A person had roti and dal for his lunch. Trace the changes in those during its passage through the alimentary canal.

Explanation

1. Digestion of Roti (Carbohydrates)
(a) Digestion of Carbohydrates in the Oral Cavity
In oral cavity, the roti is mixed with saliva. The saliva contains an enzyme salivary amylase (ptyalin) which converts in roti into maltose, isomaltose and small dextrins called `alpha`-dextrin. `30%` of strach is hydrolysed in the oral cavity.
`"Starch"overset("Salivary Amylase")underset(pH 6-8)to "Maltose"+"Isomaltose"+alpha-"Dextrin"`
(b) Digestion of Carbohydrates in the Small Intestine
The passage of party digested roti from oral cavity to oesophagus and then to stomach is regulated by peristalsis (the successive waves of muscular contraction in oesophagus). The stomach stores the food for 4-5 hours. The gastric juice does not contain carbohydrate digesting enzyme.
The partially digested food is now called as chyme. In intestine, following action occurs.
(i) Action of Pancreatic Juice Carbohydrates in the chyme are hydrolysed by pancreatic amylase into disaccharides.
`"Polysaccharides" ("starch") overset("Amylase")to "Disaccharides"`
(ii) Action of Intestinal Juice Intestinal juice contain maltase, isomaltase, sucrase(invertase), lactase and `alpha`-dextrinase. These enzymes act on food converting it into simpler compounds like glucose, fructose, galactose, etc.
`{:("Maltose"overset("Maltase")to "Glucose + Glucose"),("Isomaltose"overset("Isomaltase")to "Glucose + Gucose"),("Sucrose"overset("Sucrase")to "Glucose + Fructose"),("Lactose"overset("Lactase")to "Glucose + Galactose"),(alpha-"Dextrins"overset(alpha-"dextrinose")to "Glucose"):}`
2. Digestion of Protien
Protiens are made up of amino acids. So proteins are broken down to amino acid during the process of digestion.
Saliva does not contain any protein digesting enzyme. So, its digestion in stomach.
(a) Digestion of Protein in Stomach The stomach normally stores food for 4-5 hours. The gastric glands of the stomach secrete gastric juice. It contains HCl, proenzymes like-pepsinogen and prorennin. Various reactions in stomach are discussed below
`{:(underset("(proenzyme)")"Pepsinogen" overset(HCl)to"Pepsin"),("Proteins" overset("Pepsin")to "Peptones and proteoses"),(underset((Proenzyme))"Prorennin" overset(HCl)to "Rennin"):}`
(b) Digestion of Protein in Small Intestine
(i) Action of Pancreatic Juice The enzymes trysinogen, chymotrypsinogen and procarboxypeptidase in pancreatic juice are all concerned with the protein digestion.
Some reactions are given below
`{:("Trypsinogen"overset("Enterot kinase")to "Trypsin"),("Proteins"overset("Trypsin")to "Dipeptides"),("Chymotrypsinogen"overset("Trypsin")to "Chymotrypsin"),("Peptones"overset("Chymotrypsin")to"Dipeptides"),("Procarboxypeptidase" overset("Trypsin")to "Carboxypeptidases"),("Proteoses"overset("Carboxypeptidases")to "Dipeptides"):}`
(ii) Action of Intestinal Juice Intestinal juice contain enzymes enterokinase, amino peptidase and dipeptidase and their actions are given below
`{:("Peptides"overset("Amino peptidase")to "Amino acid"),("Dipeptides"overset("Dipeptidase")to "Amino acid"):}`
The macromolecules that are broken down into simpler components are the products of roti and dal (carbohydrates and protein) which are further absorbed by the villi in intestine and the rest undigested food is removed in the form of faeces.