Plant requires metabolic energy for carrying out’ various physical and physiological activities. They obtain this energy from food. In this chapter we will learn how and from where plants obtain the principal constituents of food such as water, carbon-dioxide how in greet leaves carbohydrate food is synthesized by chlorophyll in presence of sunlight, from different raw materials, how the prepared food in the leaves are distributed to all the organs and the cells through phloem tissues and low cells obtain metaoue energy from the carbohydrate food required for carrying out various physiological functions and how reproduction takes place in plants.
ABSORPTION OF WATER AND MINERAL SALTS BY PLANTS
Plant body is composed of different kinds of chemicals. But water constitutes the largest proportion of the plant body. All these chemical constituents are produced in the body by the various physiological processes. Again, mineral salts are required for syn1esis of different chemical substances such as carbohydrate, protein, oil etc. Plants are required to absorb the primary constituents of these chemical substances from the environment. That is why, plants absorb water and mineral salts from the soil through roots. But lower class of plants absorbs water by osmosis, the body surface and by some root like organs.
Plants absorb various mineral salts from the environment for maintaining life process and reproduction, as well as for repairing up the losses and for growth. These are known as and the mineral salts are called the nutrient elements.
DIFFERENT NUTRIENT ELEMENTS AND THEIR SIGNIFICANCE
Chemical analysis of different types of plants has shown that for most of the plants Aslxteen ini.ia1 elements are essential for their normal nutrition. Among these tei’ elements such as carbon, nitrogen, oxygen, hydrogen, iron, phosphorous,, sulphur, potassium, calcium and magnesiuin are required comparatively in higher proportion. So these are known asmacro-elements. While six other elements such as manganese, copper, Zinc, molybdenum, boron and chlorine are required in traces. So these are called micro-elements.
Different mineral elements are essential for various physiological functions of plants in varying quantities. Because different mineral elements perform special functions in various organs. That is why, the normal rultiution of plant is hindered due to the absence or shortage of any one of the above mentioned sixteen elements.
Different types of plant nutrients are absorbed from soil and atmosphere. Among the macro and micro nutrients only oxygen and carbon-dioxide are directly absorbed from the air and hydrogen is obtained through water. All other nutrients are absorbed by the root hairs from the soil in the form$ of their respective ions. But some algae and bacteria can directly absorb nitrogen from air.
Generally plant nutrients are available in the fertile soil. Soil fertility increases by the decomposition and mixing of the remains of dead plants and animals in the soil. Fertility of cultivated lands can be increased by adding cow dung. In fact, a lot of nutritive elements are added to the soil through the death and decay of plants and animals as well as through the decay of their excretory products.
Repeated cultivation and grazing reduces fertility of lands which may be replenished that is, the proportion of plant nutrient elements can be increased by adding artificial or chemical fertilizers.
ORGANS FOR ABSORPTION OF WATER AND MINERAL SALTS
For better understanding of the mechanism of absorption of water and mineral salts by plants one must have a clear idea about the external and internal structural features of the root apex. Root hairs grow just behind the tip of the root. This root hair absorbs water and minerals from the soil. If a cross section of root is examined under compound microscope, it is evident that a cell of the outer single-layered epidermis extends outwardly into a long hair-like structure, called the root hair. At the centre of the staler region lies the vascular or conducting tissue system, which transports water and of mineral salts to stems, and leaves.
Root hair cells are living, their eel wall is thin and the cell membrane is semi permeable. Water enters the root hair air cell by the process of osmosis and the mineral salts by diffusion through the semi permeable cell membrane.
When two solutions of different concentration are separated by a semi permeable membrane, the solvent from the weaker solution (that is solvent from. its higher molecular concentration side) moves through the semi permeable membrane to the solution of higher concentration (that is to solvent in its lower molecular concentration side) The process is called osmosis. The process continues until the concentration of two solutions are equal.
In fact osmosis is a physical process. In plants since osmosis happens under the control of protoplasm, it is a physiological process. Plants absorb water from soil through the process of osmosis. We need to know well, the process of osmosis first for understanding the mechanism of water absorption in plants by osmosis.
If dried grapes are immersed in water, they become swollen and the water tastes sweet. If the swollen grapes are put into highly concentrated solution of sugar, they will shrink again. Why does it happen so? In fact, it happens as a result of osmosis. Cells of grapes contain concentrated solution of sugar. Moreover every cell is surrounded by a thin semi permeable cell membrane beneath the cell wall. In the concentrated solution of sugar in the cells of grapes, the number of water molecules is less than that of sugar molecules. But The number of water molecules is much higher in the water of the pot in which the dried gropes are plead That is why, water molecules from the pot enter the cells of grapes and the sugar molecules from the grape cells passes to the pot water. As a result the grapes are swollen and’ the pot water tastes sweet. If the swollen grapes are again put into concentrated solution of sugar, they will shrink again. Because in this case, the number of water molecules in the sugar solution of the pot is less than that of the solution of sugars in the grape cells, so water comes out from the grape cell to the solution in the pot.
The process of osmosis can be easily verified or proved at home or in the school.
EXPERIMENT ON OSMOSIS
Materials: A few intact grapes, a small glass pot and some water.
Process: Take reasonable quantity of water in the pot. Then put a few dried grapes in the water.
Observation: Observe the condition of grapes immersed in the water, after two hours. It would be observed that the grapes have swollen.
Conclusion : It proves that as a result of osmosis water molecules from the pot entered. The grapes, so they become swollen up.
ABSORPTION OF WATER
The intake of water by plants from the environment by the process of osmosis is called absorption. Absorption is also a physiological process. Lower forms of plants absorp water by osmosis through their body ‘surface or through some root like structures. But higher class plants absorb water by osmosis through root hairs.
