The natural source of light is the sun,
moon, stars, bioluminescent organisms.
Whatever the energy required for the organism under natural condition
is derived directly or indirectly from the sun. light is an important abiotoc
factor of great ecological and physiological significance.
Light
is essential for synthesis of food by green plants which interns support all
animal life on the earth. It also
responsible for various structural peculiarities and behavioral patterns.
The light is of two type
1.
Visible light: It forms a visible spectrum.
2.
Invisible light: it includes X- rays, ﻻ - rays (Gama),
Cosmic rays, infrared light, radar waves, microwaves, radiation etc.
Composition
of radiant energy:
The solar radiation energy consists of
electromagnetic waves that extend from very short wave length of high frequency
to very long wave length of low frequency.
The
short wave length radiation includes
X- rays, ﻻ
- rays (Gama), Cosmic rays, infrared light
etc.
The visible
spectrum is made up of series of colour ranging from violate, indigo, blue,
green, orange, yellow and red (VIBGOYR).
Effect
of light on animal:
Light is one of the complex environmental
factor which have many effect on animal and acts as important limiting factor for many multisided
activities of the animals. The light affect on different biological process
like pigmentation, reproduction, development, growth, locomotion, migration,
etc and some other structural and behavioral characteristic of animal. Some effects of light on animal which are
summarized as follows.
a.
Effect
on metabolism:
b.
Effect of light on Reproduction
c.
Effect
of light on the development
d.
Effect
of light on eyes
e.
Effect
of light on vision
f.
Effect
of light on pigmentation
g.
Effect
of light on locomotion
h.
Effect
of light on plants:
Effect on metabolism:
Light
has significant effect on metabolism of animal.
In addition to heating the tissue, the absorbed radiations brings about
isolation of protoplasm. It leads to
increase in enzyme activities.
The
animals which live in a cave having a slow rate of metabolism and sluggish in their habit.
Effect
of light on Reproduction:
In many animal, light initiate the annual
breeding activities by activating gonads. Eg. Bird, deer, goat, etc.
Effect
of light on development:
Light in some case accelerate the development whereas in other it retard the development. Eg. Salmon larvae undergoes normal
development only when sufficient light is available. In absence of light the developments not normal
and there is heavy death of larvae.
Effect
of light on eyes:
The degree of development of eyes depends
upon intensity of light available in the environment. In deep sea water where light penetration is not take place in
such conditions eyes are very poorly developed.
Effect
of light on vision:
The most significant aspect of light for man
and for other higher animals. Man is able to see various objects only
in the presence of one or other form of light only.
Effect
of light on pigmentation:
Light energy initiates certain chemical
changes which result in the formation of pigmentation by synthesis of color
pigments.
a. Skin
colour
b. Protective
coloration
c. Color
change
a) skin colour:
Lack of pigment in cave animal is due to absence of light. Due to normal exposure to light leads to
abundance (Hkjiwj) of pigment is take place.
b)Protective
colorations:
Pigmentation of numbers of animals forms
colouration which serves them for protection from enemies. Proactive coloration is simply matching with
surroundings environment or background.
Eg. Leaf insect, chameleon, butterfly, insects etc.
c)
Color change:
Some animals are able to suit the environment
in which they live eg. Insect, fishes, amphibian, reptile etc.
Effect
of light on locomotion:
In some lower animal locomotion is controlled
by light which is termed as Photo
kinesis.
The blind larva of mussel crab moves fast
when exposed to increased light intensity.
Many animals include aquatic animals and insects showed such type of
behavior.
a) Phototaxis:
movement of animal in response to light
stimulus is called as phototaxis.
If the animal moves toward the source of light is
called the Positive (+ve) phototaxis. Eg.
Euglena
If animal moves away from the source of light or to avoid light is known as negative (-ve) phototaxis. Eg. Earthworm, planaria, etc.
a)
Phototropism. When
only a part of an organism shows response to the stimulus is called Phototropism.
a) Photoperiodism:
response of animal to the length of day light
is termed as Photoperiodism.
Eg. Light affect the gonadial actives ad
reproductive cycle, metamorphosis, migration(LFkykarj ) and other life process.
Effect
of light on plants:
Light plays very important role in the life
of plant. Nearly all aspects and activities of plants
are structured by light only. It
involves physiology, growth, reproduction, development, local distribution etc.
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Light |
