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Question Bank, Digestive System, 1. Define digestion. Why is it necessary ?, Ans. Digestion is the process by which insoluble complex food, substances are broken down into soluble and simpler form, having smaller molecules, which can easily be absorbed by, blood., It is through this process of digestion that food is converted, into simpler diffusible molecules which can easily pass, through membranes and enter blood. Food is thus carried to all, parts of the body., 2. State the importance of hydrochloric acid in stomach., Ans. Hydrochloric acid in stomach performs two functions :, (i) It kills bacteria swallowed along with the food., (ii) It provides an acidic medium for pepsin to act upon, proteins., 3. Give the end products of digestion of protein, fats and, carbohydrates., Ans. Proteins → Amino acids, Fats → Fatty acids and glycerol, Carbohydrates → Simple sugars, Starch → Maltose → Glucose, Sucrose → Glucose and fructose, Lactose → Glucose and galactose., , Biology Class-IX, , 1, , Question Bank

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4. Define peristalsis. Mention its role in digestion., Ans. The movement of food along the oesophagus and rest of the, alimentary canal is brought about by the rhythmic contraction, and relaxation of the muscular walls. The rhythmic waves of, contractions and relaxation by which food moves down the, alimentary canal is called peristalsis. Peristalsis thus help in, the movement of food downwords in the alimentary canal., , Movement of Bolus in oesophagus by peristalsis, , 5. What are villi ? How are they adapted for the absorption of, food ?, Ans. Villi are finger-like projections on the inner surface of small, intestine. Each villus is covered by a single layer of epithelium, and contains blood capillaries and lymph vessel., Villi increase the surface area for absorption. The epithelium, of villi helps in easy diffusion of digested food., 6. What is the fate of food after it is digested and absorbed ?, Ans. The food after digestion and absorption is assimilated into, body substances and protoplasm of the cells. This takes place, in following ways :, (i) The final products of fat digestion — fatty acids and, glycerol — are absorbed in the blood stream through the, lacteals. In the body, they are again converted into fats and, excess fats are stored in adipose tissue. This stored fat can, be utilized by the body in times of need., Biology Class-IX, , 2, , Question Bank

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(ii) The simple sugars absorbed through the intestinal villi are, used for generating energy for various life activities. The, excess sugars are converted in man into a complex, polysaccharide, glycogen, in the liver. It can be reutilized, during stress conditions., (iii) The amino acids are utilized to synthesize different, proteins required by the body. Amino acids are not stored, in the body, but excess amino acids may be converted into, glucose and stored for future use., 7. What are enzymes ? Give three characteristics of enzymes., Ans. Enzymes are chemical compounds, proteinaceous in nature,, produced in the cells of living organisms., Characteristics of Enzymes : Enzymes show the following, characteristics :, (a) Enzymes are proteins in nature. Being proteinaceous, they, are destroyed by heating., (b) Enzymes are biocatalysts; they accelerate the rate of, chemical reactions., (c) Enzymes are specific in their action. A particular enzyme, acts only on one substrate., (d) Enzymes always produce the same end-product., (e) Enzymes work within a narrow temperature range of, 35°C to 40°C. At higher or lower temperatures, enzyme, activity is reduced. At very high or very low temperatures,, enzymes become ineffective as they get destroyed., (f) Enzymes are sensitive to changes in acidity or alkalinity, (pH). They act most rapidly in a particular degree of, acidity or alkalinity. For example, the enzyme – pepsin, requires an acidic medium, while trypsin requires an, alkaline pH., , Biology Class-IX, , 3, , Question Bank

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8. Name the enzymes present in the succus entericus., Ans. Peptidase, lipase, maltase, sucrase and lactase., 9. State three conditions under which the enzymes become, inactive., Ans. (i) At very high or very low temperatures, enzymes become, inactive., (ii) Since enzymes require a specific pH to act upon, any, change in acidity or alkalinity of the medium affects the, enzyme activity or even inactivates them., (iii) Some chemicals inactivate the enzymes., 10. Draw a labelled diagram to show the alimentary canal of man., Ans., , Digestive System of Human, , Name the enzymes present in pancreatic juice and state their, functions., Ans. Pancreatic juice contains a number of enzymes which act in, alkaline medium. The enzymes are, (i) Trypsin : converts remaining proteins into peptones and, the peptones into peptides and amino acids,, (ii) Amylase : converts the undigested starch into maltose, (continues the process begun in mouth), and, (iii) Steapsin (Lipase) : converts fats into fatty acids and, glycerol., , 11., , Biology Class-IX, , 4, , Question Bank