If a cross section of a root with the root hairs is examined under a compound microscope a continuous connection of conducting cells between the root hair and the central pith would be revealed. In addition, every living cell contains vacuole, full of cell sap. Generally the cell sap is more concentrated than the soil solution. Again the cell sap has a higher concentration gradient from the root hair to the region. So, due to osmosis water from less concentrated soil solution enters first in more concentrated cell sap pf the root hairs. Later on, in the same process water gradually reaches from the root hairs to the endodermis cells. And under the influence of root pressure water from endodermis enters the xylem vessels and goes different part of the plant body.
Diffusion is a physiological process in which molecules of the substances pass from the region of higher concentration the region of lower concentration. This process of diffusion continues until the concentration of molecules is uniform although. If ‘atar’ or any other scented material container is kept open in any corner of a closed room, after some time, its scent could be felt from other corners of the room, Similarly, if one or two spoon of red syrup is slowly, poured into a jug of water, it would be observed that, even without any stirring, the entire water of the jug has gradually turned into pale red. Why did so happen? It so happened because of diffusion.
The rate of diffusion depends on the difference of the concentration of molecules. If the difference in the concentration of molecules is greater, the rate of diffusion will be higher. Again, if the difference in concentration is less the rate of diffusion will be lower. Of course, the surface through which diffusion occurs should be large as far as possible. Diffusion takes place in plants through cell surface. The body of multicellular plants is composed of innumerable small cells. Although individual ceils body surface area is very small, but collectively they constitute a very large diffusion surface area Infect, the root absorbs mineral salts by the process of diffusion.
ABSORPTION OF MINERALS
There are enough mineral salts in the soil Compare to that,, the concentration of mineral salts in the root hair cell are more .
So, minerals from the concentrated mineral salt soil area enter the root hair through diffusion. As a result as in the Fig. 10.4 the concentration of mineral salts increases in the cell no 1 than the neighboring cells. That is why the mineral salts from its concentrated area, i.e. cell no 1 passes to the cell no 2. Through successive repeatation of the cell to cell diffusion mineral salts gradually passes from cell No I to cell no. 2, cell no. 2 to cell no 3, 3 to 4 and so on. And this process of diffusion continues until the mineral salts enter the conducting xylem vessels through which they reach the top of the stem . Accordingly, a contineous chain or is flow of mineral salts from the root to the branches and leaves of the shoot system is established.
TRANSPIRATION AND TRANSPORT
Water first enters in the root hair from the soil by the process of osmosis; from there it gradually passes from cell to cell and enters into the conducting tissues of the root. Thus at one stage water reaches the mesophyll cells of the leaves. Here we will describe, how water from root reaches the leaves, how excess water is given off from plants in the form of water vapour and how the carbohydrate food prepared in the leaves transported to different parts or organs of the plant.
The process of giving off of water in the form of vapour through different openings in the aerial parts physiological reasons under the control or influence of living cells is known as transpiration.
There are innumerable minute pores under the dorsiventral leaf surface. These pores are called stomata. The pore of each stoma is guarded by two special epidermal cells. These cells are known as guard cells (Fig. 10.5) Most of the transpiration (80-90%) occurs through the stomata. This type of transpiration is called ‘stomata’ transpiration The upper transparent layer on the upper epidermis in known as cuticle. Some water vapour from plants is also given off through the cuticle, which is called the ‘cuticular’ transpiration. Moreover in some plants transpiration also takes place through the lenticels in the sterns. This is known as 1enticular’ transpiration During the process of transformation of stem epidermis into the cork or phellem, some openings or pores are formed surrounded by loose mass of cells. These are called lenticels.
MECHANISM OF TRANSPIRATION
Stomata generally remain open curing day light and closed during the darkness in night. While open, air enters through the stomata and reaches the mesophyll cells of leaves. Since cell walls or surfaces of mesophylicells are always, moistened, they can easily absorb carbon-dioxide from the air through the process of diffusion. On the other hand, water from these cells under the influence of temperature or heat and the differences in the diffusion pressure is converted into water vapour, then the water vapor is transported through the intercellular spaces to. the air chambers beneath the stomata, from which it escapes to outside air through stomata. This process of giving out of water in the form of vapour from living cells of plant is known as transpiration. Plants absorb the same quantity of water from soil which they lose through transpiration. The water lost from the cell Wall of the mesophyll tissue is made up by absorbing water, from the xylem tissues inside the leaf of veins. This is how a continuous flow of water is maintained from the root hair to the leaves through xylem tissues of the stem.
Experiment to show the liberation of water dui1ing transpiration:
Select a healthy plant with sufficient leaves grown in a pot. Keep the soil in the pot wet. Carefully cover a portion of the shoot system with branches and leaves with a clear polythene bag and tighten its mouth with the stem so that the passage of air in and out is stopped. After about half an hour it would be observed that droplets of water have deposited on the inner surface of the transparent polythene bag. This has happened because of the escape of water in the form of vapour from the wet mesophyll cell walls into the air as a result of physiological process. Therefore it is proved that water is given off in the form of vapour by the plants during the process of transpiration.
Transport system: Transfer of soluble inorganic ‘and organic chemical substances in the plant is known as transport. The special type of tissue system present in different organs of the plants for transport of materials is known as transport system or the transport mechanism. The xylem tissue present in the stem transport water and mineral salts from root to the leaves, and the carbohydrate produced in leaves through photosynthesis is transported along with water by phloem tissue to different parts of the plant. For better understanding of these upward and downward movements of cell sap, one need to have thorough knowledge about the internal structure of root, stem and leaves.
