Selina Concise Biology Class 6 ICSE Solutions Chapter 4 Digestive System

Selina Concise Biology Class 6 ICSE Solutions – Digestive System

Selina Concise ICSE Solutions for Class 6 Biology Chapter 4 Digestive System

Synopsis:

• The food we consume fall into seven different catagories. 

1. carbohydrates
2. fats
3. proteins
4. minerals
5. vitamins
6. water
7. roughage

• The process of nutrition is conducted in five steps 

1. ingestion
2. digestion
3. absorption
4. assimilation
5. egestion

• When some part of food is chewed, the tongue makes it a spherical mass called Bolus.

• Peristalsis is a wave of constriction in the circular muscles in the wall of the gut to push the food further into the food canal.

• The food canal is also called alimentary canal which starts from the mouth and ends at the anus.

• The digestive glands include 

1. Salivary glands
2. Liver
3. Pancreas

• The teeth which are similar in size and shape are called homodont teeth.

They are usually found in fishes, frogs, reptiles etc.

• The last molar on each side in each j aw is called wisdom tooth which appears at the age of 17-20 years.

• The human teeth develop in two sets; the first set is called milk teeth or temporary teeth while the second set which replaces the milk teeth are called permament teeth.

• The milk teeth are twenty in number while the permament are thirty two in number.

• The part of the teeth which can be seen is called crown while the part which is fixed in the jaw is called root.

• The tooth is made up of: 

1. enamel
2. dentin
3. pulp

• The hardest substance of the body is called Enamel.

• The yellow, stick substance found on the teeth due to poor oral hygeine is called plaque. It consists of sugar and bacteria.

• Mineralised or hard plaque is called tartar.

• The functions of tongue are: 

1. manipulates food while chewing
2. helps in tasting the food
3. mixes food with saliva
4. cleans the teeth.
5. helps in speaking.

• The enzyme contained in saliva is called amylase which digests starch into glucose.
• The food pipe is the oesophagus. No digestion takes here

 

The organ which serves for both digestion and absorption of the food is small intestine.

• The small intestine is 7 metres long while the large intestine is 1.5 metres long.

• No enzyme is secreted by the large intestine.

• Glucose, amino acids, vitamins and minerals are transported to the liver.

• Amino acids are used in the production of proteins for growth and repair of tissues.

Review Questions

Multiple Choice Questions :

1. Put a tick (✓) against the most appropriate alternative in the following statements.

(1) The teeth which help in tearing the food are the:

(a) Incisors

(b) Canines

(c) Premolars

(d) Molars

(ii) Last molar tooth in human beings is called:

(a) Adult tooth

(b) Wisdom tooth

(c) Child tooth

(d) Elders tooth

(iii) The hardest substance in your body?

(a) Dentine

(b) Bone

(c) Cement

(d) Enamel

(iv) Saliva converts starch into:

(a) Glucose

(b) Sucrose

(c) Maltose

(d) Lactose

(v) Proteins of the milk are converted into curd by the enzyme:

(a) Trypsin

(b) Rennin

(c) Pepsin

(d) Steapsin

(vi) Bile juice ¡s produced by :

(a) Stomach

(b) Liver

(e) Pancreas

(d) Gall bladder

1. Write True or False in the following statements.

1. Molars help in cutting and tearing food.

False

Correct — Molars help in finer crushing and grinding.

2. Carbohydrates are digested into glucose.

True

3. Proteins are digested into fatty acids.

False 

Correct — Proteins is digested into amino acids.

2. Fill in the blanks.

1. The teeth called are a total of four in number on the sides of incisors.
2. The teeth called canines are a total of four in number on the sides of incisors.
3. Pharynx is a common opening of food pipe and wind pipe.
4. Molars are meant for crushing the food.
5. Incisors are used for biting and cutting the food.
6. The canines are used for tearing the food.
7. The premolars and molars are used for crushing and grinding the food.
8. In an adult human, there are a total of 32 teeth.
9. The human teeth appear in two sets, the first set is called primary which consists of only twenty teeth.

3. Name the following :

1. End product of starch after digestion — glucose.
2. The organ where protein digestion-begins — stomach.
3. The organ into which the pancreatic juice and the bile juice are poured — small intestine.
4. The enzyme which digests fat — lipases.
5. The simplest form of carbohydrates — glucose. ‘
6. The part of alimentary canal where water from undigested food is absorbed — large intestine.
7. The end-product of proteins after digestion — amino acids.

4. Identify and name the four type of teeth shown below and give their functions.

Answer :

A — incisor

Function -Its major function is biting and cutting of food.

B — canine

Function — Its major function is tearing of the food.

C — pre-molar

Function — Used for crushing and grinding of food.

D — molar

Function — Used for crushing and grinding of food.

5. State whether the following statements are True or False.

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

(ii) The temporary set of teeth includes incisors, canines and premolars only.

(iii) The ducts from the salivary glands open into the duodenum.

(iv) Saliva changes starch into maltose.

Answer :

(iv) True (V) Saliva changes starch into maltose.

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

(steapsin, peptones, fatty acids, proteoses, protein).

Answer :

 

Question 7.

