Dr. N.L. Kachhara
The process of nutrition involves the taking of food inside the body and converting it into smaller molecules, which can be absorbed by the body. Food is kind of fuel which provides energy to all the living organisms. Nutrition is a process of intake of nutrients, like carbohydrates, fats, proteins, minerals, vitamins and water, by an organism as well as the utilization of these nutrients by the organism.
Basically these are two modes of nutrition, autotrophic and heterotrophic
Autotrophic Nutrition
It is a type of nutrition in which the living organism manufactures their own organic food from simple inorganic raw materials like carbon dioxide and water present in the surroundings with the help of sunlight. The green plants have an autotrophic mode of nutrition. The autotrophic bacteria also obtain their food by this mode. Green plants obtain the energy from solar radiation. The process is called photosynthesis and occurs in the presence of chlorophyll. The organisms capable of photosynthesis are termed phototrophs. Certain bacteria obtain energy from exergonic chemical reactions for the synthesis of organic substances. These organisms are called chemoautotrophs. The process of preparing organic food with the help of energy from chemical reactions is known as chemosynthesis.
Heterotrophic Nutrition
Animals, fungi, some protists (amoeba) and many bacteria lack chlorophyll and cannot utilize sun energy. They use chemical bond energy of organic molecules synthesized by other organisms in building their own organic molecules. This is called heterotrophic nutrition. They get organic molecules by taking plants or animals (living or dead) or their products, and obtain energy by "burning" these molecules in their body.
Heterotrophic nutrition is of three types.
1. Saprotrophic Nutrition (Roma ahara). Many organisms absorb fluid food through the body surface. This is called saprotrophic or absorptive nutrition. Bacteria and fungi (like moulds, mushrooms, yeast) flourish on dead, decaying organic matter both plant and animal origin. Some parasitic protists, such as trypanosoma, and a few invertebrates, such as tapeworms, live in a medium that contains simple organic compounds ready for absorption and straight away absorb them.
2. Holotrophic Nutrition (Kavala ahara). Majority of invertebrates and all vertebrates take plants, animals or their products through the mouth and break up the large organic molecules into smaller ones in their own body with the help digestive enzymes. This mode of taking solid or fluid organic food via mouth is called holotrophic or ingestive nutrition. The animals may take plants, or other animals, or both as food, and are respectively called herbivores (rabbit, cow), carnivores (lion, tiger) and omnivores (sparrow, man). Some animals take one type of food when young and a different type when adult. For example, frog is herbivores in the larval stage and carnivores in the adult stage. Amoeba is a unicellular animal. In unicellular animals, the single cell performs all the processes of nutrition. Amoeba eats tiny (microscopic) plants and animals as food that floats in water in which it lives. Amoeba has no mouth and ingests food by using its pseudopodia. The mode of nutrition in Amoeba is holozoic.
3. Mixotrophic Nutrition.
Euglena carries on autotrophic and soprotrophic nutrition at the same time. This is called mixotrophic nutrition.
Heterotrophic plants are broadly categorized into three main groups, depending upon the source from which they get their nourishment saprophytes, parasites and insectivores (or carnivores) plants.
- Saprophytes These plants grow and live on dead decaying organic matter including animal and plant remain. The saprophytes include a large number of fungi, bacteria, a few algae, mosses, peteridophytes and some angiosperms
- Parasites-
The parasitic plants grow and obtain their nutritional requirements from other living organisms (hosts). There are two main categories of parasitic angiosperms.
- Total or holoparasites. The parasites, which are non-green and obtain their total food from hosts, are called holoparasites.
- Partial or semi-parasites. They are green and can synthesize their own food but depend on host for water and mineral supply.
3. Insectivores (or carnivores) plants.
Most green plants derive their nitrogen from the soil as solutes conducted through the root system. However, some of them obtain nitrogen from captured animal prey. Such plants are called carnivores or insectivores plants. In fact, these plants do not live solely on the captured animals as they can manufacture their own organic food with the aid of chlorophyll present in their leaves and stems. They are therefore, partly autotrophic and partly heterotrophic.
Respiration
The process of respiration involves taking in oxygen into the cells, using it for releasing energy by burning food, and then eliminating the waste products, carbon dioxide and water, from the body. Respiration is essential for life because it provides energy for carrying out all the life processes, which are necessary to keep the organism alive. Respiration includes breathing as well as the oxidation of food in the cells of the organism.
Most of the earth's oxygen occurs in the air, but some is dissolved in water. Thus, air or water may serve as the source of oxygen for the animals.
Aerobic respiration: In most animals and plants, respiration involves use of molecular oxygen and release of carbon dioxide simultaneously. Such a respiration is called aerobic respiration. The organisms, which carry on aerobic respiration, are termed aerobes.
Anaerobic respiration: The process of releasing energy without the use of oxygen is called anaerobic metabolism. It is also termed fermentation. The organisms, which carry on anaerobic respiration, are termed anaerobes. The microscopic organisms like yeast and some bacteria obtain energy by anaerobic respiration. Anaerobic respiration takes place in our muscles also during vigorous physical exercise when oxygen gets used up faster in the muscle cells than can be supplied by the blood.
Direct and Indirect Respiration
Direct respiration: It is the exchange of environmental oxygen with the carbon dioxide of the body cells without special respiratory organs and without the aid of blood. It is found in acrobic bacteria, protists, plants, sponges, coelenterates, flatworms, roundworms and most arthropods. All the parts of a plant perform respiration individually. It occurs at a slow rate. Amoeba and Planaria breathe through their cell membranes. The earthworm absorbs the oxygen needed for respiration through its moist skin.
Indirect Respiration: It involves special respiratory organs, such as skin, buccopharyngeal lining, gills and lungs, and needs the help of blood. The respiration in the skin, buccopharyngeal lining, gills and lungs is respectively called cutaneous, buccopharyngeal, bronchial and pulmonary respiration. Cutaneous respiration takes place in annelids, some crustaceans and amphibians. It occurs both in water and air. Buccopharyngeal respiration is found in certain amphibians such as frog and toad. It occurs in the air. Bronchial respiration is found in many annelids, most crustaceans, and mollusks, some insect larvae, echinoderms, all fishes and some amphibians. It occurs in water only. Pulmonary respiration is found in snails, some amphibians and in all reptiles, birds and mammals. It takes place in air only.
Photosynthesis is an anabolic process. It produces organic molecules (glucose), having in their bonds chemical energy transformed from the radiant energy of the sun. It occurs in the green cells, during the daytime, and leads to increase in weight. Respiration is a catabolic process. It breaks organic molecules, releasing their bond energy. It occurs in all organisms, at all times, and leads to decrease in weight.
Metabolism
The transformation of energy and matter within the body is called metabolism. Metabolism is of two kinds, (1) catabolism, and (2) anabolism. Catabolism is destructive process in which large organic molecules are broken down into smaller constituents. This usually occurs with the release of energy (usually as ATP)
C6H12O6 (glucose) + O2 - Usable energy (ATP) + CO2 + H2O
Catabolism is characteristic of heterotrophs.
Anabolism is constructive metabolism in which small precursor molecules are assembled into larger organic molecules. This always requires the input of energy (often as ATP). Photosynthesis is anabolic metabolism.
CO2 + H2O + Light (energy) - C6H12O6 (glucose) + O2