There are conducting tissue made up of xylem and phloem, present in the stele of root, vascular ring of stem and in the veins of leaves.
Here the xylem vessels are joined end to end and thus they together constitute a narrow tube extending through root, stem and leaves. Of course, the xylem vessels are dead. Phloem tissue surrounds the xylem tissue. Sieves tubes of phloem are also joined end to end to form tube like xylem vessels. Bu phloem tissues are living. Water and minerals are transported from root to the leaves through the xylem tube or vessel where a food prepared in the leaves are transported to the different parts of plant body through the phloem tubes.
ASCENT OF SAP
The mechanism of ascending of water from the root to the stem, leaves and other aerial parts of plant is known as the ascent of sap. Scientists have so far failed to ascertain as to how and in what method water from root ascent and reaches the leaves. Even though plant scientists consider osmosis, capillarity of xylem, root pressure etc, as the cause of ascending of water but this could have never been proved experimentally.
The general conception about the ascent of sap is the first absorption of water from soil by root hair. Then through successive cell to cell osmosis water reaches the cells of endodermis. These living endodermal cells forces the passage of water into the xylem vessels. This is known as root pressure. The loss of water in transpiration from leaves creates a deficit of water into the capillaries of the xylem vessels, thereby’ creating a pull of water for rising to the leaves. The mineral alts absorbed through the root hairs also are carried up along with water through the stem.
EXPERIMENT WITH PEPEROMIA PLANT TO DEMONSTRATE ASCENT OF SAP THROUGH XYLEM TISSUES
The phenomenon of absorption of water and mineral salts by xylem tissues of plants can be deinonstrated by a simple experiment. Carefully take out a fresh peperomia plant from soil with roots. Put the root of the plant into water for some time so as to allow removal of soil attached to it. Peperomia plant is transparent and light green in colour. Then immerse the root system into a beaker or glass of water, coloured red by adding two drops of red ink. Observe the initial colour Of the plant. After half an hour, it will be observed that the stem and leaves of the plant have turned red. Because the root has absorbed red water and passed this to the stem and leaves. If a cross section of the stem is now examined under a compound “microscopes the xylem vessels will be seen turned into red because these contain red water.
TRANSPORT OF FOOD
Transport of carbohydrate food prepared in leaves and young green stems to different parts of the body is called transport of food. Plants need food for survival, growth and maintenance. Phloem tissues transport cabohydrate, food prepared in leaves through photosynthesis to different parts of the plant. The living cells in the phloem tissue are involved in the transport of food. That is why, food transport in plant is a physiological and a active process which takes place only in plants.
SIGNIFICANCE OF TRANSPIRATION
Transpiration is very important for plants. Transpiration carries out various important functions in plants such as absorption and ascent of soil sap (soil solution), transport of mineral salts to the leaves, increases in concentration of cell sap, increasing swet ness to truits, absorption of water for photosynthesis etc. Besides, transpiration increases air humidity, keeps the environment cool and promotes rainfall. But sometimes transpiration causes harm too.
If the rate of transpiration is higher than the rate of absorption of water, plant will droop and die due to want of water. Plants constantly absorb water from soil to compensate water loss through transpiration as result energy is wasted.
The relationship between transpiration ‘and irrigation in the cultivated land is inseparable. Generally plant absorb almost equal of water from soil which is lost through transpiration. Soil water gradually reduces because of continuous absorption by plants and loss through transpiration. This situation becomes more acute during summer, because of high temperature. If such situation of water loss from the soil is not replenished through rain or irrigation, plants dry up and die. On the proper handling or maintenance of these two processes the production of crop is closely related. For this reason irrigation in the crop field is very important.
Energy required for carrying out different physiological functions by plants and animals are obtained from food, which is produced during photosynthesis. The primary source of carbohydrate food for animals are the green plants. Different animals obtain their carbohydrate food directly or indirectly from green plants through varieties of food chains and food webs. We will know here how the primary producers, that means the green plants carbohydrate food.
The physiological process in which plants produce carbohydrate (glucose) by chlorophyll in presence of sunlight utilizing carbondi- oxide and water and liberating oxygen as a by-product is known as a by – product is known as photosynthesis This process is represented by the following generalised chemical equation:
6C02 + 12H20 C6H1206 + 6H2+ 602
carbon-dioxide water Chlorophyll glucose water oxygen
Most of the photosynthesis occurs in green leaves. So leaf is called the natural factory for. Synthesis of carbohydrate Carbohydrate food is also produced in the young green stems. A thorough knowledge about the internal structure of leaf is necessary for understanding the process of photosynthesis. Here only the tissues of the leaves which are directly associated with photosynthesis, are diseased briefly.
If a cross section of a leaf is examined under a compound microscope, it becomes evident that leaves are composed of a number of layers of cells. The uppermost layer is called the upper epidermis. A kind of waxy substance is produced by these cells which forms a layer on the surface of the upper epidermis. This waxy layer reduces dehydration of cells. The layers of cells in the middle are together called mesophyll layer. The mesophyll layer is divided into two layers, such as (1) palisade mesophyll and (2) spongy mesophyll. Both of. these layers are composed of simple. parenchyma tissue. Palisade parenchyma cells are rich in chloroplast, and so most of the photosynthesis takes place in this layer. Spongy parenchyma cells are loosely arranged, and so, they have enough inter-cellular spaces in between the cells. Air can move through these intercellular spaces allowing the cells to absorb carbon-dioxide and to release oxygen produced during photosynthesis from the leaves.
