(i) The movement of nutrient elements through the various components of an ecosystem is called biogeochemical cycle. Another name of biogeochemical cycle is nutrient cycle. Biogeochemical cycles are of two types: the gaseous and the sedimentary cycle. Example of gaseous cycle is nitrogen and carbon cycle. Example of sedimentary cycle is sulphur and phosphorus cycle.

The reservoir for gaseous type of nutrient cycle exists in the atmosphere and the reservoir for sedimentary cycle exists in the Earth’s crust.

Nitrogen is a major constituent of the atmosphere comprising about seventy eight percent of the atmospheric gases. Nitrogen fixation is a process by which nitrogen in the air is converted into ammonia or related nitrogenous compounds. The principal source of free nitrogen is the action of soil micro organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil. Nitrogen is fixed into the atmosphere by lighting and cosmic radiation. Nitrogen fixation is essential to life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen containing organic compounds, such as amino acids, proteins and nucleic acids.

(ii) Ecological balance is a term used to describe the equilibrium between living organisms such as human being, plants, and animals as well as their environment. It is a state of stability where species coexist with other species and with their environment. This occurs through competition and cooperation between different organisms where population remains stable. It is important because it leads to the continuous existence of the organisms. It ensures that no particular species is exploited or overused. Ecological imbalance is a disturbance in the balance of an ecosystem. It may be disturbed due to the introduction of new species, natural hazards or human causes.

The important measures needed to prevent ecological imbalances are:

*Creating awareness: Government should make aware people about the use of eco friendly practises through media.

*Population control: Controlling the human will reduce the strain on the ecosystem by reducing the rate at which people consume natural resources.

*Proper management of natural resources: A strong effort to use natural resources in a sustainable and efficient manner will help to protect and maintain ecological balance.

*Conservation of natural resources: Recycle to prevent the exploitation of natural resources.

*Afforestation: Plant more and more trees and stop deforestation. This will help in reducing the pressure on our ecosystem.