(i) Name the juice secreted by the liver.

Ans. Bile

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

Ans. Gallbladder

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

Ans. The main function of bile is digestion of fats.

Question 8.

Name the three enzymes found in pancreatic juice.

(i)….. (ii)….. (iii) ……

Answer :

(i) Starch digesting — amylase

(ii) Protein digesting — trypsin

(iii) Fat – digesting — lipases

Question 9.

Name the three regions of the large intestine.

Answer :

1. Caecum
2. Colon
3. Rectum

Question 10.
Given alongside is the diagram of the human alimentary canal.
(i) Name the parts 1-11 indicated by guidelines.
1. … 2. … 3. … 4. … 5. … 6. …
7. … 8. … 9. … 10. … 11 ….
(ii) State the function of the juice secreted by the part 1.
(iii) State the function of the three enzymes found in the juice secreted by part 3.

Answer :
(i) 1 Stomach
2—Bile duct
3 — Pancreas
4 — Large intestine
5 — Small intestine
6 — Rectum
7—Appendix
8 — Pancreatic duct
9— Gall Bladder
10—Liver
11—Anus
(ii) The gastric juice being acidic kills the germs and activates pepsin.
(iii)

1. amylase — digests starch
2. trypsin — digests protein
3. lipase — digests fat

Long Answer Questions
Question 1.
Define the term nutrition.

Answer :
The process by which living beings receive the food and utilise it to grow and become healthy is called nutrition.
On the basis of nutrition, living beings can be classified into the following types:

1. Holozoites
2. Parasites
3. Saprophytes
4. Symbionts

Holozoits can be further classified into

1. herbivores
2. carnivores
3. ommivores

Question 2.
What is the role of the liver and the pancreas respectively in the digestion of food ?
Answer :

1. Liver: It produces a green yellow fluid called the bile which emulsify fats making it easy to be digested. The bile also contains sodium bicarbonate which neutralises the acid of food coming from the stomach and makes it alkaline.
2. Pancreas: It produces the digestive juice called the pancreatic juice which acts on carbohydrates, proteins and fats and convert them into simpler units called glucose, amino acids and fatty acdis respectively.

Question 3.
Name the digestive juice secreted by the stomach and give its function.
Answer :
The digestive juice secreted by the stomach is the gastric juice.
The gastric juice contains

1. — water
2. — hydrochloric acid
3. — enzyme

Which have the following roles :

1. Hydrochloric acid serves to kill the germs and activates pepsin. Pepsin converts proteins into peptones and proteoses.
2. Enzyme rennin converts the milk caesin into curd.

Answer the following questions:
Question 4(i).
(i) Name the types of teeth seen in humans.
Answer :
Human teeth are of four kinds:

1. Incisors are the four front teeth at the middle of each jaw. They are chisel-shaped for biting and cutting.
2. Canines are one on either side of the incisors in each jaw. They are pointed for tearing the food.
3. Premolars are two on each side of canines in each jaw. They help in crushing and grinding the food.
4. Molars are the last three teeth on each side in each jaw. They have broad uneven surface for finer crushing and grinding of ingested food.

Question 4 (ii).
How is the small intestine best suited for the digestion and absorption of food ?
Answer :
The small intestine’s inner lining contain a large number of tiny finger-like projections called villi. The villi greatly increases the inner surface area for the absorption of digested food.

Question 4(iii).
What do you mean by absorption of food ?
Answer :
The absorption of food means to pass the digested food products into the blood system and lymph vessels to be used further by body for various life functions.

Question 5.
Define the following terms
Egestion, digestion, assimilation.
Answer :
Egestion — The process of removal of the undigested food from the body is defined as egestion.
Digestion — The process of breaking the food into smaller and simpler substances so that they can be easily used by the body is called digestion.
Assimilation — The process of using the digested food by the body is called assimilation.

Question 6.
Rewrite the following parts of the human alimentary canal in their correct sequence
Stomach, Oesophagus, Large instestine, Small intestine, Pharynx.
Answer :
Pharynx — Oesophagus → Stomach → Small-
intestine → Large intestine.

Question 7.
What is the fate of excess glucose in our body ?
Answer :
The excess glucose is converted by the liver into insoluble glycogen and stores it, whenever required. Liver can reconvert the glycogen into glucose.

Question 8.
Define the term ‘digestion’.
Answer :
The process of converting the complex food substances into simpler and smaller units so that they can be easily utilised by the body is defined as digestion.
e.g. proteins are converted to amino acids.

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. Moistens and lubricates the oral cavity and the tongue to make speaking and swallowing easy.
2. Acts as a solvent, dissolving some part of food to stimulate taste
3. Cleans the mouth and destroys germs
4. Initiates digestion by converting starch into simpler form, maltose.

Question 10.
Food are classified into three groups on the basis of the function they perform in our body. Name the three categories, and briefly give their functions. Also give their two sources each.
Answer :
Function

1. energy giving food
2. bodybuilding food
3. regulatory and protective foods

Nutrient

1. carbohydrates and fats
2. proteins
3. vitamins and minerals

Food

1. cereals, fats, sugar
2. pulses, milk, meat chicken
3. fruits and vegetables