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Circadian rhythms are physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism's environment. They are found in most living things, including animals, plants and many tiny microbes. Humans have a biological clock which inludes Hormones e.g. Melatonin is released around 10pm to induce sleep. Photoperiodism This is responding to changing day lengths. - Seeds germinate in spring to get more sunlight and nutrients. Plants produce poisons to guard against pests and herbivores e.g. lupin leaves produce alkaloids. They also use chemicals to defend against pathogens (organisms that cause disease) - If pathogens damage a crop it puts our food supply at risk Small doses of plant poison is benefitial e.g. digoxin is a chemical in foxgloves that helps heart disorders. aseptic techniques - method to keep living organisms from something (preserve) pasteurisation - heating foods to kill bacteria exponential growth - when the growth rate of a population is proportional to its current value (e.g. it doubles) Vaccines Edward Jenner was studying why milkmaids who caught cowpox didnt get smallpox. -He proved this by rubbing cowpox pus on a 8 year old boy, then small pox, the boy did not get smallpox. Smallpox is caused…

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