It is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into watery blood plasma.
Types of food:
- Diffusible food: includes water, minerals, amino acids, vitamins, etc. which are micro-biomolecules and need no digestion
- Non-diffusible food: includes proteins, fats, nucleic acids, etc. which are macro-biomolecules and need digestion.
Types of digestion:
| INTRACELLULAR DIGESTION | INTERCELLULAR DIGESTION |
| Digestion of food occurs within the cell | Digestion occurs outside the cell in the cavity of alimentary canal |
| Digestive enzymes are secreted by surrounding cytoplasm into the food vacuole | Digestive enzymes are secreted by special cells into the cavity of alimentary canal |
| Digestive products are diffused into cytoplasm | Digestive products diffuse across the intestinal wall into various parts of body |
| Less efficient method | More efficient method |
| Occurs in unicellular or lower form of organisms Pinocytosis: liquid enters Phagocytosis or Endocytosis: solid enters. | Occurs in multicellular or higher form of organism Ingressive zone: intake and mastication of food Progressive zone: conduction and early digestion Degressive zone: final digestion and absorption of food Egressive zone: temporary store the faeces. |
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