Assertion Reason Questions for Biology Chapter 16 Digestion and Absorption

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Directions: In the following questions, a statement of assertion is followed by a statement of reason.
Mark the correct choice as:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Q.1. Assertion: Thick layers of muscles are present in the wall of alimentary canal.
Reason: These muscles help in the mixing of food materials with the enzymes coming from different glands in the alimentary canal.

Answer Answer: (d) Thick layers of muscles are present in the alimentary canal. These muscles facilitate the movement of food particles through alimentary canal. Large food particles are broken down into small, semi liquid particles by the action of these muscles. Later, these help in the forward flow of food materials and mixing of enzymes coming from different glands related to alimentary canal.

Q.2. Assertion: Human beings have two sets of teeth during their life.
Reason: Human beings have thecodont dentition.

Answer Answer: (b) Majority of mammals including human beings possess two sets of teeth during their life, a set of permanent or adult teeth. This type of dentition is called diphyodont. Human beings also have thecodont dentition, i.e., teeth are embedded in the sockets of the jaw bones.

Q.3. Assertion: Oesophagus pierces the diaphragm and enters the abdominal cavity.
Reason: Peristaltic movement starts from oesophagus.

Answer Answer: (b) Oesophagus is a long and thin tube that pierces the diaphragm and enters the abdominal cavity. In oesophagus, voluntary muscle fibres are present in the anterior 1/3 and involuntary muscle fibres are present in posterior 2/3. Peristaltic movement of contraction and relaxation of muscles starts from oesophagus.

Q.4. Assertion : Chewing is one of the important process of digestion in animals.
Reason : It helps in enzyme action.

Answer Answer: (a) Chewing food helps in ptyalin action (ptyalin or salivary amylase is a starch hydrolysing enzyme present in the saliva of human), because it mixes the food with saliva. It also breaks food particles into smaller particles with greater surface area exposed to enzyme action. It also starts starch digestion in mouth.

Q.5. Assertion : Presence of HCl in stomach is necessary for the process of digestion.
Reason : HCl kills and inhibits the growth of bacteria in the stomach.

Answer Answer: (b)

Q.6. Assertion: Absorption of digested food mainly occurs in the stomach.
Reason: Stomach produces the hormone secretin and the intrinsic factor and it liquifies ingested food.

Answer Answer: (d) Absorption takes place in small intestine as it offers large surface area for absorption. Stomach produces the hormone gastrin and intrinsic factor.

Q.7. Assertion: The sight, smell and presence of food in the oral cavity can stimulate secretion of saliva.
Reason: The activities of gastro-intestinal tract are only under neural control for proper coordination of different parts.

Answer Answer: (c) The activities of the gastro-intestinal tract are under neural and hormonal control for proper coordination of different parts. The sight, smell and /or the presence of food in the oral cavity can stimulate secretion of saliva. Gastric and intestinal secretions are also similarly stimulated by neural signal. The muscular activities of different parts of the alimentary canal can also be moderated by neural mechanisms, both local and through CNS. Hormonal control of the secretion of digestive juices is carried out by local hormones produced by gastric and intestinal mucosa.

Q.8. Assertion: Gastrectomy can lead to iron￾deficiency or anaemia.
Reason: HCl of gastric juice converts Fe3+ into Fe2+ which makes iron absorbable.

Answer Answer: (a)

Q.9. Assertion : HCl in the gastric juices maintain strong pH (1.5-2.5) in the stomach but does not digest the walls of stomach and duodenum.
Reason : Protection to intestinal wall and stomach from the enzymatic actions is provided by the mucous secreted by goblet cells, bicarbonates from pancreas, mucous and bicarbonates from Brunner’s gland.

Answer Answer: (a) HCI present in the gastric juices maintains a strong pH in stomach. But the wall of stomach is not digested with its action because goblet cells secretes mucous which lubricates the innermost layer continuously in the stomach and intestine. The wall is also protected by the bicarbonates of pancreatic juices and Brunner’s gland.

Q.10. Assertion : The main part of carbohydrate digestion takes place in small intestine.
Reason : Here, pancreatic amylase converts carbohydrates into lactose.

Answer Answer: (c) In small intestine, pancreatic amylase converts starch and dextrins into maltoses and small intestine is main site for digestion of carbohydrates.

Q.11. Assertion : Pancreatic amylase digest starch to maltose.
Reason : Pancreatic amylase breaks the peptide bond of protein.

Answer Answer: (c) Pancreatic amylase is a starch splitting enzyme similar to ptyalin by hydrolysing starch and glycogen to maltose, isomaltose and limit dextrins.

Q.12. Assertion : Trypsin helps in digestion of blood of predator animals.
Reason : Trypsin hydrolyses fibrinogen.

Answer Answer: (a) Trypsin is protein digesting enzyme present in the intestine of animals. Though it cannot digest casein (a milk protein), in predator animals drinking the blood of their prey, trypsin hydrolyses fibriongen of blood into fibrin, leading to blood coagulation thus, help in blood digestion. It also activates other pancreatic proteases.

Q.13. Assertion : Lipases of bile help in the emulsification of fats.
Reason : Lipases can break large fat droplets into smaller ones. [AIIMS 2011]

Answer Answer: (d) It is not lipases but the bile salts which are responsible for the emulsification of fats. Bile salts are steroids secreted by the liver in the bile. In the intestinal lumen, they reduce the surface tension of fat dropletes, causing their breakdown into many smaller ones. A stable fine emulsion of fat is thereby formed. On the other hand, lipases are the enzymes which hydrolyse fats and oils. Lipases can digest fat in significant amounts only when large fat droplets are broken into tiny droplets to form a fine emulsion. Emulsificaion of fats by bile salts thus, increases the lipase action on fats.

Q.14. Assertion : Starch is hydrolysed by ptyalin to maltose.
Reason : Sucrase hydrolyses sucrose to lactose. [AIIMS 2016]

Answer Answer: (c) Sucrase hydrolyses sucrose to glucose and fructose

Q.15. Assertion: Blood sugar level falls rapidly after hepatectomy.
Reason: The glycogen of the liver is the principal source of blood sugar.

Answer Answer: (a) In liver, glycogen a reserve food material is changed into glucose (glycogenolysis) and released into blood. Under abnormal conditions, liver can convert proteins and fats into glucose by complex chemical reactions i.e. called gluconeogenesis. Thus, due to hepatectomy, blood sugar level falls rapidly.

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