12 BOTANY BOOK
This book has been prepared by the Directorate of School Education Botany textbook for Std. XII has been reformed, updated and designed to include. Tamilnadu 12th Standard Books to TN HSC Samacheer Kalvi Books Download. Bio-Chemistry. Available Soon. Bio-Zoology. Download. Botany. In this Book, BOTANY, a sincere attempt is made by my colleagues, on the 12 . Zinc Zinc is involved in the synthesis of indole acetic acid by activating the.
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This organelle is concerned with the oxidation of food substances to release CO2, water and energy in the form of Adenosine Triphosphate ATP. Secretion Cell secretion takes place by the organelle called the Golgi body which is referred to as the dictyosome in plants.
The plant is thus able to co-ordinate the physiological activities of the various organelles and behaves as a perfect physiological unit. Thus the cell is the seat of important physiological functions.
Properties of Protoplasm The protoplasm is the living component of the plant cell and involves four parts i the cytoplasm, ii the vacuoles, iii a number of organelles and iv the nucleus.
In young cells, the vacuoles are many, small and scattered, whereas in a mature cell, there is a single large vacuole occupying the centre of the cell and the cytoplasm forms a thin peripheral layer around the vacuole. The Physical Nature of Protoplasm Many theories have been put forth to expalin the physical nature of the protoplasm. The Alveolar Foam Theory Butschili in , said that the protoplasm is a semi-transparent, viscous and slimy substance, essentially a liquid possessing a foaming or alveolar structure.
Colloidal Theory Wilson Fischer considered the protoplasm as a polyphase colloidal system. This theory is a widely accepted one as the protoplasm is seen to exhibit the properties of colloids. Properties i. Colloidal System The protoplasm forms a colloidal system composed of a water phase in which mineral matter is dissolved, also having a protein phase, a fat phase and many minor phases.
So it is said to be a polyphase colloidal system. Solation and Gelation The protoplasm exists mostly as a sol which is semi-liquid but sometimes it becomes rigid and is viewed as a gel which is sem-solid. Brownian Movement The particles of the protoplasm show an erratic zig-zag movement.
This random motion, caused by the uneven bombardment of particle is called Brownian movement. Tyndall Effect The scattering of a beam of light by the particles of a colloid is termed tyndall effect. This is a property of the protoplasm also.
Ultrafiltration The particles of the protoplasm cannot be filtered through ordinary filter paper but can be filtered through ultrafilters such as millipore filters. Electrical Properties The particles of the colloid carry an uniform electric charge.
Flocculation or Co-agulation When the particles of a colloid lose their charges they tend to aggregate and increase in size. As a result they fall out and get precipitated. In other words protoplasm loses its living property.
These properties of the protoplasm indicate that it is a living substance and has rightly been termed as the physical basis of life vivum fluidum. The dry matter has several organic and inorganic substances. Proteins and other nitrogen-containing compounds constitute the bulk of organic matter.
Liquids like fats and oils are also present in small amounts. Compounds consisting of chlorides, phosphates, sulphates and carbonates of magnesium, potassium, sodium, calcium and iron are also present. Water Relations Water is the most important substance required for the sustenance of life.
Absorbing of substances from the environment, transporting these within and across the cells, mediating important chemical reactions and properly maintaining the shape and forms of organs to bring about their effective functioning are all advantages, the protoplasm possesses due to the presence of water in it. Thus it is clear that any factor causing loss of water and subsequent coagulation of protoplasm will eventually lead to death.
As far as plant cells are concerned water absorption for photosynthesis is one of the most essential activities. So water relations in a plant cell are of greater significance and form the fundamental process for the proper functioning of the plant cell.
A typical plant cell consists of cell wall, a central large vacuole filled with an aqueous solution called cell sap, and the cytoplasm. When a plant cell is subjected to movement of water, many factors start operating and these will ultimately determine, a property called water potential of the cell sap.
It is the water potential which controls movement of water into and out of the cells. Absorption and Movement Absorption of water Absorption of water occurs in plants through roots. The zone of water absorption in root is about 20 - mm from the root tip and this is the root hair zone.
The ultimate units of water absorption are the root hairs. The root hair is a unicellular tubular extension bound by an outer cell wall followed by plasma membrane, enclosing the protoplasm inside. The cytoplasm of the root hair contains a large central vacuole filled with cell sap. Absorption of water by plants takes place due to the process, osmosis, which is a passive diffusion. Path of water across the root The root hairs are unicellular extensions of the roots found extending into the pore spaces of the soil particles.
The pore spaces contain water and dissolved minerals in the form of soil solution. This water first gets adsorbed to the wall of the root hair, by imbibition thus wetting it. This forms a channel for further absorption of water by the living cells of the root in an active manner. The water then passes through the parenchymatous pericycle and reaches the protoxylem. The path of water is in a lateral direction and so is called lateral transport of water.
