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6.1 Types of Nutrition
Autotrophic Nutrition
1. An autotroph is an organism that synthesise complex organic molecules from inorganic molecules such as air and water.
2. Autotrophs are able to synthesise their food by
(a) photosynthesis
(b) chemosynthesis
3. Photosynthesis is the process in which green plants and algae, called photoautotrophs, produce organic molecules from carbon dioxide and water using sunlight as a source of energy.
4. Chemosynthesisis the process in which chemoautotrophs synthesise organic compounds by oxidizing inorganic substances such as hydrogen sulphide and ammonia.
Heterotrophic Nutrition
1. Heterotrophs are organisms that cannot synthesise their own nutrients but instead must obtain the nutrients from other organisms.
2. Heterotrophic nutrition is a type of nutrition in which an organism obtains energy through the intake and digestion of complex organic substances into simpler, soluble substances which are then absorbed into their bodies.
3. Heterotrophs include animals, fungi and some bacteria.
4. Heterotrophs may practice holozoic nutrition, saprophytism or parasitism.
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Holozoic Nutrition
1. Most animals like humans, herbivores and carnivores are holozoic heterotrophs.
2. In holozoic nutrition, the organisms feed by ingesting solid organic matter which is subsequently digested and absorbed into their body.
Saprophytic Nutrition (Saprophytism)
1. In saprophytism, the organisms called saprophytes, feed on dead and decaying organic matter.
2. Bacteria and fungi are examples of saprophytes.
3. Saprophytes are sometimes called decomposer.
Parasitic Nutrition (Parasitism)
1. Parasitism is a close association in which an organism, the parasite, obtains nutrients by living on or in the body of another living organism, the host.
2. Parasites which live on the body of the host called ectoparasites. For examples, fleas, ticks and leeches.
3. Parasites which live in the body of the host called endoparasites. For example, the tapeworms which infest the human intestinal tract.