CHEM181 MIDTERM2.docx - TOPIC 5 AGRICULTURE-Agriculture is based on photosynthesis without agriculture we dont have food to eat-Pesticides are used

CHEM181 MIDTERM2.docx - TOPIC 5 AGRICULTURE-Agriculture is...

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TOPIC 5 - AGRICULTURE -Agriculture is based on photosynthesis, without agriculture we dont have food to eat. -Pesticides are used small amounts and not enough to harm us. They can be used safely with proper equipment. Used to kill living things, including weeds (herbicides) and insects (insecticides). -Organic: growing crops without use of synthetic fertilizers, synthetic pesticides, relying on natural means to control insects. Use organic fertilizer manure, but there is not enough manure to sustain all crops. -Justus Von Liebig: (19th century): fertilizer concept. Figured 4 major nutrients in manure: nitrogen, phosphorus, potassium and various minerals needed in small amounts. -Each fertilizer have 3 numbers, ratio of N/P/K. Different plants need different amounts. -Fritz Haber (19th century): found a way to combine nitrogen and hydrogen to make ammonia. N 2 + 3 H 2 2 N H 3 N H 3 + HN O 3 →N H 4 N O 3 It was not possible to make ammonia synthetically. Ammonium nitrate is widely used as fertilizer. Ammonium nitrate slowly decomposes into N2O (nitrous oxide), a greenhouse gas, contibute to global warming. -When using fertilizer don't need soil. William Gericke proposed first idea of soilless gardedning, called Hydroponics. Growing without soil but need good ratio of nutrients. -One way to control insects is to use predatory insects like ladybug. Agriculture battles: 1) Apple scab: fungus, people dont buy even that there is no problem with that apple. So farmers resort to agrochemicals in order to eliminate scab. Botrytis fruit rot in strawberry, stem rust in wheat, black spot fungus in roses. 2) Weeds: suck nutrients from soil. 3) Insects: corn borer invades corn, apple orchard roots are surrounded by nematodes which are destroying the roots. Control insects/weed: 1) First chemical (insecticide) used: Sulfur, occur in nature, when burnt produce sulfur dioxide, SO2, kill many insects and fungi. 2) Tobacco plants: produce nicotine, plant evolved to protect itself against predators, natural insecticide. 3) Synthetic pesticides: -Copper acetoarsenate: combine arsenic trioxide and copper acetate. Called paris green. Used in paint and arsenic compounds evaporated, harming people. -DDT: (20th century): world war 2 soldiers sprayed with DDT to keep them free of lice and insects that could transmit disease, million lives saved. Found by Paul Muller. Farmers overused DDT and there were environmental problems like eggshells laid by birds broke too frequently, decline in population of eagle and osprey. A book called silent spring released, said pesticides are swords, it builds up in foodchain and it isnt biodegradable, it gets into water and accumulates in environment. Then it wss banned in Canada and US. In 2006, suggest of DDT use to control malaria and kill mosquitos, use it by spraying powdered version. Dangerousness of DDT, there are different results: One study said rats exposed to traces of DDT develop fewer liver tumors than unexposed rats, because exposure causes animal to generate detoxycating enzymes. One study
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