NUTRITION IN
ANIMALS Chapter 2 Class 7 (C.B.S.E.)
INTRODUCTION- Food is the basic need of living
organisms. Plants prepare this food by photosynthesis. Fungi absorb the food
from dead and decaying materials. Animals get their food directly from plants as
well as indirectly from animals. Some
varieties of Mushroom fungi are also eaten. The food items contain nutrients.
Those components of food which provide energy to do work help in growth and
development of body and keep us healthy are called nutrients. The mode of
taking in of the food inside the body and its utilization is called nutrition.
There are five steps in nutrition in animals-
1. Ingestion 2. Digestion 3. Absorption 4.Assimilation 5. Egestion |
1. Ingestion-
The mode of taking food through mouth is called ingestion. Different kind of
animals show different modes of nutrition e.g. –Swallowing in snakes, lizard,
frogs etc. chewing in cow, buffalo, goat etc. Brewing in houseflies, siphoning in
butterflies, catching in kingfisher, scraping in ants, sucking in Lice, bees
etc.
2. Digestion- The process of breaking
down of complex food materials by physical or chemical methods in our body is
called digestion. The teeth help in physical digestion by crushing food items.
The digestive juice containing enzymes help in chemical digestion in the
alimentary canal. The digestion starts from mouth. Complex carbohydrate
‘starch’ is partially digested by amylase enzyme into glucose, so on slowly
chewing of the bread it tastes sweet. Digestion also occurs in stomach.
Digestion completes in small intestine. Simple substances are formed from
complex food substances due to digestion.
3. Absorption- There are small finger
like structure in the small intestine. They absorb the simple soluble substance
formed after digestion into blood vessels. Via blood vessels these simple
soluble substances reaches upto the cells of different organs of the body. The
process of transporting simple soluble substances from small intestine into
cells of the body is called absorption.
4. Assimilation- The process of forming
complex substances from simple substances inside the cells is called
assimilation. e. g. Amino acids change into protein, glucose into complex
carbohydrate and fatty acid and glycerol change into fats.
5. Egestion-The process of removing of
undigested food material from the body is called egestion. In higher animals like Humans egestion occurs
through anus but in unicellular animals like Amoeba egestion occurs through vacuoles.
NUTRITION IN HUMAN BEINGS – The human
digestive system consists of an alimentary canal (about 21 feet long) and
associated digestive glands. Following are the main and associated organs in
human digestive system-
Fig. Human digestive System
1.
Buccal Cavity- The mouth is guarded by an upper
and a lower lip. The mouth opens in the buccal (or mouth) cavity. In the buccal
cavity a muscular tongue, teeth and salivary glands are found.
The tongue helps in ingestion, mastication and swallowing of food. Tongue
also helps in speaking. The taste of food can be known by numerous taste buds
present on it. There are different regions on the floor of tongue to know the
kind of taste like sweet, salty, bitter and sour.
Fig. Zones of different tastes
In the mouth of an adult person an adult person there are 32 teeth in two
sets. 16 teeth are found in upper jaw and another 16 are found in lower jaw.
There are four types of teeth- Incisors (8), Canines (4), Premolar (8) and
Molar (12).
TYPE OF TEETH
|
SHAPE
|
FUNCTION
|
No
|
INCISOR
|
Flat and Chisel shaped
|
Biting and cutting
|
8
|
CANINE
|
Sharp and Pointed
|
Piercing and tearing
|
4
|
PREMOLAR
|
Broad and flat
|
Chewing and grinding
|
8
|
MOLAR
|
Large, broad and flat
|
Chewing and grinding
|
12
|
TOTAL=32
|
There are two types of teeth in our entire life- Milk teeth and Permanent teeth. Milk teeth develop at the age of six months onwards and fall at
7-10 years. Then, permanents teeth develop at those places. Teeth are covered
by a white layer called ‘enamel’
which is the hardest substance of human body.
Salivary glands are found in
three pairs. Salivary glands secrete ‘saliva’
which breaks the starch (a complex carbohydrate) into glucose because of
presence of amylase enzyme in it. It
is starting of digestion process. Saliva also makes the chewed food slippery
and help in easy swallowing. The buccal cavity ends into pharynx.
2. Oesophagus or food Pipe- Pharynx opens into a
long muscular tube called oesophagus or food pipe. It is about 25 cm long in humans. The chewed
food passes into it. There is no digestive enzyme secreting glands in it. So,
no digestion occurs here. The muscles push the food by regular constriction and
relaxation called ‘peristalsis’ or
peristaltic movement.
