1. Choose the correct answer
among the following:
(a) Gastric juice
contains
(i)
pepsin, lipase and rennin
(ii) trypsin, lipase and rennin
(iii) trypsin, pepsin and lipase
(iv) trypsin, pepsin and rennin.
(b) Succus entericus is the name given to
(i) a junction between ileum and large intestine
(ii) intestinal juice
(iii) swelling in the
gut
(iv)
appendix.
Solution: (a) (i)
Pepsin, lipase and rennin
(b) (ii) Intestinal juice
2. Match column I with column
II.
Column I
Column II
(a) Bilirubin and
(i)Parotid biliverdin
(b) Hydrolysis of (ii)Bile
starch
(c)
Digestion of fat (iii)Lipases
(d) Salivary gland
(iv)
Amylases
Solution: (a), – (ii),- (b) –
(iv), (c) – (iii),- (d) – (i)
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3. 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
?
Solution: (a) The absorptive surface
area of small intestine is enormously increased by microvilli and as maximum
absorption
of digested food takes place in small intestine as compared to
other organs, therefore, villi are present in small intestine and not in
stomach. Moreover, stomach is primarily associated with temporary storage of
food.
(b) The proenzyme pepsinogen, on exposure to hydrochloric acid,
secreted by oxyntic cells of gastric glands gets converted into the active
enzyme pepsin, the proteolytic enzyme of the stomach.
(c) The wall of
alimentary canal from oesophagus to rectum possesses four layers, namely serosa,
muscularis, sub-mucosa and mucosa. Serosa is the outermost layer and is made up
of a thin mesothelium with some connective tissues. Muscularis is formed by
smooth muscles. The sub-mucosal layer is formed of loose connective tissues
containing nerves, blood and lymph vessels. In duodenum, glands are also present
in sub-mucosa. The innermost layer lining the lumen of the alimentary canal is
the mucosa. This layer forms irregular folds (rugae) in the stomach and small
finger¬like foldings called villi in the small intestine.
(d) Bile has no
enzymes but contains bile salts, namely, sodium bicarbonate, sodium glycocholate
and sodium taurocholate that reduce the surface tension of large fat droplets
and break them into many small droplets by a process known as emulsification.
These small fat droplets present large surface area for lipase (fat digesting
enzyme) to act upon them. Moreover, bile also activates lipases.
4. State the role of
pancreatic juice in digestion of
proteins.
Solution: The pancreatic
juice contains inactive enzymes – trypsinogen, chymotrypsinogen,
procarboxypeptidases. Trypsinogen is acti¬vated by an enzyme enterokinase,
(secreted by the intestinal mucosa) into active trypsin, which in turn activates
the other enzymes of the pancreatic juice. Proteins, proteoses and peptones
(partially hydrolysed proteins) in the chyme reaching the intestine are acted
upon by these proteolytic enzymes of pancre¬atic juice.
5. Describe the process of
digestion of protein in
stomach.
Solution: The gastric glands
of the stomach secrete gastric juice that contains HCl and proenzymes –
pepsinogen and prorennin. The proenzyme pepsinogen, on exposure to HCl gets
converted into the active enzyme pepsin, the proteolytic enzyme of stomach. The
pepsin converts proteins into proteoses and peptones (peptides). Prorennin is
found in gastric juice of infants and is activated by pepsin into active rennin.
It helps in digestion of milk protein casein.
6. Give the dental formula of
human beings.
Solution: The dental
formula of human beings is
It shows arrangement of teeth in each half of
the upper
and lower jaw.
7. Bile juice contains no
digestive enzymes, yet it is important for digestion. Why
?
Solution: Bile has no enzymes but
contains bile salts, namely, sodium bicarbonate, sodium glycocholate and sodium
taurocholate that reduce the surface tension of large fat drop¬lets and break
them into many small droplets by a process known as emulsification. These small
fat droplets present large surface area for lipase (fat digesting enzyme) to act
upon them. Moreover, bile also activates lipases.
8. Describe the digestive
role of chymotrypsin. Which two other digestive enzymes of the same category are
secreted by its source gland
?
Solution: Chymotrypsin is a
proteolytic enzyme of pancreatic juice secreted by exocrine part of pancreas. It
helps in digestion of proteins. It converts proteins, peptones and proteoses
into oligopeptides and dipeptides. Two other proteolytic enzymes present in
pancreatic juice are trypsinogen and procarboxypeptidase.
