TOPIC 5: AGRICULTURE Lesson 1: Agricultural Science I Photosynthesis: important for us because we live on plants. Agriculture is based upon photosynthesis. Today, about 2% of population supply all the food for the world. Pesticides Justus Von Liebig 1803-1873: First chemist to start to look at fertilizer. What is it in manure that allows for crops to grow? Figured out that various kinds of nutrients were needed. Three major: nitrogen, phosphorus, potassium. Fritz Haber 1868-1934: Found a way to combine nitrogen and hydrogen to create ammonia. Was not possible to make it synthetically before. Ammonia nitrate (combined with nitric acid) is one of the most used fertilizers in the world because it provides good amount of nitrogen. Can also be used as an explosive. BUT: Slowly decomposes to yield nitrous oxide (laughing gas), contributes to the greenhouse effect. Hydroponics: gardening without soil. 10,000 insect species 8,000 fungi 2,000 weeds These can all cause problems for agriculture. How can we control all these insects? Historically; - Sulphur is one of the elements who occurs in its elemental form in nature. SO2 kills many insects and fungi one of the first pesticides ever used. - Tobacco Plant: produces nicotine. The plant evolved in order to protect itself against predators – nicotine is a natural insecticide. - Paris green: arsenic trioxide and copper acetate (Copper Acetoarsenate). Was used to clean Paris’ sewers. - DDT: effective against all kinds of insects. Also helped shape the outcome of the 2 nd world war; ally soldiers were sprayed with it and were healthier. Problem: farmers
overused DDT. It is not biodegradable. Canada banned it in 1969 and US in 1972. In 2006, WHO suggested it should be used to control malaria in Africa. Safe to use when spraying a powdered version on the inside of homes. How dangerous was DDT? Berkeley Public Health Institute: among women who were under 14 years of age during heaviest DDT exposure (45-59) blood levels of DDT were found to correlate with future breast cancer risk. Long Island Study: No relationship between breast cancer and blood levels of DDT, but blood samples were taken after cancer was diagnosed. Paul Muller: Introduced DDT. Received a Nobel prize for it in 1948. Pesticide Risks: Placebo effect: sugar/water pill but people believe they feel better Nocebo effect: people believe they feel bad because of something that is not real REAL: Children in India died from eating food that contained pesticides. Pesticide users might bring the chemicals back home, by not wearing appropriate clothing when using them. Links between exposure to insecticides and Parkinson. (Paraquat and Rotenone have chemical similarity to substance that caused paralysis – like in end stages of Parkinson – in the drugs in 1980s) IMAGINED: Golfers who thought they were affected by spray but in fat was water.
- Spring '11
- pH, Food coloring, Food additive