Current Affairs 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 : Roots are in soil shoots or leaves are partly outside and partly inside the water. Plants show heterophilly (Amphibious plants) e.g., Typha, Ranunculus, Sagittaria, Cyperus. Morphological adaptations (i) Roots of hydrophytes are poorly developed or completely absent in Wolfia, Ceratophyllum etc. Root hair absent but root pockets may be present e.g., Pistia, Eichornia, Trapa. (ii) Stem is reduced in free floating plants e.g., Pistia, narrow and slender in submerged plants e.g., Hydrilla, Ceratophyllum and well developed in amphibious plants e.g., Typha. (iii) Petioles become long, swollen and spongy for floating. (iv) Leaves are usually long ribbon like e.g., Potamogeton, or finely divided e.g., Ranunculus or thin and broad e.g., Nelumbo, Victoria. (v) In some hydrophytes leaves of different forms are produced by same plant. Aerial leaves are not dissected but submerged leaves dissected (Heterophilly) e.g., Ranunculuc, Limnophila. Anatomical adaptations (i) Cuticle absent or poorly developed. (ii) Stomata are absent in submerged plants. Floating hydrophytes have stomata on upper surface e.g., Lotus (epistomatic). (iii) Air spaces are extensively developed in root, stem and leaves. Well developed aerenchyma helps in buoyancy and gaseous exchange. (iv) Leaves have spongy tissues and palisade is poorly developed. As light difuses from all palisade and spongy tissue. Epidermal cells contain chloroplasts for maximum capturing of difused light. (v) Mechanical tissues like sclerenchyma (lignified tissues) and collenchyma are poorly developed or absent. (vi) Vascular tissues are poorly developed. Physiological adaptation (i) Water and mineral nutrients are absorbed through general body surface. (ii) Osmotic concentration or osmotic potential of cells is equal to or is slightly higher than external water. (2) Xerophytes : They are adapted to grow in dry habitats. On the basis of pattern of life cycle, xerophytes are of three types : (i) Ephemerals : They complete their life cycle in a very short period, evade dry season by disappearing, leaving their seeds. They are referred as drought escapers or drought evaderes e.g., Cassia toria, Argemone maxicana, Solanum xanthocarpum. (ii) Succulents (Fleshy xerophytes) : They absorb large quantities of water during rainy season and store water in different body parts. They are common in deserts 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 of chemicals in the non-living environment. Types of biogeochemical cycles : The biogeochemical cycles are classified into two types, namely gaseous cycles and sedimentary cycles. (1) Gaseous cycles : In gaseous cycles the main reservoirs of chemicals are the atmosphere and ocean. e.g., Carbon cycle, \[{{N}_{2}}\] cycle, \[{{O}_{2}}\] cycle, etc. (2) Sedimentary cycle : In sedimentary cycles the main reservoirs are soil and rocks. e.g., Sulphur cycle, phosphorus cycle, etc. Important biogeochemical cycles (1) Carbon Cycle : The cycling of carbon between biotic and abiotic systems is called carbon cycle. It is a gaseous cycle. The main source of carbon is the carbon dioxide \[(C{{O}_{2}}).\,\,C{{O}_{2}}\] is present in the air and water. Air is the main reservoir. \[C{{O}_{2}}\] content of air is 0.03%. Its amount remains constant.     (i) Flow of Carbon into the biotic system : Carbon flows into the biotic system in two ways : (a) Photosynthesis : Carbon enters the biotic system through photosynthesis. In photosynthesis green plants utilize \[C{{O}_{2}}\] and incorporate the carbon of \[C{{O}_{2}}\] in glucose. Glucose is used for the synthesis of other types of carbohydrates, proteins and lipids. These compounds, containing carbon, are stored up in the plant tissues. When plants are eaten up by herbivores, the carbon flows into the body of herbivorous animals through food chain. When herbivores are eaten by carnivores, the carbon enters the body of carnivorus animals. \[6C{{O}_{2}}+6{{H}_{2}}O\to {{C}_{6}}{{H}_{12}}{{O}_{6}}+\text{ }6{{O}_{2}}.\] (b) Formation of shell : The \[C{{O}_{2}}\] dissolved in sea water is utillized by the marine animals like protozoans, corals, molluscs, algae, etc., for the construction of shell. In these animals \[C{{O}_{2}}\] is converted into calcium carbonate \[(CaC{{O}_{3}})\] which is used for the construction of shells. \[C{{O}_{2}}+{{H}_{2}}O\to {{H}_{2}}C{{O}_{3}}\](Carbonic acid) \[{{H}_{2}}C{{O}_{3}}\to {{H}^{+}}+HC{{O}_{3}}\](Bicarbonate) \[HC{{O}_{3}}+C{{a}^{+}}\to {{H}^{+}}+CaC{{O}_{3}}\](Calcium carbonate) (ii) Flow of Carbon into the abiotic system : The carbon of the biotic system flows into the abiotic system in five ways: (a) Respiration : Plants and animals release \[C{{O}_{2}}\] by respiration (biological oxidation). \[{{C}_{6}}{{H}_{12}}{{O}_{6}}\to C{{O}_{2}}+{{H}_{2}}O+\]Energy (b) Decomposition : When plants and animals die, the dead bodies are 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 tropical forests. (ii) Lianas (vascular plants rooted in soil and they only get support of trees for climbing to top) and epiphytes (air plants) are common in this biome due to excess of moisture. Further giant trees of the tropical forest support a rich and diverse community of animals on their branches. (iii) No one species dominates in this biome. (iv) The productivity of this biome is maximum. (v) The trees of this biome possess buttressed trunks and phenomenon of cauliflory (presence of flowers and fruits on main trunk and main branches) is common in this biome. (2) Savannahs : Like tropical forests, savannahs are found near the equator but in areas having less annual rainfall (90-150 cm/year). Some areas near the equator experience prolonged dry seasons. The heat, periodic dryness and poor soils cannot support a forest but have led to evolution of tropical open grasslands with scattered shrubs and trees. (i) The vegetation of this biome support large grazing herbivores like buffalo, zebra, etc., which are food for carnivores like lions, tigers, etc. The savannah also supports a large number of plant eating invertebrates like mites, grasshoppers, ants, beetles and termites. (ii) The termites are one of the most important soil organisms in savannahs. (iii) Indian tropical grasslands are not true savannahs but these are the result of destruction and modification of tropical deciduous forests by cutting, grazing and fire. (3) Deserts : These are the biomes that have 25 cm (10 inches) or less of precipitation annually. (i) Sahara of North Africa, Thar of West Asia and Gobi of Asia are most important deserts. (ii) Annual plants are abundant in deserts and tide over unfavourable dry season in the form of seeds. Succulent plants are characteristics of deserts. Trees and shrubs present in deserts have deep roots. (iii) Desert animals have also fascinating adaptations that enable them to adjust with limited water supply. (iv) Desert plants show phenomenon of Allelopathy, i.e., they secret some chemical substances which inhibit the growth of plants growing in their near vicinity. (v) Deserts show poor biodiversity and their productivity is minimum. 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 per cent), nitrogen (78.08 per cent), water vapour and minute traces of inert gases. Except the inert gases, all these components of air serve as metabolites; each circulates through a cycle in which the organisms play an important role. As all gases are dissolved in natural waters, the hydrosphere maintains an equilibrium with the atmosphere.

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 yielding dwarf varieties like Sonora-64, Lerma rojo 64 etc. He is known as father of green revolution.   (3) Dr. M.S. Swaminathan is pioneer mutation breeder. He has produced sharbati sonora variety of wheat by mutation, which is responsible for green revolution in India. Dr. Swaminathan is called father of green revolution in India. (4) Thomas Fairchild (1717) produced first hybrid plant artificially. (5) Cotton Mather (1761) recognised the process of natural selection in maize. (6) Joseph Kolreuter (1760-66) produced many hybrids in tobacco. (7) Dr. Boshisen : Famous maize breeder. Methods of plant breeding (1) Plant introduction (i) Plant introduction means introducing a plant having desirable characters (e.g., genetic improvement, high yield, disease resistance and vigorous growth) form a region or a country where it grows naturally to region or a country where it did not occur earlier. (ii) If brought from foreign country, it is called Exotic Collection (EC) but if brought from same country, then it is called Indigenous Collection (IC). (iii) Introduced plants may be used directly for cultivation (Primary introduction) or may be used after subjecting to selection/ hybridization (Secondary introduction). (iv) Acclimatization : The adjustment of newly introduced plant to new or changed environment is called Acclimatization. (v) There is a definite procedure for introducing a plant material from abroad and strict plant protection and quarantine laws have been made. If the plant material is found suitable, phytosanitary certificates are issued and only then the plant material is introduced in our country. (vi) New plants are usually introduced in the form of cuttings or seeds. (vii) Portugese traders and East India Company were foreign agencies which introduced many plants in India. National Bureau of Plant Genetic Resources, Delhi (Estd., 1976) helps in plant introduction in India. (2) Selection : It is the picking up of plant having desirable characters (e.g., high yield, disease resistant and vigorous growth) from a given population of plants based on its phenotypic characters. This involves preserving of favourable characters and gradual elimination of undesirable ones. There are two main types of selection : (i) Natural selection : This is a 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 aestivum) : Wheat (rabi crop) is an annual grass and the inflorescence is a terminal spike consisting of \[1520\] spikelets. There are two types of wheats, hexaploid, bread wheat, Triticum aestivum and tetraploid durum wheat, Triticum durum. In India, its cultivation is confined to north-west regions. The important varieties of wheat, grown in India are Sonalika, Kalyan sona, Partap, Sharbati, Sonara, Lerma Roja, Sonara 64 etc. However, \[HD-2135\] and \[HD-2189\] are disease resisting varieties. Wheat straw is used in packing and as fodder. Glutellin is stored