Class 7 Science Chapter 9 NCERT Book - Life Processes in Animals

 Page 1


Life Processes 
in Animals
9
If your food is fully digested before you eat again, you won’t need medicine for pain.
(Thirukkural 942)
In the Grade 6 Science textbook Curiosity, chapter ‘Living 
Creatures: Exploring their Characteristics’, we learnt about 
processes essential for survival of living beings like nutrition, 
respiration, excretion, and reproduction. These are collectively 
called life processes. In this chapter, we will learn about life 
processes such as nutrition and respiration in detail.
Chapter 9.indd   121 4/3/2025   4:55:07 PM
Page 2


Life Processes 
in Animals
9
If your food is fully digested before you eat again, you won’t need medicine for pain.
(Thirukkural 942)
In the Grade 6 Science textbook Curiosity, chapter ‘Living 
Creatures: Exploring their Characteristics’, we learnt about 
processes essential for survival of living beings like nutrition, 
respiration, excretion, and reproduction. These are collectively 
called life processes. In this chapter, we will learn about life 
processes such as nutrition and respiration in detail.
Chapter 9.indd   121 4/3/2025   4:55:07 PM
Curiosity | Textbook of Science | Grade 7
122
Observe your surroundings and notice what animals eat. 
Animals eat di? erent types of food. Bees and sunbirds suck the nectar 
of ? owers, while infants of humans and many other animals feed on 
their mother’s milk. Snakes, like python, swallow the animals they 
prey upon. Some aquatic animals ? lter tiny food particles ? oating 
nearby and feed upon them. 
Animals, including humans, obtain 
energy from food, which enables them to 
carry out various life processes. Animals 
consume food that contains complex 
components, such as carbohydrate, protein, 
and fat. These complex food components 
have to be broken down into simpler forms 
before the body can use them. But how does 
this process happen? 
Breaking down of complex food 
components into simpler forms occurs in a 
long tube called the alimentary canal. This 
process starts in the mouth and ends at the 
anus (Fig. 9.1). As food moves through this 
canal, digestive juices secreted at di? erent 
parts break it down into simpler forms. 
This simpler form of food is absorbed by 
di? erent parts of our alimentary canal and 
transported to various parts of our body to 
carry out various functions.
9.1 Nutrition in Animals  
How do the complex food components get broken down into 
simpler forms and used by the body in various animals? Is this 
process the same in all animals or does it vary? Let us ? rst try to 
understand this process in humans.
9.1.1 Digestion in human beings
Let us trace the journey of food inside our body as it passes 
through di? erent parts of the alimentary canal.
Beginning with the mouth cavity
The journey of the food you eat begins when it enters your 
mouth. Your teeth break down food you eat into smaller pieces 
by the processes of crushing and chewing. This process of initial 
breakdown of food into ? ne pieces is called mechanical digestion. 
Think about your favourite food. Does your mouth feel watery? 
Fig. 9.1: Human digestive system
Stomach
Oesophagus 
or Food pipe
Liver
Pancreas
Large intestine
Anus
Mouth
Small intestine
Rectum
Chapter 9.indd   122 4/3/2025   4:55:08 PM
Page 3


Life Processes 
in Animals
9
If your food is fully digested before you eat again, you won’t need medicine for pain.
(Thirukkural 942)
In the Grade 6 Science textbook Curiosity, chapter ‘Living 
Creatures: Exploring their Characteristics’, we learnt about 
processes essential for survival of living beings like nutrition, 
respiration, excretion, and reproduction. These are collectively 
called life processes. In this chapter, we will learn about life 
processes such as nutrition and respiration in detail.
Chapter 9.indd   121 4/3/2025   4:55:07 PM
Curiosity | Textbook of Science | Grade 7
122
Observe your surroundings and notice what animals eat. 
Animals eat di? erent types of food. Bees and sunbirds suck the nectar 
of ? owers, while infants of humans and many other animals feed on 
their mother’s milk. Snakes, like python, swallow the animals they 
prey upon. Some aquatic animals ? lter tiny food particles ? oating 
nearby and feed upon them. 
Animals, including humans, obtain 
energy from food, which enables them to 
carry out various life processes. Animals 
consume food that contains complex 
components, such as carbohydrate, protein, 
and fat. These complex food components 
have to be broken down into simpler forms 
before the body can use them. But how does 
this process happen? 
Breaking down of complex food 
components into simpler forms occurs in a 
long tube called the alimentary canal. This 
process starts in the mouth and ends at the 
anus (Fig. 9.1). As food moves through this 
canal, digestive juices secreted at di? erent 
parts break it down into simpler forms. 
