ICSE Living Science Biology for Class 7 Solutions Chapter 6 Ingestion, Digestion, Absorption and Assimilation of food
Check Your Progress
State if the following statements are true or false. Correct the statement if it is false.
Question 1.
Ingestion is the process of taking in food through mouth.
Answer:
True
Question 2.
The front teeth which cut food are called canines.
Answer:
False. The front teeth which cut food are called incisos.
Question 3.
Canines are used for crushing and grinding food.
Answer:
False. Canines are used for tearing food,
Question 4.
Fish and frogs have homodont dentition.
Answer:
True
Question 5.
Tartar is a digestive gland associated with the digestive system.
Answer:
False. Salivary gland is a digestive gland associated with the digestive system.
practice Question 1.
Pancreas is the largest gland in our body.
Answer:
False. Liver is the largest gland in our body.
Check Your Progress
Fill in the blanks.
Question 1.
Saliva contains an enzyme called …………
Answer:
Saliva contains an enzyme called ptyalin.
Question 2.
The upper part of the small intestine is called ………….
Answer:
The upper part of the small intestine is called duodenum.
Question 3
………….. is made in the liver and stored in gall gladder.
Answer:
Bile is made in the liver and stored in gall bladder.
Question 4.
Glucose is converted into glycogen and stored in the …………
Answer:
Glucose is converted into glycogen and stored in liver.
Question 5.
………………. changes proteins, proteoses and peptones into polypeptides.
Answer:
Trypsin changes proteins, proteoses and peptones into polypeptides.
Practice Question 2.
The wave-like motion of the muscles that pushes the food along the alimentary canal is called ………………
Answer:
The wave-like motion of the muscles that pushes the food along tiie alimentary canal is called peristalsis.
A. Tick the most appropriate answer.
Question 1.
The process of taking in food through the mouth is called
a. digestion
b. ingestion
c. assimilation
d. absorption
Answer:
b. ingestion
Question 2.
Digestion begins in the
a. large intestine
b. ingestion
c. stomach
d. mouth
Answer:
d. mouth .
Question 3.
Chemicals that help to digest food are called
a. enzymes
b. sugar
c. saliva
d. hormones
Answer:
a. enzymes
Question 4.
The peristalsis movement helps in the
a. digestion of food
b. passage of food
c. absorption of food
d. assimilation of food
Answer:
b. passage of food
Question 5.
The fluid produced by the stomach is called
a. saliva
b. gastric juice
c. bile juice
d. pancreatic juice
Answer:
b. gastric juice
Question 6.
Pepsin, a protein digesting enzyme, is present in the
a. oesophagus
b. mouth
c. stomach
d. duodenum
Answer;
c. stomach
Question 7.
Food is absorbed in the
a. mouth
b. small intestine
c. large intestine
d. liver
Answer:
b. small intestine
Question 8.
Glucose is stored in the form of
a. galactose
b. maltose
c. glycerin
d. glycogen
Answer:
d. glycogen
Question 9.
Fats are changed into fatty acids and glycerol by the action of
a. lipase
b. bile
c. lipids
d. trypsin
Answer:
a. lipase
Question 10.
No digestion takes place in the
a. mouth and pharynx
b. pharynx and oesophagus
c. oesophagus and stomach
d. pharynx and small intestine
Answer:
b. pharynx and oesophagus
Practice Question 3.
The kind, number and arrangement of teeth in an animal is called
a. dentition
b. respiration
c. digestion
d. egestion
Answer:
a. dentition
Practice Question 4.
Which of the following enzymes changes casein into insoluble curd ?
a. Pepsin
b. Renin
c. Erepsin
d. Sucrase
Answer:
b. Renin
Practice Question 5.
Which of the following is fat-digesting enzyme ?
a. Lactase
b. Lipase
c. Maltase
d. Amylase
Answer:
b. Lipase
Practice Question 6.
Protein-digesting enzyme present in the small intestine is
a. trypsin
b. pepsin
c. erepsin
d. lipase
Answer:
a. trypsin
Practice Question 7.
Which of the following enzymes converts peptides into amino acids ?
a. Sucrase
b. Pepsin
c. Lipase
d. Erepsin
Answer:
d. Erepsin
Practice Question 8.
Villi are found in the
a. small intestine
b. stomach
c. oesophagus
d. none of these
Answer:
a. small intestine
Practice Question 9.
Absorption of water takes place in the
a. small intestine
b. large intestine
c. oesophagus
d. liver
Answer:
b. large intestine
Practice Question 10.
Excess of glucose is converted into glycogen and stored in the
a. liver b. pancreas
c. adipose tissue
A stomach
Answer:
a. liver
Practice Question 11.