Lower epidermis is the outer layer in the ventral surface of a leaf. Generally stomata develops in the lower epidermis. Through the stomata air enters the leaves and reaches the inner Stomata remain open during day time photosynthesis a to occur, as a result air can enter the leaves. Photosynthesis does not take place at night, so stomata remain closed. Two guard cells of a stoma regulates the opening and closing of the stomata pore. Guard cells contain chlorophyll, so, photosynthesis take place during day time and as a result Stomata the open.
MECHANISM OF PHOTOSYNTHESIS
Photosynthesis is a complicated process, in which carbohydrate is produced after a series of chemical reactions. This process is divided mainly into two phases, such as – light phase and dark phase.
Light Reactions: In the light phase, chlorophyll absorbs light energy which is used to split water molecules into hydrogen and oxygen. Oxygen goes out through the stomata! pore and diffuses in the air. Hydrogen molecules take part in the subsequent reactions of photosynthesis.
Dark Reactions : Hydrogen produced in the light reaction after a series of successive complicated reactions reacts with carbon-dioxide and produces simple carbohydrate. These carbohydrates are subsequently converted into various complicated carbohydrates as required by plants. Even though these reactions may occur during day time, they do not require light energy. For storage in plant body carbohydrate produced in photosynthesis is changed to insoluble starch.
SOURCE OF OXYGEN RELEASED I PHOTOSYNTHESIS
Oxygen produced in photosynthesis comes from water used in photosynthesis but not from carbon dioxide. This has been proved by using radio-isotope of oxygen.
EXPERIMENT ON PHOTOSYNTHESIS
(1) Experiment on production of starch in photosynthesis:
Materials : A fresh leaf, spirit lamp, methylated spirit, iodine, beaker etc.
Method : Boil a fresh leaf taken from sunlight in water until it softens. Then boil the leaf in methylaled spirit so that all chlorophyll comes out of the leaf. In order to avoid chance of catching fire in the spirit the boiling should be carried out putting the container in a water ‘bath’. Then after washing the boiled leaf in water immerse it in dilute iodine solution.
Observation : It will be observed that the leaf has turned blackish’ blue.
Conclusion : Starch has been produced in the leaf as a result of photosynthesis.
(2) Experiment on the Release of Oxygen in Photosynthesis
Materials : A beaker, test tube, glass funnel, small quantity of water, and some aquatic plants or weeds such as Hydrella.
Method : Set the equipment and materia as in the diagram of the textbook and put in the sun. Gas will be collected the test tube pushing out the water gradually. When 4-5 contimetre of the test tube is filled with gas remove the test tube carefully and then examine the gas by putting a ignited wooden stick on its mouth.
Result: The ignited stick bursts into flames.
Conclusion: Oxygen is released in the process of photosynthesis.
IMPORT ANCE OF PHOTOSYNTHESIS
The source of all energy iii the world is the sun. All living organisms use solar energy for carrying out various physiological functions. But the solar energy cannot be used as such directly, this has to be first converted into chemical energy. Only green plants on earth can convert solar energy into chemical energy which can be used. This conversion take places place though the process of photosynthesis. The light energy from the sun is stored e form of chemical energy in the carbohydrate produced in the green plants. This energy is released by breaking down carbohydrate food during respiration in the living organism, which is used for various physiological functions.
Atmospheric oxygen is indispensable for our life or survival. Organisms use oxygen in respiration for releasing energy from food essential for life functions. Carbon-dioxide is produced as a by-product of respiration. In nature, if living organisms would continue respiration only, then oxygen would be exhausted, and the amount of carbon-dioxide would increase to such extent that sustaining life would have been impossible. Green plants maintain the balance of oxygen and carbon- dioxide in the atmosphere by producing oxygen and using carbon-dioxide in photosynthesis. From this, it can be easily assumed, how significant green plants are for human being? Green plants are the primary producer of food. So, if production of carbohydrate in photosynthesis is increased, more food would be available for herbivorous and carnivorous animals. This will increase their production, which is required for the growing population.
Scientists have proved that out of the total solar energy reaching earth, only 1-2% is used, depending on enough light energy for plants which if used properly, more and more carbohydrate can be produced.
Even though plants do not move like men and other animals, they also need energy. Because energy is required for carrying out of various chemical and physical activities which take place in every living cell of plants. Again since plants go on growing through out their life, they need to produce new cells for growth of the body. Constituents of cells, such as cellulose, protein, nucleic acids etc. are to be produced for making new cells. Energy is needed for production of these materials. Energy is also required for maintenance of old cells. Production of flower and fruits for reproduction also requires energy. Even energy is required for transport’ of carbohydrate food produced in leaves to other organs of the plants. Here we will learn how plants obtain their energy by oxidation of food through respiration.
The process of breaking down of organic food (carbohydrate, protein etc.) in presence of enzyme by oxygen in living cells with the release of energy and production of carbon-dioxi4le and water as by product is called respiration. The energy released in respiration is used in energy consuming activities of the organisms.
In every living cell of the plants respiration continues day and night 24 hours. Respiration takes place in the cytoplasm and mitochondria of cells. But mitochondria in the cells are the principal organ for respiration.
The organic compounds which are broken down to simpler substances through respiration are called respiratory substrates. Carbohydrate, protein, fat and organic acids are used as the respiratory substrate.
TYPES OF RESPIRATION
Respiration is principally of two types, such as aerobic respiration and anaerobic respiration. Respiration which uses atmospheric free oxygen is known as aerobic respiration. And respiration which takes place without utilization of atmospheric oxygen is called anaerobic respiration. Compared to aerobic respiration less energy is released in anaerobic respiration.
Generally respiration means aerobic respiration. In higher plant aerobic respiration is the normal process. During aerobic respiration atmospheric oxygen enters the cells and gets dissolved in the cell. This dissolved oxygen completely oxidize the respiratory substrate and liberate more energy (ATP). If glucose is the respiratory substrate the entire process can be represented by the following generalized equation.
C6H12O6 +602 6C02 +6H20 + Energy (ATP)
Glucose oxygen Carbon- water dioxide
Glucose is a kind of high energy compound. If 180 gram glucose (gram molecular weight or mole) is completely oxidized 2830 kilo joules (686 kilo calories) energy is produced:
The complicated biochemical process of respiration takes place through a series of sequential reactions, each of which is regulated by specific ca1yst enzyme. However, the entire respiratory process is divided into two principal phases such as glycolysis and Krebs cycle. In the first phase, one molecule of glucose (6 carbon, carbohydrate compound) on oxidization produces two molecules of pyruvic acids (3-carbon compound). In the second phase, each of the 3 carbon pyruvic acid is converted into three molecules of carbon-dioxide, that means, a total of 6 molecules of carbon-dioxide are produced out of one molecule of glucose. In addition to these six molecules of water and a definite amount of metabolic energy (ATP) and heat are produced.
EXPERIMENT ON AEROBIC RESPIRATION
Select 200 germinating gram seeds for this experiment. Take out 100 seeds and. boil them so that the embryos are killed and seeds can no longer carry on respiration. When the boiled seds1are cooled, put 100 fresh and 100 boiled) seeds two separate thermoflasks and seal their mouths with cotton plug. Insert one thermometer through the cotton plug into each of the thermo flask. Keep the flasks for4-5 days in a safe place. Everyday observe the temperature of each of the flasks.
The flask which contains the boiled seeds will show only the room temperature of the day. But the flask containing the germinating seeds will show temperature higher than the room temperature of the day. Therefore, it is proved that temperature is produced in respiration as it’s by product.
It is a process of liberating energy from food without the use of atmospheric free oxygen. In this process food is incompletely oxidized producing a number of intermediate products, like ethanol. Because of incomplete oxidation of the respiratory substrate, less energy is produced in anaerobic respiration than aerobic respiration.
Excepting some lower forms of plants, like bacteria and fungi, only a few organism can live entirely on anaerobic reparation. Only a few higher forms of pants can temporarily carry on anaerobic respiration while the land around their root system is flooded with water
Yeast is an unicellular fungal plant in which anaerobic respiration is a normal process, produces carbon-dioxide and ethanol as intermediate product out of carbohydrate food. Through anaerobic respiration the process of production of ethanol by yeast is known as fermentation. Ethanol is used in deferent industries, as disinfectant on skin before pushing injection and in the spirit lamp. Presently ethanol is mixed with petrol for reducing the cost of fuel. Yeast is mixed with our for making the bread porous and swollen, Sugar mixed in the dough is oxidize in anaerobic respiration into carbon-dioxide. This carbon-dioxide inside the bread makes it soft and porous.
Anaerobic respiration can be represented by the following generalized equation
C6H12O6 C2H5OH + 2CO2 + Energy (ATP)
Glucose Enzyme ethanol Carbon-dioxide
However, if additional oxygen is supplied to the intermediate products, ethanol on complete oxidation will liberate remaining energy, carbon-dioxide and water.
Experiment on production of carbon-dioxide during anaerobic respiration.
Materials : 10-12 germinating gram seeds, one broad test tube, one small beaker, one clamp with stand, one forceps, some caustic potash and some mercury will be required for this experiment.
Procedure : Take some mercury in the beaker. Fill up the test tube with mercury. Now close the mouth of the test tube with the thumb and carefully put into the mercury in the beaker upside down. Then put the beaker by the side of the stand and carefully fix the test tube with clamp so that there is a gap between the bottom of the beaker and the mouth of the test tube.
Now remove the outer coating of the germinating gram seeds. Insert the seeds into the test tube with the help of a forceps. The seeds will float in the mercury and collect at the end of the test tube. While setting experiment care should be taken so that air cannot enter into the test tube.
Observation : If observed after two hours it will be seen that some gas has collected at the end of the test tube after displacing the mercury down.
Proof: At this stage if some caustic potash is inserted into the beaker with the help of the forceps, it will immediately absorb the gas, and the mercury will is rise and fill up the test tube again. His proves that the gas produced in the test tube is carbon-dioxide.
Comparison between anaerobic and Aerobic respiration:
|1. More effective, more energy is produced.||1. Less effective, less energy is produced.|
|2. Higher types of organisms, such as banyan tree elephant which require more. energy and respire by aerobic process.||2. Some smaller, lower types of organisms, such as yeast, fungi, tetanus bacteria respire by anaerobic, process.|
|3. Produces lot of energy on oxidative breakdown of food.||3. Food is not completely oxidized or broken, energy is retained in the product by In most of the cases by products are used in industry.|
|4. Occurs in the cytoplasm and mitochondria of cell.||4. Occurs only in the cytoplasm.|
|5. Atmospheric oxygen is required||5. Atmospheric oxygen is not required|
|6. Carbon-dioxide, water and energy are produced at the end of chemical reactions||6. At the end of the reaction carbon-dioxide, ethanol and energy (less) are produced.|
SIGNIFICANCE’ OR NECESSITY OF RESPIRATION
Significance or necessity of respiration to living organisms is immense. Respiration continues day and night in every living cells of plants and animals and liberate energy on the breakdown or oxidation of food.
Carbon-dioxide (CO2) produced as a by-product of respiration is utilized in photosynthesis again oxygen produced in photosynthesis is used in respiration. This how respiration and photosynthesis ensure the continuity of life on earth through maintenance of the balance, between oxygen (20.71%) and earbon dioxide (0.03%) in the atmosphere.
