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LECTURE 15Agriculture – the science, art and practice of cultivating the soil, producing crops and raising livestockFor most of early history, humans survived as foragers or hunter-gathers, gathering wild plants and hunting animals in their natural environmentAround 10000 years ago, there was a shift in human endeavor from foraging to farmingWhy it happened is not known, but it appears to have formed the basis of advanced civilization in both the old and new worldsEarly Sites of AgricultureThe near East, the “Fertile Crescent” of Mesopotamia (modern day Iran, Iraq, Turkey, Syria, Lebanon, and Israel)Archeological sites with plant remnants that date up to 14000 years agoEarly plants: wheat, barley, pea, lentilEarly animals: goat, sheep, dogsThe Far EastIn southeast asia: modern day Thailand, China (along the Yellow and Yangtze rivers)8000 years ago began cultivating rice, millet, broomcorn millet, rapeseed, hempthere was also evidence of domesticated cattle, pigs, dogs, and poultryThe New WorldIn the New World, modern day Mexico and Peru12000 to 10000 years ago: Tehuacan ValleyBegan cultivating, domesticating major cropsMexico: beans, corn, tomato, peanut, chili peppers, squashPeru and South America: potato, cacaoDomesticated PlantsPlants that have been domesticated are genetically distinct from their wind progenitorsWild plants develop by Natural Selection – ensures their survival in the environmentPlants are domesticated by artificial selection – traits are selected not fo survival, but for our own benefitMost domesticated plants could not survive in the wildCultivated plantsCenters of origin: regions where many cultivated plants came fromFrom these centers, plants and animals were dispersed and spread to other areas of the world – by explorers, invaders, travelers, etc.Wild ancestors of many domesticated plants still exist – they help in the development of new varietiesThese wild ancestors are important for maintaining the genetic diversity of crop plantsModern agricultureNow that we know how agriculture began, lets look at modern day agricultureWorld: food and fiber that sustains the entire population of this planet is produced on just 3% of the plant’s land97% of the land is non-crop or non-grazing, it’s tundra, desert, forest mountain and tropical forestthe best land is already used in crop productionAgriculture in the U.S.The land area in the United States is 1.9 billion acres16% is used as crop land34% is used for pasture and grazingfour major crops are planted on 80% of crop landcorn, wheat, soybeans, and hayvegetables, fruit and nuts (potato, rice, apples, tomato, peanuts, sugarcane) are produced on 7% of the crop land; cotton on 4% of the landU.S. AgricultureThere has been a steady increase in agricultural yield per acre in U.S. crops; without any significant increase in new landHow can this be?Improved crops varieties – higher yieldImproved agricultural practicesImproved pest control – resistant cultivarsTailored fertilization of cropsHuman NutritionWe eat every day, we fulfill our energy needsLike a car that needs gas, we need the nutrients in food for energyDaily nutritional needs in human diet are supplied byMacronutrients – required in large amountsMicronutrients – required in small amountsCaloriesCalorie – a measure of energyThe amount of energy required to raise 1 gram of water 1 degree CFood energy measured in kilo calories (kcal = 1000 calories)Dietary guides use the term calories to describe kcalHumans require from 1200 to 3200 calories per day, depending on age, sex, and activity level or personMacronutrientsThere are three macronutrients, they are the fuel needed for cellular respirationCarbohydratesProteinsFatsCarbohydratesAs you recall, carbohydrates are composed of C, H, ODivided intoMonosaccharidesThe basic building block of all carbohydratesGlucose – the most abundant monosaccharide (transported into the blood), It is metabolized during cellular respiration to produce energyFructose and galactose are other important monosaccharidesDisaccharidesComposed of 2 monosaccharides joined togetherSucrose (table sugar) is the most common disaccharideGlucose + fructose = sucroseOther disaccharides: Lactose (milk sugar), Maltose (found in germinating grains)Provide no nutritional value, only caloriesPolysaccharidesContain hundreds or thousands of individual sugar units (usually glucose), aka. Complex carbohydratesStarch – long glucose chain found stored in plants (potato, wheat, rice, beans, corn)Starch is broken into glucose by enzymes in the salivaGlycogen – is the storage form of glucose in the human bodyExcess glucose is converted into fatFiber – a polysaccharide derived from plantsComes from cellulose (cell wall of plant cells) which is composed of many glucoseNot digestible, but provides bulkDietary fiber can beSoluble – found in oat, reduces cholesterol levels and risk of heart diseaseInsoluble – found in fruit, bran, vegetables. Absorbs water, prevents constipation; may prevent certain cancers (colorectal)ProteinsLarge complex molecules that perform many functions in the bodyThey are made from smaller building blocks called amino acidsThere are 20 diff. amino acids that assemble in many ways to make thousands of proteinsSources: meat, fish, cheese, milk, egg, beans, corn, whole wheat bread, oatmeal, peanut butter, soy beanCells in the human body can make 11 out of 20 amino acids, but there are 9 amino acids the body cannot makeThe 9 are called essential amino acids, must come from the dietCant be stored by the body, must constantly be taken in dietComplete proteins – contain all the essential amino acidsProteins from animal sources are completeProteins from plant sources are incomplete (they may lack one or two essential amino acids)In order to get all essential amino acids from plant sources, it’s necessary to combine different protein plant sourcesEx. Corn and beans complement each other and provide all essential amino acidsProtein digestionRequires digestive enzymes (which are also proteins)Digestibility is important: some proteins (such as egg protein) cannot be broken down completely – even through egg protein is very completeHigh quality proteinsContain all essential amino acidsAre fully digestibleFree their amino acids, which are absorbed readilyFatsFats or lipids are composed of C, H, OHave a glycerol head (hydrophilic) and a hydrophobic tail (fatty acid)Lipids are insoluble in waterHave a bad


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UMD BSCI 124 - LECTURE 15

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