Friday, December 26, 2008


The energy that powers life comes from the sun. Producers are organisms that capture sunlight energy through photosynthesis and store it in organic molecules. They obtain all the energy and inorganic materials they need directly from the environment. Consumers are organisms that harvest energy and chemicals from premade organic molecules contained in the bodies of other organisms. Nutrition is the method by which organisms obtain materials and energy needed for sustaining life. Animals, plants, and microbes have different methods to obtain energy from sources and nutrients from the environment.

Elements of Nutrition

Organisms depend on only a small number of elements to sustain life. These include carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Of these, carbon, hydrogen, and oxygen form the framework of organic molecules such as carbohydrates, proteins, fats, and nucleic acids. The other elements are restricted in distribution. Sulfur and nitrogen are present in proteins; phosphorous and nitrogen are present in nucleic acids. Many other elements also have equally important and essential roles similar to that of the biomolecules such as proteins carbohydrates, lipids, and nucleic acids. They may not be present as a component of macromolecules, but may be present as ions or as a part of other organic molecules such as vitamins and cofactors. There are a group of elements known as microelements or trace elements, which are required only in very small quantities but play an important role in metabolism. So as nutrients they are very important. Elements such as manganese, copper, zinc, cobalt selenium, and iodine are important microelements.

Plant Nutrition

Autotropic organisms such as plants are the producers of the ecosystem. Producers are organisms that capture sunlight energy through photosynthesis and store it in organic molecules. They obtain all the energy and inorganic materials they need directly from the environment. Consumers are organisms that harvest energy and chemicals from premade organic molecules contained in the bodies of other organisms. Green plants absorb light energy and inorganic molecules such as water and carbon dioxide from the environment and synthesize glucose molecules with a process known as photosynthesis. These molecules can be further modified into other types of biomolecules such as amino acids, lipids, vitamins, etc.

The chlorophyll-containing parts of the plants such as leaves are the sites of photosynthesis. The leaves are the organs specially designed to trap the maximum amount of sunlight energy and transform it into a usable form of chemical energy in organic molecules such as lipids, carbohydrates, and proteins. Leaves are flat exposing a maximum surface area against sunlight with its photosynthetic tissue, the palisade parenchyma on the upper surface. The spongy parenchyma specialized in the absorption of carbon dioxide are present on the lower half of the leaf tissue.

The root hairs are the organs adapted for the absorption of water and minerals from the soil. The root hairs are the thin-walled extension of the epidermal cells of the root and have a big vacuole in the middle. Root hairs provide increased surface area for the absorption of water and minerals actively (using energy) or passively (by osmosis). Higher plants are also able to convert inorganic nitrogen (nitrates, nitrites, and ammonia) into organic nitrogens such as amino acids and proteins but they cannot utilize elemental forms of nitrogen even though it is abundant in the atmosphere. They are also able to synthesize all types of fatty acids and other vitamins needed. But plants have symbiotic association with nitrogen-fixing bacteria. These bacteria living in the root nodules can absorb elemental forms of nitrogen and can be converted to nitrates and ammonia, and that will be further transformed into organic forms by host plants. Plants of the legume family have the symbiotic association of nitrogen-fixing bacteria in their root nodules.

Animal Nutrition

Animals and all other organisms that depend on organic food materials synthesized by producers are called heterotrophs and form the consumers of the ecosystem. The biomolecules synthesized by the green plants are the sources of energy and raw materials for the synthesis of new biomolecules needed by their systems. For example, animals consume the protein of plants and in the stomach it is converted into amino acids. These amino acids are absorbed into the cells and are used as the starting materials for the synthesis of new protein molecules. But animals are unable to synthesize amino acids. Organisms must first digest the complex macromolecules in their food before absorbing simpler chemicals into their bodies. In animals, food is first mechanically broken down and then chemically digested before being absorbed. The amount of absorptive surface area that organisms devote to nutrient acquisition is related to the type of nutrients they need. Most organisms use active transport to absorb nutrients, and large absorptive surface areas increase the rate of transport.

Some bacteria in the digestive track help the animals with their nutrition by providing some essential vitamins. Vitamins are nutrients needed in the diet in very small quantities but are very essential for normal functions of the system. Animals cannot synthesize most vitamins and should be supplemented along with the diet. There are two types of vitamins-fat-soluble vitamins (A, D, and E) and water-soluble vitamins (all B complex vitamins, C, and folic acid). Defidencyof any of the nutrients, micronutrients, or macronutrients can cause serious diseases or disorders or even deformities in the system. For example, lack of proteins in the diet can cause stunted growth in children and deficiency of certain vitamins and iron can cause anemia. Deficiency of vitamin B complex can lead to the problems related to the nervous system. The absence of vitamin C can cause scurvy (bleeding gums), deficiency of vitamin A can cause weak eyesight, and deficiency of vitamin D causes bone deformities.

The heterotrophs are classified according to the mode of nutrition. Those organisms which directly depend on the producers, are the herbivores and those animals that eat other animals are the carnivores. There are some organisms that depend on the dead organic matter of both plants animals and they are the saprophytes or (detritivores). The digestive systems of animals are diverse, but show common structural features. Most have one-way flow that allows specialized activities such as chewing, storage, digestion, absorption, and the elimination of wastes. Unlike plants, animals can move and forage for their food. Herbivores and highly mobile predators use active foraging, while less mobile predators employ sit-and-wait foraging, often with the aid of a trapping mechanism. In animals, the more difficult the diet is to digest, the more digestive specializations are present to increase the rate of nutrient acquisition. Large herbivores, in particular, have many specializations to deal with the daunting task of trying to digest enough cellulose to meet energy and nutrient needs. There are some bacteria living in the rumen of cattle and other similar herbivores, which can produce cellulase to break the cellulose present in the fodder into glucose molecules.

Nutrition in Microbes

Microorganisms include both autotrophic and heterotrophic organisms with respect to the mode of nutrition. The autotrophs include photosynthetic and chemosynthetic bacteria, and algae including cyanophyceae. The chemosynthetic bacteria use chemical energy for the synthesis of organic materials. Thus, they also belong to the producers of the ecosystem. The other bacteria, which form a greater part of the microbial population and all fungi, form the heterotrophs, which consume premade organic materials produced by plants. They live on the dead organic materials of plants and animals and are known as saprophytes. They secrete a number of enzymes to the substrate, the surface on which they grow. These enzymes digest the organic materials present on the substrate into simpler forms.

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