Q1. Choose the correct answer among the following:
- Gastric juice contains
- Pepsin, lipase and rennin
- Trypsin, lipase and rennin
- Trypsin, pepsin and lipase
- Trypsin, pepsin and renin
- Succusentericus is the name given to:
- A junction between ileum and large intestine
- Intestinal juice
- Swelling in the gut
- Appendix
Answers:
- i (Pepsin, lipase and rennin)
- ii (Intestinal juice)
Q2. Match column I and column II
| Column I | Column II |
| Bilirubin and biliverdin | Parotid |
| Hydrolysis of starch | Bile |
| Digestion of fat | Lipases |
| Salivary gland | Amylases |
Answers:
| Column I | Column II |
| Bilirubin and biliverdin | ii) Bile |
| Hydrolysis of starch | iv) Amylases |
| Digestion of fat | iii) Lipase |
| Salivary gland | i) Parotid |
Q3. Answer briefly:
- Why are villi present in the intestine and not in the stomach?
- How does pepsinogen change into its active form?
- What are the basic layers of the wall of alimentary canal?
- How does bile help in the digestion of fats?
Answers:
- Villi are finger-like projections present on the innermost layer of the intestinal mucosal wall. These villi are primarily meant for increasing the surface area for absorption. A section of the intestinal mucosa not only shows villi, but also shows blood capillaries and lacteals within these villi. When foods such as carbohydrates, proteins and lipids are digested, they are absorbed through blood capillaries and lacteals respectively. However, in the stomach, only primary steps of digestion take place. For example, proteins are digested in the stomach as proteoses and peptones only. Complete digestion of food takes place only in the small intestine, for examples, proteases and peptones are converted to amino acid.And after food digestion, they are absorbed in the small intestine itself. It is important to note that villi are present only in the small intestine. Water is absorbed by the large intestine and, therefore, villi are absent in the large intestine as well.
- Pepsinogen is an inactive form of a protein, which is present in the stomach wall. It is first activated by hydrochloric acid to form pepsin, the active form of a protein.
c. The walls of the alimentary canal are made up of 4 layers. These are mentioned below:
- Serosa: It is the outermost layer of the alimentary canal. It is made up of a thin layer of secretory epithelial cells and connective tissues.
- Muscularis: It is made up of two types of muscles, the outer longitudinal muscle and the inner circular muscle.
- Submucosa: It is made up of loose connective tissues consisting of nerves, blood vessels and lymph vessels.
- Mucosa: It is the innermost layer of the alimentary canal. The main function of mucosa is associated with secretion and absorption.
d. Bile is secreted from the liver and stored in the gall bladder connected through cystic duct. Bile contains 97% water and 3% solids. Solids are further divided into salts and pigments. Two types of salts are present, they are: glycocholate and taurocholate. The main function of bile salts is emulsification of fats. Bile salts are responsible for the breakdown of large fat molecules into small fat molecules. This process is called emulsification and this is essential for the enzyme lipase to digest small fat molecules.
Q4. State the role of pancreatic juice in digestion of proteins.
Answer:
Pancreatic juice contains inactive enzymes (proteases) such as trypsinogen, chymotrypsinogen, procarboxypeptidase and proelastase. These are the enzymes responsible for the digestion of proteins.
Protein digestion:
First of all, the enzyme enterokinase is secreted by the intestinal mucosa. This intestinal enzyme is responsible for the activation of trypsinogen into trypsin. The activated trypsin then activates another pancreatic enzymes chymotrypsinogen and procarboxypeptidase into chymotrypsin and carboxypeptidase respectively.
Q5. Describe the process of digestion of protein in stomach.
Answer:
Protein digestion begins in the stomach. However, complete protein digestion occurs in the small intestine. The innermost stomach wall i.e., mucosa contains gastric glands that secrete gastric juice. The main components of the gastric juice are HCl, pepsinogen, prorennin, and mucus.
The process of digestion of protein in stomach is as follows:
Q6. Give the dental formula of human beings?
Answer:
Dental formula represents the arrangement of teeth in each half of the upper and lower jaws. It is multiplied by two to calculate the total number of teeth.
For instance, the dental formula of human milk teeth is 2102/2102 x 2 =20
In this dental formula 2 represents incisor, 1 represents canine, 0 represents premolar and 2 represents molar teeth. Premolars are absent in milk teeth.
The dental formula of adult human is 2123/2123 = 32
Each half of the upper jaw has 2 incisors, 1 canine, 2 premolars and 3 molars.
Q7. Bile juice contains no digestive enzymes, yet it is important for digestion, why?
Answer:
Bile is secreted by liver and it is considered as a digestive juice even though it does not contain any enzyme. Bile plays an important role in the digestion of fats. The main components of bile are bile salts and bile pigments. However, bile salts are essential for the breakdown of large fat molecules. This process of breakdown of large fat molecules into small fat molecule is called emulsification. After emulsification, pancreatic lipase acts on small fat molecules to digest them.
Q8. Describe the digestive role of chymotrypsin. Which two other digestive enzymes of the same category are secreted by its source gland?
Answer:
Chymotrypsinogen is an inactive form of enzyme that is activated by the enzyme trypsin to its active form chymotrypsin. The activated chymotrypsin acts on proteins and digest them to peptides.