Once the water reaches the xylem, it has to be transported in an upward direction to the shoot system and from there to the leaves. This is referred to as Ascent of Sap. Imbibition Imbibition is the uptake of water or other solvents by non-living substances such as gum, starch or wood causing swelling of these substances. Such substances are called imbibants. The phenomenon of imbibition creates a force called imbibitional force between the imbibant and the solvent.
In plant cells, the cell wall is the imbibant which absorbs water and forms a channel for movement of water into the cell by diffusion and osmosis.
Imbibition plays a very important role in most of the activities especially seed germination which involves absorption of water by seed coats, their swelling and rupture causing the emergence of the radicle and plumule. Diffusion Diffusion is the flow of matter, solid, liquids and gases from a region of higher concentration to a region of lower concentration until equilibrium is attained.
Examples of diffusion are the smell of perfume, when we open a perfume bottle and the spread of colour when a crystal of potassium permanganate is put into a beaker of water. When a substance undergoes diffusion, its particles start moving. When the moving particles counter a surface, the surface offers resistance to the impact of diffusing particles. This leads to development of pressure called diffusion pressure. Always diffusion occurs from a level of higher diffusion pressure to a level of lower diffusion pressure.
A pure solvent has maximum diffusion pressure and addition of solutes lowers the diffusion pressure. The amount by which the diffusion pressure of a solution is lower than that of the pure solvent is called Diffusion Pressure Deficit DPD.
But the recent trend is to use the term water potential to explain diffusion of water. When two solutions of different concentrations are separated by a selectively permeable membrane, diffusion of water or solvent molecules takes place from the solution of lower concentration to the solution of higher concentration.
This process is called Osmosis. In other words Osmosis is the diffusion of water or solvent from a region of its higher concentration to a region of its lower concentration through a selectively permeable membrane. This can also be expressed as the movement of water from a region of higher free energy of water or water potential to a region of lower free energy of water potential through a selectively permeable membrane.
Hypertonic, Hypotonic and Isotonic solutions Imagine a system in which an aqueous solution A with high concentration of solute is separated by a selectively permeable membrane from an aqueous solution B with a low concentration of solute.
Solution A is said to be hypertonic to solution B, and solution B hypotonic to solution A. In this situation, there will be a net movement of water or solvent molecules through the membrane from the hypotonic solution to the hypertonic solution by osmosis.
This will continue until equilibrium is reached, at which point there is no further movement of water and the two solutions are described as isotonic. Demonstration of Osmosis The process of osmosis may be demonstrated by the simple osmometer which is the thistle funnel experiment. Potato Osmoscope Demonstration of osmosis in a living system can be done using the potato osmoscope. A potato is peeled and one side is flattened which serves as the base.
A cavity is made in the potato and is filled with concentrated sugar solution and a pin mark is made to indicate the initial level. This potato is then placed in a beaker containing coloured water for some time. Observation It is observed that the sugar solution in the cavity of the potato becomes coloured and level rises.
Plasmolysis When a plant cell is placed in hypertonic solution, the process of exosmosis starts and water from the cell sap diffuses out into the solution of external medium. This causes a reduction in the tension of the cell wall and brings about the contraction of protoplasm due to the continuous loss of water. The protoplasm becomes rounded in shape due to contraction and such a cell is said to be plasmolysed and the phenomenon is referred to as plasmolysis. The initial stage of plasmolysis where the protoplasm just starts leaving the cell wall is called incipient plasmolysis.
When a completely plasmolysed cell is again placed in water or a hypotonic solution, endosmosis takes place and the protoplasm regains its original state and shape.
This phenomenon is the reverse of plasmolysis and is called deplasmolysis. Significance of Plasmolysis 1. Helps to understand the living nature of a cell.
Helps to preserve meat, jellies and used in pickling as their salting kills bacteria by plasmolysis. Used to prove the permeability of cell wall and selectively permeable nature of plasma membrane.
Osmotic Pressure Osmotic pressure of a solution is the pressure which must be applied to it in order to prevent the passage of solvent due to osmosis. In other words, it is that pressure which is needed to check the process of osmosis. The term osmotic potential is also used in place of osmotic pressure.
Turgor Pressure When the plant cell is placed in water, it will swell but will not burst. Due to the negative osmotic potential of the cell sap, water moves into the cell and causes the plasma membrane to press against the cell wall. This pressure responsible for pressing the plasma membrane against cell wall is called turgor pressure.
Turgor pressure may also be defined as the hydrostatic pressure developed inside the cell on the cell wall due to endosmosis. Wall Pressure As a result of turgor pressure on the cell wall, the rigid cell wall exerts an equal pressure in the opposite direction called wall pressure. Under these conditions, the plant cell is said to be turgid. When solute is added, the diffusion pressure of a solution is lowered.
