Who first realized the use of yeast in fermentation?

On which bacteria was Alexander Fleming working during the discovery of penicillin?

The chemical substances which are produced by some microbes and can kill or retard the growth of other microbes are known as:

Who was the first discoverer of antibiotics?

Microorganisms or microbes are found in

Medicines are either man-made (i.e.,synthetic) or obtained from living organisms like plants,bacteria,animals,etc.,and hence,the latter are called natural products. Sometimes,natural products are chemically altered by man to reduce toxicity or side effects. Write against each of the following whether they were initially obtained as a natural product or as a synthetic chemical: $(a)$ Penicillin $(b)$ Sulphonamide $(c)$ Vitamin-$C$ $(d)$ Growth hormone.