Request a call back

Join NOW to get access to exclusive study material for best results

Class 9 SELINA Solutions Biology Chapter 11 - Digestive System

Digestive System Exercise Ex. 1

Solution A.1(a)

(iii) stomach into intestine

Solution A.1(b)

(i) HCl and pepsin

Solution A.1(c)

(iii) colon

Solution A.1(d)

(iii) Premolars, molars - Grinding 

Solution A.1(e)

(ii) Enamel 

Solution A.1(f)

(iii) Premolars 

Solution A.1(g)

(ii) 35°C to 40°C

Solution A.1(h)

(i) Humans

Solution A.1(i)

(i) Sucrase

Solution A.1(j)

(ii) Glycogenesis

Solution B.1

The dental formula of a normal human adult is:

Human adult = = 32 (Permanent teeth + Wisdom teeth)

Solution B.2

The two reflexes which occur when a person chews and swallows food are:

1. Reflex when a person chews - Secretion of saliva

2. Reflex when a person swallows - Tongue presses upward and back against the roof (palate)

Solution B.3

(ii) Both the statements are wrong. Small intestine is longer (7 metres) than large intestine (1.5 metres). Also, large intestine is so called because of its width which is larger than that of small intestine.

Solution B.4


Solution B.5

(a) Alimentary canal and Digestive glands

(b) Salivary glands, Liver and Pancreas

(c) Parotid gland, Submandibular gland and Sublingual gland

(d) Duodenum, Jejunum and Ileum

(e) Caecum, Colon and Rectum

Solution B.6

(a) Pepsin (Rest are enzymes active in the small intestine)

(b) Peptidase (Rest convert complex carbohydrates into glucose during digestion)

(c) Starch (Rest are products of digestion)

(d) Colon (Rest are parts of the small intestine)

(e) Palate (Rest are parts of a tooth)

Solution C.1

(a) Digestion is the breakdown of naturally occurring foodstuffs into diffusible form.

(b) Enzyme is a biological catalyst and is almost always a protein. It speeds up the rate of a specific chemical reaction in the cell.

(c) Peristalsis is the wave of constrictions caused by the circular muscles of the gut pushing the food along.

(d) Dentition is the make-up of a set of teeth including their kind, number, and arrangement in the mouth.

(e) Defecation is the expulsion of the undigested remains of the food from the alimentary canal.

(f) Assimilation is the conversion of the absorbed digested food into body material.

Solution C.2






Small peptides and amino acids


Fatty acids and glycerol


Solution C.3

(a) Liver: Located in the upper right side of the abdomen just below the diaphragm.

(b) Submandibular gland: Located close to the inner side of the lower jaw on each side.

(c) Pylorus: Located at the opening of the stomach into the intestine.

(d) Pancreas: Located behind the stomach.

(e) Caecum: Located at the junction of the small and the large intestine.

Solution C.4

(a) Rectum acts as a temporary storage site for undigested food and wastes.

(b) Gastric juice contains HCl and pepsin. HCl kills any germs which may have entered along with food. It also activates pepsinogen to pepsin. Pepsin digests proteins into peptides.

(c) Epiglottis prevents the entry of food into the trachea and lungs.

(d) Small intestine is the site of complete digestion in humans. It absorbs digested food completely.

(e) Tongue helps in manipulating the food while chewing and mixing it with saliva. It also helps in swallowing, tasting, cleaning the food particles from the teeth after eating and speaking.

Solution C.5

(a) Plants obtain nutrients through photosynthesis. Animals eat food which comprises of macromolecules such as proteins, lipids, and complex carbohydrates. These macromolecules must be converted into simpler substances so that they can be easily absorbed into the blood. They do so through a special organ system called the digestive system. Thus, animals require a digestive system and not plants.

(b) Cells utilise vitamins in their natural form. They do not need to be digested. Because vitamins are either water or fat soluble, no enzymes are required to digest them.

(c) It is important to thoroughly chew our food in the mouth since chewing aids in the breakdown of complex food molecules into simpler substances. Chewing stimulates the salivary glands to produce saliva. The saliva moistens the meal and forms a bolus that can be readily swallowed.

(d) Despite the fact that bile lacks digestive enzymes, it plays a crucial role in fat digestion. Bile contains sodium bicarbonate which neutralizes the acid content of the food received from the stomach and makes the food alkaline so that the pancreatic and intestinal enzymes can easily act on it. Bile salts reduce the surface tension of fats and break them into tiny droplets for providing greater surface area for the action of enzymes.

(e) Villi are tiny finger-like projections found on the inner lining of small intestine. These villi enormously increase the inner surface area of the intestine which facilitates the absorption of digested food.

Solution C.6

Roughage is a dietary fibre that largely consists of cellulose. It cannot be digested by our body as our body does not contain cellulose-digesting enzymes.

Examples of roughage:

1. Fruits

2. Green leafy vegetables

Solution C.7

Adaptations of ileum for the absorption of digested food:

(1) Very long to provide more surface area for absorption

(2) Presence of large number of villi to further increase the surface area

Solution C.8

Functions of hydrochloric acid:

(1) It gets mixed with food and kills the bacteria present in food.