This simpler form of food is absorbed by 
di? erent parts of our alimentary canal and 
transported to various parts of our body to 
carry out various functions.
9.1 Nutrition in Animals  
How do the complex food components get broken down into 
simpler forms and used by the body in various animals? Is this 
process the same in all animals or does it vary? Let us ? rst try to 
understand this process in humans.
9.1.1 Digestion in human beings
Let us trace the journey of food inside our body as it passes 
through di? erent parts of the alimentary canal.
Beginning with the mouth cavity
The journey of the food you eat begins when it enters your 
mouth. Your teeth break down food you eat into smaller pieces 
by the processes of crushing and chewing. This process of initial 
breakdown of food into ? ne pieces is called mechanical digestion. 
Think about your favourite food. Does your mouth feel watery? 
Fig. 9.1: Human digestive system
Stomach
Oesophagus 
or Food pipe
Liver
Pancreas
Large intestine
Anus
Mouth
Small intestine
Rectum
Chapter 9.indd   122 4/3/2025   4:55:08 PM
Life Processes in Animals
123
This happens because of more saliva that gets released when you 
recall your favourite food.
What do you think is the role of saliva in your mouth? What 
do you feel when you eat other types of food, such as chapati? Let 
us ? nd out.
Take a small piece of chapati or a bite-sized portion of boiled 
rice and chew it properly for 30–60 seconds. At ? rst, the chapati
or rice has its usual taste, but as you continue chewing, do you 
notice a change in taste? The food begins to taste sweet! Have you 
ever wondered why this happens?
Chapati or rice contains starch, which is a type of carbohydrate. 
Our saliva contains a digestive juice that helps break down starch 
into sugar. This explains why starchy food, like chapati, tastes 
sweet when you chew it for a long time. Saliva helps to break 
down components of food into simpler ones.
SCIENCE AND SOCIETY
A healthy mouth requires good oral hygiene. We should brush our 
teeth and clean our tongue twice a day, and rinse our mouth with 
water after each meal to prevent tooth decay and bad smell in the 
mouth. Find out the ways our elders were maintaing oral hygiene. 
Activity 9.1: Let us investigate
? Take two test tubes and label them as ‘A’ and ‘B’. 
? Take one teaspoonful of boiled rice in test tube A, and take a 
teaspoonful of boiled rice after chewing it for 30–60 seconds 
in test tube B. 
? Add 3–4 mL of water in both the test tubes. 
? Note the initial colour of the rice-water mixture in Table 9.1.
? Add 3–4 drops of iodine solution into each test tube with the 
help of a dropper. Mix the content of each test tube separately 
and observe. 
Record your observations in Table 9.1.
Test tube
Final colour 
after adding 
iodine
Possible reason 
for the change 
in colour, if any
Table 9.1: Action of saliva on starch Table 9.1: Action of saliva on starch
A: Boiled rice
B: Chewed boiled rice
Initial colour 
before adding 
iodine
Chapter 9.indd   123 4/3/2025   4:55:09 PM
Page 4


Life Processes 
in Animals
9
If your food is fully digested before you eat again, you won’t need medicine for pain.
(Thirukkural 942)
In the Grade 6 Science textbook Curiosity, chapter ‘Living 
Creatures: Exploring their Characteristics’, we learnt about 
processes essential for survival of living beings like nutrition, 
respiration, excretion, and reproduction. These are collectively 
called life processes. In this chapter, we will learn about life 
processes such as nutrition and respiration in detail.
Chapter 9.indd   121 4/3/2025   4:55:07 PM
Curiosity | Textbook of Science | Grade 7
122
Observe your surroundings and notice what animals eat. 
Animals eat di? erent types of food. Bees and sunbirds suck the nectar 
of ? owers, while infants of humans and many other animals feed on 
their mother’s milk. Snakes, like python, swallow the animals they 
prey upon. Some aquatic animals ? lter tiny food particles ? oating 
nearby and feed upon them. 
Animals, including humans, obtain 
energy from food, which enables them to 
carry out various life processes. Animals 
consume food that contains complex 
components, such as carbohydrate, protein, 
and fat. These complex food components 
have to be broken down into simpler forms 
before the body can use them. But how does 
this process happen? 
Breaking down of complex food 
components into simpler forms occurs in a 
long tube called the alimentary canal. This 
process starts in the mouth and ends at the 
anus (Fig. 9.1). As food moves through this 
canal, digestive juices secreted at di? erent 
parts break it down into simpler forms. 
