ICSE BoardEnglish MediumSTD 9BIOLOGYDigestive System5 Marks
Question
Describe the process of digestion in human beings.
✓
Answer
Digestion of proteins in humans: There is no digestion of protein in the oral cavity because protein digestive enzymes are absent in the saliva. (a) Digestion of protein in the stomach: Gastric juice contains $HCl$ and two proenzymes, pepsinogen and prorenin. $HCl$ maintains a pH of 2-3.7 and kills bacteria and other pathogens. Gastric juice mixes with food until it becomes a semi-solid mass called Chyme. Proenzymes become activated as below: Pepsinogen $\xrightarrow[2-3.7 pH ]{ HCl }$ Pepsin Prorennin $\xrightarrow{ HCl }$ Rennin These enzymes act as follows: Casein $\xrightarrow[\text { (Milk protein) }]{\text { Rennin }}$ Paracasein Paracasein $+ Ca \rightarrow$ Calcium Paracasinate (Curd) Calcium paracaseinate $\xrightarrow{\text { Pepsin }}$ Peptones Protein $\xrightarrow{\text { Pepsin }}$ Peotone (b) Digestion of protein the small intestine Action of pancreatic juice. It contains proenzymes trypsinogen, chymotrypsinogen, and procarboxy peptidase. Trypsinogen $\xrightarrow[\text { of interstinal juice }]{\text { Enterokinase }}$ Trypsin Chymotrypsinogen $\xrightarrow{\text { Trypsin }}$ Chymotrypsin Procarboxypeptidase $\xrightarrow{\text { Trypsin }}$ Carbody - peptidase Peptones $\xrightarrow{\text { Trypsin }}$ Peptides Peptones $\xrightarrow{\text { Chymotrypsin }}$ Peptides Peptides $\xrightarrow{\text { Carboxypeptidase }}$ Smaller peptides + Amino acid The action of intestinal juice. Intestinal juice contains endokinase, aminopeptidase, and dipeptidase. Actions of these enzymes are summarized below: Peptides $\xrightarrow{\text { Aminopeptidase }}$ Smaller peptides + Amino acid Peptides $\xrightarrow{\text { Dipeptidase }}$ Amino acid
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.