Phytoplanktons are found on illuminated surface of water. On the other hand, benthic organisms are found at the sediments of a lake. Three zones in a lake can be identified which are determined by gradients of light, oxygen and temperature from the water surface to bottom.

Littoral zone: It is shallow water zone present at the edge of lake. It bears rooted plants.

Limnetic zone: It is present behind littoral zone and contains often water. Here phytoplankton’s are found in plenty. Light can penetrate from 20-40m.depthdepending on clarity of water.

Profundal zone (dark zone): In this zone light fails to reach. Bottom of lake constitutes benthic region where micro-organisms, snails and sluge etc. are found.

most important role of atmosphere

Role of atmosphere

Air functions as a medium for Locomotion of insets, birds etc. Ozone layer of atmosphere protects the living organisms from harmful radiations of sun.

Air is the source of oxygen, carbon dioxide and nitrogen required for various metabolic activities of living beings. It helps in dispersal of spores, pollen, seeds etc. Air transmits sound for communication. Burning of fire takes place in presence of oxygen.


The gases present in the atmosphere are chiefly oxygen, carbon dioxide and nitrogen which greatly influence the living organisms. Atmosphere is the thick gaseous envelope around the earth. The composition of Atmospheric air is: Oxygen—20.84%, Nitrogen—-78.64%, Carbon dioxide—0.03%, Water vapors—0.1%


Light is a very important of the climatic factors which is directly responsible for the growth, development and differentiation of plants. Similarly, light as a complex physical factor, also affects the colour vision, eye-size, skin pigmentation, Migration, reproduction and biological periodicity of the animals. Thus, light is a Factor of physical and physiological importance.


Size of eye: Marine animals of 500-3,000 meters depth have larger eyes than those found in surface water.

Photo-periodism: It refers to the response of organisms to the duration of sunlight in a day (photoperiod).In many animals’ migration, hibernation and Reproductive behaviors are controlled by relative lengths of day and time. Metabolism: Light increases the enzymatic activities and general metabolic Rate. It also increases photo oxidation and respiration rates. Animals found in Caves have low rate of metabolism.

why air important for us


Gaseous envelope surrounding the earth is called atmosphere. Several concentric Layers can be identified in vertical profile of atmosphere. Density, temperature and Composition differ in these layers. Near the earth’s surface, density is highest and with increase in latitude density decreases. Starting from earth’s surface four concentric layers can be distinguished: Troposphere, Stratosphere, and Mesosphere & Thermosphere. Ionosphere has high quantity of ions and free electrons. They help in reflecting the radio waves signaled from surface of earth. Thus they help in long distance Radio-communications. Satellites are stationed at different heights in thermosphere. INSAT-1B was launched from American Space shuttle, Challenger In August 1983, so, we have an exclusive satellite now in geostationary orbit. It is the only operational satellite now in use around the world with a multipurpose capability; the others are all single purpose satellites. Air is being used as medium for aviation transport. It is main transmitting system for the communication of Sound and human voice.


Small amount of water vapors, dust, salts, smoke is also found. Movement of air up to height of 100 kms occurs largely and is responsible for Mixing up and making the atmosphere homogeneous. Particular climatic conditions and water cycle in an area is controlled by general circulation of air. Troposphere is peculiar in the sense that it contains much of air. Atmosphere provides oxygen, carbon dioxide and nitrogen to living beings.

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is spider an insect?

Although a spider looks like an insect, it is not. Spiders have eight legs whereas the insect have six. Spiders do not have the feelers and Wings which the insect have. An insect’s body is divided into three distinct parts head, Thorax & abdomen whereas a spider’s body has only two parts combined head and thorax and the abdomen.

Infect spiders belong to a different group of animals called arachinds which also include mites, ticks, Scorpions etc.

हालांकि मकड़ी एक कीट की तरह दिखती है, लेकिन ऐसा नहीं है। मकड़ियों के आठ पैर होते हैं जबकि कीट के छह। मकड़ियों के पास कीट के फीलर्स और पंख नहीं होते हैं। एक कीट के शरीर को तीन अलग-अलग भागों में विभाजित किया जाता है, सिर, थोरैक्स और पेट जबकि एक मकड़ी के शरीर में केवल दो भाग होते हैं जो सिर और छाती और पेट को मिलाते हैं। वास्तव में मकड़ियाँ जानवरों के एक अलग समूह से संबंधित होती हैं जिन्हें अरचिन्ड कहा जाता है जिसमें घुन, टिक, बिच्छू आदि भी शामिल हैं।

What is chaparral ?

Chaparral is a type of vegetation which consists of small tree or large bushes with thick waxy or fuzzy evergreen leaves that conserve water. it is unique to the coastal region bordering the desserts such as Southern California and much of the Mediterranean.

These shurbs are able to withstand for sun or frequent summer fires started by lightning. although the tops may be burned off, the roots send up new sprouts the next spring. they are very distasteful or poisonous to goats. That is why they can survive even extensive grazing by goats.

चपराल एक प्रकार की वनस्पति है जिसमें छोटे पेड़ या मोटी मोमी या फजी सदाबहार पत्तियों वाली बड़ी झाड़ियाँ होती हैं जो पानी का संरक्षण करती हैं। यह दक्षिणी कैलिफोर्निया और अधिकांश भूमध्यसागरीय जैसे डेसर्ट की सीमा के तटीय क्षेत्र के लिए अद्वितीय है। ये शरब सूरज या बिजली से शुरू होने वाली लगातार गर्मी की आग का सामना करने में सक्षम हैं। हालांकि शीर्ष को जला दिया जा सकता है, जड़ें अगले वसंत में नए अंकुर भेजती हैं। वे बकरियों के लिए बहुत अरुचिकर या जहरीले होते हैं। यही कारण है कि वे बकरियों द्वारा व्यापक चराई में भी जीवित रह सकते हैं।