The amount by which diffusion pressure of a solution is lower than that of its pure solvent is known as diffusion pressure deficit which was described as suction pressure by Renner Recently a new term called water potential is used for DPD but with a negative value.
Permeability and Water Potential Permeability The entry and exit of water into and out of the plant cells is due to a phenomenon called permeability of the plasma membrane. The plasma membrane is considered to be selectively permeable because it allows the solvent, water and a few selected molecules and ions to pass through it. Water will flow from a region of higher free energy to a region of lower free energy.
Free energy is the thermodynamic parameter which determines the direction along which physical and chemical changes should occur and may be defined as the sum of the energy of a system capable of doing work. Based on free energy, water potential may be defined as the difference between the free energy of water molecules in pure water and the free energy of water in any other Table 5.
Differences between diffusion and osmosis system eg water in a solution or water contained in D iffu sio n O sm o sis the plant cell. Thus, water co n ce n tratio n. The m e m b r a n e i s n o t s e le c t iv e l y p e r m e a b le water potential of in v o lv ed m em b ran e pure water is zero bar and water potential in a plant tissue is always less than zero bar and hence a negative number.
Components of Water Potential When a typical plant cell containing cell wall, vacuole and cytoplasm is placed in a medium containing pure water, there are a number of factors which determine the water potential of the cell sap. These are called the components of water potential and are named as i. Matric potential, ii. Solute potential and iii. Pressure Potential The cell wall exerts a pressure on the cellular contents inwards called wall pressure causing a hydrostatic pressure to be exerted in the vacuole called turgor pressure which is equal and opposite to wall pressure.
Table 5. Water potential is thus the sum of the three potentials. Thus the plant cell acts as an osmotic system having its own regulatory control over absorption and movement of water through the concerted effect of phenomena such as imbibition, diffusion and osmosis.
The protoplasm was considered as a polyphase colloidal system by a. Altmann b. Hemming c. Wilson Fisher d. Butschili 2. The movement of water into and out of cells is controlled by a.
Water potential b. Endosmosis c. Exosmosis d. Plasmolysis 3. Flow of matter from a region of higher concentration to a region of lower concentration is called a. Imbibition b. Osmosis c. Diffusion d. Plasmolysis 4. The principle used in pickling is a. Plasmolysis d. None of the above Two Marks 1. Five Marks 1. Why is the cell called a physiological unit? Explain the physical nature of protoplasm. Describe the properties of protoplasm. Explain the components of water potential.
Explain plasmolysis and bring out its significance. Differentiate between DPD and water potential. Ten Marks 1. Explain osmosis with an experiment. Write an essay on the physical nature and properties of protoplasm. Water Transport The water absorbed by the root hairs is translocated upwards through the xylem.
The mystery of the upward movement of water is yet to be solved in a satisfactory way. The upward transport of water in plants which are feet high has not been satisfactorily explained till date. Though the mechanism for upward movement of water or ascent of sap is not clear, it has been proved that ascent of sap takes place through xylem.
The girdling experiment was done is a plant with thick stem where the outer layer of phloem was removed. Still it was found that ascent of sap continued to take place proving that ascent of sap takes place through the xylem.
A young tomato or balsam seedling was taken and kept in a beaker containing water coloured with eosin. After sometime it was seen that streaks of red colour were running up the stem. When a cross section of the stem was taken, it was found that xylem was coloured proving that ascent of sap takes place through the xylem tissue.
Mechanism of Ascent of sap A number of theories have been put forward at various times to explain the mechanism of ascent of sap. These are i Vital theories, ii Root Pressure theory and iii Transpiration pull.
Vital Theories These theories had been given very early and have only historical importance. Godslewski gave the relay pump theory. According to this theory the pumping of water takes place upwards due to the vital activities of xylem parenchyma and xylem rays. Bose has put forward the pulsation theory. According to this theory water is pumped up due to the contraction and expansion of innermost cortical cells which creates a pulsation causing upward movement of water. This theory is based on a number of features.
The wall of the tracheids and vessels which transport water are made up of lignin and cellulose and have high affinity for water and this is called adhesion.
Xylem vessels have perforated end walls and form a tubular structure from roots to the shoot tip. This provides a continuous channel for movement of water which cannot be pulled away from xylem wall due to cohesive and adhesive properties. Transpiration Pull The transpiration taking place through leaves causes negative pressure or tension in xylem sap which is transmitted to the root.
This is called transpiration pull which is responsible for the movement of water column upward. Objections and Explanation Air bubbles may enter the water column due to atmospheric pressure variations.
Dixon explained that the water continuity is maintained by network of tracks of water due to interconnections between longitudinal vessels. Septa in xylem vessels may check the flow of water.
