why do organisms need to break down food in order to use it
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Answer:
Animals also need food or nutrients to survive. ... In some cases, organisms such as fungi, get their food by breaking down nutrients in organic matter (once-living things). (click here to see the lesson on 'Nutrients in food') All these contain some specific nutrients that the animals need to grow healthy.
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Explanation:
Digestion, sequence by which food is broken down and chemically converted so that it can be absorbed by the cells of an organism and used to maintain vital bodily functions. This article summarizes the chemical actions of the digestive process. For details on the anatomy and physiology for specific digestive systems, see digestive system, human, and digestive system, invertebrate.
Digestion
In order to sustain themselves, all organisms must obtain nutrients from the environment. Some nutrients serve as raw materials for the synthesis of cellular material; others (e.g., many vitamins) act as regulators of chemical reactions; and still others, upon oxidation, yield energy. Not all nutrients, however, are in a form suitable for immediate use by an organism; some must undergo physical and chemical changes before they can serve as energy or cell substance.
digestion
digestion
Using chemistry to explain how humans digest carbohydrates, proteins, and fats.
© American Chemical Society (A Britannica Publishing Partner)
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Through the act of eating, or ingestion, nutrients are taken from the environment. Many nutrient molecules are so large and complex that they must be split into smaller molecules before they can be used by the organism. This process of breaking down food into molecular particles of usable size and content is called digestion. Unusable components are expelled from the organism by a process called egestion, or excretion. Some plants, many microorganisms, and all animals perform these three functions—ingestion, digestion, and egestion (often grouped under the term alimentation)—but, as expected, the details differ considerably from group to group.
The problems associated with nutrient intake and processing differ greatly depending on whether the organism is autotrophic or heterotrophic. Autotrophic organisms can manufacture the large energy-rich organic compounds necessary for life from simple inorganic raw materials; consequently, they require only simple nutrients from the environment. By contrast, heterotrophic organisms cannot manufacture complex organic compounds from simple inorganic ones, and so they must obtain preformed organic molecules directly from the environment.
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Green plants constitute by far the majority of the Earth’s autotrophic organisms. During the process of photosynthesis, plants use light energy to synthesize organic materials from carbon dioxide and water. Both compounds can be absorbed easily across the membranes of cells—in a typical land plant, carbon dioxide is absorbed from the air by leaf cells, and water is absorbed from the soil by root cells—and used directly in photosynthesis; i.e., neither of them requires digestion. The only other nutrients needed by most green plants are minerals such as nitrogen, phosphorus, and potassium, which also can be absorbed directly and require no digestion. There are, however, a few green plants (such as sundew, Venus’s-flytrap, and pitcher plant) that supplement their inorganic diet with organic compounds (particularly protein) obtained by trapping and digesting insects and other small animal
Heterotrophy characterizes all animals, most microorganisms, and plants and plantlike organisms (e.g., fungi) that lack the pigment chlorophyll, which is necessary for photosynthesis. These organisms must ingest organic nutrients—carbohydrates, proteins, and fats—and, by digestion, rearrange them into a form suitable for their own particular needs.
Ingestion
As already explained, the nutrients obtained by most green plants are small inorganic molecules that can move with relative ease across cell membranes. Heterotrophic organisms such as bacteria and fungi, which require organic nutrients yet lack adaptations for ingesting bulk food, also rely on direct absorption of small nutrient molecules. Molecules of carbohydrates, proteins, or lipids, however, are too large and complex to move easily across cell membranes. Bacteria and fungi circumvent this by secreting digestive enzymes onto the food material; these enzymes catalyze the splitting of the large molecules into smaller units that are then absorbed into the cells. In other words, the bacteria and fungi perform extracellular digestion—digestion outside cells—before ingesting the food. This is often referred to as osmotrophic nutrition.