Vitamin $A$ is synthesized from carotene in the ...... .

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

$A$ healthy person eats the following diet: $5 \, gm$ raw sugar,$4 \, gm$ albumin,$10 \, gm$ pure buffalo ghee adulterated with $2 \, gm$ vegetable ghee (hydrogenated vegetable oil),and $5 \, gm$ lignin. How many calories is he likely to get?

Analogy type questions:
$(1)$ In saliva : Amylase :: In gastric juice : ......
$(2)$ $pH$ of gastric juice : $1.8$ :: $pH$ of saliva : .........

Describe the process of digestion occurring in the large intestine.

Choose the correct sentences.
$(1)$ Electrolytes like $Na^+, K^+, Cl^-, HCO_3^-$ are present in saliva.
$(2)$ Starch is converted into maltose by the help of salivary amylase at $pH \, 6.8$.
$(3)$ The intrinsic factor of the stomach is essential for the absorption of vitamin $B_{12}$.
$(4)$ Di- and monoglycerides are broken down into fatty acids and glycerol by lipases.