Ncert Questions
Question 1. Answer briefly: (a) Why are villi present in the intestine and not in the stomach?(b) How does pepsinogen change into its active form?(c) What are the basic layers of the wall of alimentary canal?(d) How does bile help in the digestion of fats?
Answer: (a) The digested food is passed into the intestine for absorption. The villi are present here to increase the surface area for the absorption of the digested food. (b) The inactive pepsinogen is converted into its active form called pepsin by the action of the hydrochloric acid which is present in the gastric juice. (c) The walls of the alimentary canal possess four layers. They are: 1.serosa 2.muscularis 3. sub-mucosa and 4. mucosa. (d) Bile contains bile pigments, bile salts, cholesterol, and phospholipids. These help in the emulsification of fats where the fat molecules are broken down into small micelles.
Question 2. State the role of pancreatic juice in digestion of proteins.
Answer: The enzymes trypsin chymotrypsin and carboxypeptidase, which is present in the pancreatic juice help in the digestion of proteins and the partially hydrolysed proteins, like proteoses and peptones, into dipeptides.
Question 3. Describe the process of digestion of protein in the stomach.
Answer: In the stomach the inactive proenzyme pepsinogen when acted upon by hydrochloric acid gets converted into active enzyme pepsin which coverts protein into proteoses and peptides. Renin is another enzyme, which is present in gastric juice of infants and this helps in the digestion of milk protein.
Question 4. Bile juice contains no digestive enzymes, yet it is important for digestion. Why?
Answer: Bile juice does not contain any enzyme but it contains bile pigments, bile salts, cholesterol, and phospholipids. The important role played by these enzymes is that it helps in the emulsification of fats where the fat molecules are broken down into small micelles.
Question 5. Describe the digestive role of chymotrypsin. Which two other digestive enzymes of the same category are secreted by its source gland?
Answer: Chymotrypsin is an active enzyme formed by the action of trypsin in the pancreatic juice. This helps in the digestion of proteins peptones and proteoses converting it into dipeptides. The other two digestive enzyme secreted by the source gland is amylase and lipases.
Question 6. How are polysaccharides and disaccharides digested?
Answer: The polysaccharides and disaccharides are partially digested by the amylase enzyme present in the pancreatic juice. The remaining digestion takes place by enzymes in the succus entericus. The enzyme maltase converts maltose into two molecules of glucose, lactase converts lactose into glucose and galactose, sucrase converts sucrose into glucose and fructose.
Question 7. What would happen if HCl were not secreted in the stomach?
Answer: In the stomach HCl is very essential for digestion. The HCl provides an acidic medium, which is necessary to convert the inactive pepsinogen to active pepsin. The active pepsin acts on proteins and convert it into proteoses and peptones. The HCl also plays a major role in killing the pathogens entering into the stomach along with the food.
Question 8. How does butter in your food get digested and absorbed in the body?
Answer: The bile juice acts upon the butter in the food and emulsifies the fat content. During this process the larger fat molecules are broken down into very small micelles, which can be easily digested.
Question 9. Discuss the main steps in the digestion of proteins as the food passes through different parts of the alimentary canal.
Answer: Digestion of protein starts in the stomach. The active pepsin formed by the action of HCl on inactive pepsinogen converts proteins into proteases and peptones. The digestion of proteins is continued in the small intestine by the action of certain enzymes present in the intestinal juice or succus entericus. The enzymes are trypsin chymotrypsin and carboxypeptides. These enzymes convert proteins peptones proteases into dipeptides and polypeptides. The dipeptides and polypeptides are the absorbable form of protein.
Question 10. Explain the term thecodont and diphyodont.
Answer: The type of attachment in which each tooth is embedded in a socket of jawbone is called thecodont. The type of dentition in which two sets of teeth is present during a life time is called diphyodont. The two sets of teeth are a set of temporary milk or deciduous teeth, which is replaced, by a set of permanent or adult teeth.
Question 11. Name different types of teeth and their number in an adult human.
Answer: The different type of teeth and their number in adult are:Incisors - 8Canines - 4Premolars - 8Molars - 12Totally there are 32 teeth in adult humans.
Question 12. What are the functions of the liver?
Answer: The largest gland in the body is the liver it weighs about 1.2 to 1.5 kg in an adult human. It has two lobes. The hepatic lobules are the structural and functional units of liver containing hepatic cells arranged in the form of cords. A thin connective tissue sheath called the Glisson’s capsule covers each lobule. The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the gall bladder. The duct of gall bladder (cystic duct) along with the hepatic duct from the liver forms the common bile duct .The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct, which is guarded by a sphincter called the sphincter of Oddi.