NUTRITION IN ANIMALS Chapter 2 Class VII (C.B.S.E.)

        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- 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.

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).

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).

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.

                                                      

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:    

Q.11 Match the items of Column I with those in Column II: