Class 7 Science Chapter 2

1. Nutritionh
in Animals
2
NLEARNING OBJECTIVES
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After completion of the chapter, students will be able to
1. understand the modes of nutrition in animals.
2. describe the digestive system in humans
3. illustrate different types of teeth.
4. explain nutrition in Amoeba and ruminants.
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Unlike plants, animals cannot make their own food. They get their food from
plants directly or indirectly. We know that all organisms including humans
need food for their growth, repair and functioning of the body. The process
of taking in food by an animal and its utilisation in the body is called animal
nutrition.
Animals do not make their own food but depend on the food synthesised by
plants, hence they are called heterotrophs and thus show heterotrophic mode
of nutrition. When the food is taken in the form of solid particles as a whole,
the method of food intake is known as holozoic nutrition.
4
Classification of Heterotrophs
There are different types of heterotrophs whose mode of feeding varies with
the kind of food they eat, like snake swallows its prey, tigerchewsitsfood, etc.
Based on the eating habits, the heterotrophs are classified as follows:
Herbivorous Animals: These are the animals that obtain their food only from
plants, e.g., cow, sheep, goat, deer, elephant, kangaroo, giraffe, etc
Carnivorous Animals: These are the animals that obtain their food by killing
other animals. They never eat plants or plant products, e.g, tiger, lizard, lion,
etc
Deer (Herbivorous) Lion (Carnivorous) Bear (Omnivorous)
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2. Nutrition in Animals
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Omnivorous Animals: Such animals consume plants as well as other animals
for nutrition, e.g., bear, dog, human beings, etc.
Parasites: Such organisms obtain their food from other animals either by
living inside or outside their body, e.g., tapeworm and roundworm (inside
body), tick and lice (outside body), etc.
Malarial parasite obtains its food from the human body by living inside the
body. Such parasites are known as endoparasites,
Leech sucks the blood of the human body or cattle, from outside the body.
Such parasites are known as ectoparasites.
Tapeworm (Parasite)
Scavengers: Scavengers are those animals who feed on the remains of dead
animals, e.g., vulture, crow, jackal, etc.
Vulture (Scavenger)
HETEROTROPHS
Herbivorous Carnivorous Omnivorous Parasites Scavengers
Roundworm
Jackal
Goat Eagle Hen
Endoparasites Ectoparasites
Malarial parasite Tick
ProcessofNutrition Ingestion
These are five steps in the process of
nutrition in animals: Ingestion, digestion,
absorption, assimilation and egestion.
Egestion PROCESS Digestion
OF
NUTRITION
Ingestion
Taking in of food inside the body is known Assimilation
as ingestion. Different organisms have
different ways of taking in food, eg, in case of
cats, tigers, rats or human beings the food is taken in through the mouth.
Bees and humming birds suck nectar of flowers. Snakes swallow their prey as
a whole. Some aquatic animals filter tiny food particles floating nearby and
feed upon them.
Absorption
Digestion
Digestion is the process by which the complex insoluble food is broken down
into simple soluble food substances. This way it can be easily absorbed by the
cells of an organism to carry out vital bodily functions. For example, if you eat
Process of ingestion
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3. SCience-VI
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chapati, rice, etc., it cannot be absorbed by the blood or the cells of c
Our bod
as such. These food substances have to be broken down into simnlarsy
by digestive juices for the body to assimilate them. All organisms, other
tha
parasites, must digest their food before it is absorbed and assimilated h
by trhe
body
Do You Know?
Starfish feeds on sea animals
covered by hard shells of calcium
carbonate
After opening the shell, it pops
Out its stomach through ts
mouth to eat the soft animal
Absorption
Absorption is the process in which the simple soluble digested food:
absorbed by the body fluids of living organisms. These are then
transported
to different parts of the body. In human beings, the absorption of simple forme
of food takes place in small intestine.
is
inside the shell. Then, stomach
goes back into the body andfood
IS easily digested
Assimilation
Assimilation is the process in which the soluble food substances absorbed by
the body fluids are carried to different parts of the body to be consumed for
energy, growth and repair. The absorbed substances transported to different
organs are used to build complex substances such as proteins and fats. The
food absorbed by the body is further acted upon by oxygen taken in
during
respiration. This process is known as oxidation of food which releases energy
for the various activities the organism perfor ms.
Egestion
Egestion is the process in which the undigested and unabsorbed food is
thrown out from the body.
Nutrition in Amoeba
Amoeba is a microscopic unicellular organism. It is usually found in water or
moist soil. It has no definite shape. It has a cell membrane, a rounded dense
nucleus and many small bubble like vacuoles in it
nutrition is as follows:
cytoplasm. Its process of
Ingestion: Amoeba engulfs its food by slowly wrapping finger-like projections
(called pseudopodia) around the food. The food becomes trapped in a food
vacuole.
