Current Affairs 11th Class

Ash analysis : The plant tissue is subjected to a very high temperature (550-600°C) in an electric muffle furnace and is reduced to ash. The plant ash left behind forms a very small proportion of plants dry weight ranging from 2 to 10% only. Analysis of plant ash shows that about 92 mineral elements are present in different plants. Out of these, 30 elements are present in each and every plants and rest are in one or other plants. Out of these 30 elements, 16 elements are necessary for plants and are called essential elements. Solution culture (Hydroponics) : In this method plants are grown in nutrient solutions containing only desired elements. To determine the essentiality of an element for a particular plant, it is grown in a nutrient medium that lacks or is deficient in this element. The growing of plants with their roots in dilute solutions of mineral salts instead of soil led to increased understanding of plant nutrition. This cultivation of plants by placing the roots in nutrient solution is called hydroponics. Probably the first recorded use of soilless culture was by Woodward in 1699. By 1860, the culture solution technique was modernized by Sachs and he showed the essentiality of nitrogen for plant growth. Another significant worker for studying the essentiality of elements was Knop (1865). The method of growing plants in aqueous nutrient solutions as employed by Sachs and Knop is used experimentally and commercially today and known as hydroponic culture. Now a days a chelating agent Na2-EDTA (Disodium salt of ethylene diamine tetra acetic acid. EDTA (Ethylene diamine tetra-acetic acid) is a buffer which is used in tissue cultures) is added. Hydroponics or soilless culture helps in knowing (1) The essentiality of mineral element. (2) The deficiency symptoms developed due to non-availability of particular nutrient. (3) Toxicity to plant when element is present in excess. (4) Possible interaction among different elements present in plant. (5) The role of essential element in the metabolism of plant. Solid medium culture : In this method either sand or crushed quartz is used as a rooting medium and nutrient solution is added to it. The nutrient medium is provided by one of the following methods : Drip culture : It is done by dripping over the surface. Slop culture : It is done by having the medium over the surface. Sub-irrigation : Here the solution is forced up from the bottom of the container.

Higher plants generally utilize the oxidized forms such as nitrate \[(NO_{3}^{-})\] and nitrite \[(NO_{2}^{-})\] or the reduced form \[(NH_{4}^{+})\] of nitrogen which is made available by a variety of nitrogen fixers. Nitrogen can be fixed by three methods : Process of Nitrogen fixation On the basis of agency through which the nitrogen is fixed the process is divided into two types abiological and biological. (1) Abiological : They are two types : (i) Natural or Atmospheric nitrogen fixation : By photochemical and electrochemical reactions, oxygen combines with nitrogen to form oxides of nitrogen. Now they get dissolved in water and combine with other salts to produce nitrates. Physical nitrogen fixation out of total nitrogen fixed by natural agencies approximately 10% of this occurs due to physical processes such as lightening (i.e., electric discharge), thunder storms and atmospheric pollution. Due to lightening and thundering of clouds, \[{{N}_{2}}\] and \[{{O}_{2}}\] of the air react to form nitric oxide (NO). The nitric oxide is further oxidised with the help of \[{{O}_{2}}\] to form nitrogen dioxide \[(N{{O}_{2}}).\] \[{{N}_{2}}+{{O}_{2}}\xrightarrow{\text{Lightening}}2NO\] \[2NO+{{O}_{2}}\xrightarrow{\text{Oxidation}}2N{{O}_{2}}\] \[N{{O}_{2}}\]combines with \[{{H}_{2}}O\] to form nitrous acid \[(HN{{O}_{2}})\] and nitric acid \[(HN{{O}_{3}}).\] The acid falls along with rain water. Now it acts with alkaline radicals to form water soluble \[NO_{3}^{-}\] (nitrates) and \[NO_{2}^{-}\](nitrites). \[2N{{O}_{2}}+{{H}_{2}}O\xrightarrow{{}}HN{{O}_{2}}+HN{{O}_{3}}\] \[HN{{O}_{3}}+Ca\,\,\,or\,\,K\,\,salts\xrightarrow{{}}Ca\,\,or\,\,K\,\,Nitrates\] The nitrates are soluble in water and are directly absorbed by the plants. (ii) Industrial nitrogen fixation : Nitrogen and hydrogen combines to form ammonia industrially, under pressure and temperature. (2) Biological nitrogen fixation : The conversion of atmospheric nitrogen into inorganic or organic usable forms through the agency of living organisms is called biological nitrogen fixation. The process is carried by two main types of microorganisms, those which are "free living" or asymbiotic and those which live in close symbiotic association of with other plants. (i) Asymbiotic biological nitrogen fixation : This is done by many aerobic and anaerobic bacteria, cyanobacteria (blue green algae) and some fungi e.g. : Free living bacteria : Free living N2 fixing bacteria add 10–25 kg of nitrogen /ha/annum. Aerobic                        –             Azotobacter Anerobic                      ­–             Clostridium Photosynthetic         –             Chlorobium Chemosynthetic       –             Thiobacillis Cyanobacteria (blue-green algae) e.g., Anabaena, Nostoc, Tolypothrix cylindrospermum, Calotherix and Aulosira etc. They add \[2030kg\] of \[{{N}_{2}}\]per hactare of soil and water bodies. Free living fungi e.g., Yeast cells and Pullularia. (ii) Symbiotic biological nitrogen fixation : Symbiotic bacteria are found in the root nodules of the members of family Leguminosae. The best known nitrogen fixing symbiotic bacterium is Rhizobium leguminosarum (Bacillus radicicola). Rhizobium penetrates to the cortex of root through infection thread. Simultaneously cortical cells or root are stimulated to divide more vigorously to form nodules on the root. Neither bacterium nor plant alone can fix nitrogen in such cases. Nitrogen fixation is actually the outcome of symbiotic relationship between the two. When a section of root nodules is observed the presence of a pigment, leghaemoglobin is seen to impart pinkish colour to it. This pigment is closely related to haemoglobin and helpful in creating optimal condition for more...

P.R. Stout and D.R. Hoagland (1939) proved that mineral salts are translocated through xylem. After absorption of minerals by root, ions are able to reach xylem by two pathways. (1) Apoplast pathway : In this pathway inflow of water takes place from the cell to cell through spaces between cell wall polysaccharides. Ions thus are able to move from cell wall of epidermis to cell walls of various cells in cortex, cytoplasm of endodermis, cell wall of pericycle and finally into xylem. (2) Symplast pathway : In this pathway ions move through cytoplasm of epidermis and finally move through cytoplasm of cortex, endodermis, pericycle through plasmodesmata and finally into xylem. Minerals in xylem are carried along with water to other parts of the plant along transpiration stream. Minerals reaching leaves take part in assimilation of organic compounds and then transported to other parts of the plant through phloem.

Plants absorb the minerals from the soil and translocate them to other parts of the body. Soil serves as a main source of mineral salts in which clay crystals with a central nucleus is called micelle. The micelles are negatively charged. To maintain the balance, they hold positively charged ions on their surface. When this balance is disturbed by salt absorption, the equilibrium is again restored by transferring some of the absorbed ions into the solution. The movement of ions is called as flux. The movement of ions into the cell is called influx and outward migration of ions is known as efflux. Various theories have been proposed to explain the mechanism of mineral salt absorption and can be placed under the following two categories. (1) Passive absorption : Absorption of ions without the use of metabolic energy is known as passive absorption. This type of absorption is carried out by purely physical forces. In most of the cases, the movement of mineral ions into root occurs by diffusion. Diffusion of molecules is their net movement down a free energy or chemical potential gradient. The rate of diffusion varies with the chemical potential gradient or the difference in activity (essentially equivalent to concentration) across the diffusion distance. Briggs and Robertson (1957) demonstrated the passive absorption of ions by root system. They showed : (i) Mineral salt absorption is not affected by temperature and metabolic inhibitors. (ii) Rapid uptake of ions occurs when plant tissues are transferred from a medium of low concentration to high concentration. Some of the important theories explaining the mechanism of passive absorption of minerals are given below : Mass flow hypothesis : According to Hylmo (1953, 1955), the ion absorption increases with increase in transpiration. The ions have been considered to move in a mass flow with water from the soil solution through the root and eventually to the shoot. The theory was supported by Kramer (1956), Russel and Barber (1960), etc. Later, Lopushinsky (1960) using radioactive \[{{P}^{32}}\]and \[C{{a}^{45}},\]has supported this experiment. Simple diffusion hypothesis : According to this hypothesis, if the concentration of solutes inside the plant is lower than the soil, the mineral ions are thought to migrate into the root by simple diffusion. As a result, a state of equilibrium is reached. The part of plant cell or tissue that permits free diffusion is sometimes called outer space. The apparent volume that accomodates these ions has been referred to by some workers as apparent free space. The accumulation of ions in the cell against concentration gradient can not be explained by this concept. Facilitated diffusion hypothesis : According to this concept, the ions are transported across the membrane by a carrier protein. When the ions enter the cell through protein channels and not through the lipid layer the phenomenon is called facilitated diffusion. Ion exchange hypothesis : According to this view the ions adsorbed to the cell surface are exchanged from the external medium. A cation is exchanged for a cation and anion more...