Amino acids are used for synthesis of
a. fats
b. proteins
c. carbohydrates
d. glycogen
Answer:
b. proteins
B. Answer the following in a word.
Question 1.
Which enzyme changes casein into insoluble curd ?
Answer:
Renin
Question 2.
Name the protein-digesting enzymes present in the small intestine.
Answer:
Tiypsin, erepsin
Question 3.
Which enzyme converts peptides into amino acids ?
Answer:
Erepsin ,
Question 4.
Where are villi found ?
Answer:
Small intestine
Question 5.
Whtjde does reabsorption of water occur ?
Answer:
Large intestine
C. State if the following statements are true or false. Correct the statement if it is false.
Question 1.
The process of taking in food is called assimilation.
Answer:
False. The process of taking in food is called ingestion.
Question 2.
The pancreas secretes bile juice.
Answer:
False. The liver secretes bile juice.
Question 3.
Saliva contains lipase which digests carbohydrates.
Answer:
False. Saliva contains salivary amylase which digests j carbohydrates.
Question 4.
Water is absorbed in large intestine.
Answer:
True
Question 5.
Stomach walls produce acid and enzymes which help to: digest, carbohydrates.
Answer:
False. Stomach walls produce acid and enzymes which help to digest proteins.
Practice Question 11.
The wave-like motion of stomach muscles to push the food is called peristalsis.
Answer:
False. The wave-like motion of oesophagus muscles to push die food is called peristalsis. , ;
Practice Question 12.
Digestion of food in intestine takes place in the presence of dilute hydrochloric acid.
Answer:
False. Digestion of food in stomach takes place in the j presence of dilute hydrochloric acid.
Practice Question 13.
Absorption of food takes place in small intestine.
Answer:
True
Practice Question 14.
The removal of faeces through anus is called excretion.
Answer:
False. The removal of faeces through anus is called egestion.
Practice Question 15.
All the absorbed nutrients are immediately required by the body.
Answer:
False. All the absorbed nutrients are not immediately l required by the body.
Practice Question 16.
Pancreatic juice does not contain any enzyme.
Answer:
False. Bile juice does not contain any enzyme.
D. Differentiate between.
Question 1.
digestion and absorption.
Answer:
Digestion
- It is the process of converting complex food into a simple absorbable fonn.
- It is a series of mechanical and chemical reactions.
- Many enzymes are associated with digestion
Absorption :
- It is the process of passing digested food through thin walls of blood capillaries and enters the blood stream.
- No mechanical or chemical reaction occurs in absorption.
- No enzyme is associated with absorption.
Question 2.
mechanical digestion and chemical digestion.
Answer:
Mechanical digestion :
- in mechanical digestion the ingested food is broken down in the mouth by chewing it.
- Teeth help in mechanical digestion
- Food is not completely digested in it.
Chemical digestion :
- In chemical digestion the food is digested by the action of enzymes.
- Enzymes are involved in chemical digestion.
- Proper digestion of food occurs in it.
Question 3.
Small intestine
- It is 7 metres long and 2.5 cm wide.
- It has finger like projections called villi.
- Food is completely digested here.
- Absorption of food occurs here.
Large intestine :
- It is 1.5 – 1.8 m long and 6.5 m wide.
- Villi are absent in large intestine.
- No digestion occurs here.
- Excess of water is absorbed here.
Question 4.
digestion and assimilation
Answer:
digestion :
- It is the process of conv-ersion of the complex food taken through the mouth into a simple form by the action of enzymes.
- Many enzymes are associ-ated with digestion.
- It is the second stage of nutrition (after ingestion)
- Complex food is converted into simple forms, e.g, proteins into amino acids, fat into glucose, etc.
Assimilation :
- It is the process of consuming the absorbed food material by the body to provide energy or for the growth or repair of tissues or stored.
- No enzyme is associated.
- It is the fourth stage of nutrition (after ingestion, digestion and absorption).
- Simple forms are converted into complex forms, e.g. amino acids into proteins, glucose into fats and glycogen.
E. Find the odd one out. Give reasons for your choice.
Question 1.
oesophagus, stomach, small intestine, liver
Answer:
Liver : It is a digestive gland while other all are parts of alimentary canal.
Question 2.
canines, incisors, saliva, premolars
Answer:
Saliva : It is a fluid which helps in breaking down starch into maltose by secreting enzyme ptyalin (salivary amylase) while rest all are types of teeth which help in chewing the food.
Question 3.
salivary amylase, pepsin, trypsin, erepsin
Answer:
Salivary amylase : It breaks down starch while other all break down proteins during digestion.
Question 4.
lactase, maltase, lipase, sucrase
Answer:
Lipase : It breaks down fats in duodenum while rest three enzymes break down complex carbohydrates into simple carbohydrates in ileum.
