Climatic factors; Light

Climatic factors

The climatic factors are non-living factors which are responsible for determining the climatic conditions of an area. The climatic factors include light, temperature, humidity, precipitation, wind, fire, atmosphere etc.

Light

Light is the main source of energy in the earth for the existence of life. The electromagnetic spectrum of light consists of:

• Infra-red rays
• Visible light
• UV-rays

Infra-red rays

These are the longer wavelength (more than 780nm) and helps for keeping the environment warm.

Visible light

The visible light with wavelength 390 to 780nm is made up of a series of colors like indigo, violet, blue, green, yellow, orange and red.

UV-rays

These are the shorter wavelength of about 100-390nm and helps for ionization.

Among all above these, the visible light is the most ecological important because it is necessary for photosynthesis, so called photosynthetically active radiation (PAR). The duration of intensity and color of light keeps great ecological value to living organisms.

Ecological importance of light

• Light is very important for plants in photosynthesis. The duration, intensity, and color of light affect the rate of photosynthesis.
• The light plays the important role in opening and closing of stomata. Mostly the stomata are opened in the light but they are closed in the dark. So, the transpiration rate is influenced by the light.
• Light influence the number and position of the chloroplast. The upper part of the leaf which receives direct sunlight has the greater number of chloroplast than that of the lower part of the leaf.
• Light influenced the movement of plant parts. The effect of light on the movement of plant part is called phototropism. The stem shows positive phototropism whereas root shows negative phototropism.
• Light influenced in the distribution of plants. Some plants grow well in full sunlight called heliophytes or shade hating plants eg: pine, maize etc. while some plants grow well in the shade called sciophytes or shade loving plants. Eg: moss, fern etc.
• Plants show the response in the duration and intensity of light for flowering. On this basis plants are of three types:

Long-day plants- which need photoperiod more than 12hrs/day for flowering.

Short-day plants- which need photoperiod less than 12hr/day for flowering.

Day-neutral plants- plants which show very little or no any response to the duration of light for flowering.

• Light influenced in the movements of animals. The movement of animals towards or away from the source of light is called phototaxis. Eg: Euglena and butterfly show positive phototaxis whereas planaria and earthworm show negative phototaxis.
• Light influenced in the pigmentation of the animal. The animals living in proper light conditions comparatively have more pigment and are colorful. Eg: cave living animals have the lack of skin pigment, whereas animals or humans living in the tropical region have more skin pigment.
• Light is essential for colored and sharp vision in animals so the animals live in a cave, deep sea, burrows etc. have poorly developed eyes and poor vision.
• In some of the animals, the regular activities of migration and reproduction are induced by intensity and duration of light. It has also the important effect on daily behavioral activities of animals. Eg: some animals are nocturnal, whereas some are diurnal.
• Light is essential for the synthesis of vitamin D in humans. 7-dehydrocholestrol gets converted into vitamin D in the presence of sunlight.
• Light influenced on the protoplasm of animals and sometimes the sun rays penetrate the body covers and cause excitation, activation, ionization and heating of protoplasm of different body cells results in the mutational changes in the DNA of various organisms.