12th Class

Water as an important ecological factor was first recognized by Warming. On the basis of water requirement plants are divided in to 3 major types : (1) Hydrophytes : They live in abundance of water. They require abundance of water to complete their life cycle. They are of following types : (i) Rooted submerged : The hydrophytes, which are rooted in mud at bottom and remain under water. e.g., Hydrilla, Vallisnaria. (ii) Submerged floating : They are not rooted in the soil but completely submerged and floating e.g., Ceratophyllum, Utricularia. (iii) Rooted with floating leaves : They are rooted in the soil but the leaves are floating on the surface of water e.g., Nelumbo, Trapa, Victoria. (iv) Free floating : They are not rooted in soil and mud. These hydrophytes float freely on the surface of water e.g., Wolfia (Smallest angiosperm), Lemna, Spirodella, Pistia, Azolla, Salvinia. (v) Rooted emergent : more...

Organisms are built up on chemical substances. They require certain chemicals like \[{{N}_{2}},{{O}_{2}},{{H}_{2}},P,C,\] etc. continuously for their survival. These chemicals enter the organisms from the environment and come out after undergoing changes or without changes. Thus these elements tend to circulate in a characteristic path from the environment to the organism and back to the environment. This cyclical path of the elements from the abiotic system to the biotic system and back is called biogeochemical cycles (Bio = living organism; Geo = water, air, earth). As these chemicals form the components of food, these cycles are also called nutrient cycles. Phases of biogeochemical cycles : Each biogeochemical cycle has two phases, namely the biotic phase (organic phase) and the abiotic phase. (1) Biotic phase : It refers to the flow of chemicals in the living organisms through food chain. (2) Abiotic phase : It refers to the distribution and flow more...

Definition : Each of the major terrestrial ecosystems or distinctive terrestrial areas with their group of climax plants and associated animals constitutes biomes. A biome is the largest terrestrial community. Rainfall, temperature range, nature of soil, barriers, latitude and altitude determine the nature and extent of biomes. Major biomes of world : Biomes are often classified in seven categories : (1) Tropical rain forests : The tropical rain forest, a biome occurs in regions of high temperature (average 25°C) and high rainfall (\[200-450\,\,cm\] per year). These tropical rain forests occur in Central America, around Amazon basin in South America, in Africa and in South-East Asia. (i) This biome is characterized by multistoried vegetation (upto five distinct layers or storeys of vegetation). Further maximum biodiversity on land is shown by this biome and it is estimated that one half to two-thirds of all species of terrestrial plants and insects live in more...

All the thousands of ecosystems together constitute the biosphere, which exists as a thin envelope around the earth’s surface. The global environment consists of three main sub division : (1) Hydrosphere : All the water (liquid) component of the oceans, seas, rivers and other island water bodies. (2) Lithosphere : The solid components of the earth crust, rocks, soil and minerals. (3) Atmosphere : The gaseous cover which envelops the hydrosphere and the lithosphere and the atmosphere. The entire inhabited part of the earth and its atmosphere (including the living and the non-living components) forms the biosphere. As a result of manipulation by man, the biosphere has become transformed into a human dominated environment of noosphere \[(noo=\]mind). Role of atmosphere in metabolism : Of much greater significance to metabolism, however, are the biogeochemical cycles of the atmosphere. The air consists mainly of oxygen (20.95 per cent), carbon dioxides (about 0.03 more...

The development of new variety of plants possessing desirable characters from the existing ones is called plant breeding. The crop improvement depends upon favorable environment (Good irrigation, better fertilizers and precautions to avoid losses due to disease) together with superior hereditary characters. This superiority or improvement may be in following respects : (1) Quantitative characters : Increase in yield of seeds, grains, fibres, oil etc. (2) Qualitative characters : Increase in biochemical components as well as taste, milling, baking, cooking etc. (3) Resistance : To diseases, insects, pests, drought, frost, cold, lodging etc. (4) Earliness or lateness : In maturity period or change in maturity behaviour. (5) Adaptability : To wider range of conditions etc. Important plant breeders (1) N.I. Vavilov famous Russian plant breeder, who gave centres of origin of cultivated plants. (2) N.E. Borlaug famous Mexican plant breeder, who was awarded Nobel peace prize (1970) for developing high more...

Cereals : These are the members of family Gramineae and grown for their edible seeds. They are characterised by the presence of caryopsis a type of fruit in which seed wall becomes fused with the ovary to form the husk. The three major cereals are as follows : (1) Rice (Oryza sativa) : The rice plant is an annual herbs attaining a height of \[24\] feet and produces a panicle, an inflorescence consisting of a number of fine branches; it grows best on damp soils where it can be flooded. Paddy is the term used for rice grain surrounded by husk. Basmati rice is cultivated in U.P. and Haryana. It contains about 90% carbohydrate, 8-10% protein, 1% fat and about 1% mineral. Rice bran yields oil. Rice grains are used as a food after cooking; stem, husk etc., Rice flour is an ingredient of idli and dosa. (2) Wheat (Triticum more...

The term 'virus' has been derived from Latin, which means poison or venom or viscous fluid. They remain inactive outside a living host but become active inside the host and multiply in it. They represent a transitional form of life between non–living and living world. Luria (1953) defined virus as "Sub-microscopic entities capable of being introduced into specific living cells and reproducing inside such cells only. "Single virus is called 'Virion', most of the plant virus are RNA virus. Most of the animal virus are DNA virus. (i) Important discovery of virus Carolous causius (1576) recorded first viral disease in tulips.

Mayer (1886) found a disease in tobacco caused by virus and called it tobacco mosaic disease.

Ivanowski (1892), a Russian Botanist, discovered the infectious nature of the viruses. He was the person, who discovered the virus.

Beijerinck (1898) first used the word Virus.

Twort (1915) and more...

(i) Lamarckism : Lamarck (1744 –1829) was one of the most brilliant stars on the horizon of the history of evolution. Though he was a man of great intellect yet he had to cut a sorry figure because of poverty, and secondly, as he could not get the approval of the famous and influential Cuvier. His work was recognized only few years after his death. He was the first naturalist to put forward a general theory of evolution in his famous book.  Philosophic Zoologique published in 1809. His evolutionary theory may be summarised in the form of following laws: (a) The internal forces of life tend to increase the size of an organism : Lamarck believed that there is some kind of internal force which is constantly working in living beings. Its tries to make the animal bigger in size. (b) The necessity in animals to produce new structures : more...

Philosophers and scientists have been busy to solve the riddle as to how the universe and our earth were formed and how and when 'life' originated on earth. The branch of life science for the study of 'Origin of life' and evolution of different forms of life on earth was called Bioevolution or Evolutionary Biology by Mayer, (1970).       The study of universe or cosmos is called Cosmology. Our earth belongs to the Solar system having nine stars called planets constantly rotating around a common Sun. On the basis of the order of the distance from the sun these planets include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto while moon is a satellite of earth. The universe is made up of matter and energy and it was formed about 10 to more...

Life is the part and parcel of the universe and both are very intimately associated with each other. We know that “Life is the most unique, complex organisation of molecules, expressing itself through chemical reactions which lead to growth, development, responsiveness, adaptation and reproduction” that matter has achieved in our universe. Origin of life is a unique event in the history of universe. (i) Ancient theories of origin of life :  Various theories have been put forward to explain the phenomenon of origin of life. A few of them were only speculations while others were based on scientific grounds. These theories are – (a) Theory of special creation : According to a Spanish Priest Father Suarez (1548 – 1617 B.C.), the whole universe was created in six days by the God. First day Earth and heaven, second day sky, third day dry land and vegetation, fourth day Sun, Moon and more...