ADAPTATIONS FOR NUTRITION AND DIGESTION 'The human digestive system'                                                                             — illustration for About Science Book 3 by Science Press                                                                                ---- by David Dickson

DIGESTION AND ABSORPTION For a nutrient to be used by cells of an organism, it must pass through the cell membranes. This process is called absorption. The nutrient molecules in food are usually too large to pass through cell membranes. Thus, to be absorbed by the cells, most food molecules must be broken down into smaller, simpler forms. The process by which food molecules are broken down is called digestion.

DIGESTION AND ABSORPTION MECHANICAL DIGESTION Pieces of food are first cut,crushed or, broken into smaller particles without being changed chemically Mechanical break down increases the surface area of food and prepares the food for faster chemical digestion

DIGESTION AND ABSORPTION Examples for mechanical breakdown Cutting of food particles with teeth Emulsification Big oil small oil Droplets droplets bile

Sudan III has been used to stain oil Sudan III has been used to stain oil. The effect of emulsification is shown below :

Large oil drops are physically broken down into numerous smaller oil droplets.

Numerous oil droplets are formed as a result of emulsification.

Numerous oil droplets are physically formed as a result of emulsification.

DIGESTION AND ABSORPTION 2.CHEMICAL DIGESTION It is carried out by digestive enzymes which act only on the surface of the food particles. Chemical digestion takes place in stages - large molecules are broken down into smaller molecules - smaller molecules are broken down into digestive end products

DIGESTION AND ABSORPTION Examples for chemical digestion lipid fatty acids+ glycerol lipase

NUTRITION IN PROTISTS Intracellular digestion takes place in protists

NUTRITION IN HYDRA

NUTRITION IN HYDRA DIGESTION IN HYDRA IS BOTH INTRACELLULAR AND EXTRACELLULAR

NUTRITION IN PLANARIAN The pharynx can suck small bits of food into the digestive cavity. Most digestion takes place within food vacuoles in the cells lining the intestine.

Digested food diffuses to all cells of the body Digested food diffuses to all cells of the body. Indigestible materials are expelled through the pharynx and mouth.

NUTRITION IN EARTHWORM Food passes through it Food is pulled into the mouth by muscular pharynx Storage chamber, gradually releases food into the gizzard Chrushes the food and mechanical break down occur. By muscular movement , food and sand grains crush each other.

NUTRITION IN EARTHWORM Undigested materials and soil are removed through the anus Chemical digestion absorption take place

NUTRITION IN INSECTS It has teeth like plates made of chitin and food is ground in it Wastes stored temporarily and water is absorbed Food is stored temporarily The dried wastes are eliminated gizzard Food is broken down by mechanically Undigested material passes through intestine Chemical digestion and absorption occurs Secrete saliva and food is mixed with saliva in mouth for chemical break down

NUTRITION IN BIRDS http://www.biologycorner.com/resources/bird_anatomy.jpg

NUTRITION IN BIRDS Food is stored and softened. First part of stomach. Food is partially digested by gastric juice. Second part of stomach, thick-walled and muscular. May contaion small stones. Food is ground up and thoroughly mixed with gastric juice. Digestion is completed, and nutrients are absorbed into the blood stream. http://numbat.murdoch.edu.au/Anatomy/avian/fig4.1.GIF

The digestive systems of different mammals reflect their diet

DIGESTION IN RUMINANTS

DIGESTION IN RUMINANTS