Digestion: Digestive juices are released in the food vacuole. These juices
break down the food into simple soluble substances.
Absorption: The digested food in the food vacuole is absorbed into the
cytoplasm.
Assimilation: Theabsorbed food gets stored and then utilised for its growth,
energy and multiplication.
Pseudopodium
forming food
vacuole around
Prey Pseudopodia food item
Digestive juices secreted
in the food vacuole
leading to digestion
of the prey
Undigested
material
is voided
Contractile
vacuole
Process of nutrition in Amoeba
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4. Nutrition in Animals
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Egestion: The cell membrane of the Amoeba abruptly rips apart from any
place and the waste material (undigested food) is expelled out from its body.
SampleQuestions
Q. Explain the digestion process in Amoeba with the help of diagram.
Ans. Amoeba is unicellular organism, it captures food with the help of finger like
projections called pseudopodia that
helps amoeba to engulf the food. Food Vacuole Nucleus
now become trapped in food vacuole
and with the help of digestive juices,
complex food is converted into simple
substances. Gradually the digested
food is absorbed and undigested
food is expelled
Food
Pseudopodia
Food
particle
-Egested
waste
outside by the Digestion in Amoeba
vacuole.
MCHECK YOUR PROGRESS
1. Complete the following flow-chart of the process of nutrition in animals.
transport to
Ingestion of food
different body parts- egestion ofundigested food
2. Match the animals in Column I with their category in Column II.
Column I Column II
Vulture Herbivore
Bear Scavenger
Kangaroo Parasite
Tiger Omnivore
Leech Carnivore
Process ofNutritionin Human Beings
Much of the food we eat consists of particles that are too big to pass through
the cell membrane. Therefore, the food must first be broken down into small
molecules before it can diffuse into the bloodstream and carried to the cells of
the body. The process of breaking down complex food into smaller molecules
that can be easily absorbed is called digestion. This process takes place in
the digestive system of the body. The human digestive system consists of the
alimentary canal and its associated glands.
Digestive System in Human Beings
The food that is eatern passes from mouth to the anus through a long tube
called the alimentary canal. The alimentary canal is a muscular tube about
10m long. Its various parts are: mouth, oesophagus, stomach, small intestine,
large intestine, rectum and anus. The glands associated with the canal are
salivary glands, liver and pancreas.
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5. .. ******n
SCience-VII
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Oral cavity-
Tongue
Salivary gland-
Pharynx
Oesophagus
Liver Stomach
Gall bladder
Duodenum
Pancreas
Largeintestine Small intestine
Appendix Rectum
Anus
Human digestive system
The Mouth and Buccal Cavity
The mouth is an opening between the lips. It leads t the buccal or oral cayity
The oral cavity has a number of teeth and a muscular tongue. The food is
ingested through the mouth. Digestion begins insiIde our mouth when we
chew the food. While chewing the food, the teeth help to cut and grind it into
smaller pieces, and the tongue mixes it with saliva for digestion. This process
is called mastication. The mouth and buccal cavity contains teeth, tongue and
salivary glands.
Teeth
Teeth are hard structures covered with white substance
called enamel. Enamel is the hardest substance in the
body. The first set of teeth that grow during infancy and
fall off at the age of 6-8 years are called milk teeth. There
are 20 teeths in total 10-in each jaw. They are replaced
by a second set of teeth called permanent teeth that are
never replaced. There are 32 teeth-16 in each jaw. Each
tooth is rooted in a separate socket in the gums.
Molars
Premolars
Canines
There are four types of teeth inside the moutn.
They are: 4 incisors, 2 canines, 4 premolars and
6 molars in each jaw. Each type of teeth has separate
function. They also differ in size, shape and number.
Incisors are at the front and centre of the mouth. The
nave a sharp, straight cutting edge to cut and bite fO00
Canines are next to incisors. They are sharp and pointEd
Incisors
Arrangement of teeth in humans
They are used to stab, tear and pierce food.
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6. Nutrition in Animals
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Premolars and molars are found at the back and sides of the jaw. They are
used for chewing and grinding the food before it is swallowed.
ACTIVITY21
To study different types of teeth
Run your tongue over your teeth while reading thissentence
You will be able to identify allthefourtypesofteeth.
We have all the four types of teeth but no one type is bigger than the other.
