Nutrition is a process by which animals obtain essential and nonessential substances called nutrients and utilize these produce to energy required for various life process such as growth, repair, development, reproduction and other activities from the surrounding as food.
MODES OF NUTRITION
Autotrophic nutrition • Preparation of organic food from the inorganic materials is called autotrophic nutrition.
• It is of two types : Photoautotrophic and chemoautotrophic.
a) Photoautotrophic nutrition
• All green plants, certain Protists ( Euglena viridis) and some bacterial ( green sulphur bacterium, chlorobium) take carbon dioxide and water from the environment and transform these into glucose and oxygen with the help of Sun’s energy trapped by chlorophyll.
b) Chemoautotrophic nutrition
• Some bacteria utilize light as source of energy during the synthesis of food, utilize the energy obtained in the form of A.T.P
• Examples of chemoautotrophic bacteria
i) Sulphur bacteria – Beggiatoa, thiothrix and Thiobacillus thiooxidans
ii) Iron bacteria
iii) Nitrifying bacteria – Nitrosomonas, Nitrosococcus, Nitrobacter and Nitrocystis
• Animals, fungi etc. cannot manufacture their food. They depends upon autotrophs directly or indirectly.
i) Holotrophic ( Holozoic) nutrition
• Most vertebrates and invertebrates take solid or liquid food through their mouth is called holozoic nutrition.
ii) Saprozoic nutrition
• It consists of obtaining food from dead and decaying organic food by first pouring digestive juices over the same and then sucking the digested food. Example – Spider, housefly
iii) Parasitic nutrition
• In this type of nutrition, food is obtained in liquid form from the body of another killing him
• Example – Plasmodium, Trypanosoma, Taenia, Ascaris
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