F. Answer the following in short.
Question 1.
What is dental plaque ?
Answer:
When a mixture of saliva, food and bacteria begins to form over the teeth within half an hour of eating, is called a dental plaque.
Question 2.
What is emulsification of fats ?
Answer:
Digestion of fats in to tiny droplets to provide larger surface area for the enzymes to act is called emulsification of fats.
Question 3.
Names the enzymes found in pancreatic juice.
Answer:
Three enzymes found in pancreatic enzymes are :
(a) Trypsin – act on proteins, proteoses and peptones and changes them in to polypeptides.
(b) Lipase – acts on fats and changes them to fatty acids and glycerol.
(c) Erepsin – acts on peptones and peptides and changes them to amino acids.
Question 4.
How do teeth aid in digestion ?
Answer:
Teeth grow twice in human lifetime, temporary teeth and permanent teeth. The teeth which grow at the age of 6-7 months are called temporary teeth. They are 20 in number. These teeth start falling off around the age of 6-12 years and are replaced by a new set of teeth, called permanent teeth. There are total 32 teeth in the two jaws. There are four kinds of teeth in each jaw. These are incisors (8), canines (4) premolars (8) and mo 1 ar&i (12VJhere are 16 teeth in each jaw.
Incisors : These are situated at the front and are flat and straight with sharp edges, which are used for biting and cutting the food.
Canines : These are situated one on either side of the incisors in each jaw. There are two canines in*each jaw. These are sharp and pointed and are used for holding and tearing the food.
Premolars : There are 4 premolars in each jaw, situated next to the canines. Each premolar has one or two roots and two cusps. These are used for crushing and grinding the food.
Molars : These are 6 molars in each jaw. The molars have more than one root. These are used for crushing and grinding the food. The last molar of each side in each jaw is also called wisdom tooth because it appears last generally at the age of 17-20 years.
The ingested food is first broken down in mouth when we chew it with our teeth. This process is called mastication or mechanical digestion. It prepares the food for chemical digestion that is, the digestion by the action of enzymes.
Question 5.
How are the teeth of a carnivore different from those in herbivores ?
Answer:
Carnivores are meat eating organisms such as dogs, wolves and lions. They have long pointed canines that are used for tearing flesh. Their incisors are chisel-shaped and are used for cutting. Herbivores are plant eating animals such as sheep, deer, horses and cows. They have large flat premolars and molars. These are used for grinding plant material. They don’t have sharp and pointed canines.
G. Answer the following in detail.
Question 1.
What is meant by digestion ? How does it differ from nutrition ?
Answer:
The process of changing complex food into simple, absorbable form by the action of certain enzymes is called digestion. Many organs are associated with digestion. Digestion is of two types mechanical and chemical digestion, hi mechanical digestion, food is broken down in the mouth when we chew it with our teeth. In chemical digestion, the food is digested by the actions of certain enzymes.
Digestion is necessary because the food which is obtained is in complex form and our body is not able to absorb nutrients from it. So it is converted in to simple absorbable form. Nutrition is the process of obtaining and using food by the organisms. It is different in different organisms. Ingestion, digestion, absorption, Assimilation and egestion are the various steps involved in nutrition.
Question 2.
Name the four types of teeth in humans and mention their number and functions.
Answer:
The four types of teeth are :
incisors : i nese are situated at ttie Iront and are flat and straight with sharp edges which are used for biting and cutting the food.
Canines : These are situated one on either side of the incisors in each jaw. There are two canines in each jaw. These are sharp and pointed and are used for holding and tearing the food.
Premolars : There are 4 premolars in each jaw, situated next to the canines. Each premolar has one or two roots and two cusps. These are used for crushing and grinding the food.
Molars : These are 6 molars in each jaw. The molars have more than one root. These are used for crushing and grinding the food. The last molar of each side in each jaw- is also called wisdom tooth because it appears last generally at the age of 17-20 years.
the mgesieu iooa is nrsi oroKen aown in mourn wnen we chew it with our teeth. This process is called mastication or mechanical digestion. It prepares the food for chemical digestion that is, the digestion by the action of enzymes.
Question 3.
Liver does not secrete any enzymes yet it helps in digestion. How ?
Answer:
Liver does not secrete any enzyme yet it helps in digestion because it secretes bile which helps in digestion of fats by breaking down fats in to tiny droplets to provide larger surfaces area for the enzymes to act. This process is called emulsification of fats. Bile secreted by liver is stored in gall bladder. Bile provides an alkaline medium in the duodenum for the action of enzymes of the pancreatic juice. Liver also helps in regulating blood-sugar level and in storage of carbohydrates.
Question 4.
What happens to the nutrients absorbed in the blood stream from the small intestine ?
Answer:
The villi of the small intestine increase the inner surface area for absorption of digested food. Villi contain blood capillaries. The digested food passes through these blood capillaries and enters the blood stream. This process is called absorption. All the absorbed nutrients are not required immediately by the body. So they are changed in to various forms that can be stored until they are needed. This process is called assimilation.
(a) Glucose is converted in to glycogen and is stored in the liver. When it is required by the liver, glycogen is converted into glucose. Excess of glucose is also converted in to fat and stored in the adipose tissue. Fatty acids either provide energy or are used for synthesis of fats which is stored under the skin.
(b) Amino acids are used for synthesis of protein. Excess amount of amino acids are converted in to urea which is removed by the kidneys.
Question 5.
How do villi help in absorption ? Show with a diagram.
Answer:
Digestion of proteins, fats, and carbohydrates is completed in the small intestine. The small intestine not only digests but also absorbs food. The villi present in the small intestine increases the surface area for absorption of the digested food. The villi are in constant motion waving back and forth. Villi contain blood capillaries. The digested food passes through the blood capillaries and enters the blood stream. This process is called absorption.
Question 6.
You ate bread in the morning. Starting from the mouth, explain how it was digested ?
Answer;
Bread contains starch. The digestion of starch starts in the mouth. When we chew the bread, saliva gets mixed with it.
It softens the food. Saliva is secreted by salivary glands. Saliva contains the enzyme salivary amylase (ptyalin) which acts on starch to convert it in to maltose
After chewing, the food is swallowed in to the pharynx. No .further digestion takes place in pharynx. From here the food moves in to the oesophagus, by peristaltic movements it is pushed in to the alimentary canal. In the small intestine (duodenum) rest of the starch is broken down in to smaller units by pancreatic amylase. Further Maltose is changed in to glucose by maltose in small intestine (ileum).
H. Number the following processes in their correct sequence of occurrence during digestion.
peristalsis ; tongue pushes the food ; grinding and mixing saliva ; cutting and tearing of food
Answer:
Cutting and tearing of food → grinding and mixing → saliva → tongue pushes the food → peristalsis.
I. Give reasons for the following :
Question 1.
Meat eating animals have strong canines.
Answer:
Meat eating animals have strong canines as they have to tear the flesh. Meat eating animals like dog, wolves and lions eat raw meat by tearing it so they have sharp canines.
Question 2.
Small intestine has villi.
Answer:
mis oiiioii uu&aiurc; iiad vuu wmcn increase ure uujcr surruec urea for absorption of digested food.
Question 3.
All teeth in the mouth are not alike.
Answer:
The dentition in animals is based on the type of food they eat. So we have different kinds of teeth. All teeth in the mouth are not alike as we eat both meat and plants. Due to different type of food eating habits teeth are of different types.
Question 4.
Food is assimilated in the body
Answer:
All the absorbed nutrients are not immediately required by the body. So, they are changed into various forms that can be stored until they are needed. This is a assimilation.
J. You have eaten food containing fats and proteins. Now fill in the blanks numbered 1-12 to complete some stages of digestion of this food.
In the mouth grinding of food is brought about by 1 and 2. The saliva contains 3 enzyme. The food then passes to stomach through pharynx and 4. Peristalsis of food is caused by 5. In the stomach, pepsin acts on proteins to change them into 6 and 7. Bile is secreted by 8. In duodenum, pancreatic juice has 9 and 10 enzymes. Lipase acts on fats and converts them into 11 and 12.
Answer:
In the mouth grinding of food is brought about by lpremolars and 2molars. The saliva contains Jsalivary amylase (ptyalin) enzyme. The food then passes to stomach through pharynx and 4oesophagus. Peristalsis of food is caused by swave-like motion by contraction of muscles of oesophagus. In the stomach pepsin acts on proteins to change them into 6proteoses and 7peptones. Bile
9tyrpsin and 10lipase enzymes. I ipase acts dttj fats and converts them into “fatty acids and “glycerol.
K. Given alongside is a diagram showing internal structure of a part of the alimentary canal.
Question 1.
identify the part shown in the figure. Give reasons.
Answer:
It is avvillus(plural valli) in small. intestine arefingerlike projections in the inner walls of small intestine.
Question 2.
What is the role of this part in the digestion of food.
Answer:
The villi help to increase the surface area so as to enable maximum absorption of digested food molecules.
Question 3.
Name the parts labdiled 1 and 2 ¡n the diagram.
Answer:
1 → Blood capillaries
2 → Villus
L. draw macro digram of the folloing
Question 1.
Digestive system of human beings.
Question 2.
Structure of a tooth
Living Science Biology Class 7 ICSE Solutions