9. How are polysaccharides
and disaccharides digested
?
Solution: Digestion of
polysaccharides (starch and glycogen) starts from buccal cavity. In buccal
cavity, polysaccharides are acted upon by salivary amylase or ptyalin which
splits starch and glycogen into disaccharides and small dextrins called ‘a’
dextrin.
The digestion of carbohydrates does not occur in stomach
because gastric juice itself has no carbohydrase.
In small intestine, the
food mixes with two juices, pancreatic juice and intestinal juice. Pancreatic
juice contains a carbohydrase named pancreatic amylase. This enzyme hydrolyses
more starch and glycogen.
Intestinal juice contains carbohydrases; maltase, isomaltase,
a-dextrinase, sucrase and lactase which act on disaccharides as follows:
fructose and galactose are monomers of carbohydrates. These
are absorbed by intestinal mucosa.
10. What would happen if HCl
were not secreted in the
stomach?
Solution: HCl is secreted by
parietal or oxyntic cells of gastric glands. It serves the following
functions:
11. How does butter in your
food get digested and absorbed in the body
?
Solution: Butter is a saturated fat.
Fats and oils of the ingested food are triglycerides.
They are digested by
lipases. Small intestine is the principal organ for fat digestion.
In the
small intestine food meets three secretions, bile, pancreatic juice and
intestinal juice, all alkaline in nature.
Bile contains no enzyme but it
contains bile salts which reduces the surface tension of large fat droplets and
breaks them into smaller ones (emulsification).
Emulsified triglycerides Pancreatic juice contains pancreatic
lipase, which is the principal fat digesting enzyme. It is activated by
bile.
Fatty acid + Glycerol Intestinal lipase found in intestinal
juice hydrolyses some triglycerides, diglycerides and monoglycerides to fatty
acids and glycerol like pancreatic lipase.
Fatty acids, glycerol and
monoglycerides are the end products of fat digestion and being insoluble in
water cannot be directly absorbed from the intestinal contents. So they combine
with the bile salts and phospholipids to form micelles (water soluble). From the
micelles fatty acids, glycerides, sterols and fat soluble vitamins are absorbed
into the intestinal cells by diffusion where they are resynthesised in the ER
and are converted into very small protein coated fat molecules (droplets) called
chylomicrons. The latter are released from the intestinal cells into the lymph
present in the lymphatic capillaries, the lacteals. These lacteals ultimately
release the absorbed substances into the blood stream.
12. Discuss the main steps in
the digestion of proteins as the food passes through different parts of the
alimentary canal.
Solution: Proteins of
ingested food are broken down into amino acids by proteases (peptidases).
Proteases are secreted in inactive forms called proenzymes which are converted
into active forms at site of their action. Protein digestion starts in the
stomach and is completed in the small intestine. Saliva contains no
protease.
Digestion of proteins in stomach : Chief cells of gastric gland
secrete pepsinogen and prorennin, which act as follows:
Digestion of proteins in small intestine: In small intestine,
peptones and proteoses are acted upon by enzymes of pancreatic juice and
intestinal juice.
Pancreatic juice contains 3 inactive proteases;
trypsinogen, chymotrypsinogen and pro-carboxypeptidase. Their action is as
follows:
Dipeptides + Amino acids Intestinal juice contains two
digestive pro-teases; aminopeptidases and dipeptidases and a nondigestive
enterokinase (enteropep- tidase).
Amino acids are the end products of protein digestion which
are absorbed by intestinal cells.
13. Explain the term
thecodont and
diphyodont.
Solution: Thecodont: In
human, each tooth is embedded in a socket of jaw bone. Such teeth are described
as thecodont.
Diphyodont: Majority of mammals including human beings form two
sets of teeth during their life, a set of temporary milk or deciduous teeth
replaced by a set of permanent or adult teeth. This type of dentition is called
diphyodont.
14. Name different types of
teeth and their number in an adult
human.
Solution: Adult human has 32
teeth with the
Human has heterodont dentition i.e., having four different
types of teeth. The number of different types of teeth in human are as
follows:incisors = 8, canines = 4, premolars = 8, molars = 12
15. What are the functions of
liver?
Solution: Liver is the largest
gland of the body and consists of hepatic cells. Besides being a digestive
gland, the liver performs a number of functions for the welfare of body. Its
varied functions are as follows