But the suction force or negative tension developed by transpiration pull is sufficient to overcome resistance developed by septa. Experiment to Demonstrate Cohesion - Tension Theory A young transpiring twig is fixed to a glass tube filled P o rou s with water.
The lower end of p o t Tra nsp irin g the tube is kept dipping in a tw ig dish containing mercury. As W a ter transpiration occurs in the twig the level of mercury rises in W a ter the tube due to the suction force created. Instead of the transpiring M ercu ry twig, if a porous dry pot filled M ercu ry with water is used, the same results are got.
Thus the cohesion - F ig: Factors Affecting Rate of Transpiration The process of transpiration is influenced by a number of factors which may be broadly classified as External factors and Internal factors.
External Factors These include conditions of the environment which affect the rate of transpiration. The external factors are humidity, wind, atmospheric pressure, temperature, light and water.
Humidity Humidity refers to the amount of water vapour present in the atmosphere. If humidity is high, rate of evaporation is low and so the rate of transpiration is slow. Wind Wind is air in motion which enhances the rate of evaporation. Wind increases the rate of transpiration.
But winds at high velocity bring about closure of stomata and thus reduce the transpiration rate. Atmospheric Pressure Low atmospheric pressure increases the rate of transpiration. Water vapour from transpiring surfaces rapidly moves into the atmosphere which is at low pressure. Temperature Increase in temperature increases the rate of transpiration as high temperature causes the water in intercellular spaces to vaporize at a faster rate.
Light Light influences opening of stomata and so rate of transpiration is high in light and less in darkness. Water Less amount of soil water decreases the rate of transpiration. If the rate of transpiration exceeds the rate of absorption, the stomata get closed the cells lose their turgidity and the plant wilts.
If the wilting is irreversible it is called permanent wilting. Internal Factors These are factors prevailing within the plant which are inherent properties of the plant itself and include leaf structure, root-shoot ratio and age of plants. Leaf Structure In xerophytes, the rate of transpiration is reduced due to structural modifications such as less surface area, thick cuticle with hard and leathery surface, leaf rolling, sunken stomata, waxy coating, lower stomatal frequency, hairy covering and development of mechanical tissue.
In the case of the plants such as Opuntia and Asparagus the leaf is modified into thorns and the stem becomes flattened and green to perform the function of the leaf. Such a structure is called a Cladode. Root - Shoot Ratio Transpiration shows a direct relation with the amount of water absorbed by the roots and the water lost through leaves. Therefore the increase in the root- shoot ratio will also increase the rate of transpiration.
Age of Plants Germinating seeds generally show a slow rate of transpiration. It increases with age and becomes maximum at maturity. But rate of transpiration decreases during senescence. The rest of the water is lost through the aerial parts of the plant by a process called transpiration.
The loss of water in the form of vapour from the aerial parts of the plant is referred to as transpiration. Types of Transpiration Transpiration in plants is essentially of three types. Cuticular b. Lenticular c.
Cuticular Transpiration Cuticular transpiration takes place through outer covering of the epidermis called cuticle made up of substance called cutin. Only a very little part of transpiration takes place by this process.
Lenticular Transpiration Lenticels are regions on the bark having loosely arranged cells called complementary cells. A very little amount of water is lost by transpiration through lenticels.
Stomatal Transpiration Stomata are minute openings on the epidermis of leaves and stems. Structure of Stoma A stoma is a minute pore on the epidermis of aerial parts of plants through which exchange of gases and transpiration takes place.
Each stoma is surrounded by a pair of kidney shaped guard cells. Each guard cell is a modified epidermal cell showing a prominent nucleus, cytoplasm and plastids. The wall of the guard cell is differentially thickened. The inner wall of each guard cell facing the stoma is concave and is thick and rigid. The outer wall is convex and is thin and elastic. The guard cells are surrounded by a variable number of epidermal cells called subsidiary cells.
Mechanism of Stomatal Opening and Closing Opening and closing of stomata takes place due to changes in turgor of guard cells. Generally stomata are open during the day and close at night. The turgor changes in the guard cells are due to entry and exit of water into and out of the guard cells. During the day, water from subsidiary cells enters the guard cells making the guard cells fully turgid.
As a result, the thin elastic convex outer walls are bulged out causing the thick and rigid concave inner walls to curve away from each other causing the stoma to open. During night time, water from guard cells enters the subsidiary cells and as a result, the guard cells become flaccid due to decrease in turgor pressure.
This causes the inner concave walls to straighten up and the stoma closes. The actual mechanism responsible for entry and exit of water to and from the guard cells has been explained by several theories.
The most important theories are i. The starch-sugar interconversion theory of Steward ii. Proton-potassium pump theory of Levitt. The Starch - Sugar interconversion Theory Steward holds that during the day the enzyme phosphorylase converts starch to sugar, thus increasing osmotic potential of guard cells causing entry of water.
