NCERT Textbook: Nutrition in Animals - Science & Technology for UPSC CSE

 Page 1


Nutrition in Animals
2
Y
ou have learnt in Chapter 1 that
plants can prepare their own food
by the process of photosynthesis
but animals cannot. Animals get their
food from plants, either directly by
eating plants or indirectly by eating
animals that eat plants. Some animals
eat both plants and animals. Recall that
all organisms including humans require
food for growth, repair and functioning
of the body. Animal nutrition includes
nutrient requirement, mode of intake
of food and its utilisation in the body.
You have studied in Class VI that food
consists of many components. Try to
recall and list them below:
1. ______________________
2. ______________________
3. ______________________
4. ______________________
5. ______________________
6. ______________________
The components of food such as
carbohydrates are complex substances.
These complex substances cannot be
utilised as such. So they are broken
down into simpler substances. The
breakdown of complex components of
Table 2.1 Various modes of feeding
Name of Kind of Mode of
animal food feeding
Snail
Ant
Eagle
Humming-bird
Lice
Mosquito
Butterfly
House fly
(Scraping, chewing, siphoning, capturing
and swallowing, sponging, sucking etc.)
food into simpler substances is called
digestion.
2.1 DIFFERENT WAYS OF TAKING FOOD
The mode of taking food into the body
varies in different organisms. Bees and
humming-birds suck the nectar of
plants, infants of human and many
other animals feed on mother’s milk.
Snakes like the python swallow the
animals they prey upon. Some aquatic
animals filter tiny food particles floating
nearby and feed upon them.
Activity 2.1
What is the type of food and mode of
feeding of the following animals? Write
down your observations in the given
Table. You may find the list of modes of
feeding given below the Table helpful.
Complex substance Simpler substances
Rationalised 2023-24
Page 2


Nutrition in Animals
2
Y
ou have learnt in Chapter 1 that
plants can prepare their own food
by the process of photosynthesis
but animals cannot. Animals get their
food from plants, either directly by
eating plants or indirectly by eating
animals that eat plants. Some animals
eat both plants and animals. Recall that
all organisms including humans require
food for growth, repair and functioning
of the body. Animal nutrition includes
nutrient requirement, mode of intake
of food and its utilisation in the body.
You have studied in Class VI that food
consists of many components. Try to
recall and list them below:
1. ______________________
2. ______________________
3. ______________________
4. ______________________
5. ______________________
6. ______________________
The components of food such as
carbohydrates are complex substances.
These complex substances cannot be
utilised as such. So they are broken
down into simpler substances. The
breakdown of complex components of
Table 2.1 Various modes of feeding
Name of Kind of Mode of
animal food feeding
Snail
Ant
Eagle
Humming-bird
Lice
Mosquito
Butterfly
House fly
(Scraping, chewing, siphoning, capturing
and swallowing, sponging, sucking etc.)
food into simpler substances is called
digestion.
2.1 DIFFERENT WAYS OF TAKING FOOD
The mode of taking food into the body
varies in different organisms. Bees and
humming-birds suck the nectar of
plants, infants of human and many
other animals feed on mother’s milk.
Snakes like the python swallow the
animals they prey upon. Some aquatic
animals filter tiny food particles floating
nearby and feed upon them.
Activity 2.1
What is the type of food and mode of
feeding of the following animals? Write
down your observations in the given
Table. You may find the list of modes of
feeding given below the Table helpful.
Complex substance Simpler substances
Rationalised 2023-24
SCIENCE 12
Fig. 2.1  Starfish
Amazing fact
Starfish feeds on animals covered by
hard shells of calcium carbonate.
After opening the shell, the starfish
pops out its stomach through its
mouth to eat the soft animal inside
the shell. The stomach then goes back
into the body and the food is slowly
digested.
2.2 DIGESTION IN HUMANS
We take in food through the mouth,
digest and utilise it. The unused parts
of the food are defecated. Have you ever
wondered what happens to the food
inside the body? The food passes
through a continuous canal (Fig. 2.2)
which begins at the buccal cavity and
ends at the anus. The canal can be
divided into various compartments:
(1) the buccal cavity, (2) foodpipe or
oesophagus, (3) stomach, (4) small
intestine, (5) large intestine ending in
the rectum and (6) the anus. Is it not a
very long path? These parts together
form the alimentary canal (digestive
tract). The food components gradually
get digested as food travels through the
various compartments. The inner walls
of the stomach and the small intestine,
and the various glands associated with the
canal such as salivary glands, the liver
and the pancreas secrete digestive juices.
The digestive juices convert complex
substances of food into simpler ones. The
digestive tract and the associated glands
together constitute the digestive system.
Now, let us know what happens to
the food in different parts of the digestive
tract.
The mouth and buccal cavity
Food is taken into the body through the
mouth. The process of taking food into
Fig. 2.2  Human digestive system
Buccal cavity
Salivary gland
Stomach
Pancreas
Small
intestine
Large
intestine
Rectum
Anus
Gall bladder
Liver
Oesophagus
Rationalised 2023-24
Page 3


Nutrition in Animals
2
Y
ou have learnt in Chapter 1 that
plants can prepare their own food
by the process of photosynthesis
but animals cannot. Animals get their
food from plants, either directly by
eating plants or indirectly by eating
animals that eat plants. Some animals
eat both plants and animals. Recall that
all organisms including humans require
food for growth, repair and functioning
of the body. Animal nutrition includes
nutrient requirement, mode of intake
of food and its utilisation in the body.
You have studied in Class VI that food
consists of many components. Try to
recall and list them below:
1. ______________________
2. ______________________
3. ______________________
4. ______________________
5. ______________________
6. ______________________
The components of food such as
carbohydrates are complex substances.
These complex substances cannot be
utilised as such. So they are broken
down into simpler substances. The
breakdown of complex components of
Table 2.1 Various modes of feeding
Name of Kind of Mode of
animal food feeding
Snail
Ant
Eagle
Humming-bird
Lice
Mosquito
Butterfly
House fly
(Scraping, chewing, siphoning, capturing
and swallowing, sponging, sucking etc.)
food into simpler substances is called
digestion.
2.1 DIFFERENT WAYS OF TAKING FOOD
The mode of taking food into the body
varies in different organisms. Bees and
humming-birds suck the nectar of
plants, infants of human and many
other animals feed on mother’s milk.
Snakes like the python swallow the
animals they prey upon. Some aquatic
animals filter tiny food particles floating
nearby and feed upon them.
Activity 2.1
What is the type of food and mode of
feeding of the following animals? Write
down your observations in the given
Table. You may find the list of modes of
feeding given below the Table helpful.
Complex substance Simpler substances
Rationalised 2023-24
SCIENCE 12
Fig. 2.1  Starfish
Amazing fact
Starfish feeds on animals covered by
hard shells of calcium carbonate.
After opening the shell, the starfish
pops out its stomach through its
mouth to eat the soft animal inside
the shell. The stomach then goes back
into the body and the food is slowly
digested.
2.2 DIGESTION IN HUMANS
We take in food through the mouth,
digest and utilise it. The unused parts
of the food are defecated. Have you ever
wondered what happens to the food
inside the body? The food passes
through a continuous canal (Fig. 2.2)
which begins at the buccal cavity and
ends at the anus. The canal can be
divided into various compartments:
(1) the buccal cavity, (2) foodpipe or
oesophagus, (3) stomach, (4) small
intestine, (5) large intestine ending in
the rectum and (6) the anus. Is it not a
very long path? These parts together
form the alimentary canal (digestive
tract). The food components gradually
get digested as food travels through the
various compartments. The inner walls
of the stomach and the small intestine,
and the various glands associated with the
canal such as salivary glands, the liver
and the pancreas secrete digestive juices.
The digestive juices convert complex
substances of food into simpler ones. The
digestive tract and the associated glands
together constitute the digestive system.
Now, let us know what happens to
the food in different parts of the digestive
tract.
The mouth and buccal cavity
Food is taken into the body through the
mouth. The process of taking food into
Fig. 2.2  Human digestive system
Buccal cavity
Salivary gland
Stomach
Pancreas
Small
intestine
Large
intestine
Rectum
Anus
Gall bladder
Liver
Oesophagus
Rationalised 2023-24
NUTRITION IN ANIMALS 13
Fig. 2.3   Arrangement of teeth and different
type of teeth
Milk teeth and permanent teeth
Do you remember about falling of your teeth some years ago? The first set of
teeth grows during infancy and they fall off at the age between six to eight
years. These are termed milk teeth. The second set that replaces them are the
permanent teeth. The permanent teeth may last throughout life or fall off
during old age or due to some dental disease.
the body is called ingestion. We chew
the food with the teeth and break it
down mechanically into small pieces.
Each tooth is rooted in a separate socket
in the gums (Fig. 2.3). Our teeth vary in
appearance and perform different
functions. Accordingly they are given
different names (Fig. 2.3).
Activity 2.2
Wash your hands. Look into the
mirror and count your teeth. Use
your index finger to feel the teeth.
How many kinds of teeth could you
find? Take a piece of an apple or
bread and eat it. Which teeth do
you use for biting and cutting, and
which ones for piercing and tearing?
Also find out the ones that are used for
chewing and grinding?
Record your observations in Table 2.2
Boojho is fascinated by the
highly coiled small intestine seen
in Fig. 2.2. He wants to know its
length. Would you like to make a
wild guess? We have given its
approximate length on page 16.
Just imagine how such a long
structure is accommodated in a
small space within our body!
Type of teeth Number of teeth Total
Lower jaw Upper jaw
Cutting and
biting teeth
Piercing and
tearing teeth
Chewing and
grinding teeth
Table 2.2
Molar
Canine
Premolar
Incisor
Rationalised 2023-24
Page 4


Nutrition in Animals
2
Y
ou have learnt in Chapter 1 that
plants can prepare their own food
by the process of photosynthesis
but animals cannot. Animals get their
food from plants, either directly by
eating plants or indirectly by eating
animals that eat plants. Some animals
eat both plants and animals. Recall that
all organisms including humans require
food for growth, repair and functioning
of the body. Animal nutrition includes
nutrient requirement, mode of intake
of food and its utilisation in the body.
You have studied in Class VI that food
consists of many components. Try to
recall and list them below:
1. ______________________
2. ______________________
3. ______________________
4. ______________________
5. ______________________
6. ______________________
The components of food such as
carbohydrates are complex substances.
These complex substances cannot be
utilised as such. So they are broken
down into simpler substances. The
breakdown of complex components of
Table 2.1 Various modes of feeding
Name of Kind of Mode of
animal food feeding
Snail
Ant
Eagle
Humming-bird
Lice
Mosquito
Butterfly
House fly
(Scraping, chewing, siphoning, capturing
and swallowing, sponging, sucking etc.)
food into simpler substances is called
digestion.
2.1 DIFFERENT WAYS OF TAKING FOOD
The mode of taking food into the body
varies in different organisms. Bees and
humming-birds suck the nectar of
plants, infants of human and many
other animals feed on mother’s milk.
Snakes like the python swallow the
animals they prey upon. Some aquatic
animals filter tiny food particles floating
nearby and feed upon them.
Activity 2.1
What is the type of food and mode of
feeding of the following animals? Write
down your observations in the given
Table. You may find the list of modes of
feeding given below the Table helpful.
Complex substance Simpler substances
Rationalised 2023-24
SCIENCE 12
Fig. 2.1  Starfish
Amazing fact
Starfish feeds on animals covered by
hard shells of calcium carbonate.
After opening the shell, the starfish
pops out its stomach through its
mouth to eat the soft animal inside
the shell. The stomach then goes back
into the body and the food is slowly
digested.
2.2 DIGESTION IN HUMANS
We take in food through the mouth,
digest and utilise it. The unused parts
of the food are defecated. Have you ever
wondered what happens to the food
inside the body? The food passes
through a continuous canal (Fig. 2.2)
which begins at the buccal cavity and
ends at the anus. The canal can be
divided into various compartments:
(1) the buccal cavity, (2) foodpipe or
oesophagus, (3) stomach, (4) small
intestine, (5) large intestine ending in
the rectum and (6) the anus. Is it not a
very long path? These parts together
form the alimentary canal (digestive
tract). The food components gradually
get digested as food travels through the
various compartments. The inner walls
of the stomach and the small intestine,
and the various glands associated with the
canal such as salivary glands, the liver
and the pancreas secrete digestive juices.
The digestive juices convert complex
substances of food into simpler ones. The
digestive tract and the associated glands
together constitute the digestive system.
Now, let us know what happens to
the food in different parts of the digestive
tract.
The mouth and buccal cavity
Food is taken into the body through the
mouth. The process of taking food into
Fig. 2.2  Human digestive system
Buccal cavity
Salivary gland
Stomach
Pancreas
Small
intestine
Large
intestine
Rectum
Anus
Gall bladder
Liver
Oesophagus
Rationalised 2023-24
NUTRITION IN ANIMALS 13
Fig. 2.3   Arrangement of teeth and different
type of teeth
Milk teeth and permanent teeth
Do you remember about falling of your teeth some years ago? The first set of
teeth grows during infancy and they fall off at the age between six to eight
years. These are termed milk teeth. The second set that replaces them are the
permanent teeth. The permanent teeth may last throughout life or fall off
during old age or due to some dental disease.
the body is called ingestion. We chew
the food with the teeth and break it
down mechanically into small pieces.
Each tooth is rooted in a separate socket
in the gums (Fig. 2.3). Our teeth vary in
appearance and perform different
functions. Accordingly they are given
different names (Fig. 2.3).
Activity 2.2
Wash your hands. Look into the
mirror and count your teeth. Use
your index finger to feel the teeth.
How many kinds of teeth could you
find? Take a piece of an apple or
bread and eat it. Which teeth do
you use for biting and cutting, and
which ones for piercing and tearing?
Also find out the ones that are used for
chewing and grinding?
Record your observations in Table 2.2
Boojho is fascinated by the
highly coiled small intestine seen
in Fig. 2.2. He wants to know its
length. Would you like to make a
wild guess? We have given its
approximate length on page 16.
Just imagine how such a long
structure is accommodated in a
small space within our body!
Type of teeth Number of teeth Total
Lower jaw Upper jaw
Cutting and
biting teeth
Piercing and
tearing teeth
Chewing and
grinding teeth
Table 2.2
Molar
Canine
Premolar
Incisor
Rationalised 2023-24
SCIENCE 14
Fig. 2.4  Effect of saliva on starch
Iodine solution
Water
Boiled rice
Boiled and chewed rice
Sweets and tooth decay
Normally bacteria are present in our mouth but they are not harmful
to us. However, if we do not clean our teeth and mouth after eating,
many harmful bacteria also begin to live and grow in it. These bacteria
break down the sugars present from the leftover food and release
acids (see Chapter 4 to know what an acid is). The acids gradually
damage the teeth (Fig. 2.5). This is called tooth decay. If it is not
treated in time, it causes severe toothache and in extreme cases
results in tooth loss. Chocolates, sweets, soft drinks and other sugar
products are the major culprits of tooth decay.
Therefore, one should clean the teeth with a brush or datun and
dental floss (a special strong thread which is moved between two
teeth to take out trapped food particles) at least twice a day and
rinse the mouth after every meal. Also, one should not put dirty
fingers or any unwashed object in the mouth.
Fig. 2.5  Gradual decay of tooth
(a)
(b)
(c)
(d)
Our mouth has the salivary glands
which secrete saliva. Do you know the
action of saliva on food? Let us find out.
Activity 2.3
Take two test tubes. Label them ‘A’ and
‘B’. In test tube ‘A’ put one teaspoonful
of boiled rice; in test tube ‘B’ keep one
teaspoonful of boiled rice after chewing
it for 3 to 5 minutes. Add 3–4 mL of
water in both the test tubes (Fig. 2.4).
Now pour 2–3 drops of iodine solution
in each test tube and observe. Why is
there a change in colour in the test
tubes? Discuss the results with your
classmates and your teacher. The saliva
breaks down the starch into sugars.
The tongue is a fleshy muscular
organ attached at the back to the floor
of the buccal cavity. It is free at the front
and can be moved in all directions. Do
you know the functions of the tongue?
We use our tongue for talking. Besides,
it mixes saliva with the food during
chewing and helps in swallowing food.
