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Biology Class 11 Science Notes Digestion in Mouth

Biology Class 11 Science Notes Digestion in Mouth

Biology Class 11 Science Notes Digestion in Mouth

Biology Class 11 : Takshila Learning offers online coaching classes by the experienced faculty members. We provide Physics, Chemistry, and Biology notes, as per the CBSE syllabus, last year question papers for board exams preparation. Our motive is to provide quality and result oriented education as well as guidance to the students in their preparation. In the following article, the topic “Digestion in Mouth” from the unit Human Physiology of Class 11 Biology (Class 11) is discussed. In the following article, sub topic – Salivary glands and their role in digestion is explained.


We eat food by our mouth, inside the mouth; teeth are present that helps in cutting down the food into smaller parts. Further teeth help in chewing (masticate) the food. The broken food material is thoroughly mixed up with the saliva (the first of the digestive juices) and forms a paste like substance. Saliva is produced by the salivary glands present in the mouth. Let’s discuss salivary glands-

SALIVARY GLANDS: The salivary glands in mammals are exocrine glands (glands that pour their secretions by way of a duct) that produce saliva. The saliva breaks down the starch into sugars. There are three pairs of salivary glands;

  • Parotid glands: They lie inside the mouthjust in front of the ears. They are the largest of the salivary glands. Their secretions enter the buccal cavity/ oral cavity (mouth) via the parotid duct or Stensen duct. The parotid glands are serous (producing water like secretions) glands. They produce thin and watery secretions. About 20% of the total salivary content in the oral cavity is produced by the parotid glands. The inflammation of the parotid glands causes parotitis also known as mumps.
  • Submaxillary (submandibular) glands: These glands are located beneath the angles of the lower jaw. Their secretions are released into the mouth through Wharton’s They are the mixed type of glands as they contain cells which produce both serous and mucous type secretions. Even though the submaxillary glands are much smaller than parotid glands, but their secretions contribute approximately 65-70% of saliva in the mouth.
  • Sublingual glands:These glands lie beneath the tongue.They produce mucous secretions.The mucous contains mucin. The secretions reach the oral cavity through a number of ducts called as Rivinius About 5% of the saliva entering the oral cavity comes from these glands.

Biology Class 11 Science Notes Digestion in Mouth
Salivary juice and its composition

Saliva is produced in and secreted from salivary glands. The basic secretory units ofsalivary glands are clusters of cells called acini. These cells secrete a fluid that contains water, electrolytes, mucus, and enzymes, all of which flow out of the acinus into collecting ducts.

The secretions from the three salivary glands (as discussed above) mix with each other and forms salivary juice.  This juice is a colorless, opalescent, and viscous liquid with pH ranging from 5.6 to 7.6. Although, the production of saliva is continuous in the mouth, the secretion of saliva increases while the food is being eaten. About 98 to 99% of saliva is water and the rest of it contains organic and inorganic substances. The main inorganic components present in saliva are electrolytes like sodium, potassium, calcium, magnesium, chlorides, phosphates and sulfates.


The organic components of saliva are mucus and enzymes. The mucus is made up of mucin(mainly consists of mucopolysaccharides and glycoproteins) granules dissolved in water of saliva. This makes the mucus, viscous in nature. The mucus helps in lubricating the food materialand help in making a food bolus, so it can be swallowed easily.Salivary juice contains many enzymes like;


Salivary Amylase:  It is also called as Ptyalin. It appears to be a mixture of two enzymes namely, alpha/ α amylase and Beta/βamylase, with α amylase predominating. Salivary amylase acts on the starch present in the food and converts it into maltose (a disaccharide sugar having two glucose units), iso-maltose (an isomer of maltose), dextrin and glucose. It acts at a pH optimum of 7.4.

Action of salivary amylase

Biology Class 11 Science Notes Digestion in Mouth



Lysozyme: The enzyme lysozyme acts on the polysaccharides present in the cell wall of bacteria. Thus it helps in killingand dissolving the bacteria.

Functions of Saliva

  1. It lubricates and makes the passage of food easy.
  2. The water of saliva evaporates making the oral surface moist and prevents desiccation.
  3. The salivary amylase in saliva helps in converting starch into simple sugars like maltose, glucose.
  4. The enzyme lysozyme helps in dissolving the bacteria and prevents from harmful organisms.
  5. It also helps in the speech by facilitating the movements of lips and tongue.

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