Give scientific reasons:
$(1)$ Food tastes sweet after chewing.
$(2)$ Excretory substances are seen in bile juice.

(N/A) $(1)$ Salivary glands are located in the mouth. Saliva mixes with food during the process of chewing,making it soft and moist.
The enzyme salivary amylase (ptyalin) present in saliva acts on starch and converts it into maltose. Maltose is a disaccharide which is sweet in taste. Therefore,food tastes sweet after chewing.
$(2)$ Bile juice secreted by the liver does not contain any digestive enzymes. It contains bile salts and bile pigments (bilirubin and biliverdin),which are produced from the decomposition of hemoglobin.
Moreover,it contains cholesterol,phospholipids,and $Ca^{++}$ ions. Since these are metabolic waste products eliminated via bile,they are considered excretory substances.