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Summary of 8 pages for the course Biology at 4 (Exam)
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Organisms and Environment● Ecology deals with interactions among different organisms and their
environment.
● Organisms get adapted to their environment for their survival and
reproduction.
● The rotation of the earth about its axis brings about changes in the
environment, leading to different seasons. This leads to the formation
of various biomes such as desert, grassland, etc.
● Life not only exists in favourable habitats, but also in harsh and
extreme conditions.
● The environment of an organism can be divided into:
○ Abiotic factors
○ Biotic factors
Abiotic Factors
● Some of the major abiotic factors that interact with the organisms are:
○ Temperature
− It is the most relevant abiotic factor since all
organisms require an optimum temperature for their metabolism
and other body functions. Depending upon their ability to
tolerate temperature range, organisms are of two types
stenothermal (restricted to a narrow range of temperature) and
eurythermal (can tolerate a wide range of temperature).
○ Water − Water also is a major influencing factor. Life on earth is
impossible without water as it forms the major constituent of all
living cells. In oceans where quantity of water is not a limitation,
the quality of water becomes one. Depending upon the ability to
tolerate salinity, organisms can be stenohaline (restricted to
narrow range of salinity) and euryhaline (tolerant to wider range
of salinity).
○ Soil − The nature and composition of soil differs from one place
to another depending upon the climate, weathering process, and
soil development method. The characteristic features such as soil
composition, grain size, percolation, water holding capacity, etc.
, determine the native of the organisms it can support.
○ Light
− The major source of light on earth is the Sun. Light is
essential for plants to perform photosynthesis. Certain plants
become adapted to perform photosynthesis under very low light
since they are constantly overshadowed by tall trees. Many
plants also depend on light for their flowering (photoperiodism).
The availability of light on land is comparatively higher than that
in water.
Responses to Abiotic Factors
● All organisms in order to sustain maximum functionality maintain a
constant internal environment (homeostasis). An organism may adopt
one of the following strategies for homeostasis:
○ Regulate
− Certain animals have the ability to maintain a
constant temperature and a constant osmolarity to keep up their
homeostasis. Mammals have a constant body temperature
(37°C) irrespective of the outside temperature. In summers, to
maintain the temperature, we sweat and in winters we shiver,
which produces heat.
○ Conform
− Animals and plants except mammals do not have a
constant body temperature and their body temperature changes
in accordance with the outside temperature. Such organisms are
called conformers. Conformers have not evolved. They have
become regulators since regulation is energetically more
expensive.
○ Migrate
− The organism can move temporarily from stressful
habitats to more hospitable areas and return once the period
changes. Birds can migrate from cold regions to relatively
warmer regions during winter and viceversa during summers.
○ Suspend
− Some organisms cease to be metabolically active
during stressful period. They suspend all activity and enter a
period of dormancy. For example − Spores in bacteria and lower
plants; and hibernation (winter sleep) and aestivation (summer
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