(2) It activates pepsin to act on proteins.

Solution D.1

Main characteristics of an enzyme:

1. It is a protein and therefore, gets destroyed by heating.

2. It acts only on one kind of substance called the substrate. So, it is very specific.

3. It acts as a catalyst, so it can be used again and again.

4. It only affects the rate of a chemical reaction and always speeds up the reaction.

5. It always forms the same end products from the fixed substrate.

6. It acts best only at a particular pH.

7. It acts best within a narrow temperature range, usually between 35°C-40°C.

Solution D.2

The small intestine is the most important organ of the digestive system as it serves both, for digestion and absorption. It receives two digestive juices; the bile and the pancreatic juice in the duodenum. These two juices virtually complete the digestion of starch, proteins, carbohydrates, etc. After the breakdown of food, the small intestine absorbs simple substances such as glucose, amino acids, etc.

Solution D.3

Liver is an important organ in our body as it serves the following functions:

  • Production of bile
  • Control of blood sugar levels
  • Control of amino acid levels
  • Synthesis of foetal red blood cells
  • Produce fibrinogen and heparin
  • Regulate blood volume
  • Destroy dead red blood cells
  • Store vitamin and minerals
  • Excrete toxic and metallic poisons
  • Produce heat
  • Detoxification

Solution D.4







Acts on proteins and converts it into polypeptides

Small intestine






Acts on starch and converts it into maltose



Acts on remaining proteins, proteoses and peptones to produce peptides and amino acids






Acts on proteins and polypeptides and converts them into small peptides and amino acids


Acts on sucrose and converts it into glucose and fructose


Acts on lactose and converts it into glucose and galactose


Solution D.5

Test for starch:

1. Take the food item to be tested. Put it into a test-tube containing water and boil to make a solution.

2. Cool the solution and add 2-3 drops of dilute iodine solution to it.

3. Blue-black colour of the solution indicates the presence of starch in the food item.

Test for proteins:

1. Take the food item to be tested in a test tube.

2. Add few drops of dilute nitric acid to it.

3. Heat the test-tube gently.

4. Rinse off the acid with water and add few drops of ammonium hydroxide to it.

5. Colour change from colourless to yellow and then from yellow to orange red indicates the presence of protein in the food item.

Solution E.1


      Internal structure of a mammlian tooth

Solution E.2


Organ Enzyme Food acted upon Find product
(1) Stomach Pepsin (2) Proteins (3) Polypeptide
Mouth (4) Amylase (5) Starch Disaccharide
(6) Ileum (7) Maltase Maltose (8) Glucose

Solution E.3


1 → Enamel

2 → Dentine

3 → Pulp

4 → Gum

5 → Crown

6 → Cement

(b) The tooth shown in the diagram has only one root, so it is an incisor or canine which is used for biting and piercing.

(c) The part labelled '3' (pulp) is a soft connective tissue present in the pulp cavity of the tooth. It consists of blood capillaries, lymph vessels and nerve fibres. These extend from the crown of the tooth and open through the pulp cavity at the base of the root.

(d) Type of teeth in the mouth of an adult:

1. Incisors (8) → Used for biting and cutting

2. Canines (4) → Used for holding and tearing of food

3. Premolars (8) → Used for grinding and crushing of food

4. Molars (12)→ Used for grinding and crushing of food 

Solution E.4

(a) (i) upper jaw - 22 teeth and (ii) lower jaw - 12 teeth

(b) A total of 20 teeth are present in the given dentition.

(c) Dental formula of an adult human being is  .

Solution E.5

(a) A - Incisor, B - Canine, C - Premolar, D - Molar

(b) Structural feature/shape of each type of teeth:


(c) Number of teeth of each kind in one jaw with their specific position:

 Incisors are 4 in number, positioned in the centre of each jaw.

 Canines are 1 in number, located on either side of the incisors in each jaw.

 Premolars are 2 in number, located on each side in each jaw next to the canines.

 Molars are the last 3 teeth, on each side in each jaw.

(d) Calcium and phosphorus are the two minerals present in teeth.

(e) The last molar of each side in each jaw is called wisdom tooth. Wisdom teeth are so called because they appear last at an age of about 17-20 years when the human body is reaching maturity.

Solution E.6

Microscopic structure of an intestinal villus 


(a) A large number of villi on the inner surface of small intestine enormously increase the inner surface area of the intestine which facilitates the absorption of digested food.

(b) Role of lacteals:

 They help in the absorption of fatty acids and glycerol from the small intestine.

 They act as a passage to transport the contents in the form of lipoproteins into the lymphatic system.

(c) Intestinal juice is the yellowish watery fluid released by the glandular cells of the small intestine.

(d) Secretions:

(1) Salivary gland - Saliva

(2) Stomach - Gastric juice and HCl

(3) Liver - Bile

(4) Pancreas - Pancreatic juice

Get Latest Study Material for Academic year 24-25 Click here