The energy required for carrying out various life or physiological processes such as growth, reproduction, maintenance of body etc. by living organisms are supplied through respiration.
PLANT GROWTH AND PEVELOPMENT
Growth is a natural process of living organism which takes place within the body as a result of metabolic activities. The shape and size of the body changes as a result of growth and development. There is a time limit of this growth for each of the animals. But there is no such tine limit for growth in plants. Of course, after attainment of maturity, growth is restricted only at the tips or apical regions of roots and shoots. The stems of dicotyledonous plants go on increasing in girth as a result of secondary growth. Do we know how this growth takes place?
NECESSITY OF GROWTH
Though growth is a normal characteristic of plants, the rate of growth is not uniform throughout the body. Through growth plants attain maturity in shape and size.
In natural environment a matured plant can survive better than a seedling. A young plant easily becomes the prey of grazing animals. Again, if the young plants are under the tall trees they are deprived of the sun light essential for preparation of food by photosynthesis. Plants are also to compete for absorption of water and minerals salts from the soil. To facilitate absorption water and mineral salts from soil, root spread their branches in all direction. The stem supports leaves, flowers and fruits. If number of leaves is larger for absorption of sunlight, more food is prepared. Production of flowers and fruits increase, there by increases the probability of reproduction. For these reasons, growth is essential for plants for survival through competition.
More or less, all pants of plants show growth, if observed specially it will be evident that the, rate of growth is more in the apex of roots and stems. The rate of growth of different pants of plants can be determined by a simple experiment.
Experiment : Equipment and materials essential for determining the rate of growth bf plants are (1) some germinating bean seeds, (2) black dye which does not dissolve in water, (3) a thistle funnel, (4) a bottle suitable for fitting the thistle funnel, (5) black paper and (6) water.
The radicle or the root of The germinating bean seeds have to be marked With the black dye at regular intervals from the base to the tip. Then the seed is to be put into the mouth of thistle funnel so that the root can pass through the tube and the swollen portion is on the upper side. The tube of the thistle funnel has to be covered with the black paper, so that light cans not directly the root.
If observed after one day, it will be observed that the markings on the root are no more at equal distance. The region just behind root tip will show comparatively much increase in the distances between the markings. What is the reason behind ? The reasons are : growth has taken place in this region, the root has elongated, and as a result the distances between the markings have increased.
GROWING REGIONS OF ROOT
A growing root can be differentiated into three regions; such as meristematic zone zone of elongation and the zone of maturation,
1) Merestematic : Most of the root growth takes place in this region. The Meristematic is located just behind the root cap. Because of continuous cell division at this region the root grows. The follow diagram shows how a cell divides into two.
2) Zone of elongation : The zone of elongation is located just behind the Meristematic zone . Here, new cells produced in the zone of cell division attain maturity by elongating their cell walls. For this, the cells are to produce additional materials required for the formation of cell wall and cell membrane, such as cellulose, protein, lipid etc. Since additional cytoplasmic materials are not produced, proportionately large vacuoles appear in the new cells.
3) Zone of maturation : The zone of maturation is located just behind the zone of elongation. Here the new cells attain maturity. The branches of root develop from this zone. Like root, the growing stem also has similar zones. The different in the growing root and stem have been shown in the following diagram.
GROWTH OF MATURED STEM AND ROOT
The mature regions of stem and root only grow in girth. We have learned about the cambium tissue in the chapter on cellular nature of plants. These are meristematic cells capable of cell division. They generally produce new cells for production of xylem and phloem tissues.
Cambium produces new xylem tissues towards the Center and the phloem tissues towards the periphery. As a result, stern and root grow in girth, that mean’s go on increasing in thickness, such as mango, black berry, jackfruit etc. This is called the secondary growth of plants. The plants (such as the monocotyledonous plants) in which secondary growth does not take place are generally made up of narrow stem, such as betel nut, paddy, wheat etc. How plant growth is regulated can be understood through a simple experiment.
Experiment: If the apical bud of a growing stem is removed, then after several days it would be observed that the dormant lateral buds have started growing into branches. According to plant scientist, a phytohormone named auxin is produced in the apical bud which promotes cell elongation in stem and inhibits the growth of lateral buds.
This characteristic of apical buds is known as apical dominance. Removal of the apical -bud stops production of hormone in the stem apex, thereby stopping the elongation of cells. As a result the lateral buds start growing. For this reason, instead of the whole potato, the potato tubers are ent into pieces each with one eye before sowing.
REGULATING THE DIRECTION OF GROWTH
Plants respond to stimuli. Light, water, different chemical substances, heat, ravitation etc. work as stimuli. The respond of a plant organ to stimuli is known as tropism. The respond of plant organ towards the stimuli is called positive tropism. The tropism may be of different kinds
(a) Phototropism : Since stem grow towards light, it is a positive phototropic. Again, roots grow away from the light, so it is a negative phototropic. What is the cause behind it? This can be explained by an experiment with the coleoptiles of a young plant as follows. The first short coming out of a monocotyledonous seed is the coleoptile. The maize coleoptile bend or grow towards light. If its tip is covered with thin tin or if the tip is removed by a fine knife carefully it will no more bend towards light.
From the above experiment plant scientists have inferred that a kind of hormone is produced in the apex in presence of light which promotes growth of buds. If the tip or apical bud is covered or removed hormone is not produced, as a result growth stops.
b) Geotropism : During germination of seeds it is observed that the radicle grows down towards the soil, and the stem grows up opposite to the soil. This is a positive geotropism’ for root. But, for stem, it is a negative geotropism.
