Chapter 2 – Nutrition in Animals

 Chapter 2 – Nutrition in Animals

 

1. Nutrition in Animals

• Nutrition in animals includes  ingestion, digestion,  absorption,  assimilation, and  egression.
• Most animals are heterotrophs, which means they depend on plants directly or indirectly for their food.

 

2. Process of Digestion

There are five main steps in the digestion of food in most animals, including humans:

• I.  Ingestion:  The process of taking food inside the body.
• ii. Digestion:  The process of breaking down complex foods into simpler substances.
• iii.  Absorption: The process of absorbing digested food into the blood.
• iv.  Assimilation:  The use of absorbed food by the body for energy, growth, and repair.
• V.  Egestion: The   process of expelling undigested food from the body.

 

3. Digestion in Humans

In humans,  digestion occurs in a long tube extending from  the mouth to the anus, which is called  alimentary canal.

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1. Buccal Cavity – Mouth and Mouth Cavity:

• • Ingestion: Food is inhaled by mouth.
  • Teeth: Chewing food and breaking it into small pieces.
  •  Tongue: Helps in mixing food with saliva and swallowing.
  •  Salivary glands:  secrete saliva which  contains an enzyme called  amylase that initiates the digestion of starch.

1. Oesophagus – Food Pipe:

• • The chewed food travels through the oesophagus to the stomach.
  • Contraction and expansion (peristalsis) of the walls of the esophagus pushes food down.

iii.  Stomach:

• • A thick-walled J-shaped pouch.
  • Churns food for about 3-4 hours.
  • Inner lining:  Secretes  mucus, hydrochloric acid and digestive juices.
    • Hydrochloric acid: Kills bacteria and makes food acidic so digestive juices can work.
    • Digestive juices: Initiate the digestion of proteins.

1. Small Intestine:

• • The longest part of the alimentary canal (about 7.5 m).
  • Complete digestion takes place here.
  • It  receives secretions from  the liver and pancreas.
  • Liver: The largest gland in the body. Bile secretes juice, which helps in the digestion of fats. Bile accumulates in the  gallbladder.
  • Pancreas: Secretes pancreatic juice  that acts on carbohydrates, fats, and proteins.
  • The walls of the small intestine also secrete digestive juices that convert carbohydrates into glucose, fats into fatty acids and glycerol, and proteins into amino acids.
  • Absorption: The inner walls of the small intestine contain thousands of finger-like bulges called villi follicles. These increase the surface area for the absorption of digested food. The absorbed nutrients reach different parts of the body through blood vessels.
  • Assimilation: The absorbed nutrients are used by the body for energy production and growth.

1. Large Intestine:

• • Smaller and wider than the small intestine (about 1.5 m).
  • The main function  is to absorb water and some salts from the downcycled food.
  • The remaining percolated waste material goes into the rectum  and accumulates as semi-solid faeces.

1. Anus :

• • The feces are expelled from the body by the anus. This process is  called  egression.

 

4. Digestion in Other Animals
5. Digestion in Grass-Eating Animals – Ruminants:

• • Grass-eating animals like cows and  buffaloes are called  ruminants.
  • They swallow grass quickly and store it in a part of their stomach called  rumen.
  • In rumen, food is partially digested which is  called  cud.
  • Later, the ruminant comes back into the mouth in small lumps, and the animal chews it again. This process is  called  ruminating.
  • Grass is rich in  cellulose, which cannot be digested by humans. Romanthians contain a special type of bacteria that helps digest cellulose.

1. Digestion in Amoeba:

•  Amoeba is a unicellular microorganism.
• It consists of a cell membrane, a round, dense nucleus, and many small vacuoles in the cytoplasm.
• When it detects food, it  spreads its temporary finger-like amprifications (Pseudopodia – false feet) around the food particle and swallows it.
• Food  gets trapped in a  food vacuole.
• The digestive juices are secreted in the food vacuole which act on the food and break it down into simpler substances.
• The digested food is slowly absorbed and used for energy, growth, and maintenance.
• The scavenging waste is excreted by the food vacuole itself.