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Thursday, November 11, 2010
Thursday, November 11, 2010 - 0 Comments
Energy is the capacity to work. Work is the transfer of energy. Energy can also be transformed. For example a plant can transform solar (radial) energy into chemical energy. Plant can then be burned in a stream generator and the energy transformed into the energy of motion that is the turning of the wheel. Energy has many forms: the heat from furnace, the sound of jet plane, the electric current that lights a bulb, the radioactivity in a heart pacemaker or the pull of magnet.
Forms of Energy:
Energy exists in two states, kinetic energy and potential. Kinetic energy is the energy of motion that is a thundering waterfall. Potential energy is stored energy like a gait boulder poised on a pinnacle. In a living animal, energy in chemical bonds is a form of potential energy. Animals use thin bond energy in organic molecules to accomplish biological work. Much of the work an animal performs, involves the transformation of potential energy to kinetic energy in its cells.
Units of Energy:
Employed unit for measuring heat in an animal is the kilocalorie (K cal :) or nutritional calorie (C). A kilocalorie is the amount of heat necessary to raise the temperature of 1 kg: of water through 1°C and is equal to 1000 calories. A reasonable daily intake of energy for an average person is approximately 2000 to 2500 K.
A calorie (C) is the amount of heat required to raise the temperature of 1g (K. C) of water 1°C from 14.5 to 15.5°C. Cal.
The Laws of Energy Transformations:
There are two laws of thermodynamics that control energy transformations namely first law of thermodynamics and second law of thermodynamics.
First Law of Thermodynamics:
It is also known as Law of energy Conservation. It states that ‘energy can neither be created nor destroyed but only transformed. Energy can change from one form to another form like electric energy passes through a hot plate to produce heat energy. It can be transformed from potential to kinetic energy as when a squirrel eats a nut and then uses this energy to climbs a tree, but it can never be lost or created. As the energy is neither created nor destroyed thus the total amount of energy in the universe remains constant.
Second Law of Thermodynamics:
It states that all objects in the universe tend to become more disordered and that the total measure of this degree of disorganization is called entropy. The natural gas burns in a stove, the potential chemical energy stored in bonds of the gas molecules is converted to light in the form of blue flame and heat. Some of heat energy can be used to boil water on the stove and some is dispersed into the kitchen, where it is no longer available to do work. This unusable energy represents increased entropy.
Activation energy: Most chemical reactions require an input of energy to start a reaction is match is lit and the heat energy is used to start wood-burning in a fireplace. At the chemical level, the input energy must break existing chemical bonds before new bonds can form. In thermodynamics this input energy is called activation energy. It is reaction with net release of energy; the reactant contains more energy than the products. In other words, the amount of this excess energy (free energy) released into the environment is greater than the activation energy required to initiate the reaction. These reactions occur spontaneously and are called exergonic. In constant a chemical reaction in which the product contains more energy than the reactants require greater input of energy from the environment than is released. Because these reactions do not occur spontaneously, they are called endergonic. The amount of reactant substance converted to product substance in a given period of time is the reaction rate. The reaction rate of exergonic reaction does not depend on how much energy the reaction releases but on the amount of activation energy required for the reaction to begin. The larger the activation energy of chemical reaction, the more slowly the reaction occurs, because at a given temperature, fewer molecules succeed in overcoming the initial energy hurdle. Activation energies are not fixed. For example when certain chemical bonds are stressed, they may break more easily.
It is composed of several different types of cells but two are important named Neuron and neuroglia. Neurons are impulse conducting cells and consist of three parts, dendrites, cell body and axon. Dendrite receives nerve impulses and pass on to the cell body. The cell body is thickest area that contains muscles and other cell organelles of the cell. Axon is long thread like extension of cell body which conducts nerve impulse away from the cell body. In some peripheral nerves, the axon is enclosed by Schwann cells that act as insulating material. Neurons are specialized to transmit signals called nerve impulses from one neuron to the other, from sense organs to the brain, from brain to effectors that is the muscles and glands. Neuroglia is non nervous cell that insulates the membranes of neurons, provides protection support and nourishment to the neurons. Nervous tissue is located in brain, spinal cord and nerves.
Muscle tissues are composed of long, excitable cells capable of considerable contraction. In the cytoplasm of muscle cells are present large number of parallel arranged structures called microfilaments that are made up of contractile proteins actin and myosin. Muscle is the most abundant tissue in animals and the contraction of muscle accounts for much of the energy consuming cellular working in an active animal. There are three types of tissues called Smooth muscle, skeletal muscle and Cardiac muscle.
(1) Smooth Muscle Tissue:
Smooth muscles lack cross striations and are spindle shaped containing single nucleus. These are involuntary in action and are thus named as involuntary muscles. The contract slowly than the skeletal muscles but for longer periods of time than skeletal muscles. These cells are arranged closely to form sheets and are mostly located in the walls of hollow organs like gut, blood vessels, and ducts of reproductive and excretory systems. It helps in the movement of substances like food, urine.
(2) Skeletal Muscle Tissue:
Skeletal fibre is composed of striated muscle fibres that are long, cylindrical and contains many peripheral nuclei. They are voluntary in nature and are attached with bones by tendons. The contraction helps in the bone to move and hence it helps in locomotion of animal.
(3) Cardiac Muscle Tissue:
It consists of striated branched spindle shaped cells that are shorter than the skeletal cells. Each cell contains single nucleus and specialized cell junctions called inter calated dises that allow ions to move quickly from one cell to the other. These are located in wall of the heart and it has involuntary control. As the walls of the heart contract cardiac muscle tissue pumps blood into circulation.