Various elements perform the following major roles in the plants : Construction of the plant body : The elements particularly C, H and O construct the plant body by entering into the constitution of cell wall and protoplasm. They are, therefore, referred to as framework elements. Besides, these (C, H and O) N, P and S, Mg and Fe also enter in the constitution of protoplasm. They are described as protoplasmic elements. Maintenance of osmotic pressure : Various minerals present in the cell sap in organic or inorganic form maintain the osmotic pressure of the cell. Maintenance of permeability of cytomembranes : The minerals, particularly \[C{{a}^{++}},{{K}^{+}}\] and \[N{{a}^{+}}\]maintain the permeability of cytomembranes. Influence the pH of the cell sap : Different cations and anions influence on the pH of the cell sap. Catalysis of biochemical reaction : Several elements particularly \[Fe,Ca,Mg,Mn,Zn,Cu,Cl\]act as metallic catalyst in biochemical reactions. Toxic effects : Minerals like Cu, As, etc. impart toxic effect on the protoplasm under specific conditions. Balancing function : Some minerals or their salts act against the harmful effect of the other nutrients, thus balancing each other.

The process of mineral absorption is influenced by the following factors : Temperature : The rate of absorption of salts and minerals is directly proportional to temperature. The absorption of mineral ions is inhibited when the temperature has reached its maximum limit, perhaps due to denaturation of enzymes. Light : When there is sufficient light, more photosynthesis occurs. As a result more food energy becomes available and salt uptake increases. Oxygen : A deficiency of \[{{O}_{2}}\] always causes a corresponding decrease in the rate of mineral absorption. It is probably due to unavailability of ATP. The increased oxygen tension helps in increased uptake of salts. pH : It affects the rate of mineral absorption by regulating the availability of ions in the medium. At normal physiological pH monovalent ions are absorbed more rapidly whereas alkaline pH favours the absorption of bivalent and trivalent ions. Interaction with other minerals : The absorption of one type of ions is affected by other type. The absorption of \[{{K}^{+}}\] is affected by \[C{{a}^{++}},M{{g}^{++}}\]and other polyvalent ions. It is probably due to competition for binding sites on the carrier. However, the uptake of \[{{K}^{+}}\] and \[B{{r}^{}}\] becomes possible in presence of \[C{{a}^{++}}\] ions. There is mutual competition in the absorption of K, Rb and Cs ions. Growth : A proper growth causes increase in surface area, number of cells and in the number of binding sites for the mineral ion. As a result, mineral absorption is enhanced.

