Science world


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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what is Ecosystem (part – 1)

The interaction between the living organism and the non-living environment is called ecosystem.

ECOSYSTEM – STUCTURE AND FUNCTION: Interaction of biotic and abiotic components results in a physical structure that is characteristic of each type of ecosystem. Identification and description of plant and animal species of an ecosystem gives its species composition. Vertical distribution of different species occupying different levels is called stratification.

The components of the ecosystem are seen to function as a unit:

  • Productivity.
  • Decomposition.
  • Energy flow and
  • Nutrient cycle.

Description of pond as an ecosystem

The abiotic components include all dissolved inorganic and organic substances and the rich soil deposit at the bottom of the pond. The solar input, cycle of temperature, day length, regulates the rates of function of the entire pond.

The producer (autotrophic) includes phytoplankton, some algae and the floating, submerged and marginal plants found in edge of pond.

  • The consumers are represented by zooplankton, free swimming and bottom dwelling animals.
  • The decomposers are the fungi, bacteria especially abundant at the bottom of the pond.
  • Basic events (in terms of function) in an ecosystem:
  • Conversion of inorganic into organic material (photosynthesis) by producers.

Consumption of the autotrophs by heterotrophs.

Decomposition and mineralization of the dead organic matter to release them back for reuse by the autotrophs there is unidirectional flow of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.