protein in wheat. It is consumed in three forms of flour-suji, atta and maida. (3) Maize (Zea mays) : It is the second important cereal crop. Maize is a tall annual grass attaining a height of 4 to 10 feet; plants are monoecious. It is grown in North India and is a kharif or summer crop because maize cannot tolerate frost. In India common varieties grown are Sona, Vijay, Jawahar, Amber etc. The maize grains are very nutritious; they contain high percentage of easily digestible carbohydrates, proteins zein and fats. But lacks two amino acids, tryptophan and lysine. As a result excessive intake of corn causes pellagra-like deficiency disease. The grains are also used in the manufacture of corn starch, glucose and alcohol; also used as a chief food for livestock; the fibre from stem and spathe is used in paper industry. Zein is used for preparation of artificial fibres and as foaming agent in fire extinguishers.  Millets : These are a group of cereals which have smaller and rounded grains. The millets were the first cereals to be domesticated. These are nutritious but have poor bread making capacity. (1) Sorghum (Sorghum vulgare) : Sorghum is staple food for millions of peoples in Asia and Africa. The grains are made into flour, often mixed with wheat, forming a nutritious food. The plants are used as fodder, in the manufacture of brushes, syrup and also in the paper industry and preparation of alcoholic beverages and acetone. Important varieties are Maldhani, Ramkal and Aspuri. (2) Barley (Hordeum vulgare) : Barley is an annual plant attaining a 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 D. Herelle (1917) discovered bacteriophages, a kind of virus which infected bacteria and destroyed them.

M. Stanley (1935) first time isolated tobacco mosaic virus (TMV) in crystalline form and showed that crystals were made up of proteins. Nobel prize was awarded to him for this work.

(ii) Nature of viruses : Viruses are regarded as intermediate between non-living entities and living organisms. It is very difficult to as certain whether they are living or non-living. Some characters of viruses suggest their non-living nature where as many other characters suggest their living nature. The two views are listed below – Viruses are non-living : The following characters state that they are non-living. (a) Viruses have no complete cellular structure. They are not surrounded by cell membrane or cell wall. (b) They do not show cellular metabolism and lack respiration. (c) They possess high specific gravity unlike living organisms. (d) Viruses are active only when they are inside the living host cells. Out side the host, they are good as chemical substances. Thus, they do not have their independent existance. (e) The viruses can be precipitated just like chemical substances. (f) Postulates of Robert Koch are not true for the viruses. Virus cannot grow in “invitro” condition in lab. Viruses are living organisms : The following characters state that they are living organisms – (a) They have definite shape and morphology like that of a living organism. (b) They possess genetic material (DNA or RNA), which determine their structure and development. Genetic material passes from generation to generation in usual manner. (c) All viruses are intracellular obligate parasite and attack specific hosts. The bacteriophages recognise the real bacterial surface. (d) They show property of mutation. (e) They show irritability and respond to environmental conditions such as heat, ultraviolet rays, humidity, drought, alcohol, etc. (f) They can grow inside the host and multiply enormously showing one of the most important property of living organisms. (iii) Chemical composition : Chemically viruses are nucleoproteins. They are made up of central core of nucleic acid. Nucleic acid is only one, either DNA or RNA. This 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 : According to this law, each organ and structure is the product of some continuous necessity in the animals, to develop it. He believed that it was not due to the direct influence of the environment, but acted through the nervous system, the process being very slow. The plants, he said, were directly influenced by their environmental conditions. (c) The effect of use and disuse : Lamarck thought that the continuous use of a particular organ or structure tends to increase its size and its development. On the other hand, disuse results in disappearance of that structure, the process being slow and gradual. He supported this by a number of well-known examples. The long neck of giraffe was the result of continuous stretching to obtain food from the trees (long neck was acquired due to excessive use).  