The other digestive enzymes of the same category are trypsinogen and procarboxypeptidase. These two enzymes are secreted by the same source gland i.e., pancreas.
Trypsinogen is an inactive form of enzyme, which is activated by another enzyme enterokinase secreted by the intestinal mucosa. Once, trypsin is formed, it also activates procarboxypeptidase to carboxypeptidase. These two enzymes act on protein molecules and break them into peptides. Carboxypeptidase acts on the terminal end of the polypeptide and one-by-one breaks an amino acid.
Q9. How are polysaccharides and disaccharides digested?
Answer:
Dietary carbohydrates include starch, sucrose, lactose and cellulose (indigestible). Digestion of carbohydrates start from the mouth itself, however, complete digestion of carbohydrates takes place in the small intestine.
Digestion of Carbohydrate in the Mouth
30% of the starch digestion takes place in the mouth.
In the stomach, salivary amylase gets denatured at acidic pH. No further digestion of carbohydrate takes place in the stomach. Remaining carbohydrate digestion takes place in the small intestine.
Digestion of Carbohydrate in the Small Intestine:
Pancreatic juice containing pancreatic amylase acts on starch.
Similarly, the intestinal juice (succusentericus) containing a variety of enzymes act on carbohydrates and help in the digestion of disaccharides to monosaccharides.
From Intestinal Juice (Succusentericus):
Q10. What would happen if HCl were not secreted in the stomach?
Answer:
Hydrochloric acid is secreted by the gastric gland called oxyntic cell or parietal cell. When food reaches the stomach, it gets mixed with HCl and makes it acidic. The acidic medium is essential for the activation of inactive pepsinogen to pepsin for protein digestion. If HCl is not secreted in the stomach, pepsinogen would not be converted into pepsin. As a result, protein digestion would get hampered in stomach. Besides pepsinogen, another enzyme prorennin present in child would not get activated in the absence of hydrochloric acid. Prorennin once converted into rennin acts on milk protein casein to digest it.
Q11. How does butter in your food gets digested and absorbed in the body?
Answer:
Digestion of fat
The main composition of butter is fat and it is digested in the small intestine only. For fat digestion, bile secretion is essential that occurs from the liver. However, bile is stored in the gall bladder. When we take food containing fat, bile containing bile salts are mixed with the food and break large fat molecules into small fat molecules, and this process is called emulsification. This process is essential as small fat molecules increase the surface are so that the pancreatic enzyme lipase could effectively work on it. The enzyme lipase finally breaks fats into triglycerides and diglycerides and then into fatty acids and glycerol.
Absorption of Fat:
Q12. Discuss the main steps in the digestion of proteins as the food passes through different parts of the alimentary canal.
Answer:
Protein digestion initiates in the stomach and completes in the small intestine.
Digestion of proteins in the stomach:
In stomach, only digestion of proteins takes place.First HCl is mixed with bolus to form it acidic food, called CHYME. HCl then activates PEPSINOGEN (inactive) to PEPSIN (active). On the other hand, PRORENNIN (an enzyme present only in child) is activated by HCl to RENNIN, responsible for the digestion of milk protein, called CASEIN PROTEIN.
Digestion of protein in the small intestine
The acidic chyme from the stomach reaches the first part of the small intestine i.e., duodenum where pancreatic juice, bile and intestinal juice mix together. It is the small intestine where complete digestion and absorption of food takes place. It is important to note that the final digestion of food is done by the intestinal juice (succusentericus).
Pancreatic juice contains inactive enzymes. TRYPSINOGEN is activated by an enzyme, ENTEROKINASE, secreted by the intestinal mucosa into active trypsin.
These activated enzymes will act on proteins, proteoses and peptones to digest and form dipeptides.
Proteins, peptones and proteoses were digested to dipeptides by the pancreatic juice, the final digestion of dipeptides are done by the intestinal juice containing enzyme dipeptidases.
Q13. Explain the term thecodont and diphyodont.
Answer:
Thecodont: It is a type of dentition in which teeth are embedded in the socket of jaw bones.
Diphyodont: It means teeth erupt twice in life, i.e., milk teeth and permanent teeth. The number of milk teeth is 20 whereas the number of permanent teeth is 32.
Q14. Name different types of teeth and their number in an adult human.
Answer:
In humans, four different types of teeth are present namely:
Incisors: They are two in numbers in each quadrant of the jaw meaning a total of 8 incisors are present in the jaw bone. The main function of incisors is cutting.
Canines: these are pointed teeth present on either side of the incisors. A total of 4 incisors are present in the jaw bone. Canines are meant for tearing and they are more prominent in carnivores.
Premolars: they are present beside the canines. They are eight in numbers and meant for grinding.
Molars: They are present at the end of the jaw. The total number of molars is 12. They are meant for grinding. The last molar is called wisdom tooth.
The dental formula of adult human is: 32
Q15. What are the functions of liver?
Function of Liver:
- Liver carries out more than 200 functions.
- Liver is involved in metabolic regulationi.e., carbohydrate metabolism (gluconeogenesis, glycogenolysis, and glycogenesis); lipid metabolism, amino acid metabolism, waste product removal and drug inactivation.
- Liver is involved in haematological regulation. For example, phagocytosis of antigen presentation, synthesis of plasma proteins, removal of toxins.
- Liver is involved in BILE PRODUCTION