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6.1 Digestion 6.1.1 Explain why digestion of large food molecules is essential Adequate diets provide 3 main functions, 1.fuel to make ATP 2. raw materials for biosynthesis, 3. essential nutrients.- those that the animal cannot make itself. Large polymers of carbohydrates, proteins, and fats provide lots of ATP when they are hydrolysed. Fats liberate twice the energy of carbohydrates and proteins. Essential nutrients- Of the 20 amino acids, humans cannot make 9 of them. It is essential that we obtain them in our diet. ( Tryptophan, Methionine, Valine, Threonine, Phenalalanine, Leucine, Isoleucine, Lysine …. Histidine is required by infants.) We also cannot make a fatty acid - linoleic acid. It is an essential fatty acid It is used to make some of the phospholipids in membranes. 1 Vitamins are organic molecules that are required in very small amounts. Humans require 13 essential vitamins. These are grouped into the water-soluble and fat-soluble categories. Water-soluble vitamins such as Vitamin C are excreted in urine so overdoses are not usually possible. Vitamins A,D,E, and K are fat-soluble and when taken in excess amounts, they can accumulate in fatty tissues to toxic levels. Minerals are inorganic nutrients also required in small amounts. Calcium, phosphorous, and iron are examples (see page 855) 6.1.2 Explain the need for enzymes in digestion [The need for increasing the rate of digestion at body temperature should be emphasized.] Enzymes are used to hydrolyse the macromolecules of life into their monomers. Enzyme function changes with the temperature. Warm blooded organisms need more energy, and the warmth increases enzyme function. 2 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease, and one lipasesee page 864 Carbohydrates--glucose, example: salivary amylase Carbohydrate hydrolysis begins in the mouth, but the Stomach acids inactivate the amylase, further hydrolysis occurs in the small intestine with other enzymes like pancreatic amylase, sucrase and lactase. Proteins-- amino acids, example: pepsin in the stomach pepsin likes acidic environment of the stomach since the low pH unfolds the proteins making their peptide bonds more accessible. More protein hydrolysis occurs in the small intestine. lipids-- glycerol + fatty acids, example: lipase in small intestine. Bile salts are secreted from the gall bladder to act as a detergent in breaking up masses of lipids. ( emulsification) Nucleic acids-- nucleotides, example: Nucleases in small intestine. Nucleotides can be broken down further into ribose sugars, phosphate groups, and nitrogenous bases 3 6.1.4 Draw a diagram of the digestive system [The diagram should show the mouth, esophagus, stomach, small intestine, large intestine, anus , liver, pancreas and gall bladder.The diagram should clearly show the interconnections between these structures. ] { see page 863 fig 41.16) 6.1.5 Outline the function of the stomach, small intestine,and large intestine Mouth: breaks up the food increases surface area for enzyme action, saliva lubricates, salivary amylase begins hydrolyzing carbohydrates. esophagus: Muscular tube from mouth to stomach. The epiglottis flap of skin keeps food out of the trachea.Peristaltic contractions move food towards the stomach. It is not lined with mucus, so acid from the stomach can ulcerate it. Stomach: A muscular sack that stores food, sterilizes it with acid, mechanically and chemically breaks up the food, and begins the hydrolysis of proteins. Note that the acid environment and protease enzymes make a dangerous environment for the stomach itself. Mucus secreted in the stomach protects it from the acid, the protease is not secreted in its active form. It is activated by the acid in the stomach. The stomach lining regenerates every 3 days. The pyloric sphincter separates the stomach from the small intestine. Small intestine: Where most of the digestion takes place. The upper portion, the Duodenum, is where the enzymes from the pancreas, bile from the gall bladder, and enzymes from glands in the wall of the small intestine. Most absorption of monomers and nutrients take place here. 4 pancreas: produces enzymes for digestion and transports them to the small intestine. liver: digestive function is to produce bile which is stored in the gall bladder. Bile acts as a detergent breaking up lipid molecules. The liver also stores glycogen, controls glucose levels in the blood, neutralizes poisons in the blood and removes worn out red blood cells. large intestine: the main function is to re-absorb water that has been used as a lubricant and solvent in the processing of the food. Waste becomes more solid as water is removed. Excess salts can be excreted into the large intestine. Symbiotic Bacteria Escherichia Coli ( E. Coli) help produce some vitamins, as well as methane and hydrogen sulfide. 6.1.6 Distinguish between absorption and assimilation Absorption is when the nutrients are moved into the blood stream and cells via diffusion and active transport. Assimilation is when these nutrients are incorporated into the body. New proteins, new carbohydrates, etc. 6.1.7 Explain how the structure of the villus is related to its role in absorption of the end products of digestion see p 865 figure 41.19 Lots of surface area for absorption, 300m2 for humans Villi have microvilli on them, all closely associated with blood capillaries. Surfaces have active pumps for many nutrients. 5