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Chapter 4

Digestive System

Class 6 - Concise Biology Selina


Multiple Choice Questions

Question 1

The teeth which help in tearing the food are the:

  1. Incisors
  2. Canines
  3. Premolars
  4. Molars

Answer

Canines

Reason — Canines are one on either side of the incisors in each jaw. They are pointed for tearing the food.

Question 2

Last molar tooth in human beings is called:

  1. Adult tooth
  2. Wisdom tooth
  3. Child tooth
  4. Elder's tooth

Answer

Wisdom tooth

Reason — The last molar in each side in each jaw is called the wisdom tooth.The wisdom tooth appears at the age of 17-20 years.

Question 3

The hardest substance in your body is:

  1. Dentine
  2. Bone
  3. Cement
  4. Enamel

Answer

Enamel

Reason — Enamel is the hardest substance of the human body. It is the white visible part of the tooth and serves as the first line of defense against plaque and cavities.

Question 4

Saliva converts starch into:

  1. Glucose
  2. Sucrose
  3. Maltose
  4. Lactose

Answer

Maltose

Reason — Saliva contains an enzymes (amylase) which helps in the break down of starch to simple sugars (maltose).

Question 5

Proteins of the milk are converted into curd by the enzyme:

  1. Trypsin
  2. Rennin
  3. Pepsin
  4. Erepsin

Answer

Rennin

Reason — The protein Casein present in the milk is converted into curd by the help of another enzyme, the Renin.

Question 6

Bile juice is produced by:

  1. Stomach
  2. Liver
  3. Pancreas
  4. Gall bladder

Answer

Liver

Reason — Bile juice is produced by the Liver and stored in the Gall Bladder.

Short Answer Questions

Question 1

Write True or False in the following statements.

(i) Molars help in cutting and tearing food.

(ii) Carbohydrates are digested into glucose.

(iii) Proteins are digested into fatty acids.

Answer

(i) False
Reason — Molars help in finer crushing and grinding the food.

(ii) True
Reason — The end products of carbohydrate digestion are simple sugars (glucose & fructose) which can easily be absorbed in our blood system.

(iii) False
Reason — Proteins are digested into amino acid.

Question 2

Fill in the blanks:

(i) The teeth called ............... are a total of four in number on the sides of incisors.

(ii) ............... is a common opening of food pipe and wind pipe.

(iii) Molars are meant for ............... the food.

(iv) Incisors are used for ............... and ............... the food.

(v) The ............... are used for tearing the food.

(vi) The ............... and ............... are used for crushing and grinding the food.

(vii) In an adult human, there are a total of ............... teeth.

(viii) The human teeth appears in two sets, the first set is called ............... which consists of only ............... teeth.

Answer

(i) The teeth called Canines are a total of four in number on the sides of incisors.

(ii) The mouth is a common opening of food pipe and wind pipe.

(iii) Molars are meant for finer crushing and grinding the food.

(iv) Incisors are used for biting and cutting the food.

(v) The Canines are used for tearing the food.

(vi) The Premolars and Molars are used for crushing and grinding the food.

(vii) In an adult human, there are a total of 32 teeth.

(viii) The human teeth appears in two sets, the first set is called temporary teeth which consists of only 20 teeth.

Question 3

Name the following:

(i) End product of starch after digestion.

(ii) The organ where protein digestion begins.

(iii) The organ into which the pancreatic juice and the bile juice are poured.

(iv) The enzyme which digests fat in ileum.

(v) The simplest form of carbohydrates.

(vi) The part of alimentary canal where water from the undigested food is absorbed.

(vii) The end product of protein digestion.

Answer

(i) Glucose

(ii) Stomach

(iii) Duodenum

(iv) Lipase

(v) Glucose

(vi) Large intestine

(vii) Amino acid

Question 4

Identify and name the "four" types of teeth shown below and state their functions.

Identify and name the four types of teeth shown below and state their functions. Digestive System, Concise Biology Solutions ICSE Class 6.

Answer

The four types of teeth shown in the figure are listed below along with their functions:

  • A → Incisors
    Function — Incisors are used for biting and cutting.
  • B → Canines
    Function — Canines are used for tearing the food.
  • C → Premolars
    Function — Premolars help in crushing and grinding the food.
  • D → Molar
    Function — Molars help in finer crushing and grinding of food.

Question 5

State whether the following statements are True or False.

  1. Wisdom tooth appears at the age of 5-6 years when the child starts going to school.

  2. The temporary set of teeth includes incisors, canines and premolars only.

  3. The ducts from the salivary glands open into the duodenum.

  4. Saliva changes starch into maltose.

Answer

  1. False
    Reason — Wisdom tooth appears at the age of 17-20 years.

  2. False
    Reason — Children have only twenty teeth, called primary, temporary or milk teeth. They include the same 10 teeth in the upper and lower jaw:

    1. 4 Incisors
    2. 2 Canines
    3. 4 Molars
  3. False
    Reason — The ducts from the salivary glands open into the mouth.

  4. True
    Reason — Saliva contains an enzyme called amylase which converts starch int maltose.

Question 6

Fill in the blanks in the table (1-5) by selecting the suitable names of substances from the list given below:

[lipase, peptones, fatty acids, proteoses, protein].

Digestive
Enzymes
acts onto form
(i) Pepsin.......(2)...............(3)........ and .......(4)........
(ii) .......(1)........fats.......(5)........

Answer

  1. Lipase
  2. Proteins
  3. Peptones
  4. Proteoses
  5. Fatty acids

Question 7

(i) Name the juice secreted by the liver.

(ii) Name the organ where this juice is temporarily stored.

(iii) What is the main function of this juice?

Answer

(i) Bile juice.

(ii) Gall Bladder

(iii) Bile juice breaks down the fats into tiny droplets and this process is called emulsification.

Question 8

Name the three enzymes found in the pancreatic juice and mention their functions.

Answer

Three enzymes found in the pancreatic juice and their functions are given below:

  1. Amylase — It acts on the starch converting it into maltose.
  2. Trypsin — It converts proteins and peptones into peptides.
  3. Lipase — It converts emulsified fats into fatty acids and glycerol.

Question 9

Name the three regions of the large intestine.

Answer

The three regions of the large intestine are:

  1. Caecum
  2. Colon
  3. Rectum

Question 10

Given alongside is the diagram of the human alimentary canal.

Given alongside is the diagram of the human alimentary canal. Name the parts 1-11 indicated by guidelines. State the function of the juice secreted by part 1. State the function of the three enzymes found in the juice secreted by part 3. Digestive System, Concise Biology Solutions ICSE Class 6.

(i) Name the parts 1-11 indicated by guidelines.

(ii) State the function of the juice secreted by part 1.

(iii) State the function of the three enzymes found in the juice secreted by part 3.

Answer

(i) The parts are

  1. Stomach
  2. Bile duct
  3. Pancreas
  4. Large intestine
  5. Small intestine
  6. Rectum
  7. Appendix
  8. Duodenum
  9. Gall bladder
  10. Liver
  11. Anus

(ii) The juice secreted by part (1) is the Gastric juice.Gastric juice being acidic in nature kills the germs and activates pepsin.

(iii) The function of the three enzymes found in the gastric juice are

  1. Amylase enzyme digest starch into maltose.
  2. Trypsin enzyme digest proteins into peptides.
  3. Lipase enzyme digest emulsified fats into fatty acids anf glycerols.

Long Answer Questions

Question 1

Define the term nutrition.

Answer

The process by which all organisms obtain or synthesize their food and convert it into simpler substances, so that it can be absorbed and utilized by the cells of the body is called nutrition.

Question 2

What is the role of liver and pancreas respectively in the digestion of food?

Answer

Liver — The role of liver in the digestion of food is to produce a greenish yellow fluid called the bile that helps in emulsification (breaking down fats into tiny droplets).

Pancreas — It secretes the pancreatic juice that contains enzymes namely amylase, trypsin and lipase. This pancreatic juice acts on carbohydrates, proteins and fats and converts them into simpler units called glucose, amino acids and fatty acids respectively.