This simpler form of food is absorbed by 
di? erent parts of our alimentary canal and 
transported to various parts of our body to 
carry out various functions.
9.1 Nutrition in Animals  
How do the complex food components get broken down into 
simpler forms and used by the body in various animals? Is this 
process the same in all animals or does it vary? Let us ? rst try to 
understand this process in humans.
9.1.1 Digestion in human beings
Let us trace the journey of food inside our body as it passes 
through di? erent parts of the alimentary canal.
Beginning with the mouth cavity
The journey of the food you eat begins when it enters your 
mouth. Your teeth break down food you eat into smaller pieces 
by the processes of crushing and chewing. This process of initial 
breakdown of food into ? ne pieces is called mechanical digestion. 
Think about your favourite food. Does your mouth feel watery? 
Fig. 9.1: Human digestive system
Stomach
Oesophagus 
or Food pipe
Liver
Pancreas
Large intestine
Anus
Mouth
Small intestine
Rectum
Chapter 9.indd   122 4/3/2025   4:55:08 PM
Life Processes in Animals
123
This happens because of more saliva that gets released when you 
recall your favourite food.
What do you think is the role of saliva in your mouth? What 
do you feel when you eat other types of food, such as chapati? Let 
us ? nd out.
Take a small piece of chapati or a bite-sized portion of boiled 
rice and chew it properly for 30–60 seconds. At ? rst, the chapati
or rice has its usual taste, but as you continue chewing, do you 
notice a change in taste? The food begins to taste sweet! Have you 
ever wondered why this happens?
Chapati or rice contains starch, which is a type of carbohydrate. 
Our saliva contains a digestive juice that helps break down starch 
into sugar. This explains why starchy food, like chapati, tastes 
sweet when you chew it for a long time. Saliva helps to break 
down components of food into simpler ones.
SCIENCE AND SOCIETY
A healthy mouth requires good oral hygiene. We should brush our 
teeth and clean our tongue twice a day, and rinse our mouth with 
water after each meal to prevent tooth decay and bad smell in the 
mouth. Find out the ways our elders were maintaing oral hygiene. 
Activity 9.1: Let us investigate
? Take two test tubes and label them as ‘A’ and ‘B’. 
? Take one teaspoonful of boiled rice in test tube A, and take a 
teaspoonful of boiled rice after chewing it for 30–60 seconds 
in test tube B. 
? Add 3–4 mL of water in both the test tubes. 
? Note the initial colour of the rice-water mixture in Table 9.1.
? Add 3–4 drops of iodine solution into each test tube with the 
help of a dropper. Mix the content of each test tube separately 
and observe. 
Record your observations in Table 9.1.
Test tube
Final colour 
after adding 
iodine
Possible reason 
for the change 
in colour, if any
Table 9.1: Action of saliva on starch Table 9.1: Action of saliva on starch
A: Boiled rice
B: Chewed boiled rice
Initial colour 
before adding 
iodine
Chapter 9.indd   123 4/3/2025   4:55:09 PM
Curiosity | Textbook of Science | Grade 7
124
Did you observe that the colour of boiled rice turned blue-black 
in test tube A, while in test tube B, chewed boiled rice either did 
not change colour or turned only a very light blue-black colour? 
What causes the change of colour in test tube A? In Grade 6, we 
learned that iodine gives a blue-black colour when it reacts with 
starch. In test tube A, the appearance of the blue-black colour 
indicates the presence of starch. In test tube B, which contains 
chewed boiled rice, if there is no change in colour, it indicates 
that the starch is no longer present; if there is only a slight 
change in colour, it indicates that starch is present only in very 
small amount. It has been broken down into simple sugars by 
the action of saliva. If the colour still appears in test tube B, what 
changes would you make in the activity to explore it further? 
Would the colour change if chewing time is increased? Try to 
? nd out by repeating the activity.
Now, we know that saliva secretion in the mouth helps break 
down starch into sugars. This process of breaking complex food 
components into simpler forms in the body is called digestion. Food 
is partially digested in the mouth. Let us learn how this partially 
digested food gets further digested through the alimentary canal. 
Food pipe (Oesophagus): A passage from the mouth to the 
stomach
When you chew your food, your 
saliva not only helps in digesting 
the starch but also moistens 
it, making it soft and easy to 
swallow. Your tongue helps in 
mixing chewed food with saliva 
and pushing this softened food 
into a long, ? exible tube called 
the food pipe or oesophagus
(Fig. 9.2). But how does the food 
move down? 
The walls of the food pipe gently contract and relax in a 
wave-like motion to push the food down into the stomach. This 
movement takes place throughout the alimentary canal and 
pushes the food forward.