The wings of certain birds Ratitae were not used for long, as there were no formidable enemies and food was available in abundance. So they did not fly and consequently lost the power of flight. Their wings became rudimentary (flightless condition acquired due to the disuse of wings). (d) Inheritance of acquired characters : Lamarcks stated that all the characters, which are acquired in one's own lifetime are inherited by offsprings. Criticism : The greatest draw-back in the Lamarck's work was that it was too theoretical and there were no proofs to support it. His ideas were theoretically sound but practically they had no standing. He met a severe criticism from various workers – (1) The most serious blow came from Weisman who put his theory of continuity of germplasm which states that the inheritance is the sole concern of germ cells. Characters introduced in the germ cells will only be inherited and not those which are present in somatic cells. (2) If the acquired characters were to be inherited, as Lamarck said, the world would have been full of cripples, blinds and deformed persons, as most of these characters are acquired. (3) Some workers have practically proved that mutilations are not inherited by offspring’s even if practiced for generations. Lamarck's second and third 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 13 billion years ago as a red hot, dense, rotating gaseous cloud of cosmic dust called Ylem or primaeval matter. The Ylem consisted of particles of matter (like neutron, proton and electron) and antiparticles of antimatter. Scientists like Lemaitre (1931), Gamow (1948), Dicke (1964) etc. supported the Big-Bang Hypothesis which explains that collision between these particles and antiparticles caused a tremendous explosion to form atoms of hydrogen. Cosmic evolution began with the fusion of hydrogen atoms with progressively heavy atoms of different elements. Stellar systems and stars were formed by spreading of original gaseous cloud into the space and divided into smaller and larger masses. Most of the stars are masses of red hot gases even today. Kant (1755) and Laplace (1796) supported Nebular Hypothesis which explains our solar system to have evolved about 4.5 to 5 billion years ago from a rotating red-hot gaseous cloud containing millions of free atoms of different varieties. First of all sun was formed when this cloud condensed, next the planets were thrown off from the sun and later on, in turn satellites were thrown off by planets. However, Nebular hypothesis was rejected by astronomers of present century like Weizsacker (1944), Alfen (1950) and Hoyle (1955). According to them the sun was originally surrounded by a disk of rotating gas. Later many rotating concentric whorls were formed by break up of the disc and by gravitation and rotation particles of each whorl collected and condensed to form a planet. Our earth was formed about 4.6 billion years ago as a red hot gaseous cloud of free atoms with temperature of 5000o to 6000oC. Structure of present earth : The earth is orange like in shape. Its pole to pole diameter is 12640 km and equatorial diameter is 12783 km. It is about 15 crore km away from sun and about 484000 km away from moon. Due to tremendous temperature gases existed in atomic form but gradually they cooled down in hundreds and millions of years into molten core. According to density other elements got stratified. Earth contains the central solid core, the middle mantle 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 other planets, fifth day fishes and birds, and sixth day human beings other animals were created by God. This theory was based on some supernatural power. (b) Theory of spontaneous generation or Abiogenesis : This theory postulates that life originated from non-living matter spontaneously from time to time. This theory was supported by Plato, Aristotle, Anaximander, John Ray, Needham, Von Helmont, etc., upto the end of seventeen century. Huxley (1870) criticised this theory and propounded the theory “life originated from preexisting life only.”

• Abiogenesis means origin of life from non-living organisms.

(c) Biogenesis : Scientists like Redi (1668) Spallanzani (1767), Louis Pasteur (1866–1862) provided experimental support for the Biogenesis concept of Huxley. Francesco Redi (1668) showed that maggots could not be created from meat. Actually, the smell of meat attracts flies which lay eggs on the flesh. These eggs hatched into flies. Spallanzani (1767) showed that even primitive, unicellular organisms cannot arise from non-living matter. Louis Pasteur (1860-62) obtained air samples in the flasks of broth (yeast and sugar solution) whose drawn-out necks were sealed cooling these contained a partial vaccum. Where a sample was required, the flask was opened. Air was drawn in and the flask was resealed. Flasks were incubated. These flasks which were opened in the streets became turbid while those exposed to dust-free air rarely contained bacteria. Louis Pasteur also, used swan-necked flasks whose long, curved necks permitted exchange of air between outside and inside of the flask, but dust and bacteria were trapped along the wall of the neck. On tilting the flask, the bacteria got washed down into the broth, so that the latter became cloudy due to bacterial growth. (d) Cosmozoic or Extraterrestrial or Interplanetary or Panspermiatic Theory : Richeter (1865), Preyer (1880), Arrhenius (1908), Hoyle (1950) and Bondi (1952) believed in eternity of life. According to Arrhenius life was transferred from “cosmozoa” (life of outer space) to different planets small units called ‘spores’. The spores were covered by a thick protective covering. When the spores got favourable conditions and temperature, the spore coat was dissolved and gave birth more...