Question 3

Name the digestive juice secreted by the stomach and give its function.

Answer

Digestive juice secreted by the stomach is the Gastric juice. The gastric juice contains water, hydrochloric acid and an enzyme pepsin. Its functions are:

  1. Hydrochloric acid kills the germs preventing rotting of food during its long stay in stomach. It activates the enzyme pepsin.
  2. Pepsin converts proteins into a simpler compound called peptones.

Question 4

Answer the following questions:

(i) Name the types of teeth present in humans.

(ii) How is the small intestine best suited for the digestion and absorption of food?

(iii) What do you mean by absorption of food?

Answer

(i) Four types of teeth present in humans are:

  1. Incisors
  2. Canines
  3. Premolars
  4. Molars

(ii) Small intestine is a long coiled tube of about 7 metres. The food remains in it for about 3-5 hours for digestion and absorption. Small intestine has Duodenum and Ileum. Duodenum receives bile from liver and pancreatic juice from pancreas that help in the digestion of carbohydrates, proteins and fats. Semi-digested food is completely digested in the Ileum by the intestinal juices secreted by the intestinal glands present in the inner lining of Ileum. Villi are tiny finger-like projections present in the inner lining of the small intestine that greatly increase the inner surface area for absorption of the digested food. They absorb the amino acids and glucose. Vitamins and minerals salts are mostly soluble in water and are directly absorbed through the walls of the intestine.

(iii) Absorption of food means passing the digested food into the blood system and lymph vessels to be supplied to the rest of the body. Major portion of the digested food is absorbed by the villi present in the small intestine. It absorbs the amino acids and glucose to pass them into the blood system, whereas the fatty acids pass into the lymph vessels. Vitamins and minerals are soluble in water and are mostly absorbed through the walls of the intestine.

Question 5

Define the following terms : Egestion, Digestion, Assimilation.

Answer

Egestion — The process of eliminating the undigested food through the anus is called Egestion.

Digestion — The process by which the complex chemical compounds present in the food are broken down into simpler substances that are readily absorbed and utilized by the body is called Digestion.

Assimilation — The utilization of the digested food and nutrients by the body cells is called Assimilation.

Question 6

Rewrite the following parts of human alimentary canal in their correct sequences:

Stomach, Oesophagus, Large intestine, Small intestine.

Answer

Oesophagus, Stomach, Small intestine, Large intestine.

Question 7

What is the fate of excess of glucose in our body?

Answer

Our body stores excess glucose as glycogen. During fasting or vigorous exercise, glycogen is rapidly broken down again to form a glucose unit.

Question 8

Define the term "digestion".

Answer

The process by which the complex chemical compounds present in the food are broken down into simpler substances that are readily absorbed and utilized by the body is called digestion.

Question 9

State the four ways in which saliva is useful to us.

Answer

The four ways in which saliva is useful to us are:

  1. It moistens and lubricates the mouth cavity and the tongue to make speaking and swallowing easy.
  2. It cleans the mouth and destroys germs.
  3. The saliva binds the food particles and makes it into a mass called the bolus.
  4. Digestion begins in the mouth. Saliva contains an enzyme (amylase) which helps in the breakdown of starch to simple sugars (maltose).

Question 10

Foods are classified into three groups on the basis of the functions they perform in our body. Name these three groups, and briefly state their functions. Also give two sources of each.

Answer

The three groups into which the foods are classified are:

  1. Energy-giving foods — They are made up of carbohydrates and fats. Carbohydrates provide us with instant energy, while fats are stored as energy resources. Its sources are:
    1. Rice
    2. Potato
    3. Fats
  2. Body-Building foods — Proteins are considered to be body building food. Such foods help in the growth and repair of damaged cells and tissues. Its sources are:
    1. Pulses
    2. Milk
  3. Protective foods — They are mainly vitamins and minerals. Minerals are needed for their specific roles in the body. Vitamins are needed for the normal functioning of various body processes. Its sources are
    1. Fruits and Vegetables
    2. Dairy products
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