Stomach
In the stomach, the walls contract and relax to churn the food. The 
churned food is then mixed with a secretion from the inner lining 
of the stomach. The secretion from stomach contains digestive juice, 
acid, and mucus. 
Fig. 9.2: Movement of food in the food pipe
Site of 
relaxation
Stomach Stomach
Food
Food
Food
Site of contraction
Chapter 9.indd   124 4/3/2025   4:55:09 PM
Page 5


Life Processes 
in Animals
9
If your food is fully digested before you eat again, you won’t need medicine for pain.
(Thirukkural 942)
In the Grade 6 Science textbook Curiosity, chapter ‘Living 
Creatures: Exploring their Characteristics’, we learnt about 
processes essential for survival of living beings like nutrition, 
respiration, excretion, and reproduction. These are collectively 
called life processes. In this chapter, we will learn about life 
processes such as nutrition and respiration in detail.
Chapter 9.indd   121 4/3/2025   4:55:07 PM
Curiosity | Textbook of Science | Grade 7
122
Observe your surroundings and notice what animals eat. 
Animals eat di? erent types of food. Bees and sunbirds suck the nectar 
of ? owers, while infants of humans and many other animals feed on 
their mother’s milk. Snakes, like python, swallow the animals they 
prey upon. Some aquatic animals ? lter tiny food particles ? oating 
nearby and feed upon them. 
Animals, including humans, obtain 
energy from food, which enables them to 
carry out various life processes. Animals 
consume food that contains complex 
components, such as carbohydrate, protein, 
and fat. These complex food components 
have to be broken down into simpler forms 
before the body can use them. But how does 
this process happen? 
Breaking down of complex food 
components into simpler forms occurs in a 
long tube called the alimentary canal. This 
process starts in the mouth and ends at the 
anus (Fig. 9.1). As food moves through this 
canal, digestive juices secreted at di? erent 
parts break it down into simpler forms. 
This simpler form of food is absorbed by 
di? erent parts of our alimentary canal and 
transported to various parts of our body to 
carry out various functions.
9.1 Nutrition in Animals  
How do the complex food components get broken down into 
simpler forms and used by the body in various animals? Is this 
process the same in all animals or does it vary? Let us ? rst try to 
understand this process in humans.
9.1.1 Digestion in human beings
Let us trace the journey of food inside our body as it passes 
through di? erent parts of the alimentary canal.
Beginning with the mouth cavity
The journey of the food you eat begins when it enters your 
mouth. Your teeth break down food you eat into smaller pieces 
by the processes of crushing and chewing. This process of initial 
breakdown of food into ? ne pieces is called mechanical digestion. 
Think about your favourite food. Does your mouth feel watery? 
Fig. 9.1: Human digestive system
Stomach
Oesophagus 
or Food pipe
Liver
Pancreas
Large intestine
Anus
Mouth
Small intestine
Rectum
Chapter 9.indd   122 4/3/2025   4:55:08 PM
Life Processes in Animals
123
This happens because of more saliva that gets released when you 
recall your favourite food.
What do you think is the role of saliva in your mouth? What 
do you feel when you eat other types of food, such as chapati? Let 
us ? nd out.
Take a small piece of chapati or a bite-sized portion of boiled 
rice and chew it properly for 30–60 seconds. At ? rst, the chapati
or rice has its usual taste, but as you continue chewing, do you 
notice a change in taste? The food begins to taste sweet! Have you 
ever wondered why this happens?
Chapati or rice contains starch, which is a type of carbohydrate. 
Our saliva contains a digestive juice that helps break down starch 
into sugar. This explains why starchy food, like chapati, tastes 
sweet when you chew it for a long time. Saliva helps to break 
down components of food into simpler ones.
SCIENCE AND SOCIETY
A healthy mouth requires good oral hygiene. We should brush our 
teeth and clean our tongue twice a day, and rinse our mouth with 
water after each meal to prevent tooth decay and bad smell in the 
mouth. Find out the ways our elders were maintaing oral hygiene. 
Activity 9.1: Let us investigate
? Take two test tubes and label them as ‘A’ and ‘B’. 
? Take one teaspoonful of boiled rice in test tube A, and take a 
teaspoonful of boiled rice after chewing it for 30–60 seconds 
in test tube B. 
? Add 3–4 mL of water in both the test tubes. 
? Note the initial colour of the rice-water mixture in Table 9.1.
? Add 3–4 drops of iodine solution into each test tube with the 
help of a dropper. Mix the content of each test tube separately 
and observe. 
Record your observations in Table 9.1.