The reverse reaction occurs at night bringing about closure. Phosphorylase day Starch Sugar stoma opens night stoma closes ii. The sequence of events taking place are i.
Under the influence of light, protons formed by dissociation of malic acid move from cytoplasm in to the chloroplasts of guard cells. Potassium malate causes increase in the osmotic potential of guard cells causing entry of water into the guard cells as a result of which the stoma opens.
Factors Affecting Stomatal Movement There are a number of factors which influence stomatal movements. These include light, temperature, potassium chloride, organic acid, carbondioxide concentration, water and abscissic acid. Light Light greatly influences the opening and closing of stomata as it stimulates production of malic acid due to conversion of starch to sugar.
Stomata do not open in U-V light and green light but remain opened in the blue and red regions of the spectrum. But higher temperatures also cause stomatal closure. Potassium Chloride Accumulation of potassium chloride causes opening of stomata. Organic Acid The increase of organic acid content in the guard cells causes the stomata to open.
Carbondioxide Concentration Stomatal movement is influenced by the concentration of carbondioxide. At low concentrations of CO2, the stomata open. With increase in the concentration of CO2, the stomata begin to close and when CO2 concentration of cells is higher than its concentration in the air, the stomata completely close.
Stomatal movement is always influenced by the CO2 concentration of the intercellular spaces of the leaf and not the concentration of the air.
Water Water is responsible for causing changes in the turgor of the guard cells. Guard cells become flaccid on losing water and so the stomata close. Similarly the guardcells become fully turgid on gaining water and the stomata open.
Under conditions of water scarcity also, the stomata close. Abscissic Acid Abscissic acid accumulates in the leaves when the plants experience water stress or water deficit. It has been observed, that ABA Abscissic acid stimulates closure of stomata under these conditions. During the day the guard cells experience a. The starch - sugar interconversion theory was given by a. Steward b. Scarth c. Levitt d. Raschke 3. Scarth put forward the a. The relay pump theory was put forward by a.
Godslewski b. Bose c. Stocking d. Dixon 5. Bose gave the a. The term root pressure was coined by a. Stocking b. Stephan Hales c. Dixon d. Bose 7. Lignin and cellulose have affinity for water. This is called a. The transpiration pull theory was supported by a. Renner b. Curtis c. Clark d. All the above Two Marks 1. Explain the mechanism of stomatal opening and closing.
Describe the Proton - potassium pump hypothesis. Demonstrate root pressure with the help of an experiment. Give an experiment to demonstrate cohesion - tension theory. Explain the objections to the root pressure theory. Give an account of the inherent properties of the leaf which affect the rate of transpiration.
Written an essay on the theories explaining mechanism of stomatal movement. Give an account of the factors influencing stomatal movement. Explain the postulates of the cohesion - tension theory. Add a note on the objections and explanation. List and explain the factors affecting transpiration. Give an account of the various theories explaining the ascent of sap.
Mineral Nutrition Mineral nutrition of plants was a phenomenon known from very ancient times. Woodward observed for the first time that plants grow better in muddy water than rain water. Later it was proved that minerals have specific functions in plant metabolism. When this ash was analysed it was found to contain 40 elements besides C,H,O,N and S which were oxidized. All these are not essential for plant nutrition but on analysis the important essential elements have been identified and based on their role in plant metabolism and requirement, they have been classified as major elements and trace elements.
The functions of the various minerals in general depends on the role of the mineral in plant metabolism. Criteria for Essentiality of a Mineral Element Essential elements should have the following characteristics i.
Normal growth and reproduction must be dependent on particular mineral elements. An essential element must have direct influence on the plant.
Essential elements must be indispensable and their substitution by other elements must be impossible. Some elements are required in very low quantities and the status of essentiality or non essentiality is doubtful.
For example silicon. Functions of Minerals i Mineral elements are constituents of the various parts of plant body, for example calcium which is found in the middle lamella, nitrogen and sulphur in proteins, phosphorus in nucleic acids.
Hydroponics The term hydroponics has been used for growth of plants in water culture. This may also be referred to as soil-less agriculture, test-tube farming, tank farming or chemical gardening.
Commercially hydroponic cultures are maintained in large shallow concrete, cement wood or metal tanks in which gravel and nutrient solutions are taken. The tanks are provided with pumps and empty auxiliary tanks to pump out and circulate the growth solution and to maintain proper aeration of the nutrient solution. The technique of hydroponics is employed to know which mineral element is essential for the growth and development of the plant.
Commercially the application of hydroponics involve the production of horticultural and floricultural crops. This method may be used to increase yield of ornamentals such as gladioli, snapdragon, roses and vegetables such as carrot, radish, potatoes, tomatoes and lettuce. Advantages of Hydroponics i. It is possible to provide the desired nutrient environment.
