Selina Concise Ch 11 Digestive System ICSE Solutions Class 9 Biology

ICSE Solutions for Chapter 11 Digestive System Class 9 Biology Selina

Exercise 1

Progress Check

1. Given below is a jumbled sequence of the different parts of the human alimentary canal. Rewrite them in correct sequence

Stomach, Oesophagus, large intestine, small intestine, Pharynx

Solution

The correct sequence is as follows:
Pharynx → Oesophagus → Stomach → Small intestine → Large intestine

 

2. Name the following:
(i) The three subdivisions of the small intestine
(ii) The three subdivisions of the large intestine
(iii) The three salivary glands

Solution

(i) The three subdivisions of the small intestine — Duodenum, Jejunum, Ileum

(ii) The three subdivisions of the large intestine — Caecum, colon and rectum

(iii) The three salivary glands — Parotid gland, submandibular gland, sublingual gland

 

3. Give the technical names for the following types of teeth in humans (on each side, in each jaw)
(i) The three last grinders
(ii) The pointed tooth for holding and tearing
(iii) The broad sharp cutting teeth.
(iv) The two temporary (deciduous) grinding teeth.

Solution

The technical terms are as follows:

(i) The three last grinders - Molars

(ii) The pointed tooth for holding and tearing — Canines

(iii) The broad sharp cutting teeth - Incisors

(iv) The two temporary (deciduous) grinding teeth — Milk teeth

 

4. Name the following parts of a tooth:
(i) Part exposed above the gum.
(ii) The hard substance making the covering of the tooth.
(iii) The soft connective tissue contained in the central space of the tooth.
(iv) Bone-like structure fixing the root in position.
(v) Slight constriction between the root and the crown.

Solution

(i) Part exposed above the gum - Crown

(ii) The hard substance making the covering of the tooth - Enamel

(iii) | The soft connective tissue contained in the central space of the tooth - Pulp

(iv) Bone-like structure fixing the root in position - Cement

(v) Slight constriction between the root and the crown - Neck

 

5. Mention if the following statements are true (T) or false (F):
(i) Saliva moistens and lubricates food
(ii) Saliva contains a protein-digesting enzyme
(iii) Saliva tends to destroy germs in the mouth
(iv) Peristalsis occurs through all regions of the gut
(v) The food in stomach stays for about 10 hours
(vi) Gastric juice is alkaline
(vii) Gastric juice contains pepsinogen.

Solution

(i) True.

(ii) False. Salina contains salivary amylase (ptyalin) that converts starch into maltose.

(iii) True.

(iv) True.

(v) False. The food stays in the stomach for about 3 hours

(vi) False. Gastric juice is highly acidic.

(vii) True.

 

6. Mention if the following statements are true(T) or false(F)
(i) Intestinal villi have a lymph vessel called lacteal.
(ii) Intestine is narrow for fast movement of food.
(iii) Large intestine secretes no enzymes
(iv) Bile neutralizes the acid content of the food received from the stomach
(v) Pancreatic juice has enzymes to digest all the major components of food.
(vi) The anus is surrounded by circular muscles

Solution

(i) True.

(ii) False. Intestine is narrow for slow movement of food allowing absorption.

(iii) True.

(iv) True.

(v) The statement is true.

(vi) True.

 

7. Name the enzyme which digests:
(i) Starch in the mouth
(ii) ‘Fats in the ileum
(iii) Protein in the duodenum
(iv) Sucrose in the ileum

Solution

(i) The enzyme that digests starch in the mouth is salivary amylase or ptyalin.

(ii) The enzyme that digests fats in the ileum is Lipase

(iii) The enzyme that digests proteins in the duodenum is trypsin

(iv) The enzyme that digests sucrose in the ileum is sucrose

8. What are the end-products of digestion of:
(i) Proteins
(ii) Fats
(iii) Starch
(iv) Sucrose

Solution

Listed below are the end products:

(i) Proteins — Peptides and amino acids

(ii) Fats — fatty acids, glycerol,

(iii) Starch - Maltose

(iv) Sucrose — Glucose and fructose

 

9. Fill in the blanks:
(i) Liver stores glucose as ____
(ii) Liver produces only in embryo ____
(iii) Urea is produced in by the de-amination of extra ____
(iv) For testing the action of saliva on starch the material has to be kept at a temperature of about °C.

Solution

(i) Glycogen

(ii) Red blood cells (RBCs)

(iii) Liver, amino acids

(iv) 38

 

11. Mention the constituents of food if the end result of the test shows:
(i) White to yellow and yellow to orange colour (after adding ammonium hydroxide).
(ii) Turning blue-black after adding iodine solution.
(iii) Blue green to deep red with appearance of precipitate when added to Fehling solution.
(iv) Ash that does not burn after continued heating.

Solution

(i) The food contains protein.

(ii) The food contains starch.

(iii) |The food contains glucose.

(iv) The food contains mineral substance.

