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Chapter
               Five




                                 Nutrition
          FOR ONLINE READING ONLY










           Introduction

           Living organisms require energy in order to accomplish various metabolic activities.
           The main  source of energy for organisms in all  ecosystems is the sun. Organisms
           obtain their food in different ways. In this chapter, you will learn about physiology
           of photosynthesis which include mechanism of light reaction and dark reaction in C3
           and C4 plants.  You will also carry out anatomical and physiological investigations
           related to digestive system in mammals.  The competences developed will enable you
           to improve human health and agricultural practices.

                                                      namely; autotrophs and heterotrophs. All
                    Think                             organisms that can make their own food
                                                      from simple  inorganic  substances, such
            The world without knowledge on plant  as water and carbon dioxide are called
            and animal nutrition.                     autotrophs. Autotrophs, such as plants, green
                                                      algae, and some bacteria, have the green
           5.1 Concept of nutrition                   pigment (chlorophyll) used to synthesise
                                                      their own food through the process known
             Task 5.1
             From biology books and internent         as photosynthesis. Some other autotrophs
             sources, search for information on the   use the process known as chemosynthesis
             concept of nutrition.                    to make their own food. Sulphur bacteria,
                                                      for example, use inorganic sulphur as the
                                                      source of energy for synthesising  their food,
           There are different modes of nutrition by   and Methanobacterium sp. (bacteria living
           which living  organisms obtain  food in    in deep oxygen-depleted oceans) obtain their
           order to obtain energy and nutrients that   energy from conversion of organic substrate
           are required for survival and for different   such as alcohol and esters to methane as
           metabolic  activities.  Nutrition entails  a   a source of energy. Other organisms that
           process by which living  organisms take    cannot make their own food but depend
           in food and use it for metabolic activities,
           such as growth, and body repair. Based on   on other organisms for food and energy are
           their modes of nutrition, living organisms   called heterotrophs. These include animals,
           are  categorised  into  two  main  groups,   fungi and some bacteria.


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