Question

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

Answer 1

Roti is rich in carbohydrates and fibre, but dal is full of proteins. Dal may include fat due to the inclusion of oil or ghee during the cooking process. During their journey through the alimentary canal, these foods would undergo the following transformations.

Oral Cavity: Food is chewed in the oral cavity until it becomes a semisolid paste. Food is combined with saliva. Saliva aids in the digestion of meals. Furthermore, salivary amylase digests starch. During this process, starch is transformed into maltose.

\[\ce{Strach ->[Sali var amylase][pH = 6.8] Maltose}\]

Stomach: Food passes from the buccal cavity into the stomach via the oesophagus. In the oesophagus, there is no digestion of food. Food is churned into an even smoother paste in the stomach. Further, the food is mixed with hydrochloric acid. If there are germs in the food, HCl destroys them and makes the pH acidic enough for pepsin to work appropriately. In the stomach, just a portion of the protein is digested. Pepsin converts dal protein into peptones and proteases in this step.

\[\ce{Protein + Pepsin -> Peptones + Proteases}\]

Small Intestine: Pancreatic amylase present in the pancreatic juice converts the polysaccharides into disaccharides. In this step, the carbohydrates in the roti are further assimilated.

\[\ce{Polysaccharides ->[Pancreatic Amylase] Disaccharides}\]

The proteins, peptones and proteases are converted by Chymotrypsin present in pancreatic juice into dipeptides.

\[\ce{Proteins, peptones, proteoses ->[Trysin/Chymotryp sin][Carboxypeptidose] Dipeptides}\]

Lipase digests the fats in the roti.

\[\ce{Fats ->[Lipase] Diglycerides -> Monoglycerides}\]

Intestinal juice includes several enzymes that aid in the breakdown of all nutrients. The digestion of several nutrients in roti and dal are shown below:

\[\ce{Sucrose ->[Sucrase] Glucose + Fructose}\]

\[\ce{Lactose ->[Lactase] Glucose + Galactose}\]

\[\ce{Maltose ->[Maltase] Glucose + Glucose}\]

\[\ce{Dipeptides ->[Dipeptidase] Amino acids}\]

\[\ce{Di and Monoglycerides ->[Lipases] Fatty acids + Glycerol}\]

The simple molecules are absorbed by the small intestine walls after all of the nutrients have been transformed into simpler compounds.

Food that has not been digested is subsequently passed via the large intestine and stored in the rectum until it is ejected through the anus.