Chem 181 Topics 5-7.docx - Photosynthesis-without it thered be no life-plants take up CO2 and water and produce O2 plus all chemicals that make up the

Chem 181 Topics 5-7.docx - Photosynthesis-without it thered...

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Photosynthesis -without it there’d be no life -plants take up CO2 and water and produce O2 plus all chemicals that make up the plant -one way or another we live off plants -agriculture based on photosynthesis Agriculture -Up to ~50yrs ago, 70% of the world was involved in farming -Today ~2% of the population supply all food - organic food : growing without synthetic fertilizers or pesticides, relying on natural means to control insects Justus Von Liebig ( 1803- 1973) : did chemical analysis, figured out that major nutrients needed – N, P, K and First one to figure out specific plants need a different ratio of nutrients in the fertilizer Fritz Haber (1868-1934) : found way to combine N and H to make ammonia (NH3) -Pesticides are designed to kill Ammonium Nitrate -Nitric acid + ammonia -> ammonium nitrate (most widely used fertilizer because of the good source of N) -Can be used as fertilizer or an explosive or laughing gas -Explosion in Oklahoma City caused by ammonium nitrate (can be used as an explosive too) -NH4NO3 slowly decomposes to yield nitrous oxide (laughing gas) which is a greenhouse gas -don’t need soil with fertilizers Hydroponics -growing crops without using soil, but need good ratio of nutrients - can use ground up shells -William Gericke in early 1900s had this idea -largest hydroponic farm is in Montreal -don’t need to use pesticides, but rather, predatory bugs to control aphids -10000 insect species, 8000 fungi, 2000 weeds that compete for food supply -Apple scab- fungus but really a cosmetic problem, people don’t buy them even though they’re fine -Botrytus fruit rot on strawberries, stem rust on wheat that destroys the crop, black dots that can wipe out flowers (eg. roses), weeds suck nutrients out of the soil so there’s few nutrients left for the crops, insects “clamber” all over the crops - corn borer invades corn, large piles of grain with rats and mice, apple orchards surrounded by nematodes, in homes - bedbugs & cockroaches Control Sulfur - occurs in nature in elemental form and when burned, produces SO2 that kills many bugs and fungi
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Tobacco Plant - produces nicotine to protect itself from predators, nicotine is a natural insecticide, but when inhaled, is a carcinogenic Copper Acetoarsenate - made from arsenic trioxide and copper acetate, known as “Paris Green” to get rid of rats and mice in Paris sewers, also sold as paint because it was a pigment, theory that Napoleon was poisoned by Paris Green because the wallpaper in his prison had it DDT - effective against mice and insects and helped Allies during WW2, soldiers doused in DDT and protected them from lice and insects that transmitted typhoid (~25 million lives were saved) Paul Miller received Nobel Prize (1948) for introducing DDT -problem is that DDT was too effective, farmers overused DDT, bird eggshells were becoming too fragile and weren’t hatching, Rachel Carson introduced idea that pesticides were double sided sword -DDT causes bioaccumulation and isn’t biodegradable -Banned in Canada (1969), Banned in US (1972)
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  • Spring '11
  • Multiple
  • Bacteria, pH, E number, food poisoning, Food additive

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