Science: Natural Environment: Nutrient, Carbon, Nitrogen and Water Cycle (For CBSE, ICSE, IAS, NET, NRA 2022)

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Nutrient Cycle

Biogeochemical cycle is the cycle in which nitrogen, carbon, and other inorganic elements of the soil, atmosphere, etc. of a region are converted into the organic substances of animals or plants and released back into the environment.

Carbon Cycle

The carbon cycle is the biogeochemical cycle by which carbon is exchanged between soil, water and atmosphere (air) of the earth. It is the most important cycle of the earth and allows for carbon to be recycled by all of its organisms.

Nitrogen Cycle

Nitrogen cycle is the biogeochemical cycle that describes the transformation of nitrogen and nitrogen-containing compounds in nature. Atmospheric nitrogen is the biggest source of nitrogen. Green plants absorb nitrogen in the form of nitrates and nitrites from the soil and water. Animals get nitrogen when they feed upon plants. Nitrogen is an essential component of proteins and nucleic acids in living organisms.

Water Cycle

water is very essential for all living organisms, but the earth has a limited amount of water. The water keeps going from one component of an ecosystem to another component in a cyclic manner which is called the water cycle.

Water Cycle


Adaptations are special features that allow a plant or animal to live in a particular place or habitat.

The living things adapt themselves so that they can:

  • successfully compete for food.
  • defend themselves from attack by other organisms.
  • find favorable conditions to reproduce.
  • respond efficiently to the change in environment.

Aquatic Adaptations in Plants

Aquatic plants are called hydrophytes (hydro: water; phyte: plant) . For a life in water: Hydrophytes have reduced root system as water is easily available, Floating leaves have stomata only on their upper surface while the submerged ones have no stomata at all, the leaves are thin and narrow for example Hydrilla, or long, flat, ribbon shaped for example Vallisneria. These adaptations protect the plant body from any damage due to water currents.

Aquatic Adaptations in Animals

The animals that live in water show the following characteristics:

  • Streamlined body (pointed at both ends) that reduces friction when the animal moves through the water.
  • Smooth, almost hairless body helps aquatic mammals move through the water with little friction.
  • Webbed feet in ducks, (formed from thin skin between the toes) , work like paddles for swimming.
  • Flattened tail that serve as oar.
  • Fins of fish help to swim, steer and maintain balance. A whale has flippers for swimming.

Terrestrial Adaptations in Plants

Terrestrial plants include mesophyte and xerophytes.

Mesophytic Adaptations

  • Mesophytes are terrestrial plants which are adapted to neither a particularly dry nor particularly wet environment. Mesophytes include the majority of terrestrial plants which have the following adaptations
  • Mesophytes generally require a continuous water supply and have large, thin and broad leaves with a large number of stomata on the undersides of leaves.

Xerophytic Adaptations

Xerophytes are desert plants, well adapted to high temperature and water shortages. They are adapted to store and conserve water. The adaptations that xerophytes may exhibit are.

Succulent leaves and stems to store water e. g. cacti. Succulent: soft, fleshy, water storing structures.

Adaptations in Desert Animals

  • Most of the desert animals avoid being out in the sun during the day. Many desert mammals, reptiles, and amphibians live in burrows to escape the intense desert heat. They come out during the night when the temperatures are low.
  • Due to constant exposure to high temperatures, desert animals need to maintain their body temperatures at an optimum level for which some of them have developed long body parts that provide greater body surface to dissipate heat.

Adaptations to Survive in Extreme Cold and Scarcity of Water

The animals which live in cold climates have very thick fur over the body to trap air and insulate it. They also have a layer of stored fat under the skin to give additional insulation. The body shape and size of many cold climate mammals is well adapted to the cold climate. They are round and bulky with short legs, ears and tail. These adaptations help to conserve heat.

Aerial Adaptations in Animals

Aerial animals include a small number of animals that are able to fly in air. These animals come to the trees or land or water for safety or shelter. These are called arboreal animals (which dwell on trees) . They may walk or run on land or glide in air for a short while to land on the tree or ground.

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