C) Hydrotropism : Plant root grows towards water and the stem grows away from the water. This is why, root is. positively hydrotopic. It has been observed by keeping water near the seedling that the, root instead of growing directly downward bends towards water.
d) Chemotropism : Growth in respond to chemical substance is known as chemotropism. The growth of pollen tubes towards ovules into the ovary through the style under the stimuli of a chemical substance secreted by the ovary is an important example of chemotropism.
e) Thigmotropism : Bending response to the stimuli of lateral contact is called thigmotropism. The movement of sweet gourd, bean, bottle gourd etc. Towards the sutdrort are good examples of thigmotroism.
INFLUENCE OF LIGHT AND HEAT ON PLANTS
Influence of light and heat on seasonal growth and yield of plants is of highly significant. Light and heat vary widely in different seasons and from country to county. As a result different types of seasonal plants, and flowers, fruits grow in different seasons in different countries. In countries of the cold regions especially Soviet Union and Europe and some parts of America, this situation becomes extreme. Growth of short-day plants stops in the coldest or ice-cold months in these countries. Again with the advent of summer plants grow faster in the long day hat weather and produce flowers and fruits before the commencement of winter. Extremes of these kinds are rare in our country.
(a) Photo periodisan. : Influence of the lenght of light-darkness or of day- night on flowering in plants is known as photoperiodism. Based on relationship of light period on the production of flowers the flowering plants ae of three types, such as 1) short-day plants, (2) long -day plants, and (3) day -neutral plants.
(1) Short-day plants – These plants require daily on average 8 to 12 hours continuous light for flowering. Examples of this kind of plants are Aman paddy. mustard, dalia etc. In the advent of short-days of winter these plants start bearing flowering buds which later develop into flowers and fruits.
(2) Long-day plants – These plants require daily on average 12 to 16 hours of continuous light for production of flower buds, such as jute plants.
(3) Day- neutral plants: These plants are not dependent on the light and dark period for production of flower. bud, that means, they are independent of light- dark. Examples of these kinds of plants are cotton, gourd, peper, papaya etc.
IMPORTANCE OF PHOTOPERIODISM
Economically photoperiodism is of great significance. By applying this method crops of one season can be grown in another season. As a result crops can he grown in suitable time or season thereby saving them from different types of natural calamities like flood, cyclone, hailstorm, diseases etc. Moreover, by production of crop of one season in season and marketing in another season brings more profit. Photoperiodism is largely practised in agriculture in many countries—The United States of America, United Kingdom, the Netherlands, Sweden, Denmark etc. So in these countries vegetables like cabbage, cauliflower, lettuce, bean etc. and various other agricultural products are available tan in all the seasons.
The seeds of crop plans of the countries in the temperate and tropical regions are kept respectively in low (00 c) and high (450c) temperature treatment, before sowing they are found to produce flower earlier than the seeds which were not treated with heat. From this, it can be understood that the application of appropriate or required temperature treatment to seeds before sowing reduces the time required for flowering. That means, temperature determines the time required for flowering in plants. This process of advancing or hastening of flowering in plants by high or low temperature treatment be sowing is known as verbalization.
In fact temperature influences life cycle of plants in various ways. Plants in cold countries are capable of sustaining life in very lower temperature. Even though plants can generally survive under temperature below the freezing point, growth does not take place during that time. But with increase of temperature metabolic activity resumes at certain level. Then photosynthesis takes place and growth of plant starts. Accordingly in the course of these processes a critical temperature level, affect flowering in most of the plants. The timing of harvesting ‘Aus’ and ‘Boro’ paddy is also determined by the changes in temperature. Flowering and grain formation in boro paddy take place with the rise in temperature, but there must be a low-temperature level just prior to flowering and fruiting.
Hence, receiving of low temperate at certain stage in the life cycle of plants or seeds to bring about flowering is called verbalization.
The process of vernalization: It has not been clearly known or understood as to how temperature incidences flowering. According to the Russian scientist cajlachjan (1936) a kind of hormone known as Florien is responsible for flowering in plants whose effectiveness is dependent on another ‘hormone, called vernal in. If seeds get appropriate temperature treatment before sowing, the production of vernal in is accelerated. As a result, effectiveness of Florien is enhanced thereby expediting the flowering.
Verbalization process is specially effective in case of ‘the bi-ennial carrot plants in the temperate regions. The carrot plants grown from seeds, store food in the tap root during the first year. Even after death of the plants in winter the tap root survive, remains unaffected under the soil. Verbalization takes place in these roots during the lower temperature of winter. New plants grow from these roots in the second year utilizing stored food in the root, grow rapidly and flower.
In the cold countries most of the seeds do not germinate until they ,are verbalized under such low temperature. This process facilitates the survival and continuation of- progeny or species by withholding germination of seeds under unfavorable weather of winter and -by allowing germination under favorable conditions. The temperature induced activities are linked with the of hormones.
Significance of ‘Vernalization : Vernalization is very important. Most of-the countries in the-cold-regions have brought about revolutionary advancements in their agricultural practices through the application of vernalization principle. Normal agricultural practices in these countries are severely affected -because of severe cold weather and hailstorm almost throughout the year. Because of these, countries of the cold regions arrange crop production within the few months of favourable weather by applying vernalization principles. Under these practices plants of one country can be easily adapted in another country of unfavourable weather.
There is good prospect for revolutionizing our agricultural system -by applying vernalization principles. Under these practices, crops such as paddy, jute etc. can be grown in the shortest possible time by saving from the unfavourable impact of drought, waterlogging, flood, diseases etc. On the otherhand, the game land can be used for multiple cropping. But for these initiative, endeavour and research are essential.
