SELINA Solutions for Class 9 Biology Chapter 11 - Digestive System

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Chapter 11 - Digestive System Exercise Ex. 1

Question A

Multiple Choice Questions:

1. Pylorus is an opening from

(i) oseophagus into stomach

(ii) mouth cavity into stomach

(iii) stomach into intestine

(iv) intestine into rectum

2. Gastric juice contains

(i) HCl and pepsin

(ii) pepsin and trypsin

(iii) trypsin and HCl

(iv) amylopsin and pepsin

3. The water from the digested food is mainly absorbed by

(i) stomach

(ii) duodenum

(iii) colon

(iv) rectum

4. Which one of the following pairs of types of teeth perform one common function as stated against it?

(i) Incisors, canines - Holding

(ii) Canines, premolars - Biting

(iii) Premolars, molars - Grinding

(iv) Molars, incisors - Tearing

Solution A

1. (iii) stomach into intestine

2. (i) HCl and pepsin

3. (iii) colon

4. (iii) Premolars, molars - Grinding

Question B.1

What is the dental formula of a normal human adult?

Solution B.1

The dental formula of a normal human adult is:

Human adult = Selina Solutions Icse Class 9 Biology Chapter - Digestive System= 32 (Permanent teeth + Wisdom teeth)

Question B.2

Mention two reflexes which occur when a person chews and swallows food.

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)

Question B.3

Consider the following two statements A and B and select the right option from (i)-(iv) about their correctness.

A. Small intestine is shorter than large intestine.

B. Small intestine is wider than large intestine.

Options :

(i)Both the statements are correct

(ii) Both the statements are wrong

(iii) Statement A is correct, B is wrong

(iv) Statement B is correct, A is wrong

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.

Question C.1

What is digestion? Why do only animals require a digestive system?

Solution C.1

Digestion is the process of breaking down complex food materials into simpler substances by the action of enzymes.

Need for a digestive system:

(i) Large complex molecules like carbohydrates, proteins and lipids need to be broken down to simpler molecules. These simpler molecules can then be absorbed and utilized by the body.

(ii) The breaking down of complex food molecules into their simpler form is possible only through the process of digestion.

(iii) During digestion, large complex macromolecules present in food are converted into small simpler molecules, which can be simplified in different compartments of digestive system only.

Question C.2

What are the end products of the digestion of: starch, proteins and fats respectively?

Solution C.2






Small peptides and amino acids


Fatty acids and glycerol


Question C.3

Why is there no enzyme to digest vitamins?

Solution C.3

Vitamins are used in their original form by the cells. They do not require digestion. They are either water soluble or fat soluble, hence no enzyme is required to digest vitamins. They are absorbed directly from the digestive tract, transported by blood to the cells, and the cells absorb and use them whenever they need. Besides, vitamins themselves act as catalysts or enzymes in essential chemical reactions that take place in the body.

Question C.4

How is thorough chewing of food helpful in digestion?

Solution C.4

It is very important to chew our food thoroughly as chewing of food helps to break down complex food materials into simpler substances. The act of chewing stimulates the salivary glands to release saliva. The saliva helps to moisten the food and form bolus, which can be swallowed easily. Saliva also contains special enzymes that help to break down carbohydrates.

Question C.5

What is the function of rectum?

Solution C.5

Rectum acts as a temporary storage site for undigested food. It has voluntary smooth muscles that remove the faeces out of the body through the anus.

Question C.6

What is roughage? Give two examples.

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

Question C.7

Mention two ways in which the ileum of the mammal is adapted for the absorption of digested food.

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

Question C.8

The stomach secretes gastric juice, which contains hydrochloric acid. What is its function?

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.

Question D.1

Prepare a possible vegetarian menu for your dinner which would provide all the necessary nutrients.

Solution D.1

Vegetarian menu for dinner: 


Weight (gm/ml)





Green leafy vegetables


Root vegetables






Fat and oil


Brown sugar and jaggery


Question D.2

What are the main characteristics of an enzyme?

Solution D.2

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.

Question D.3

Why is the small intestine the most important organ of the digestive system?

Solution D.3

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.

Question D.4

How is the liver an important organ in our body?

Solution D.4
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
Question D.5

Define the following terms :

(i) Peristalsis

(ii) Omnivore

(iii) Pylorus

(iv) Kilocalorie

(v) Basal metabolic rate

Solution D.5

(i) Peristalsis: Peristalsis is the rhythmic contraction and relaxation of the muscles of the alimentary canal that pushes the food along the gut.

(ii) Omnivore: Omnivores are organisms that consume both plants and animals.

(iii) Pylorus: Pylorus is the passage at the lower end of the stomach that opens into the duodenum.

(iv) Kilocalorie: A kilocalorie is a unit of energy. It is the energy required to raise the temperature of 1 kg of water by 1 Celsius.

(v) Basal metabolic rate: Basal metabolic rate refers to the minimum amount of energy in the form of calories that our body requires to complete its normal functions.

Question D.6

List the enzymes and their action on food in the stomach and intestine.

Solution D.6






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


Question D.7

Give any four reasons why water is necessary in our body.

Solution D.7

Importance of water in our body:

1. Water is the major component of blood, which carries nutrients and oxygen, to and from all the cells.

2. It is the major component of saliva and mucous, which lubricate the membranes that line our digestive system beginning with the mouth.

3. It helps in regulating the temperature of the body.

4. Water is very essential for digestion as well as absorption of food.

Question D.8

You have been supplied with a sample of food. How will you perform tests for the presence of starch and proteins on it?

Solution D.8

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.

Question E.1

Draw a labelled diagram to show the internal structure of a mammalian tooth with two roots.

Solution E.1

Selina Solutions Icse Class 9 Biology Chapter - Digestive System 

      Internal structure of a mammlian tooth

Question E.2

Try to swallow the saliva in your mouth, and feel with your hand your neck. What happens in the neck?

Solution E.2

While swallowing saliva in the mouth, the larynx is pulled upwards to bring it close to the back of the tongue, when a flap called epiglottis closes its opening. Then, it goes towards the oesophagus.

Question E. 3

Complete the following table by filling in the blanks 1 to 8.



Food acted upon

Find product





Mouth 4 5 Disaccharide





Solution E. 3

Organ Enzyme Food acted upon Find product
Stomach Pepsin Proteins Polypeptide
Mouth Amylase Starch Disaccharide
Ileum Maltase Maltose Glucose
Question E.4

Study the diagram given below and then answer the questions that follow:


Selina Solutions Icse Class 9 Biology Chapter - Digestive System 


(a) Name the parts labelled 1, 2, 3, 4, 5 and 6.

(b) Identify the tooth and give a reason to support your answer.

(c) Describe the structure of the part labelled '3'.

(d) Give the total number of the type of tooth mentioned in '1' above, in the mouth of an adult and state its function.

Solution E.4


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 

Question E.5

Study the following dental formula and then answer the questions that follow:

Selina Solutions Icse Class 9 Biology Chapter - Digestive System 

(a) What is the total number of teeth in the

(i) upper jaw and (ii) lower jaw?

(b) State the total number of teeth present in the dentition.

(c) Give the dental formula of an adult human being.

Solution E.5

(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 Selina Solutions Icse Class 9 Biology Chapter - Digestive System.