The acid-base balance can be easily maintained. Mulching, changing of soil and weeding are eliminated. Proper aeration of nutrient solution is possible. Labour for watering of plants can be avoided. Tilling is not necessary. Production is limited when compared to field conditions.
Technical skill is required to design equipment. If a disease appears all plants in the container will be affected. Can be used only for short duration. Essential Major Elements and Trace Elements The plant ash reveals the presence of 40 elements but all are not essential for plant nutrition, only a few are essential for growth and development of plants. These are called the essential elements. The essential elements may be grouped as major elements or macronutrients and trace elements or micro nutrients, based on their requirement by plants.
Major elements or Macro Nutrients These elements are required in large amounts and form the plant consituents. The major elements are otherwise known as macronutrients.
These include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. These elements form an integral part of complex organic molecules. Some of these elements help in the functioning of enzyme systems. The sources of macronutrients are generally the soil or the atmosphere.
Carbon is got from carbodioxide of the atmosphere. Oxygen is derived from water and atmospheric oxygen. Nitrogen is present in the atmosphere as an inert substance which is brought to the soil and converted to soluble nitrates either by asymbiotic or symbiotic nitrogen fixation.
Phosphorous and sulphur and derived from rocks during weathering. The source of hydrogen is water. Trace elements or Micronutrients Elements like iron, boron, managanese, copper, zinc and molybdenum are required for plants only in very small amounts but these are indispensable for the normal growth and development of plants. They are a part of carbohydrates, proteins, and fats. Thus these elements have a role to play in the general metabolism of plants. Deficiency symptoms Deficiency of these elements is very rare because the plants have a steady supply of these through water and gaseous exchange.
Deficiency affects the normal growth and developments of plants. Nitrogen Nitrogen is an essential constituent of proteins, nucleic acids, vitamins and many other organic molecules such as chlorophyII. Nitrogen also forms a constitutent of various hormones, coenzymes and ATP. Deficiency symptoms i Stunted growth ii Chlorosis iii Reduction in flowering iv Excessive colouring in apple and peach and reduction in fruit size.
Phosphorus It is present in plasma membrane, nucleic acids, nucleotides, many co-enzymes and organic molecules. It plays an important role in energy metabolism. Phosphorus promotes healthy root growth and fruit ripening. Deficiency symptoms i.
Loss of older leaves ii. Reduction in growth iii. Increase in phosphatase enzyme activity iv. Causes accumulation of carbohydrates in soyabean 4. Potassium Potassium is required in the meristematic regions and regions of cell differentiation. It accumulates in older leaves.
Though it does not have a structural role, it is involved in stomatal opening and closing. It is an activator of many enzymes and has a role in protein and carbohydrate metabolism. Leaf tips curve downward ii.
Causes mottled chlorosis iii. Development of chlorosis at tips and margins of leaves. Shortening of internodes and stunted growth. Sulphur Sulphur is the constituent of certain vitamins such as thiamine and biotin. It is constituent of coenzyme - A playing an important role in respiration. It forms the sulphydryI group in many enzymes and is a constitutent of sulphur containing aminoacids such a cystine, cysteine and methionine.
Causes inhibition of protein synthesis.
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Younger leaves show chlorosis first iii. Chloroplasts of mesophyII show a decrease in stroma lamellae but grana increase. Magnesium Magnesium is a constituent of chlorophyII molecule which cannot be formed without magnesium. It has a vital role in carbohydrate metabolism and the binding of ribosomal sub-units. Interveinal chlorosis takes place. Anthocyanin pigment deposition takes place after chlorosis.
Necrotic spots appear in acute cases. Calcium Calcium forms an important constituent of the cell wall occurring in the middle lamella as calcium pectate.
It has an important role in the formation of plasma membrane. Calcium plays a role in mitotic cell division and is a constitutent of enzymes like phospholipase and adenyl kinase where it acts as an activator. Affects the carbohydrate metabolism. The process of respiration is badly affected as number of mitochondria are decreased. Meristematic tissues are affected and leaf and root tips die.
Cell wall may become brittle or rigid. Micro Nutrients 8. Iron Soil is generally not deficient in iron. Iron is a constituent of various flavoproteins and forms a part of enzymes such as catalases, peroxidases and cytochromes. It plays an important role in the electron transport system of photosynthesis being part of cytochrome and ferredoxin. Causes interveinal chlorosis and the leaves become yellow or white. Impairs aerobic respiration and related processes.
Fruit trees particularly show sensitivity to iron deficiency. Boron Leaves and seeds require boron.
