41 Digestion 2009

41 Digestion 2009 - Biol 61 Digestion (Chapter 41)...

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Biol 61 – Digestion (Chapter 41) 4/1/09-4/3/09 Autotrophs , like plants, produce cellular energy from sunlight, and can build the organic molecules they need through photosynthesis. Heterotrophs are organisms that get their essential nutrients and organic molecules by eating other organisms, and that is why they have digestive systems. Whether it’s a unicellular organism or a single cell that is just one of billions found in a multicellular organism, all heterotrophic cells need a source of fuel and organic building blocks. We need the food calories for fuel and the organic molecules for building blocks, but we also need other essential compunds- essential nutrients - that we can’t make ourselves. There are compounds like amino acids and unsaturated fatty acids that we can’t make but must get in our diet. Vitamins are organic substances needed in trace amounts. There are two general classes of vitamins, water soluble vitamins and fat soluble vitamins. Water soluble vitamins are mostly protein cofactors (or the building blocks for protein cofactors). Excess supplies of these chemicals are usually eliminated in the urine. Fat soluble vitamins generally are not related to enzyme cofactors but play different roles. Ingestion of too much of any of these fat soluble vitamins is potentially quite dangerous, since we have no mechanism for removing them from the body - they will build up in the fat and can potentially cause vitamin intoxication. The fat soluble vitamins are vitamins A, D, E, and K. All of the others are water soluble. Minerals are inorganic substances, ions like Cl- and Na+, iron, magnesium, etc. Some we need, like salts, to maintain the correct ionic balance in our cells and bodily fluids, while other inorganic substances play an important role as cofactors for the correct function of many proteins in our body (see Table 41.1 & 41.2 for some examples). If an organism can’t get enough calories to maintain its own body weight, it is considered to be undernourished . But an organism can have plenty of calories from its diet and yet be malnourished because it is lacking required essential nutrients (so don’t just live off of macdonalds, doritos and mountain dew, folks). Processing Food When we eat another organism, we usually start by ingesting big pieces that have to be broken down into successively smaller fragments that can ultimately be absorbed by our cells and put into our blood to be distributed to all the cells of the body. So, a body goes to tremendous lengths to break food apart, digest it as much as it can, and get every last molecule that’s worth keeping. Prokaryotes absorb food molecules directly from their environment. For eukaryotes food processing involves: ingestion (get it into the digestive system), digestion (turn polymers monomers), absorption (move monomers into cells), and elimination (remove what you can’t use). Single-cell protists and sponges digest their food
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41 Digestion 2009 - Biol 61 Digestion (Chapter 41)...

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