Organisms : Environmental factors
All living organisms, including human beings live in some sort of
abiotic component of environment, that contains matter and energy. Various environmental
factors can be divided into following two groups:
1. Climatic factors 2. Edaphic factors 3. Biotic Factors. The former two
factors are abiotic components that contain matter and energy.
I. Climatic Factors
These are related to the aerial environment of the organisms e.g. light,
precipitation, temperature, atmospheric humidity, wind, etc.
II. Edaphic Factors
They include the factors related to the soil. e.g. soil composition,
organic matter, soil water, soil air, soil organisms etc.
1. Climatic Factors
Light is a factor of great physiological
importance. It affects structure, growth and activities of organisms
Sunlight is the source of energy for all organisms. Light is essential
for photosynthesis, a process by which green plants synthesise their food on
which rest of the living world depends.
Development of photosynthetic pigments, pigments for floral colour, red -
far red absorbing phytochrome pigments which regulate morphogenetic processes,
induction and regulation of many enzymes are all light regulated processes. 'Photoperiod'
is an important factor in the flowering of plants.
Most living organisms can survive only in a narrow range of temperature
(50-350C). However, there are notable exceptions to it. Certain
bacteria, cyanobacteria (blue green algae), seeds, spores and encysted
protozoans can occur in hot springs or in very low temperature. Many organisms
have developed physiological and behavioural adaptations to avoid extremes of
Temperature varies in various quarters of the earth according to
latitute and altitude. It is also influenced by plant cover, atmospheric
humidity, water reservoirs, air current and snow. According to the change of
temperature with the increase of latitude, various vegetation zone have been
recognized. Similarly , on the basis of change in temperature due to altitude,
many vegetation zones can be observed.
Water is an essential requirement of life. No life can exist without
water. The protoplasm of the cell contins 80-90% of water. The requirement of
water varies from organism to organism. The distribution of organisms depend
upon the extent of the need and special adaptations
for conserving water. Plants of dry area are called xerophytes. They develop modifications to increase water
absorption, reduce transpiration and store absorbed water.
Plants of aquatic habitats are called hydrophytes. They possess aerenchyma
(air containing parenchyma) to support themselves in water. The depth, salt
content, clarity and water currents determine the growth and distribution of
plants in water.
Air currents determine the weather conditions and also affect living
organisms, particularly plants. Wind helps in pollination and dispersal of
fruits and seeds of many plants. It increases transpiration, which may lead to
desiccation and wilting of many plants. Strong winds uproot the plants and
cause lodging (flattening of plants on the ground) of many crops. Areas
frequented by unidirectional winds develop flag trees, which have branches on
one side only. Persistent strong winds restrict the height of plants due to
excessive loss of water by transpiration. The plants of such areas usually
possess strong spreading roots and strong but flexible shoots.
II. Edaphic Factors
Soil is the upper weathered and humus (organic matter) containing layer
of the earth, which sustains plant life and contains numerous living organisms
along with their dead remains. Soil provides water, mineral salts and anchorage
to plants. The characteristics of soil such as its constitution, origin,
temperature range, water holding capacity, aeration, minerals, etc. determine
flora and fauna of a particular place.
A productive, well aggregated soil is composed of mineral matter (derived
from parent rocks as a result of weathering), organic matter, water and air.
ii) Mineral Matter
The physical attributes of the soil are due to the size of the soil
particles. The different particles which are present in the soil vary in their
size and depending on this as the soils have been classified into sandy soils
(sand with poor representation of silt and clay), loam soils (fine sand with
well representation of silt and clay), silt soils (more silt than sand and
clay) and clay soils (soils with high percentage of clay).
Sandy soils are porous and hence well aerated but they have very little
water holding capacity and are chemically inert. Clay soils have a greater
capacity of retaining water and are rich in nutritive salts. They are, however
badly aerated. The loam soils are ideally suited for plant growth because they
possess appreciable porosity or aeration, sufficient nutritive salts and good
water retaining capacity.
iii) Organic Matter
The organic matter (humus) is highly important for all types of soils
because it increases both aeration and hydration. It maintains the structure of
the soil and also provides inorganic salts and some growth promoting substances
to the soil.
iv) Soil Water
Soil water is of paramount importance in the physiology of plants. It
occurs in various forms, such as gravitational, capillary, hygroscopic and
combined water. Rain is the principal source of water for the soil. Water which
flows down due to the force of gravity is known as gravitational water. The gravitational water is not available to
the plants. However, it is a big soil water reservoir and is trapped out
through tube wells.
A certain amount of rain water is retained within the intercellular
spaces of the soil particles in the form of a capillary network. It is called capillary water and is used by the
plants. Some water molecules form a thin sheet of water around soil particles.
It is called hygroscopic water
(water of imbibition). The hygroscopic water is also not absorbed by the
plants. The water, which is bound up in chemicals is called combined water or crystalline water.
(e.g. MgSo4.7H2O). It is not available to plants.
The total water present in the soil is called as field capacity. Addition of water beyond field capacity causes
water logging. It excludes soil air and thus inhibits plant growth. The soils
that have poor water holding capacity, cannot afford luxuriant vegetation. In
such soils, the plants generally show wilting of their leaves.
v) Soil Air
It is essential for the growth of root and micro-organisms. A badly
aerated or water-logged soil will have more of carbon dioxide and lesser amount
vi) pH (Hydrogen ion concentration).
Most organisms thrive in an optimal pH range, pH of soil and water has a
strong influence on the distribution of organisms. Some plants and aquatic
animals require acidic conditions, others need neutral or alkaline conditions.
vii) Mineral elements.
of minerals are essential for normal growth of organisms. Their availability
and concentration control the distribution of microbes, plants, and animals.
Deficiency or absence of anyone, results in abnormal growth. Excess of mineral
is equally harmfull. Plants growing in nitrogen deficient soils have developed
special adaptations for obtaining it. For example, leguminous plants harbour
nitrogen fixing bacteria in root nodules and the insectivorous plants have devices
to trap insects and absorb nitrogen from their bodies. The salts of calcium,
magnesium and phosphorus are most important for aquatic forms. Salinity of soil
and water greatly affects the distribution of organism..
III. Biotic factor
The biotic factor deals with interaction among living organisms. This
along with abiotic component, forms the overall ecosystem.
Under natural situations, organisms live together influencing each other's
life directly or indirectly. Vital processes such as growth, nutrition and
reproduction depend very much upon the interactions between the individuals of
same species and different species. Pollination, seeds and fruits dispersal,
grazing, parasitism and symbiosis are the common examples of such interactions.