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12. What is bile ? Give its function., Ans. (i) Bile : It is a yellowish fluid produced in liver and stored in, gall bladder. It contains, (a) Sodium salts : These reduce the acidity of chyme (making, the medium alkaline) and emulsify fats (breaks them into, smaller globules and lowers the surface tension), and, (b) The pigments which are the excretory products resulting, from desintegration of red blood cells (this gives yellow, colour to the bile). Bile contains no enzymes., 13. How is ileum adapted for the absorption of food?, Ans. The ileum is well adapted for the process of digestion. It is, long so that food is retained in it for a longer period, and, shows following characters:, (a) The inner lining of small intestine has millions of fingerlike projections called villi throughout its length. These, increase the surface area for absorption., (b) The epithelium of villi has mucus lining throughout its, length for easy diffusion of digested food., , (A.) Section through small intestine showing villi on the inner surface; B. Single villus (enlarged.), , Biology Class-IX, , 5, , Question Bank

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14. One should not talk during swallowing. Give reasons., Ans. During swallowing, the food has to pass over the windpipe, (trachea) to enter the oesophagus. To avoid the entry of food, into the trachea and choking, one should not talk during, swallowing., 15. What is dentition? Give dental formula of man, dog and rabbit., Ans. Dentition, The arrangement of different types of teeth on the jaws is, called dentition., 2, 1, 2, 3 8, Dental formula of man I = , C = , Pm = , M = = 2 = 32, 2, 1, 2, 3 8, 3, 1, 4, 2 10, Dental formula of dog I = , C = , Pm = , M = =, 2 = 42, 3, 1, 4, 3 11, 2, 0, 3, 3 8, Dental formula of rabbit I = , C = , Pm = , M = = 2 = 28, 1, 0, 2, 3 6, 16. Distinguish between the following :, (i) Homodont and Heterodont teeth., (ii) Milk teeth and Permanent teeth., (iii) Dentine and Enamel., Ans. (i) Differences between Homodont and Heterodont teeth, Homodont teeth, All the teeth are of same kind., , Heterodont teeth, More than one type of teeth differing, in shape, size and function present., Example - Mammals, , Examples - Reptiles, fish., , (ii) Differences between Milk teeth and Permanent teeth, Milk teeth, 1. These are temporary or deciduous, teeth, as they fall off., 2. Present in children., 3. Full milk dentition consists of 20 teeth., , Biology Class-IX, , 6, , Permanent teeth, They do not fall, and replace milk teeth., Present in adults., Full permanent dentition consists of 32, teeth., , Question Bank

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(iii) Differences between Dentine and Enamel., Dentine, 1. It is present below the enamel., 2. It is not as hard as the enamel., 3. It is supplied with blood, Capillaries and nerves in the pulp cavity., 4. It contains living cells., , Enamel, It is the outer white covering of the, crown of teeth., It consists of the hardest substance in, the body., It is not supplied with blood, capillaries and nerves., No living cells present., , 17. Draw a labelled diagram to show the internal structure of a, tooth., Ans., , L.S. of an incisor tooth to show the internal structure., , Biology Class-IX, , 7, , Question Bank

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18. Write the functions of the following parts :, (i) Enamel, (ii) Pulp cavity, (iii) Cement, Ans. (i) Enamel — Being hard, it helps in biting, crushing and, grinding food., (ii) Pulp cavity — It supplies the tooth blood vessels and, nerves. Blood nourishes the tooth, while the nerves receive, and transmit sensations of pain to the brain., (iii) Cement — It holds the tooth firmly in the sockets of the, jaw., 19. Name the different kinds of teeth in mammals and state their, functions., Ans. Different kinds of Mammalian teeth and their functions, Type of tooth, Incisors, , Number of each kind in half, of each of jaw in man, 2 Front teeth, , Canines, , 1, , Premolars, , 2, , Molars, , 3, , Structure, , Function, , Have flat, sharp, edges., Pointed edge, Bicuspid (two, cusps), and have one or, two roots., Four or five, cusps. Have, more than one, root., , Cutting and, biting the food., Tearing and, piercing., Crushing and, grinding., Crushing,, grinding and, mastication., , 20. Explain the following terms:, (i) Diastema, (ii) Dentine., Ans. (i) Diastema : In herbivores like rabbit, canines are absent, and a gap is present between the incisors and the, premolars. This gap is called diastema., (ii) Dentine : Dentine is the hard yellowish bone-like tissue, below the enamel in a tooth. It is not as hard as the, enamel., , Biology Class-IX, , 8, , Question Bank

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21. Mention whether the following statements are True (T) or, False (F) :, (i) In an adult human, there are 4 molar teeth in each jaw., (ii) Cats and dogs are carnivorous animals., (iii) Teeth in fish are of one type only (homodont)., (iv) The last molar tooth is called wisdom tooth., (v) The part of the tooth lying above the gum is called the, neck., (vi) Blood capillaries and nerves are present in the pulp cavity, of the teeth., Ans. (i) F, (ii) T, (iii) T, (iv) T, (v) F, (vi) T, , Biology Class-IX, , 9, , Question Bank