We also taste food with our tongue. It
has taste buds that detect different
tastes of food. We can find out the
AB
Rationalised 2023-24
Page 5


Nutrition in Animals
2
Y
ou have learnt in Chapter 1 that
plants can prepare their own food
by the process of photosynthesis
but animals cannot. Animals get their
food from plants, either directly by
eating plants or indirectly by eating
animals that eat plants. Some animals
eat both plants and animals. Recall that
all organisms including humans require
food for growth, repair and functioning
of the body. Animal nutrition includes
nutrient requirement, mode of intake
of food and its utilisation in the body.
You have studied in Class VI that food
consists of many components. Try to
recall and list them below:
1. ______________________
2. ______________________
3. ______________________
4. ______________________
5. ______________________
6. ______________________
The components of food such as
carbohydrates are complex substances.
These complex substances cannot be
utilised as such. So they are broken
down into simpler substances. The
breakdown of complex components of
Table 2.1 Various modes of feeding
Name of Kind of Mode of
animal food feeding
Snail
Ant
Eagle
Humming-bird
Lice
Mosquito
Butterfly
House fly
(Scraping, chewing, siphoning, capturing
and swallowing, sponging, sucking etc.)
food into simpler substances is called
digestion.
2.1 DIFFERENT WAYS OF TAKING FOOD
The mode of taking food into the body
varies in different organisms. Bees and
humming-birds suck the nectar of
plants, infants of human and many
other animals feed on mother’s milk.
Snakes like the python swallow the
animals they prey upon. Some aquatic
animals filter tiny food particles floating
nearby and feed upon them.
Activity 2.1
What is the type of food and mode of
feeding of the following animals? Write
down your observations in the given
Table. You may find the list of modes of
feeding given below the Table helpful.
Complex substance Simpler substances
Rationalised 2023-24
SCIENCE 12
Fig. 2.1  Starfish
Amazing fact
Starfish feeds on animals covered by
hard shells of calcium carbonate.
After opening the shell, the starfish
pops out its stomach through its
mouth to eat the soft animal inside
the shell. The stomach then goes back
into the body and the food is slowly
digested.
2.2 DIGESTION IN HUMANS
We take in food through the mouth,
digest and utilise it. The unused parts
of the food are defecated. Have you ever
wondered what happens to the food
inside the body? The food passes
through a continuous canal (Fig. 2.2)
which begins at the buccal cavity and
ends at the anus. The canal can be
divided into various compartments:
(1) the buccal cavity, (2) foodpipe or
oesophagus, (3) stomach, (4) small
intestine, (5) large intestine ending in
the rectum and (6) the anus. Is it not a
very long path? These parts together
form the alimentary canal (digestive
tract). The food components gradually
get digested as food travels through the
various compartments. The inner walls
of the stomach and the small intestine,
and the various glands associated with the
canal such as salivary glands, the liver
and the pancreas secrete digestive juices.
The digestive juices convert complex
substances of food into simpler ones. The
digestive tract and the associated glands
together constitute the digestive system.
Now, let us know what happens to
the food in different parts of the digestive
tract.
The mouth and buccal cavity
Food is taken into the body through the
mouth. The process of taking food into
Fig. 2.2  Human digestive system
Buccal cavity
Salivary gland
Stomach
Pancreas
Small
intestine
Large
intestine
Rectum
Anus
Gall bladder
Liver
Oesophagus
Rationalised 2023-24
NUTRITION IN ANIMALS 13
Fig. 2.3   Arrangement of teeth and different
type of teeth
Milk teeth and permanent teeth
Do you remember about falling of your teeth some years ago? The first set of
teeth grows during infancy and they fall off at the age between six to eight
years. These are termed milk teeth. The second set that replaces them are the
permanent teeth. The permanent teeth may last throughout life or fall off
during old age or due to some dental disease.
the body is called ingestion. We chew
the food with the teeth and break it
down mechanically into small pieces.
Each tooth is rooted in a separate socket
in the gums (Fig. 2.3). Our teeth vary in
appearance and perform different
functions. Accordingly they are given
different names (Fig. 2.3).
Activity 2.2
Wash your hands. Look into the
mirror and count your teeth. Use
your index finger to feel the teeth.
How many kinds of teeth could you
find? Take a piece of an apple or
bread and eat it. Which teeth do
you use for biting and cutting, and
which ones for piercing and tearing?
Also find out the ones that are used for
chewing and grinding?