An essential element is defined as 'one without which the plant cannot complete its life cycle, or one that has a clear physiological role'. Therefore, in 1939 Arnon and Stout proposed the following characters for judging the criteria of essentiality of an element in the plant : (1) The element must be essential for normal growth and reproduction, which cannot proceed without it. (2) The requirement of the element must be specific and cannot be replaced by another element. (3) The requirement must be direct that is, not the result of any indirect effect e.g., for relieving toxicity caused by some other substance.  Essential elements are divided into two broad categories, based on the quantity in which they are required by plants. Macro-elements and micro-elements. Their ionic forms are respectively called macronutrients and micronutrients. Mineral salts dissolved in soil solution are constantly passing downwards along with percolating (gravitational) water. The phenomenon is called leaching. Leaching is more in case of anions. Macronutrients (Macroelements or major elements) : Which are required by plants in larger amounts (Generally present in the plant tissues in concentrations of 1 to 10 mg per gram of dry matter). Of the non-essential functional elements, silicon and sodium often occur in the range of macroelements. Macroelements are usually involved in the synthesis of organic molecules and development of osmotic potential. Micronutrients (Microelements or minor elements or trace elements) : Which are required by plants in very small amounts, i.e., in traces (equal to or less than 0.1 mg per gram dry matter). Cobalt, vanadium, aluminium and nickel, may be essential for certain plants. Microelements are mostly involved in the functioning of enzymes, as cofactors or metal activators. The usual concentration of essential elements in higher plants according to D.W. Rains (1976) based on the data of Stout are as follows :    
Elements % of dry weight
Macronutrients
           Carbon 45
           Oxygen 45
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It is a mobile connective tissue derived from mesoderm which consists of fibre-free fluid matrix and specialised living cells that are not formed in situ, can neither divide nor secrete matrix. Vascular tissue regularly circulates in the body, takes part in transport of material and performs such activities as scavenging healing of wounds and defence against pathogens. Vascular tissue is of two types, blood and lymph, Blood In chordates, and in annelids amongst the non chordates, the blood is a red and opaque fluid of salty taste and peculiar smell. It is a little heavier than water. The study of blood is called haematology. It is red coloured liquid connective tissue which originates from the mesoderm. It reaches into the various organs through the blood vessels and transports various chemical substances between different tissues. During embryonic state, the blood is mainly formed in the liver but little blood is also formed in the spleen and ribs. In adults, the blood is formed in the red bone marrow. The blood formation is called as haemopoiesis. Viscosity \[\,4.7,\text{ }{{p}^{H}}7.4\] Specific gravity \[\text{ }10.4\text{ }1.07\] Volume \[\text{ }5-6\text{ }litre/70\text{ }Kg~\,or\text{ }1/{{13}^{th}}\] part of total body weight Plasma It constitutes about 5% of body weight. It represents matrix of blood. Plasma is slightly alkaline and transparent. It forms 55-60% by volume of blood. Plasma contains : Water \[(91-92%),\] Solid \[(8-9%).\]Plasma solid part consists of organic (7%) and inorganic (1%) substances which are as follows : Organic constituents of plasma : Some are its own constituents, while others are those which are transported by it. All these are divisible into following categories : (1) Plasma proteins : Protein constitute about 7% part of plasma and remain in it as colloid particles. These mainly include albumins, globulins, prothrombin and fibrinogen. Globulins are mainly formed by plasma cells in lymphoid organs. Other plasma proteins are mainly formed in liver. These render the plasma viscous, and maintain its osmotic pressure (7.5 atmospheric) and pH. Prothrombin and Fibrinogen are essential for blood clotting. Albumins are mainly responsible for maintaining osmotic pressure in plasma and for osmoregulation in cells and tissue fluids. Globulins help in osmoregulation and transport of proteins and other substances, but most globulins are immunoglobulins, which act as antibodies, destroying harmful bacteria, virus and toxins in blood and tissue fluids. Some proteins, acting as enzymes, also occur in the plasma. (2) Digested nutrients : These include glucose, fats, fatty acids, phospholipids, cholesterol, nucleosides, amino acids, vitamins etc. These are the supplied by the blood to all cells of body. (3) Excretory substances : These chiefly include ammonia collected by blood from body cells and urea, uric acid, creatine, creatinine etc., collected mainly from the liver and transported to kidneys for excretion. (4) Hormones : These are secreted and released in blood by endocrine glands. (5) Dissolved gases : Each 100 ml. of water of blood plasma contains about \[0.29\text{ }ml\]of \[{{O}_{2}},\text{ }5\text{ }ml.\] of \[C{{O}_{2}}\] and 0.5 ml of nitrogen dissolved in it. (6) Defence compounds : more...