 

Review Questions

A. Multiple Choice Type

1. Pylorous is an opening from
(a) Oesophagus into stomach
(b) Mouth cavity into esophagus
(c) Stomach into intestine
(d) Intestine into rectum

Solution

(c) stomach into intestine
Pylorus is an opening from the stomach into the duodenum to be precise.

 

2. Gastric juice contains
(a) HCl and pepsin
(b) Pepsin and trypsin
(c) Trypsin and HCI
(d) Amylopsin and pepsin

Solution

(a) HCI and pepsin
Gastric juice is strongly acidic and consists of HCI and essential digestive enzyme pepsin.

 

3. The water from the digested food is mainly absorbed by
(a) Stomach
(b) Duodenum
(c) Colon
(d) Rectum

Solution

(c) Colon
Colon is part of the large intestine and mainly absorbs water and some remnants of digested food.

 

4. Which one of the following pairs of types of teeth perform one common function as stated against it?
(a) Incisors, canines – Holding
(b) Canines, premolars – Tearing
(c) Premolars, molars – Grinding
(d) Molars, incisors - Tearing

Solution

(c) Premolars, molars – Grinding
Both premolars and molars are involved in grinding the food.

 

B. Very short answer type

1. What is the dental formula of a normal human adult?

Solution

(d) Dental formula of an adult human being is 2/2, 1/1, 2/2, 3/3

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

Solution

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).

 

3. Consider the following two statements A & B and select the right 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

(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.

 

C. Short Answer Type

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

Solution

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

Need for a digestive system:

1. 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.
2. The breaking down of complex food molecules into their simpler form is possible only through the process of digestion.
3. 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.

 

2. What are the end-products of the digestion of:
Starch, proteins and fats respectively?

Solution

The substrate and end products are:

• Starch: Maltose
• Proteins: Small peptides and amino acids
• Fats: Fatty acids and glycerol

 

3. Why is there no enzyme to digest vitamins?

Solution

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.

 

4. How is thorough chewing of food helpful in digestion?

Solution

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.

 

5. What is the function of rectum?

Solution

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.

 

6. What is roughage? Give two examples.

Solution

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

 

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

Solution

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.

 

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

Solution

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.

 

D. Long Answer Type

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

Solution

Vegetarian menu for dinner:

Foodstuffs	Weight (gm/ml)
Cereals	320
Pulses	70
Green leafy vegetables	100
Root vegetables	75
Fruits	75
Milk	600
Fat and oil	30
Brown sugar and jaggery	30

 

2. What are the main characteristics of an enzyme?

Solution

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.

 

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

Solution

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.

 

4. How is the liver an important organ in our body?

Solution

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

 

5. Define the following terms:
(a) Peristalsis
(b) Omnivore
(c) Pylorus
(d) Kilocalorie
(e) Assimilation

Solution

(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.

 

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

Solution

Region	Enzyme	Action on Food
Stomach	Pepsin	Acts on proteins and converts it into polypeptides.
Small intestine- Duodenum	Amylopectin	Acts on starch and converts it into maltose
	Trypsin	Acts on remaining proteins, proteoses and peptones to produce peptides and amino acids
	Steapsin	Acts on emulsified fats to produce fatty acids and glycerol
Small intestine- Ileum	Erepsin	Acts on proteins and polypeptides and converts them Into small peptides and amino acids
	Maltase	Acts on maltose to produce glucose
	Sucrose	Acts on sucrose and converts it into glucose and fructose
	Lactase	Acts on lactose and converts it into glucose and galactose
	Lipase	Acts on fats to produce fatty acids and glycerol

 

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

Solution

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.

 

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

Solution

Test for starch:

1. Take the food item to be tested. Put it into a test-tube containing water and boll 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 indicates the presence of protein in the food item.

 

E. Structured/Application/Skill Type

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

(a) State the total number of teeth present in the dentition
(b) Is the dentition that of a carnivore or herbivore? Give a reason to support your answer.
(c) Name an animal possessing such a dentition.
(d) Give the dental formula of an adult human being.

Solution

(a) The total number of teeth present in the given dentition are — 20 teeth

(b) The given dentition is that of a herbivore as canines are not present in the given dentition.

Carnivore requires canines as it assists in tearing and holding food. The teeth in herbivores helps to bite gnaw and cut while the teeth in carnivores are much more sharper that help to catch, kill and tear the prey.

(c) Goat is an example of a herbivore having this dentition

(d) The dental formula of an adult is:
Human adult: 2/2, 1/1, 2/2, 3/3 = 32 (Permanent teeth + Wisdom teeth)

 

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

Solution

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.

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

Organ	Enzyme	Food acted upon	Final product
1	Pepsin	2	3
Mouth	4	5	Disaccharide
6	7	Maltose	8

Solution

Organ	Enzyme	Food acted upon	Final product
Stomach	Pepsin	Proteins	Polypeptides
Mouth	Amylase	Starch	Disaccharide
Ileum	Maltase	Maltose	Glucose

 

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

(a) Name the parts labeled 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 labeled ‘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

(a) 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

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

Solution