Nutrition (also called nourishment or aliment) is the provision, to cells and organisms, of the materials necessary (in the form of food) to support life. Many common health problems can be prevented or alleviated with a healthy diet.
Animal nutrition.The human body contains chemical compounds, such as water, carbohydrates (sugar, starch, and fiber), amino acids (in proteins), fatty acids (in lipids), and nucleic acids (DNA and RNA). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, calcium, iron, zinc, magnesium, manganese, and so on. All of these chemical compounds and elements occur in various forms and combinations (e.g. hormones, vitamins, phospholipids, hydroxyapatite), both in the human body and in the plant and animal organisms that humans eat.
Carbohydrates may be classified as monosaccharides, disaccharides, or polysaccharides depending on the number of monomer (sugar) units they contain.Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so.
Proteins are the basis of many animal body structures (e.g. muscles, skin, and hair). They also form the enyzmes which control chemical reactions throughout the body. Each molecule is composed of amino acids which are characterized by inclusion of nitrogen and sometimes sulphur (these components are responsible for the distinctive smell of burning protein, such as the keratin in hair).
Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen that are present in nearly all organic molecules.
Many elements are essential in relative quantity; they are usually called "bulk minerals". Some are structural, but many play a role as electrolytes. Elements with recommended dietary allowance (RDA) greater than 200 mg/day are, in alphabetical order (with informal or folk-medicine perspectives in parentheses):
* Cobalt required for biosynthesis of vitamin B12 family of coenzymes
* Copper required component of many redox enzymes, including cytochrome c oxidase
* Chromium required for sugar metabolism
* Iodine required not only for the biosynthesis of thyroxin, but probably, for other important organs as breast, stomach, salivary glands, thymus etc. (see Extrathyroidal iodine); for this reason iodine is needed in larger quantities than others in this list, and sometimes classified with the macrominerals
* Iron required for many enzymes, and for hemoglobin and some other proteins
* Manganese (processing of oxygen)
* Molybdenum required for xanthine oxidase and related oxidases
* Nickel present in urease
* Selenium required for peroxidase (antioxidant proteins)
* Vanadium (Speculative: there is no established RDA for vanadium. No specific biochemical function has been identified for it in humans, although vanadium is required for some lower organisms.)
* Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase
This type of nutrition involves the taking in of solid particles of food which have to be further broken down into simpler particles inside the organism (there are exceptions which are called fluid feeders. Think of at least two of them. Look for answers in the Q & A section). These particles may be big or small.
For example, Hydra and sea anemone are called macrophagous feeders as they take in large pieces of food. Animals like the earthworm and mussels are called microphagous feeders as they take in food which is in very small particles. Earthworms are also called detritivores as they feed on dead plant and animal matter. However, the digestion takes place inside the body and hence they are also considered holozoic. Holozoic nutrition involves ingestion of food, its digestion, absorption and assimilation.
'Sapros' refers to rotten and 'trophic' refers to food. Saprotrophic nutrition is the process by which the organisms feed on dead and decaying matter. The food is digested outside the cells or even the body of the organism - extracellular digestion. The organism secretes digestive juices that contain enzymes directly on to the food. The digestion makes the food soluble and it is then absorbed by the organism.
Examples of saprophytes:
Plants which have saprotrophic nutrition are Rhizopus (bread mould), Mucor (pin mould), Yeast, Agaricus (mushroom), many bacteria etc.
Examples of saprozoans:
(animals which have saprotrophic nutrition) are Mastigamoeba and Chilomonas. The digestive juices are secreted by the cell membranes which means the general body surface as they are single-celled protozoans.
Saprotrophs are different from detritus feeders which do not digest their food outside the body.