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PinkMonkey Online Study Guide-Biology


5.0 Introduction

All forms of life have one basic common requirement, and that is energy. Energy gives the capacity to do work. Organisms need energy for existence and maintenance of life. The cell is the basic structural and functional unit of an organism and it performs various metabolic and other vital activities. These activities need energy, i.e. biologically usable forms of chemical energy, such as the energy-rich organic compound called ATP (adenosine tri-phosphate). ATP molecules act as energy mediators in cells. For example, ATP undergoes a breakdown (hydrolysis) and provides energy for energy requiring reactions. On the other hand, ATP is synthesized by input of energy made available through some energy-yielding reactions in the cell.

Figure 5

The solar energy that is trapped by green plants is converted into chemical energy during photosynthesis and is stored as food energy in carbohydrates and other organic food materials (e.g. fats, oils, organic acids, proteins, etc.)

In cell metabolism, these energy-rich organic food materials are oxidized and the stored energy is released as free energy. This is utilized by the cell to perform various cellular activities. Part of the energy is lost as heat.

In the cells, the process which supplies energy through oxidation of organic compounds is called cellular respiration.

Definition : "Respiration is an intracellular process of oxidation-reduction reactions in which the complex organic food materials are broken down in a step-wise manner to form simpler end products, with the release of energy and carbon dioxide."

It is basically an energy releasing and supplying process. The energy released in respiration is of two types :

(a) Chemical energy, i.e. ATP. It is utilized for the cellular activities.

(b) Heat energy. It is mostly lost. Depending upon the availability of oxygen as an oxidant, respiration is of two types : (1) aerobic respiration, in which oxygen in used in the respiratory break down of organic substrate, and (2) anaerobic respiration, in which oxygen is not used in the respiratory breakdown of organic substrate.

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Table of Contents

5.0 - Introduction
5.1 - Ultrastructure and Functions of Mitochondrion
5.2 - An Overview of Cellular Respiration
5.3 - Glycolysis
5.4 - The T.C.A. Cycle(Tricarboxylic Acid Cycle)
5.5 - Electron Transport Chain
5.6 - Fermentation
5.7 - Significance of Respiration

Chapter 6


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