Teeth type Incisors Canines Premolars Molars
Front of teeth
(4 in each
jaw)
(4 in each
jaw)
(2 in each
Number in Ist set
jaw) Total 20
(Milk Teeth) 8
8 4
4 8 12
Number in 2nd set
Total 32
(4 in each| (6 in each
jaw)
Stabbing&Chewing
(4 in each (2 in each
(Permanent Teeth)
jaw) jaw) jaw)
Function Cutting Mastication
Tearing
Toothache and Gum Disease
f you don't brush your teeth regularly, a yellow, sticky substance
called plaque is deposited ontheteethwhich initialy causes toothache.
Bacteria break down the sugars present in the food and release
acids, which gradually damage the teeth. This is called toothdecay
Over a long period of time the tooth may become loose and may
even fall out. Brushing teeth regulanly to remove bacteria from your
teeth can help prevent tooth decay and gum disease. Adental floss
is a special strong thread which is moved between two teeth to remove trapped food particles
Do You Know?
We produce about 1-7 litres of
saliva everyday.
Tongue
The tongue is a fleshy muscular organ attached at the back of the floor of
buccal cavity. It is free at the front and can be moved in all possible directions
and it helps us in speaking, moving food around our mouth while we chew
mixing the saliva with food, pushing and swallowing the food inside the food
pipe. It has taste buds which allow us to know the taste of the food we eat.
Our tongue can distinguish four types of tastes-salty, sweet, sour and bitter.
Bitter-
Sour Sour
Saliva Salty Salty
Saliva is the clear liquid secreted by salivary glands inside our mouth. It is
made up of water and other chemicals. Saliva helps to keep the mouth moist
and starts to break down food even before it reaches our stomach. It breaks
down the starch in the food to sugars.
Sweet
Taste buds on tongue
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7. SCience - VIl
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ACTIVTY22
To study the effect of saliva on starch
Take two test tubes and label them as A and B.
In test tube A, put one teaspoonful of boiled rice.
In test tube B, keep one teaspoonful ofboiled rice after chewing it for a +
minutes.
to 5
Add 3-5 ml water in both the test tubes.
Pour 2-3 drops of iodine solution in each test tube and observe.
You will observe that a blue-black (or violet) colour is produced in test tube n
whereas no blue-black (or violet) colour is produced in test tube B.
Hence, it is proved that while chewing, the saliva breaks down the Starch
present in boiled rice to form sugar. Since, no starch is left in the test tube R
so no blue-black (or violet) colour is produced after adding iodine solution.
lodine solution
water
A
Boiled nce
Boiled and chewed nce
B,
A B
Oesophagus (or Food Pipe)
Oesophagus is a tube which runs from the back of the throat down the chest
and opens into the stomach. When the food has been swallowed, it moves down
the oesophagus through the progressive wave of contraction and relaxation
of muscles in its wall to reach the stomach. Such a movement of muscles is
called peristalsis. The food moves in the entire alimentary canal by peristalsis,
Sometimes, the food is not accepted by our stomach and is vomited out. The
windpipe runs along the food pipe. It carries air from the nostrils to the lungs. If
by chance, food enters the windpipe, we feel choked or get hiccups. It lasts only
for a few minutes. The common remedy is drinking a glass of cold water.
Contracted
muscle
Direction of
food movement|
Relaxed
muscle
Food-
Oesophagus
(showing peristalsis movement) The Stomach
The stomach is a thick-walled muscular bag with the lining that contains
digestive glands. These glands produce three important secretions in the inner
lining of stomach:
Mucous: It protects the walls of the stomach from attack by acidic
stomach (gastric) juices.
Digestive juices (containing pepsin): They help in break down of the
proteins into simpler substances.
Hydrochloric acid: The acid kills many bacteria that enter along with the
food and provides the acidic conditions needed for the action of digestive
juices
The muscles of the stomach mix the food with digestive juices. The food, thus,
gets partly digested. It moves into small intestine for further digestion.
Do You Know?
The walls of the stomach contain
about 40 million gastric glands.
Do You Know?
During digestion, minerals and
vitamins do not need to be
changed. The cells are able to
absorb them as they are.
Do You Know?
The liver weighs 16 kg and is the
largest gland of our body. The Small Intestine
Digestion: The digestion offood completes in the small intestine. The small
intestine of an adult person is about 7.5 metres long. It receives secretions
from the liver and pancreas. Besides, its wall also secretes juices. The liver
is a reddish brown, largest gland in the body situated in the upper part of
abdomen on the right side. It secretes bile juice which is stored in the gall
bladder. Fats are more difficult to digest than proteins and carbohydrates.
This is because they are not soluble in water. Bile helps to break down fats
into tiny droplets that can be further digested.
