NCERT Class 11-Biology: Chapter –16 Digestion and Absorption Part 6

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Question 3:

Discuss mechanisms of absorption.


The absorption of digested food happens through passive, active or facilitated transport mechanism.

Mechanism of absorption for different molecules is as follow

(i) Simple Diffusion: Small amounts of monosaccharide like glucose, amino acids and some electrolytes like chloride ions are absorbed by simple diffusion. The passage of these substances into the blood depends upon the concentration gradient

(ii) Facilitated Transport: Fructose and some amino acids are absorbed with the help of carrier ions like Na+. This mechanism of transport is called facilitated transport or active transport.

(iii) Transport of water depends on osmotic gradient.

(iv) Transport of Fatty acids and glycerol: As these substances are insoluble, they cannot be absorbed into the blood. They are first converted into micelles (small droplets) which move into intestinal mucosa. Here these micelles are covered into very small protein-coated fat globules called chylomicrons which are transported to the lymph vessels in the villi. These lymph vessels release the absorbed substances into the blood stream.

Question 4:

Discuss the role of hepato – pancreatic complex in digestion of carbohydrate, protein and fat components of food.


The hepato – pancreatic complex plays a major role in the digestion of carbohydrates, proteins and fats.

Role of Liver: Liver secretes bile juice. Bile helps in emulsification of fats. Bile also provides alkaline medium which is useful for working of enzymes present in the small intestine.

Role of Pancreas: here pancreatic juice is secreted. The pancreatic juice contains inactive enzymes Trypsinogen, Chymotrypsinogen, Procarboxypeptidases, amylases, lipases and nucleases. Trypsinogen is activated by an enzyme, Enterokinase, (secreted by the intestinal mucosa) into active trypsin, which in turn activates the other enzymes in the pancreatic juice. Amylase digests carbohydrates and trypsin/chymotrypsin digests protein.

Pancreatic juice and bile are released through the hepato-pancreatic duct. The bile released into the duodenum contains bile pigments (bilirubin and billiverdin), bile salts, cholesterol and phospholipids but no enzymes. Bile also activates lipases, which converts triglycerides into di and monoglycerides.

The action of hepato-pancreatic secretion on digestion on carbohydrate, proteins and fats are summarised below

(i) Carbohydrates in the chyme are hydrolysed by pancreatic amylase into disaccharides.

Polysaccharides (starch) Disaccharides

(ii) Fats are broken down by lipases with the help of bile into di and monoglycerides

Triglycerides Emulsified triglycerides Diglycerides → Monoglycerides

(iii) Proteins in the chyme reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice.

Question 5:

Explain the process of digestion in the buccal cavity with a note on the arrangement of teeth.


The buckle cavity or oral cavity performs two major functions i.e., mastication of food (chewing the food into semisolid paste) and facilitation of swallowing (by mixing food with saliva).

Firstly, food gets mixed with saliva which softens and lubricates the food and cheering process breaks the food into smaller pieces.

In buckle cavity digestion of same food components takes place. Digestion of carbohydrates starts in the buckle cavity. The food is mixed with saliva which contains salivary anylase. This enzyme converts starch into maltose, is maltose and . 30% of the starch in food is hydorlysed in the buckle cavity.


The oral cavity has a number of teeth and a muscular tongue. Each tooth is embedded in a socket of jaw bone. This type of attachment is called the phycodont. The human gets two sets of teeth in their lifetime they are temporary teeth and permanent teeth.

Temporary teeth or milk teeth are deciduous and are replaced by permanent teeth. This type of arrangement is called diphyodont. The arrangement of teeth is illustra

Mouth (Oral Cavity)

Mouth (Oral Cavity)

There are four types of teeth in human beings – incisors, canines, premolars and molars, denoted as I, C, PM and M respectively.

Arrangement of teeth in each half of the upper and lower jaw in the order I, C, PM, M is represented by a dental formula which in human is

That is two incisors, one canine, two premolars and three molars on each side of jaws. Thus there are teeth in an adult human.

Incisors is for cutting, canine is for tearing, premolars and molars are for grinding and crushing.

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