroom-based introduction to ecology‘ is available to download copyright free from the British Ecological Society and contains a plurality of resources for ecological investigations including teaching notes, technicians’ guides and background information. The activities are primarily aimed at key stage 3 and key stage 4 students but could also provide the starting point for post 16 biology projects.
Blades Biological (based in the UK but accepting international orders) can supply brine shrimp eggs and algal cultures to get you started.