Record your observations in Table 2.2
Boojho is fascinated by the
highly coiled small intestine seen
in Fig. 2.2. He wants to know its
length. Would you like to make a
wild guess? We have given its
approximate length on page 16.
Just imagine how such a long
structure is accommodated in a
small space within our body!
Type of teeth Number of teeth Total
Lower jaw Upper jaw
Cutting and
biting teeth
Piercing and
tearing teeth
Chewing and
grinding teeth
Table 2.2
Molar
Canine
Premolar
Incisor
Rationalised 2023-24
SCIENCE 14
Fig. 2.4  Effect of saliva on starch
Iodine solution
Water
Boiled rice
Boiled and chewed rice
Sweets and tooth decay
Normally bacteria are present in our mouth but they are not harmful
to us. However, if we do not clean our teeth and mouth after eating,
many harmful bacteria also begin to live and grow in it. These bacteria
break down the sugars present from the leftover food and release
acids (see Chapter 4 to know what an acid is). The acids gradually
damage the teeth (Fig. 2.5). This is called tooth decay. If it is not
treated in time, it causes severe toothache and in extreme cases
results in tooth loss. Chocolates, sweets, soft drinks and other sugar
products are the major culprits of tooth decay.
Therefore, one should clean the teeth with a brush or datun and
dental floss (a special strong thread which is moved between two
teeth to take out trapped food particles) at least twice a day and
rinse the mouth after every meal. Also, one should not put dirty
fingers or any unwashed object in the mouth.
Fig. 2.5  Gradual decay of tooth
(a)
(b)
(c)
(d)
Our mouth has the salivary glands
which secrete saliva. Do you know the
action of saliva on food? Let us find out.
Activity 2.3
Take two test tubes. Label them ‘A’ and
‘B’. In test tube ‘A’ put one teaspoonful
of boiled rice; in test tube ‘B’ keep one
teaspoonful of boiled rice after chewing
it for 3 to 5 minutes. Add 3–4 mL of
water in both the test tubes (Fig. 2.4).
Now pour 2–3 drops of iodine solution
in each test tube and observe. Why is
there a change in colour in the test
tubes? Discuss the results with your
classmates and your teacher. The saliva
breaks down the starch into sugars.
The tongue is a fleshy muscular
organ attached at the back to the floor
of the buccal cavity. It is free at the front
and can be moved in all directions. Do
you know the functions of the tongue?
We use our tongue for talking. Besides,
it mixes saliva with the food during
chewing and helps in swallowing food.
We also taste food with our tongue. It
has taste buds that detect different
tastes of food. We can find out the
AB
Rationalised 2023-24
NUTRITION IN ANIMALS 15
Paheli wants to know how
food moves in the opposite
direction during vomiting.
Fig. 2.6  Regions of the
tongue for different tastes
Fig. 2.7  Movement of the
food in the oesophagus
of the alimentary canal
position of taste buds by the following
activity.
Activity 2.4
1. Prepare a separate sample each of
(i) sugar solution, (ii) common salt
solution, (iii) lemon juice and (iv) juice
of crushed neem leaf or bitter gourd.
2. Blindfold one of your classmates and
ask her/him to take out the tongue
and keep it in straight and flat position.
3. Use a clean toothpick to put the
above samples one by one on
different areas of the tongue as
shown in Fig. 2.6. Use a new
toothpick for each sample.
4. Ask the classmate which areas of the
tongue could detect the sweet, salty,
sour and bitter substances.
5. Now write down your observations
and label Fig. 2.6.
Repeat this activity with other
classmates.
The foodpipe/oesophagus
The swallowed food passes into the
foodpipe or oesophagus. Look at Fig. 2.2.
The foodpipe runs along the neck
Sometimes when you eat in a hurry, talk or laugh while eating, you may cough,
get hiccups or a choking sensation. This happens when food particles enter the
windpipe. The windpipe carries air from the nostrils to the lungs. It runs adjacent
to the foodpipe. But inside the throat, air and food share a common passage.
Then how is food prevented from entering the windpipe? During the act of
swallowing a flap-like valve closes the passage of the windpipe and guides the
food into the foodpipe. If, by chance, food particles enter the windpipe, we feel
choked, get hiccups or cough.
Food
Oesophagus
Stomach
Rationalised 2023-24