3.
Stomach- Oesophagus leads to a large muscular
structure called stomach. It is flattened U shaped and widest part of alimentary
canal. The wall of stomach secretes mucus,
hydrochloric acid and digestive
(gastric) juices. The mucus layer protects the stomach wall from the action
of hydrochloric acid and digestive
enzymes. The hydrochloric acid kills
the germs, if any, present in the food and makes the medium acidic for enzymes
to work well. In stomach partial digestion of food occurs that forms a semi
liquid substance called chyme.
4.
Small Intestine- The stomach opens into small
intestine. It is highly coiled and about
7.5 m long in an adult person. The small intestine secretes intestinal juice. Intestinal juice
helps in digestion of carbohydrate, protein and fats. It also receives
secretions of liver and pancreas. The liver is largest gland
located just below the diaphragm. Liver secretes ‘bile juice’ which is temporarily stored in gall bladder. On eating of oil and fats, the bile juice is
released. The digestion of fat by lipase enzyme occurs only after emulsification by bile juice.
Pancreas is the second largest gland of human body. It secretes pancreatic
juice that helps in digestion of carbohydrate, protein and fats. The partially
digested food (chyme) undergo following reactions by intestinal juice, bile
juice and pancreatic juice to be digested into following simple substances.
a.
Carbohydrate -------Intestinal
Juice------------> Glucose
b.
Protein---------------Intestinal
juice------------->Amino Acids
c.
Fats-------------------Intestinal
Juice-------------> Fatty Acids + Glycerol
The digestion process completes in small
intestine. There are numerous very small fingers like structures in the small
intestine called villi (singular-Villus) which absorb the digested simple
substances and pass to blood vessels. Then, they reach into the cells of
different organs of body. Inside the cells glucose forms energy, amino acids
form useful protein and fatty acids and glycerol form lipids (fat).
Fig. Villi of small intestine
5.
Large Intestine- It is wider and shorter than
small intestine. The length of large intestine is about 1.5 m in humans. In
large intestine, extra water and some salts are absorbed from the undigested
food materials. The E. coli bacteria
are found in the large intestine. The waste materials pass to the rectum and
remain there as semi-solid faecal material (faeces).
6. Anus-
The semi-solid faecal material (faeces) is removed occasionally from the body
through anus. This process is called egestion.
DIGESTION
IN RUMINANT ANIMALS- The grass eating animals which have four
compartments of stomach like rumen, reticulum, abomasums and omasum, as four
parts of their stomach, chew the eaten food twice. Such animals quickly swallow
their grass and store in rumen. The partly digested food is called cud. Later,
the cud returns back to the mouth in small lumps and animals chew it
continuously with release of white leather in general. This process is called rumination and such
animals are called ruminant animals. e. g.- Cow, buffalo, camel, Goat, Sheep,
deer, Giraffe, elk etc.
Fig. Cow: A ruminant animal
The grass has a complex carbohydrate called cellulose. Humans, Dogs, Pigs,
horses, rabbits, rhinoceroses etc. can cant digest the grass because they have
a single stomach (monogastric). The ruminants have a large sac like structure
called caecum in between small intestine and large intestine. In caecum, the bacteria
help in digestion of cellulose.
DIGESTION IN AMOEBA - Amoeba is a
unicellular, eukaryotic organism of Protista Kingdom. Amoeba is a protozoan. It
is a microscopic organism which does not have mouth and anus. Their cytoplasm
surrounded by cell membrane contains a nucleus and many vacuoles. The shape and
position of amoeba change continuously. It forms a finger like outgrowth called
pseudopodia or false foot. Pseudopodium (singular) helps in capturing food and
movement.
Fig. Amoeba
When amoeba
sense the food like plant cells, algae, bacteria etc. they capture the food by
pseudopodia and engulf the food. The food is stored in ‘food vacuole’ in which
digestion occurs by digestive juices. The simpler substances formed by
digestion are absorbed in the cytoplasm for growth, maintenance and
reproduction. The waste material and extra water are released from the body by
excretory vacuole and water vacuole respectively.
CO-CURRICULAR
PROJECTS-
1. Mode
of feeding in the starfish.
2. Human
teeth – structure and functions.
3. Vestigial
organs in humans.
4. Modes
of nutrition in amoeba.
1. Draw a well
labeled diagram of Human digestive system
2. Write the
types of teeth in a mature person and function of each type.
3. Why ruminant
animals can digest the grass?
4. Where
digestion occurs in amoeba? Write one similarity and one difference of amoeba
with humans.
Q.1 Fill in the blanks:
(a) The main
steps of digestion in humans are …………….., ……………., ……………, …….., and ……………..
(b) The largest
gland in the human body is ………………..
(c) The stomach
releases hydrochloric acid and ………………juices which act on food.
(d) The inner
wall of the small intestine has many finger-like outgrowths called ………………..
(e) Amoeba
digests its food in the …………………..
Answer- (a) ingestion, digestion, absorption,
assimilation, egestion
(b) liver (c) digestive( or gastric) (d) villi (e) food vacuole
Q.2 Mark ‘T’ if the statement is true
and ‘F’ if it is false:
(a) Digestion of starch starts in the
stomach.
(b) The tongue helps in mixing food with
saliva.
(c) The gall bladder temporarily stores bile.
(d) The ruminants bring back swallowed grass
into their mouth and chew it
for some time.
Answer- (a) False (b) True (c) True (d) True
Q.3 Tick (√) mark the correct answer in
each of the following:
(a) Fat is
completely digested in the
(i) stomach (ii) mouth
(iii) small intestine (iv) large intestine
(b) Water from
the undigested food is absorbed in the
(i) stomach (ii) foodpipe (iii) small intestine (iv) large intestine
Q.4 Match the items of Column I with those
in Column II:
Column
I Column II
Food Components Product(s) of digestion
(a) Carbohydrate (i) Fatty acids and
glycerol
(b) Proteins (ii) Sugar
(c) Fats (iii) Amino
acids
Ans- (a)- ii (b)- iii (c)- i
Q.5 What are villi? What is their
location and function?
Ans-
The small finger-like projections present on the inner wall of small intestine
are called villi. The villi absorb the products of digestion like glucose,
amino acids, fatty acids and glycerol and transfer them into the blood
capillaries. The absorbed products of digestion are transported by arteries to
different organs of the body.
Q.6 Where is the bile produced? Which
component of the food does it digests?
Ans-
Bile or bile juice is produced by the cells of the liver. Bile helps in
digestion of fats in the small intestine.
Q.7 Name the
type of carbohydrate that can be digested by ruminants but not by humans. Give
the reason also.
Ans- Cellulose is a complex carbohydrate found
in plants. Ruminant animals can digest it but not the humans because in the
caecum of ruminants’ cellulose digesting bacteria are found. Humans do have any
such bacteria.
Q.8 Why do we
get instant energy from glucose?
Ans- Glucose is a simple carbohydrate. It does
not undergo digestion and easily absorbed by villi in small intestine. After
transportation glucose reaches to cells where it breaks down into carbon
dioxide, water and energy (A.T.Ps).
Q.9 Which part of the digestive canal
is involved in:
(i)
absorption of food ……………………………….
(ii)
chewing of food ………………………………….
(iii)
killing of bacteria ………………………………
(iv)
complete digestion of food ………………..
(v)
formation of faeces …………………………….
Ans-
(i) small intestine (ii) buccal
cavity (iii) stomach (iv) small intestine (v) large intestine
Q.10 Write one
similarity and one difference between the nutrition in amoeba and human beings.
Ans- Similarity- Amoeba engulfs the food as
like humans /Food is digested by digestive enzymes as like in humans
/absorption of digested food and excretion occurs as like humans.
Difference- All the vital activities are completed within the
cell of amoeba whereas different vital activities are completed in different
parts of the human body.
Q.11 Match the items of Column I with those
in Column II:
Column
I Column II
(a)
Salivary gland (i) Bile juice secretion
(b)
Stomach (ii) Storage of
undigested food
(c)
Liver (iii) Saliva
secretion
(d)
Rectum (iv) Acid release
(e)
Small intestine (v)digestion is completed
(f)
Large intestine (vi) Absorption of water
(vii) Release of faeces
Ans-
(a) –iii (b)-iv (c)-I (d)- ii (e)- v
(f)- vi
Q.12 Label the figure of the digestive system.
Ans-
Q.13 Can we survive only on raw, leafy
vegetables/grass? Discuss.
Ans-
We cannot survive only on the raw, leafy vegetables/grass. Humans do not have
enzymes and bacteria to digest grass. Humans require all the nutrients like carbohydrates,
proteins, lipids (fats), vitamins and minerals which vegetables alone cannot
provide.
Good one...
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