The biosphere is part of the earth in which life exists. It is 20 km thick from
the bottom of the ocean to the lower atmosphere. It consists of three layers:
the lithosphere, which is the land on the surface of the earth; the hydrosphere,
which comprises of the water on the earth as well as water vapor in the air; and
the atmosphere, which is made up of the air that surrounds the earth. The living
organisms in the biosphere interact and affect each other in many ways. This is
called a biotic factor. Similarly, there are non-living elements that have an
effect on living organisms, these are considered abiotic factors. Examples of
abiotic factors are air, temperature, water, soil, light, and minerals. In a
biosphere, organisms live in special groupings. For instance, a population
consists of all individuals of a species living in a general area. A community
is a population located in a certain area living among different species. An
ecosystem is yet a larger conglomeration of a population, a community, and
abiotic factors. Ecosystems can be aquatic or terrestrial. The earth's aquatic
ecosystem makes up about 75% of the earth's surface. This aquatic environment is
divided into marine and freshwater environments. The earth's terrestrial
ecosystem is mainly made up of forests and deserts, which make up for 25% of the
earth's surface. The role or function of an organism in a community is that
organism's niche. An organism's niche is an area picked by that organism based
on physical factors such as temperature, light, oxygen and carbon dioxide
content and biological factors such as food, competition for resources and
predators. This niche provides the organism a place to live in. A habitat
remains consistent with an organism's niche as well as provides the organism
with a place to reproduce. In this case, organisms may have the same habitat,
but different niches. There are three types of relationships involving the
interactions between organisms. They are mutualism, commensalism, and
parasitism. Mutualism is a relationship where both organisms benefit from their
interaction with each other. An example is the honey bee and a flowering plant.

Commensalism only benefits one organism, but the other organism is not affected.

Parasitism only benefits one organism and harms the other organism, which most
of the time is the host. In the ecosystem, matter and nutrients are cycled via
biogeochemical cycles such as water, carbon dioxide, nitrogen, and phosphorous.

The burning of fossil fuels contributes to the industrial cycle of carbon
dioxide in the atmosphere. This contributes to the greenhouse effect, which has
been a reason for global warming. Nitrogen is found in the atmosphere and makes
up about 78% of the earth's air mixture. Oxygen makes up about 22% of the
earth's air mixture, and pollutants make up about 1% of the earth's air mixture.

Nitrogen is important in the development of organisms on earth, as the make
compounds such as proteins and amino acid. These compounds are important because
they make up DNA and other compounds crucial to the formation and sustenance of
life. Changes in an ecosystem are brought about by different factors. For
example, ecological succession brings about the replacement of one community by
another in an ecosystem. In other instances, organisms that colonize an area
with no community present are considered pioneer organisms. A climax community
is the final stage of development of organisms and can be disrupted by a major
catastrophe like a volcanic eruption.