It provide support and surface for attachment of muscle. Skeletal connective tissue form the frame work of body. It provide rigidity to body. These protect the various organ and help in locomotion. It is of three types : Cartilage, Bones, Notochord. Cartilage Cartilage is a solid but semi-rigid and flexible connective tissue. Cartilage is a nonvascular connective tissue, consisting of cells embeded in a resilent matrix of chondrin. Chondrin is a protein of cartilage. Regeneration of cartilage can occur from its peri-chondrium. Cartilage is said to be metabolically nearly inactive. In kids the cartilage cells show 2 types of growth. (1) Appositional or Perichondral or Secondary or Exogenous growth : It is due to deposition of matrix and division of chondrogenic cells of periphery. It leads to growth in thickness. (2) Endogenous or Interstitial growth : It is due to deposition of matrix and division in inner cells of cartilage. It leads to growth in size. Types of cartilage : It is of following types – (1) Hyaline cartilage : It is most primitive and glass like cartilage. Its matrix is transparent homogenous and pearly white or bluish green in colour, contain chondrin. It is slightly elastic and also known as articular cartilage because it forms the articular surface of joints. Hyaline cartilage is found in trachea, larynx and bronchi, limb bones (called hyaline cap), sternum, in the hyoid apparatus nasal septum, ribs (sternal parts) larynx (cricoid, thyroid), nasal cartilage (nasal septum).      (2) Fibro cartilage (White fibrous cartilage) : In this cartilage, the small amount of matrix of cartilage is packed with large number of bundles of thick white (collagen) fibres. So it is toughest and less flexible. It is found in intervertebral discs and acts as shock absorber. It is also found in pubic symphysis and helps in parturition (child birth). The intervertebral discs remain contracted when the body is active, but relaxed when the body is at rest. That is why, our body becomes a bit taller during sleep and after death.     (3) Elastic cartilage (Yellow elastic cartilage) : In this cartilage, the matrix is packed with yellow or elastic fibres which run in all directions to form a network. Owing to the presence of yellow fibres, it is very flexible. It gives recoiling power to structures. It is found in mammalian pinna, pharyngotympanic tube, epiglottis, some laryngeal and bronchiolar cartilages.     (4) Calcified cartilage : It is modified hyaline cartilage, It is hard and non elastic due to deposition of calcium salt-hydroxy appetite  in matrix. It is found in pubis of old frog, supra-scapula of frog, quadrate cartilage of frog, shark vertebrae, in man ends of long bone, head of humerus and femur. Calcification may also occur as a regular more...

A most complex tissue in the body, composed of densely packed interconnected nerve cells called neurons (as many as \[{{10}^{10}}\] in the human brain). It specialized in communication between the various parts of the body and in integration of their activities. Nervous tissue is ectodermal (from neural plate) in origin. It forms the nervous system of the body which controls and coordinates the body functions. There is no intercellular matrix between neurons. These have permanently lost the power of division as have no centriole and have minimum power of regeneration. So these cannot be cultured in vitro. Irritability is the main function of nervous tissue. Composition of nervous tissue : Nervous tissue is formed of four types of cells : (1) Neurons (nerve cells)              (2) Neuroglia (3) Ependymal cells                         (4) Neuro-secretory cells Neurons A neuron is a nerve cell with all its branches. Neuron is formed from neuroblast. It is the structural and functional unit of nervous system. It is the longest cell of the body. (1) Cyton : It is also called perikaryon or soma or cell body. Its granular cytoplasm is called neuroplasm which has following structures : (i) A large, spherical, centrally placed nucleus with a single nucleolus. (ii) Numerous fine threads called neurofibrils for the conduction of nerve impulses. (iii) A number of small, basophilic granules called Nissl’s granules formed of rough endoplasmic reticulum with ribosomes and are sites of protein synthesis. (iv) Neuroplasm has large number of mitochondria to provide high energy for impulse conduction. (v) Neuroplasm may have melanophores with melanin pigment and lipochromes with orange or yellow pigment. (vi) A mature neuron has no centriole, so it cannot divide. (vii) A “Barr body” is often seen abutting against the inner surface of nuclear membrane of cytons in females. This has been proved to be a transformed ‘X’ chromosome. (viii) Certain neurons having flask-shaped cytons and called purkinje cells, occur in the cerebellum of the brain. (2) Neuron processes : The processes of neurons, called neurites, extend varying distances from the cyton and are of two types – dendrites or dendrons and an axon or axis cylinder (neuraxon). (i) Dendron : These are several short, tapering much branched processes. The dendrites contain neurofibrils, neurotubules, Nissl’s granules and mitochondria. They conduct nerve impulse towards the cell body. (ii) Axon : This is a single very long, cylindrical process of uniform diameter. It arises from a conical projection, the axon hillock, of the cyton. The axon contains neurofibrils and neurotubules but lacks Nissl’s granules. Axon is usually branched only terminally into slender branches called telodendria. The latter have knobbed ends called endbulbs or axon terminals or buttons or synaptic knobs or end plates. The synaptic knobs contain mitochondria and secretory vesicles.       Types of neurons : Neurons are divided into different categories on different basis. (1) On the basis of functions : Neurons are divided into three categories : Sensory (afferent) more...


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