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

2. 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.

3. 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

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

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

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

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

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

9. 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

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

11. NUTRITION IN PROTISTS
Intracellular digestion takes place in protists

14. NUTRITION IN HYDRA

15. NUTRITION IN HYDRA
DIGESTION IN HYDRA IS BOTH INTRACELLULAR AND EXTRACELLULAR

16. 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.

17. 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.

18. 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.

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

20. 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

21. NUTRITION IN BIRDS

22. 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.

24. The digestive systems of different mammals reflect their diet

25. DIGESTION IN RUMINANTS

26. DIGESTION IN RUMINANTS