Understanding the influence of light on various beings

Hyderabad: Influence of light on vision & behavior:

• Light is essential for vision, to procure food, self-protection, identification and selection of mate for sexual reproduction.
• Light also influences the behavior of organisms
• Some animals are active during the day time are called diurnal animals. Example: Majority of birds, reptiles, mammals.
• Some animas are active during night time are called Nocturnal animals. Example: Earthworms, cockroaches, etc.

Effect of light of Metabolism: The intensity of light influences the rate of metabolism in animals. At lower intensities of light the rate of metabolism slows down, where as in higher intensities it increases.
Effect of light on biological rhythms:

• By definition rhythm is a change that is repeated with similar pattern in a time frame.
• In the bodies of organisms many behavioral activities are repeated at regular intervals and these are called biological rhythms.
• Biological rhythms that occur in a time period of 24 hours are circadian rhythms if the biological rhythms repeat annually (every year), they are called circannual rhythms.
• They are controlled by “biological clocks” present in many living organisms.
• Light has a role in setting/resetting the biological clocks.

Effect of photoperiod on animals (Photoperiodism):

• The duration of the light hours/exposure to light in a day is known as photo period the response of organisms for the photoperiod is called photoperiodism.
•  The response to photoperiod often centers on reproduction and survival (production of flowers, the migration of birds etc)
• The specific day length which is essential for the initiation of seasonal events is called “critical photoperiod”
• The length of critical photoperiod is not the same in all the species, it varies from species to species and also within the same species inhabiting of various latitudes.

For example: When winter sets in Siberia, the light available time period in a day decreases, and so some birds migrate all the way to the new feeding and breeding grounds in various parts of India.

• When it is summer time back in Siberia, they migrate back to their homeland.
•  Note: Exposure of young fowls in poultry to more lighted hours in a day induces speedy maturity and the egg laying process it is familiar example to most of us.
  Bioluminescence:
•  Production of light by certain living organisms is called bioluminescence.
•  The light emitted by living organisms is devoid of infrared rays and so it is called “cold light”
• Example: some jellyfishes(cnidarian), chaetopterus (annelid), firefly (arthopod), squid (molluse), pyrosoma (protochordata) and some fishes.
• It is believed to influence life in the dark habitat by providing intraspecific communication, sexual attraction, attracting the prey, sending protective warning signals, etc.

Effect of UV Rays:-

• The short wave lengths of light ranging from 100nm to 380nm are called ultraviolet rays.

UV Radiation is classified into three categories.
a. UV-C Light – 100nm to 280nm
b. UV-B Light – 280nm to 320nm

• c. UV-A Light – 320nm to 380nm
• UV Radiation kills the microorganisms present on the body surfaces of animals.
• UV Radiations helps in the conversions of sterols present in the skin in to vitamin-d in animals
• Compared to UV-A Ray’s UV-B & UV-C Rays are more harmful to organisms.