A person had roti and dal for his lunch. | Class 11 Biology Chapter Digestion and Absorption, Digestion and Absorption NCERT Solutions

Roti mainly contains carbohydrates and fibres. Dal may also contain fat because of addition of oil or ghee during cooking.

At first, saliva will play its role and convert carbohydrates into simple sugar in mouth. Then food passes through oesophagus. No digestion occurs in oesophagus. Food will pass to stomach where HCl and pepsin are secreted. Food will churned for 3 hours. Then food will go to pancreas where it will treated with pancreatic juice, bile juice and food will move to small intestine where absorption of digested food will take place with the help of finger like projection called villi. Then food will go in large intestine where excess water is absorbed. The waste material will store to rectum.

• Oral cavity: in this, the food is masticated with the help of saliva which makes it easier to swallow. The enzyme salivary amylase which is present in saliva make the food digestible which starch is digested, which is then converted into maltose with pH 6.8.
• Stomach: After reaching the buccal cavity, food goes into the stomach through oesophagus. Stomach contains HCL acid which mixes with the food, kills germ and also provides acidic pH for the activity of Pepsin. Protein partial digestion occurs in the stomach. Here, protein of the dal is converted through the pepsin enzyme into peptones.

Protein + Pepsin → Peptones + Proteoses

• Small intestine: Here food receives alkaline secretions: bile from the liver, pancreatic juice from the pancreas and intestinal juice from the intestinal glands. Their alkalinity stops the action of pepsin. There are amylase in the pancreatic juice which converts polysaccharides into disaccharides. It contains various inactive proteases like Trypsinogen, Chymotrypsinogen and Procarboxypeptidase.

Trypsinogen converts first into the trypsin by the enzyme enterokinase; and then trypsin breaks down proteins into Proteoses and peptides. Chymotrypsinogen also splits the proteins into the peptides. Procarboxypeptidase converts first into the carboxypeptidase with the help of trypsin enzyme and then these peptides converts into dipeptides and amino acids by the enzyme carboxypeptidase.

Intestinal juice contains two digestive proteases and a non- digestive proteases. Digestive proteases converts peptides into dipeptides and the amino acids. And then the dipeptides converts into amino acids by the dipeptidase. This enzymes acts on the surface of microvilli and within the mucosal cells.

All the enzymes are proteins which are hydrolyzed to amino acids which are absorbed.