b. The slow decomposition of organic matter into simpler substances in the presence of an enzyme is known as fermentation. The formation of curd from milk is an example of fermentation. The Lactobacilli converts lactose (a type of sugar found in milk) to lactic acid. This reduces the pH and results in separation of milk proteins from the milk an the yoghurt is formed.
c. An antibiotic is an organic compound produced by a micro-organism that inhibits the growth of or kills other microorganisms.