Digestion

     Organisms must break down their foodstuffs into their components for passing through the cell membrane. This process is called digestion. 

   There are two types of digestion.     These are;

nMechanical digestion

nChemical digestion

MECHANICAL DIGESTION

Pieces of food are firstly cut, crushed, or broken into smaller particles without being changed chemically. This process is called mechanical digestion.

 Mechanical breakdown increases the surface area of the food particles.                                                                                                                                  .                                                                                                                                       Protein                   

nChemical digestion is series of reactions in which foods are hydrolyzed, aided by water and enzymes. Food split into its monomers by means of chemical digestion.

TYPES OF DIGESTION              ACCORDING TO THE THEIR MEDIUM

nThere are two types digestion according to the their medium.These are

nEXTRACELLULAR DIGESTION

nINTRACELLULAR DIGESTION

INTRACELLULAR DIGESTION

nIn unicellular organisms foodstuffs are digested within food vacuoles in the cytoplasm. They are taken into cell by pinocytosis or phagositosis.

nWhen pass food into cell lysosomes fuse with food vacuole and digest foodstuffs. The amount of lysosome within the cell is directly effects to rate of digestion.

EXTRACELLULAR DIGESTION

In this process, digestion of food takes place within an area external to the organism by the secretion of digestive enzymes.

 Extracellular digestion is seen in protista, invertebrates and all vertebrates.

 DIGESTION IN                    UNICELLULAR ORGANISMS

nUnicellular organisms digest their foodstuffs by means of intracellular digestion.

 nEX   Paramecium and Amoeba

DIGESTION IN BREAD MOLDS AND SAPROPHYDIC BACTERIA
nSaprophyte bacteria and bread molds digest extracellularly. Their steps

nSecretion of digestive enzymes an extracellular medium

nEnzymes break down complex organic molecules into small parts.

nDigested molecules are taken by the cell through different methods of transport.

Digestion in insectivorus  plants

    Insectivorous plants obtain nitrogen from insects.

nSteps in digestion:

u The plant attracts insect

u The proteins of insect are digested by plant enzymes

u Amino acids are taken up and used

DIGESTION IN BIRDS

nBirds use beak to collect food. 

nThe esophagus in birds is enlarged and forms pharynx in which food is stored.

n Mechanical digestion takes place in gizzard.

n Chemical digestion occurs in the crop, where food and digestive enzymes are mixed together.

n The undigested particles are expelled from the body through the cloaca.

  DIGESTION IN MAMMALS

nMammals have different number of lobes in their stomach.

nHerbivores have four lobed stomach but carnivores has only one lobe.

nThe length of intestine in herbivore is longer than carnivores because digestion of plant is difficult.

DIGESTION IN HERBIVORE

nIn Cows the stomach includes following parts;

Rumen, Reticulum, Omasum and Abomasum.

nFood enters the rumen mix with saliva and ligthly chewed.

nCellulase enzyme is secreted in rumen by cellulosic bacteria. Food is digested by the action of cellulase.

nThe mixture is returned and rechewed in mouth again and turn back stomach.

nDigestion is considered to have been completed when the food passes from the third into the fourth region of the stomach and the abomasum sectates its enzymes onto the food.

nThe digested foodstuffs pass through the small intestine,