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It plays a role in nitrogen metabolism, hormone and fat metabolism. It causes brown heart-rot disease in beetroots. In apple internal tissues become corky. Causes leaf to curl and become brittle. Premature fall of fruits and flowers. Managanese Managanese is required by leaves and seeds. It is an activator of enzymes like carboxylases, oxidases, dehydrogenses and kinases. Causes grey spot disease in oat.
Poor development of root system. Interveinal chlorosis occurs. Copper This is required in all plant parts. Copper forms a component of enzymes such as phenolases and tyrosinase. Copper being a constituent of plastocyanin plays a role in photophosphorylation. Copper maintains the carbohydrate - nitrogen balance. Causes die back of shoots especially in Citrus. Reclamation disease is caused in plants growing on newly reclaimed soil where seed formation is affected.
Zinc Zinc is involved in the synthesis of indole acetic acid by activating the enzyme tryptophan synthetase. It plays a role in protein synthesis. It acts as an activator of many other enzymes such as carbonic anhydrase, alcohol dehydrogenase, hexokinase and so on. Causes distortion of growth. Leaves become very small and rosetted called as little leaf disease. Interveinal chlorosis and stunted growth of stems is seen. Molybdenum Molybdenum has an important role to play in the metabolism of nitrogen.
It affects the synthesis of ascorbic acid. It activates the enzymes involved in nitrogen metabolism. Hydroponics is otherwise called a soil-less agriculture b tank farming c chemical gardening d all the above 2. This element is a constituent of chlorophy11 a Manganese b Magnesium c Potassium d Zinc Fill in the blanks 1.
Exanthema is a disease caused due to deficiency of Deficiency of Molybdenum causes Sulphur containing amino acids are Explain the advantages and disadvantages of Hydroponics.
Describe the technique of hydroponics with a diagram. Describe the criteria for essentiality of an element. Explain the role and deficiency symptoms of any three macronutrients. Describe the deficiency symptoms of copper, boron and molybdenum. Write an essay on the role and deficiency of macro and micronutrients. Theories of Translocation Plants absorb minerals from the soil and translocate them to other parts of the body. Minerals are absorbed in the form of soil solution contained in the pore spaces between the soil particles and the root hair.
The soil solution contains the mineral salts in the dissolved state. Several theories have been put forth to explain the mechanism of translocation of mineral salts. These theories can be placed under two headings i Passive absorption and ii Active Absorption which can be further subdivided as follows. Passive Absorption When the movement of mineral ions into the roots occurs by diffusion without any expenditure of energy in the form of ATP it is called Passive Absorption.
This form of absorption is not affected by temperature and metabolic inhibitors. Rapid uptake of ions is observed when a plant tissue is transferred from a medium of low concentration to a medium high concentration.
Various theories have been put forward to explain mineral salt uptake by passive absorption. The anions and cations within the plant cells are exchanged with the anions and cations of equivalent charge from the external medium in which the cells are kept.
This mechanism can be explained by two theories. According to this theory ions are transferred from soil particles to root or vice versa without passing into solution. These ions oscillate within a small volume of space called oscillation volume. Donnan in which the fixed or indiffusible ions play an important role.
These ions are present on the inner side of the cell and cannot diffuse out. When a cell having fixed anions is immersed in sals solution, anions equal in number and charge to the fixed ions move into the cell. To balance the negative charges of the fixed ions additional cations also move into the cell and the cell sap cation concentration becomes higher than the external medium. This is called Donnan Equilibrium. In the same way if there are fixed cations, additional anions will accumulate from the external medium.
Active Absorption The absorption of ions against the concentration gradient with the expenditure of metabolic energy is called active absorption. The mechanism of active absorption of salts can be explained by several theories.
The carrier may be an enzyme or a protein. Metabolic energy is expended in this process. This concept is supported by Isotopic exchange using radioactive isotopes, saturation effect and specificity of carriers.
The carrier concept is explained by two theories: Lecithin which carries both anions and cations and forms a lecithin- ion complex. Lecithin is regenerated with the help of enzymes Choline esterase and choline acetylase. This requires expenditure of metabolic energy. Lundegardh who suggested that anions could be transported across the membranes by cytochrome system utilising energy released by direct oxidation of respiratory intermediates. The important postulates are: Therefore this theory explains respiration due to anion absorption which was called anion respiration or salt respiration.
Translocation of Solutes In higher plants food is synthesised only in the green leaves which are the sites of Photosynthesis. From here the food is traslocated to the different parts of the plant in the soluble form. Therefore thisis also referred to as translocation of solutes. Direction of translocation Translocation of food occurs in the downward upward and lateral directions. Down ward translocation Downward trnaslocation takes place from the leaves downwards to the stem, roots and storage organs.