USE OF ARTIFICIAL HORMONE
We know that hormone is behind the growth of plants. Plants growth can be expedited by spraying artificial hormones. But plants which will be capable of absorbing more hormone will grow, faster than others. The essence of this relationship between plants and hormones is applied in using many hormones as herbicides. While spraying hormones in the crop fields, weeds with large leaves absorb more hormone than the crop plants with narow leaves, grow faster and die because of unusual growth. Crop plants absorbing lesser quantity of hormone survive and become free of weeds. The extent -of the use of hormone for suppressing the growth of weeds is very limited in our county. The 2, 4-D named hormone is some times applied depending on the circumstances.
Hormone is also used -in the artificial propagation or reproduction. The easiest or simplest method to -produce plants with the characteristics of mother plants is cutting or grafting. But grafting is rather time consuming since it takes longer time for producing roots at the cut portion. -Here better results can be achieved by using hormone. If the cut portion of -plant -is immersed in the hormone -solution, roots, grow fast.
PLANT REPRODUCTION OR PROPAGATION
Plant a similar from another plant is known as reproduction. Plant reproductions can be divided into two types, such as asexual reproduction and sexual reproduction.
The reproduction which occurs without the fashion of made and female gametes (fertilization) are called asexual reproduction. Asexual reproduction is of two types such as reproduction by spores and vegetation reproduction. Many plants especially the non-flowering plants reproduce by producing special types of cells (spore) . Plants like fungi, algae, moss, fern etc. produce spore sacs for reproduction. In these spore sacs, one kind of unicellular spores are produced.
Form each of the mature spore, new plants are developed under favourble condition.
Production of new plants directly or indirectly from the organs other than the flowers and especially reproductive organs is called vegetative reproduction. The new plants generally bear the characteristics of mother plants. But in some cases new blunt characteristics of new Plant can be induced through this method. Vegetative reproduction takes place in two ways: natural vegetative reproduction and artificial vegetative reproduction.
NATURAL VEGETATIVE REPRODUCTION
Different ways of natural vegetative reproduction through common plant organs are described below :
(1) Fragmentation of body : Her a plant body is divided into fragments, each of which later develops into an independent plant, such as Spirogyra Riccia etc,
(2) Root : Reproduction of pants through roots is of two types :
(a) Through normal roots e.g. patal
(b) Through tuberous soots, e.g. sweet potato. Here root eyes develop into a new plant.
(3) Stern tubers : Reproduction of plants through stem occurs in different ways as follows:
(a) Stolon : Here new plants grow from each of the nodes of horizontal stem or stolon the soil surface e.g. arum. water hyacinth etc.
(b) Rhizome: Here plants grow from each of the bud of. the fibrous stem horizontally placed below the soil surface, e.g. zinger, fern etc.
(c) Phylloclade: The stem of man9 plants is modified to perform the functions of leaves. New plants grow from parts of these stem, eg., cactus.
(d) Tuber: New plants grow from each of the eyes or buds, eg., potato.
(e) Bulb: New plants grow from each of the lateral and the axial buds, eg., Onion.
4) Leaves: New plants grow from the buds grown on edge or margin of leaf, eg. Bryophyllum.
As described above new plants normally grow from different common organs or parts of plants. Plants produced so, possess the some characteristics of mother plants. This method is quite suitable for producing a large number of better plants exactly like the mother plants. But this method plants of desired characteristics are not produced. This method is applied in producing different kinds of vegetable crops.
ARTIFICIAL VEGETATIVE REPRODUCTION
In this process new plants are produced artificially from some plant parts. A few of such artificial vegetative reproductions are described below:
1) Cutting : Here a branch from a tree is cut and planted into wet soil. The branch develops into a new plant in a Norma way, eg., rose, variegetum, sugarcane etc., If hormone is applied, root formation is accelerated in the cutting or the graft.
2) Rooting Layering : Here root is artificially grown in a portion of a young stem branch which is later cut along with the root and planted in the soil, eg., layering or rooting etc. In rooting or layering, a low-lying intact branch of plant is, pulled down and covered with soil, or humus mixed soil is tied around the stem branch with the help of polythene sheet. After root formation the branch is cut with the root and planted in soil.
3) Grafting : Generally two plants of the same type are grafted together where stem of one plant is artificially grafted with the branch of another (better type) plant to produce a new plant. The branch portion is called the scion while the stem portion is called the root-stock. In this process, at first the head of the root-stock is cut off with a sharp knife in a definite shape say like a ‘N’-shape. Later the scion Part carefully is cut in the same shape, and carefully fixed into the cut end of the root-stock and then tied the two together with cotton thread spreading wax and fungicides. After the grafting is successful the branches and buds from the root are to be cut off. Such artifical reproduction is possible in lemon types of plants and in mango.
3) Budding : In budding, bud from one plant is planted into another plant. First a ‘T’- shaped hole is made in the skin or bark of the plant in which the bud from another plant is to be planted or fixed. Then take a bud along with the epidermis with the help of a knife from the plant of which grafting is to be made, cut in the form of ‘T’ and then carefully put the bud into ‘T’ shaped hole earlier cut into other plant. Finally tie the bud with the stem with thick thread as shown in the figure.
Reproduction through the union of male and female gametes is known as sexual reproduction. Here by the union of male and female reproductive cells, a zygote is formed. From this zygole new generation of plants develop. Sexual reproduction in plants is described below.
ORGAN FOR SEXUAL REPRODUCTION
Flower is the sexual reproductive organ of higher plants. The male and female reproductive cells are produced in the flower. Their union results in the producti