Test tube
Final colour 
after adding 
iodine
Possible reason 
for the change 
in colour, if any
Table 9.1: Action of saliva on starch Table 9.1: Action of saliva on starch
A: Boiled rice
B: Chewed boiled rice
Initial colour 
before adding 
iodine
Chapter 9.indd   123 4/3/2025   4:55:09 PM
Curiosity | Textbook of Science | Grade 7
124
Did you observe that the colour of boiled rice turned blue-black 
in test tube A, while in test tube B, chewed boiled rice either did 
not change colour or turned only a very light blue-black colour? 
What causes the change of colour in test tube A? In Grade 6, we 
learned that iodine gives a blue-black colour when it reacts with 
starch. In test tube A, the appearance of the blue-black colour 
indicates the presence of starch. In test tube B, which contains 
chewed boiled rice, if there is no change in colour, it indicates 
that the starch is no longer present; if there is only a slight 
change in colour, it indicates that starch is present only in very 
small amount. It has been broken down into simple sugars by 
the action of saliva. If the colour still appears in test tube B, what 
changes would you make in the activity to explore it further? 
Would the colour change if chewing time is increased? Try to 
? nd out by repeating the activity.
Now, we know that saliva secretion in the mouth helps break 
down starch into sugars. This process of breaking complex food 
components into simpler forms in the body is called digestion. Food 
is partially digested in the mouth. Let us learn how this partially 
digested food gets further digested through the alimentary canal. 
Food pipe (Oesophagus): A passage from the mouth to the 
stomach
When you chew your food, your 
saliva not only helps in digesting 
the starch but also moistens 
it, making it soft and easy to 
swallow. Your tongue helps in 
mixing chewed food with saliva 
and pushing this softened food 
into a long, ? exible tube called 
the food pipe or oesophagus
(Fig. 9.2). But how does the food 
move down? 
The walls of the food pipe gently contract and relax in a 
wave-like motion to push the food down into the stomach. This 
movement takes place throughout the alimentary canal and 
pushes the food forward.
Stomach
In the stomach, the walls contract and relax to churn the food. The 
churned food is then mixed with a secretion from the inner lining 
of the stomach. The secretion from stomach contains digestive juice, 
acid, and mucus. 
Fig. 9.2: Movement of food in the food pipe
Site of 
relaxation
Stomach Stomach
Food
Food
Food
Site of contraction
Chapter 9.indd   124 4/3/2025   4:55:09 PM
Life Processes in Animals
125
The digestive juice of the stomach breaks 
down proteins present in the food into simpler 
components. 
The acid not only helps break down proteins 
but also kills many harmful bacteria. The mucus 
protects the stomach lining from the acid, preventing 
damage. In the stomach, the food is partially digested 
and transformed into a semi-liquid mass, preparing 
it for the next stage of digestion. 
Fig. 9.3: Stomach
Digestive juice, 
acid and mucus
Stomach wall
FASCINATING FACTS
How did scientists learn about digestion in the human body?
The discovery of how the stomach works happened 
by chance. In 1822, a man named Alexis St. Martin 
was accidentally shot in the stomach. He was treated 
by a doctor, William Beaumont. However, his wound 
never fully healed, leaving a small permanent hole. 
This opening allowed Dr. Beaumont to observe 
digestion in the stomach as it happened. He conducted 
experiments on how di? erent foods were broken 
down and studied how emotions a? ect digestion.
Alexis St. Martin’s 
shotgun wound
Small Intestine
After its journey through the stomach, the partially 
digested food moves into the small intestine. Look 
at Fig. 9.4. It is a sketch of a stretched-out alimentary 
canal. Guess how long it is. You will be surprised 
that although it is called small intestine, it is almost 
6 metres long—almost twice the height of your 
classroom! You will be surprised to know that the 
small intestine is the longest part of the alimentary 
canal. 
The small intestine receives digestive secretions 
from three sources—the inner lining of the small 
intestine itself, and two more structures associated 
with the alimentary canal—the liver and the 
pancreas (Fig. 9.4). The liver secretes bile, which 
is mildly basic in nature. Recall the neutralisation 
reaction in chapter ‘Exploring Substances: Acidic, 
Basic, and Neutral’. Bile neutralises acids present 
in the food moving down from the stomach and 
breaks down fats into tiny droplets, making its 
digestion easier. 
Stomach
Mouth
Food pipe
(Oesophagus)
Pancreas
Small 
intestine
Liver
Large 
intestine
Anus
Fig. 9.4: Alimentary canal if it is 
stretched out
Chapter 9.indd   125 4/3/2025   4:55:10 PM