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 mainly contains carbohydrate and fibres while dal contains protein. Dal may also contain fat because of addition of oil or ghee during cooking. Following changes would happen in these food items during their passage through the alimentary canal.
Oral Cavity:
In the oral cavity, food is chewed so that it can change into a semisolid paste. Saliva is mixed with food. Saliva makes it easier to swallow the food. Moreover, salivary amylase in saliva digests starch. Starch is convened into maltose during this process.
$Starch\underset{pH6.8}{\overset{SalivaryAmylase}{\to }}Maltose$
Stomach:
After buccal cavity, the food reaches the stomach through oesophagus. No digestion occurs in the oesophagus. In stomach. food is further churned into even finer paste. Hydrochloric acid gets mixed with the food. HCI kills germs in the food, if any, and provides acidic pH for optimum activity of pepsin. Partial digestion of protein takes place in the stomach. Here. protein of the dal is converted by pepsin into peptones and proteoses.
$Protein+Pepsin⟶Peptones+Proteoses$
Small Intestine:
Pancreatic juice contains pancreatic amylase. Amylase in pancreatic juice converts polysachharides into disaccharides. This step shows further processing of carbohydrates from the roti.
$Polysaccharides\left(starch\right)\stackrel{Amylase}{\to }Disaccharides$
Chymotrypsin from pancreatic juice digests peptones and proteoses into dipeptides.
$\begin{array}{c}Proteins\\ Peptones\\ Proteoses\end{array}\}\underset{Carboxypeptodase}{\overset{\text{Tryp sin/ Chymotrypsin}}{\to }}Dipeptides$
$Fats\stackrel{Lipases}{\to }Diglycerides⟶Monoglycerides$
Intestinal juice contains various enzymes; which help in digestion of all the nutrients. Digestion of various nutrients in roti and dal can be shown as follows:
$Dipeptides\stackrel{Dipeptidases}{\to }Aminoacids$
$Maltose\stackrel{Maltase}{\to }Glucose+Glucose$
$Lactose\stackrel{Lactase}{\to }Glucose+Galactose$
$Sucrose\stackrel{Sucrase}{\to }Glucose+Fructose$
$DiandMonoglycerides\stackrel{Lipases}{\to }Fattyacids+Glycerol$
Once all the nutrients are convened into simple substances, the simple substances are absorbed by the wails of the small intestine. After that, undigested food is sent to the large intestine and finally to the rectum.