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8. Nutrition in Animals
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Pancreas, a large cream coloured gland present just below the stomach,
secretes pancreatic juices and helps to digest carbohydrates, fats and
proteins into simpler forms. The partly digested food reaches the lower
part of small intestine where intestinal juice, secreted by small intestine,
completes the digestion of all the components of food. The carbohydrate
gets broken down into simple sugars, proteins into amino acids and fats
into fatty acids and glycerol.
Absorption and Assimilation: Digested food, together with some vitamins
and minerals is absorbed by the walls of the small intestine and then
transferred into the bloodstream. This process is called absorption. The
small intestine is the longest part of the alimentary canal. The inner surface
of small intestine contains a large number of finger-like projections called
villi (singular-villus). These tiny projections on its inner walls further increase
their surface area for absorption. Each villus has a network of thin and small
blood vessels close to its surface. The surface of villi absorbs the digested
food materials.
Pancreatic
duct
Bile duct-
Duodenum-
Pancreas
Uver
Stomach
The absorbed substances are transported to different organs of the body
by the blood where they are used to build complex substances like proteins,
required by the body and give energy. This process is called assimilation.
Glucose is broken down in the cell with the help of oxygen into carbondioxide
and water to provide energy.
Pancreas
Gall bladder
Small
intestine
The Large Intestine Water and
mineral salts
Undigested food along with digested food passes into the large intestine from
the small intestine. The length of large intestine is about 1.5 metres. Its chief
function is the absorption of water and salts from undigested food material. Here, intestine
most ofthe water and mineral salts are absorbed into the bloodstream. The large
intestine secretes no digestive juices. The material that remains now is more
semi-solid. This material is called faeces or stool. Faeces is stored temporarily in
the rectum and then passed out ofthe bodythrough the anus. The act of expelling
the faeces is called egestion or defecation.
areabsorbed
intot
Large blood stream
Faeces
Rectum
Anus-
Digestion pathway of food
Diarrhoea: The condition in which a person passes out watery stools frequently
is called diarrhoea. It is caused by an infection, food poisoning or indigestion.
This leads to the loss of useful salts from the body and can cause dehydration.
It can be prevented by giving ORS (Oral Rehydration Solution) to the patient
Suffering from diarrhoea.
Ruminants
Animals like cows, buffaloes, deer, sheep and bison eat grass, leaves
and hay. They chew their food and mix the saliva with their food and keep
swallowing quickly. They do this so that they can rest and hide themselves
trom carnivorous animals. Once the ruminant has finished eating, the food is
brought back up and rechewed. This is called chewing the cud or rumination
and these animals are known as ruminants, If the animal stops ruminating
this is a sign of ill health. The grass is rich in cellulose. The cellulose digesting
bacteria are not present in the body of human beings due to which human
beings cannot digest cellulose carbohydrate present in plant foods. Animals
like horses, rabbit, etc., digest the cellulose of the food by the action of bacteria
in a large sac like structure called 'caecum.
Do You Know?
In a cow, the process of
digestion takes 70-100 hours,
as compared to 2-24 hours in
humans.
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9. SCience- VII ... *********.
The stomach of a ruminant has four chambers. It is called a compounr
stomach.
Rumen: This is the first chamber and is very large. The food reaches
rumen after swallowing. Here, it gets partially digested and is called cud
Reticulum: This is the second chamber where the cud goes and is sent
back to the mouth to be chewed further.
Omasum: This is the third chamber where the rechewed food reaches after
swallowing again. Here the food is further digested by digestive juices.
Abomasum: This is the fourth chamber. The food is further digested here
After digestion, the food, goes to small and large intestines for absorption
of nutrients.
Rumen
Omasum Intestine
Reticulum Abomasum or
rennet bag
Digestive system in ruminant
Sampleuestions
Q.1. Ruminants such as cows and buffaloes swallow their food hurriedly and
then sit restfully and chew their food. Can you reason why?
[NCERT Exemplar]
Ans. This is done for complete digestion of the food. When the food is swallowed
by ruminants, it is only partially digested. It is then again chewed for its
completedigestion
Q.2. Why we cannot digest celluloselikethe cattle do?
Ans. Cattle is grass eating animal, that contains cellulose and human being
cannot have certain enzymes or bacteria to digest cellulose.
Q.3. A got her gall bladder removed surgically as she was diagnosed with
stones in her gall bladder. After the surgery, she faced problems in
digestion of certain food items when consumed in bulk. Can you tell
which kind of food items would they be and why? [NCERT Exemplar)
Ans. The food tems would be fat because bile juice of the gall bladder helps in
the digestion of fat. Removal of gall bladder leads to difficulty in digestion
of fatty substances.
MCHECK YOUR PROGRESS
1. Name the following:
(a) Teeth used to pierce food
(b) Protein digesting enzyme
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