Biological activity involves the use of energy that comes from the sun. This solar energy is transformed from the radiant to the chemical form in photosynthesis and from chemical to mechanical forms and heat forms in cellular metabolism.
The sun radiates energy in the form of electro-magnetic waves. This radiation extends from high frequency short wave and gamma rays to low frequency, long wave radio waves. The sun is essentially a thermonuclear reactor with a temperature and composition such that hydrogen is transmuted to helium releasing radiant energy in the form of electromagnetic waves. About 9% of the total energy is in the region of wavelengths from 0.136 to 0.4 microns (µ), ranging from the ultraviolet through the near infrared.

Solar flux is the amount of radiant energy of all wavelengths that crosses a unit area of surface per unit of time, solar flux is estimated to be 1.94 gram cal/ Sq.cm./min for a total of 13 x 1023 g.cal./year. (A. gram cal is the amount of heat required to raise the temperature of 1 gram of water by 1 degree centigrade). Because of the revolution of the earth around the sun and the inclination of the earth’s equatorial plane, the flux at any given spot varies seasonally with latitude. Because of the earth’s rotation, the flux at a given place varies diurnally.Radiant energy in the form of sunlight is used in the photosynthetic process, which converts carbon dioxide and water to sugars is called as photosynthesis process. The organisms which perform this vital function are the producers. Typically they are the chlorophyll - bearing plants, the algae of a pond, the grass of a field, and the trees of a forest. Less significantly in most ecosystems the purple bacteria also assimilate carbon dioxide from inorganic compound with the energy of sunlight. These bacteria are the photosynthetic bacteria; producers also include chemosynthetic bacteria, all of which obtain energy by oxidizing simple inorganic compounds. 

Because the energy incorporated in the producers by photosynthesis is subsequently synthesized into molecules that serve the nutritional requirements of the producers. Organisms whose nutritional needs are made by feeding on other organisms are referred as heterotrophic. A primary consumer (herbivore) is a heterotroph that derives its nutrition directly from plants. A carnivore is secondary consumer if a heterotroph deriving its energy indirectly from the producer by the way of the herbivore. Some ecosystems contain tertiary consumers - carnivores that feed on other carnivores. Omnivores are consumers that they derive their energy from both producers and herbivores. 

Energy movement is unidirectional and non cyclic. Bacteria and fungi which are decomposers or reducers is another major group of heterotrophs in ecosystem. Decomposers do not consume food in the ingestive manner of herbivores or carnivores, they do so by absorption. Enzymes produced within their bodies are released into dead plant and animal material and some of the degraded and digested material products are then absorbed by decomposers, minimizes the organic matter. Through their exo-enzyme digestive activity basic elements bound in protoplasm are released to the environment and there by made available for reuse, primarily by producers but also by other organisms.

Movement of energy and movement of nutrients, these two processes proceed concurrently. Energy movement is unidirectional and non-cyclic. 

These two ecological processes of energy flow and mineral cycling involving interaction between the physicochemical environment and the biotic assemblage are fundamental to the structures of the ecosystem and to the pyramid complex that takes place within ecosystem. 

Energy not only flows unidirectional but is also lost irretrievably from the system in various ways. This loss occurs largely in the form of heat as a by product of metabolic reactions and also by export to the other ecosystems through such agencies as wind, floods and animal movements. Although minerals circulate in an ecosystem there is net loss in several ways by being bound of in the sediments. 

Radiant energy absorbed in the troposphere is also radiated outward in all directions in the far infrared portion of the electromagnetic spectrum. Some of it strikes the Earth and here some of it is in turn radiated. These two energy income components – direct solar radiation and indirect far infrared radiation – heat the lower air, the soil and water at the surface, and the organisms living there, affecting climate, weathering processes and physiological responses. In addition the visible light component of direct radiation is requisite to initiating the photosynthetic machinery.

It is nothing but the development which meets the needs of present generation and also future. Equal standard of living and all resources should be available for future generation also.

Balance between resource and output is needed. Three E’s (earth, ecology and environment) are the central concerns of sustainable development.

It causes whole progress of the community with peace and comfort. The development has to be there not for human being but for other living being also.

Ecological balance is maintained naturally through the prey-predator relationships existing in the nature. Nature keeps control on each and every destructive activity.

Man and his environment :- In initial days, man started using natural resources like water, wood, fruits and so on. He improved his life standards through successive inventions. For the betterness of mankind, he disturbed eco-balance. Eco-balance is disturbed as below-

1) De-forestation:- Animals and bird species starts vanishing. Temperature rise occurs. Food production becomes less.

2) Excessive industrialization:- Air, water, noise and ground pollution problems increased.

3) Spraying of chemical fertilizers in the fields:- It increases air pollution and ground pollution problems.

4) More land acquisition for building constructions:- It reduces the area requirements of other ecosystems

For maintaining eco balance all above things should be in controlled manner.

terns of rainfall, insects and pathogens, and history of human influence. 

The entire assemblage of organisms (trees, shrubs, herbs, bacteria, fungi, and animals, including people) together with their environmental substrate (the surrounding air, soil, water, organic debris, and rocks), interacting inside a defined boundary.

Forests and woodlands occupy about 38% of the Earth\'s surface, and they are more productive and have greater biodiversity than other types of terrestrial vegetation.

Forests grow in a wide variety of climates, from steamy tropical rainforests to frigid arctic mountain slopes, and from arid interior mountains to windy rain-drenched coastlines.

The type of forest in a given place results from a complex of factors, including frequency and type of disturbances, seed sources, soils, slope and aspect, climate, seasonal patterns of rainfall, insects and pathogens, and history of human influence.

These are ecosystems in which fresh water from rivers meets the ocean water, the two being mixed by action of tides.

The degree of mixing of salt and fresh water depend on part of the morphology of the estuary basin, the rate and volume of fresh water flow and the amount of tides in the flow.

The biota of estuaries is in turn regulated by the degree of mixing, however the major components are species restricted to the estuarine situation such as oysters and crabs and those that come from the sea such as shrimp.

The high productivity of estuaries than adjacent sea or river results from being nutrient traps for both physical and biological reasons also estuarine producers which includes sea weeds, marsh grasses as well as benthic algae and phytoplankton are capable of nearly year round photosynthesis.

Further more,r higher the fluctuations of the water level higher is the productivity, tide serving to remove waste and to transport food and nutrients