Class 11 Biology Chapter-16 Digestion and Absorption

CLASS 11

BIOLOGY

CHAPTER-16

DIGESTION AND ABSORPTION

NUTRITION: The process by which an organism takes in and uses food.

Autotrophic(Holophytic) nutrition: The form of nutrition esp. by plants which utilizes energy from sun forming complex good particles from simple inorganic substances.

Heterotrophic nutrition: In this nutrition organisms are dependent on the other plants or animals.

Holozoic nutrition: The process of taking solid food particle.

STEPS OF HOLOZOIC NUTRITION:

1. Ingestion: The act of taking in food. 2. Digestion: The process of conversion of complex food substances to simple absorbable forms 3. Absorption: Uptake of soluble products of digestion into the blood stream and then into the cells. 4. Assimilation: The process whereby the already digested foodstuffs are absorbed and utilized by the tissues. 5. Egestion: Elimination of undigested waste from the body.

Herbivores: organisms feeding on plants only.

Carnivores: organisms feeding on animals.

Omnivores: organisms feeding on both plants and animals. Saprozoic nutrition: organisms which depend on dead and decaying matter.

Digestion: The process of conversion of complex food substances to simple absorbable forms.

TYPES OF DIGESTION:

Intracellular digestion: when the process of digestion takes place inside the cell.

Extracellular digestion: the process of digestion which takes place outside the cells in narrow cavities(digestive tract).

DIGESTIVE SYSTEM

A. Alimentary canal(digestive tract) 1. Mouth and buccal cavity: mouth is a transverse slit bounded by two lips. Buccal cavity consists of tongue and teeth. a. Tongue: (i) It is musculo-sensory organ. (ii) Located on the floor of buccal cavity. (iii) Frenulum is located on the posterior part. (iv) Filiform papillae located on the anterior two-third of the tongue. (v) Fungiform papillae located at the tip of the tongue. (vi) Vallate papillae on the posterior-lateral surface of tongue. (vii) Tongue helps in ingestion,chewing and swallowing of food. b. Teeth: (i) Dental formula: 2123/2123 (ii) Types of teeth: incisors meant for cutting and biting Canines for tearing Premolars and molars for mastication c. Structure of tooth 2. Oesophagus: (i) Narrow,muscular and tubular. (ii) It carries food to the stomach. 3. Stomach: (i) Large, muscular and j-shaped. (ii) Located on the left side of the upper part of abdominal cavity. (iii) Four parts of stomach: cardiac(fundus); body; pyloric(antrum). (iv) Longitudinal folds inside the stomach is called rugae.

4. Small intestine a. Duodenum: it is c-shaped which continues into jejunum. b. Jejunum c. Ileum 5. Large intestine a. Caecum b. Colon c. Rectum: it is guarded by two anal sphincter muscles.

B. Associated glands 1. Salivary glands: a. Parotid: (i) Located between thye ramus of mandible. (ii) It has Duct of stensen. b. Submaxillary: (i) Located median to mandible. (ii) It has duct of Wharton. c. Sublingual: (i) Located beneath the tongue. (ii) It has duct of Rivinus. 2. Gastric glands: (i) Located in the stomach. (ii) Fundus part secretes HCl, pepsinogen and soluble mucin. (iii) Pyloric glands secrete gastrin. (iv) Cardiac glands secrete mucin and pepsinogen. 3. Intestinal glands a. Crypts of Lieberkuhn b. Brunner’s gland PHYSIOLOGY OF NUTRITION:

A. INGESTION: 1. solid food is chewed and masticated in the mouth and is converted into bolus. 2. Bolus is conveyed to pharynx and then into oesophagus by swallowing(deglutition) and further passes by muscular contractions (peristalsis). 3. Peristalsis is the successive waves of involuntary contraction passing along the walls of the digestive tract.

B. DIGESTION: 1. Digestion of carbohydrates:

2. Digestion of proteins:

QUESTIONS-ANSWERS:

Q1. Answer briefly:

(i) Why are villi present in the intestine and not in the stomach? (ii) How does pepsinogen change into its active form? (iii) What are the basic layers of the wall of alimentary canal? (iv) How does bile help in digestion? A1.

(i) All absorption takes place in the intestine. Thus villi helps to increase the surface area for more absorption. (ii) Pepsinogen is converted into its active pepsin in the presence of strongly acidic pH (1-2%) in the stomach. (iii) Serosa, muscularis,sub-mucosa are four basic layers of the wall of the alimentary canal. (iv) Bile helps in the emulsification of fats by lowering the surface tension.

Q2. Differentiate between:Rennin and rennin

A2. Rennin is a hormone, produced by the kidneys, whereas rennin is a milk coagulating enzyme , found in the gastric juice of human beings during infancy. Rennin helps in digestion of milk proteins.

Q3. Write the main function of pepsin.

A3. To hydrolyse proteins into proteases and peptones.

Q4. Name two diseases caused by PEM.

A4. Marasmus, Kwashiorkor.

Q5. Name the three types of gastric glands.

A5. Fundicglands, pyloric glands and cardiac glands.

3. Digestion of fat: