Exercises
Distinguish between intracellular and extracellular digestion?
Intracellular digestion:
- Digestion occurs INSIDE the cell, within food vacuoles.
- Food particles are engulfed by the cell (phagocytosis) and digested by enzymes within the vacuole.
- Occurs in organisms at lower levels of organisation.
- Example: Sponges (Porifera) — digestion is entirely intracellular by choanocytes and amoebocytes.
Extracellular digestion:
- Digestion occurs OUTSIDE the cell, in a digestive cavity or gut lumen.
- Digestive enzymes are secreted into the cavity where food is broken down.
- Products are then absorbed by the surrounding cells.
- More efficient as it can handle larger food particles.
- Example: Most higher animals (Annelida, Arthropoda, Vertebrates, etc.).
Note: Some animals like Cnidarians and Ctenophores carry out BOTH intracellular and extracellular digestion.
Answer: Intracellular digestion: food is digested inside the cell within food vacuoles (e.g., Porifera). Extracellular digestion: food is digested outside the cell in a digestive cavity by secreted enzymes, then absorbed (e.g., most higher animals). Cnidarians and Ctenophores do both.