CHAPTER 4 : PHOTOSYNTHESIS

4.0 Introduction

Energy is needed for existence as well as maintenance of life. Solar radiation is the unending source of energy for all forms of life on earth. However, living organisms can use only one form of energy for various life activities i.e. the biologically usable form of chemical energy. It is represented by the energy-rich organic compound called ATP (adenosine tri-phosphate). Photosynthesis is the only process in which the solar energy is trapped and converted into the chemical energy ATP. This process is described as photophosphorylation. This energy is stored in food molecules as food energy. In respiration, organic food is oxidized and the food energy is released as free energy and is made available for various cellular activities. In cells, the ATP molecules act as energy mediators.

Organisms which can synthesize their own organic food from simple inorganic nutrients are called autotrophs or producers. These are mostly photosynthetic (e.g. green plants) which take energy from light. A few are chemosynthetic (e.g. certain soil bacteria) which obtain energy from chemicals.

Photosynthesis is the most important and essential physiological process in green plants. This is because it is the primary source of organic food and ATP energy for all forms of life. It utilizes carbon dioxide and converts it into organic food (carbohydrates). It also releases oxygen into the atmosphere. In fact, oxygenic photosynthesis was responsible for converting the totally anaerobic atmosphere on earth into the aerobic atmosphere that exists today.

Table of Contents

4.0 Introduction
4.1 Chloroplasts
4. 2 Overall Equation of Photosynthesis
4.3 Primary Process of Photosynthesis
4.4 Secondary Processes of Photosynthesis (Biochemical Phase, Dark Reaction)
4.5 Diversity in Photosynthesis Pathway
4.6 Significance of Photosynthesis

Chapter 5

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