A person had roti and dal for his lunch.

Question:

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

Solution:

1. Roti and dal are chewed in the mouth which is the first part of the alimentary canal. Then it became a semisolid paste and mixed with saliva. The enzyme called salivary amylase is present in the saliva which helps in the digestion of starch to maltose.

2. The oral cavity then leads into short pharynx followed by oesophagus and stomach. The semisolid food with salivary amylase passes through this path without any reaction and reaches the stomach.

3. HCl is present in the stomach which is mixed with the food and thus kills the germs left in the food. It also makes the pH food to acidic so that pepsin acts optimally. Protein + pepsin → Peptones + Proteoses

3. The pancreas releases pancreatic juice on the way. The pancreatic juice contains pancreatic amylase.

Pancreatic juice also contains Chymotrypsin which helps in digestion of peptones and proteoses

Intestinal juice contains various enzymes which help in digestion of all the nutrients.

After all the nutrients are converted into simple substances, these are absorbed by small intestine walls.

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