What are four biological systems . …

There are four principal biological systems of the earth. These systems are fisheries, forests, grasslands and croplands. In addition to supplying our food, these four systems provide virtually all the raw material for the industry. However, due to the increasing demand of human beings to such an „unsustainable‟ extent, the productivity of these systems is being hampered. The excessive demand results in deterioration and depletion of these resources. A country where protein is consumed on a large scale, over-fishing is common, which leads to the collapse of fisheries in that area. Grasslands have been turned into deserts and production of crops is decreasing. The forests are destroyed in large proportions to obtain firewood. Depletion of tropical forests has also led to the extinction of several species.