Upward translocation In some stages of plant life such as seed germination, emergence of new shoots from underground storage organs and development of buds, flowers and fruits, the food materials are translocated upward. Lateral translocation In certain parts of stem and roots food is translocated in lateral direction through medullary rays. The portion from where tissues are removed is sealed with melted wax. After 7 or 8 days the epidermis and cortex of upper portion of the ring become very much swollen and from this swollen part the adventitious roots emerge out.
It happens because the food material translocated from the leaves does not pase through the ring and is stored in the upper portion. Mechanism of Translocation Following theories were proposed to explain the mechanism of translocation of solutes. Based on this Munch in proposed a hypothesis according to which the soluble food materials in the phloem show mass flow.
The fundamental idea behind this hypothesis is that the sugars synthesized by mesophyll cells of leaves increase the osmotic pressure OP of these cells causing entry of water into mesophyll due to absorption of water by the xylem cells of root. In other words a turgor pressure gradient exists through phloem, between the source which is the mesophyll cell and the sink which refers to regions of requirement.
As a result, the turgor pressure of mesophyll cells increases on the upper side which forces the solutes dissolved in water to flow en masse into the phloem of stem and finally into the roots.
This can be explained by a physical system. It consists of a glass tube bent at right angles. At the two ends differentially permeable membranes are tied. The two osmometers are kept in two separate water containers connected with each other through a tube. The most important objection for this hypothesis is that it explains only unidirectional flow of solutes. Phloem loading is caused by movement of photosynthates from mesophyll to phloem. Unloading of phloem is caused by movement of photosynthates from phloem to other parts where required.
This is the source-sink relationship. It is an important mineral present in the bodies olf living organisms. It forms a component of proteins and aminoacids and is also present in nucleic acids, cytochromes, chlorophyll, vitamins, alkaloids and so on. Nitrogen cannot be used directly and is converted to Nitrites, Nitrates and Ammonia by a process called Nitrogen Fixation.
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There are many free living organisms like bacteria and blue-green algae which are involved in nitrogen fixation. The ammonia and urea present in the soil are directly absorbed by plants. Nitrogen Cycle The atmosphere is the source of elemental nitrogen which cannot be used directly by plants.
The atmospheric nitrogen is converted to ammonia, nitrite, nitrate or organic nitrogen in the soil. The death and decay of organic systems causes cycling of ammonia from amino acids, purnies and pyrimidines. Some of these forms may also be converted to Nitrogen gas and may be cycled back into the atmosphere. The process by which these forms get inter converted to maintain a constant amount of nitrogen in atmosphere, by physical and biological processes is called nitrogen cycle.
Ammonification ii. Nitrification iii. Nitrate assimilation iv. Denitrification and v. The sources of organic nitrogen in the soil are animal excreta and dead and decaying plant and animal remains which are acted upon by ammonifying saprotrophic bacteria such as Bacillus ramosus, Bacillus vulgaris, certain soil fungi and actinomycetes. Nitrifying bacteria like Nitrosomonas convert ammonia to nitrite and another bacterium called Nitrobacter converts nitrite to nitrate.
But is cannot be used by plants directly. So it is first reduced to nitrite by the enzyme nitrate reductase.
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Nitrite is then converted to Ammonia by the enzyme nitrite reductase series of steps requiring a total of eight electrons provided by reduced NAD and Ferredoxin Fd. This reduction of Nitrate of Ammonia and its incorporation into cellular proteins by aerobic micro organisms and higher plants is called nitrate assimilation. This process ends in the release of gaseous nitrogen into the atmosphere and thus completes the nitrogen cycle.
A number of bacteria such as Pseudomonas denitrificans, Bacillus subtilis and Thiobacillus dentrificans are involved in this process. Biological Nitrogen Fixation Nitrogen fixation that takes place by living things is called biological nitrogen fixation. These include some bacteria and blue-green algae, which have acquired the capaicity to fix atmospheric nitrogen during the evolutionary process by possessing a set of genes called 'nif ' Nitrogen fixing genes.
They fix Nitrogen as given in the 6e following reaction. Non-Symbiotic Nitrogen Fixation This is carried out by free living organisms in the soilsuch as Bacteria, blue green algae.
Bacteria include aerobic bacteria such as Azotobacter and anaerobic baceria such as Clostridium, Chlorobium and Chromatium. These organisms contain an enzyme system called Nitrogenase which is a Mo- Fe Molybdenum-ferredoxin protein. Rafirasith December 17, at 9: Unknown March 22, at 6: Unknown March 4, at 5: Unknown March 25, at 3: Satya Veera March 13, at 1: Unknown March 21, at 1: Unknown March 24, at 7: Unknown March 26, at 4: Bharanitharan Janarthanan March 26, at Manikandan R March 26, at Unknown March 27, at 7: Unknown March 27, at 9: Unknown March 27, at Unknown March 27, at 6: Unknown March 28, at 7: Unknown March 28, at Unknown March 31, at 1:
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