Biology · Animal Kingdom · NEET
In sponges it is ONLY intracellular. Sponges have no mouth, no gut and no cavity for digestion. Water carrying food enters through tiny pores (ostia) into the central cavity called spongocoel. The choanocytes (collar cells) that line the spongocoel trap the food and take it inside their own cells. Digestion then happens inside these cells in food vacuoles. NCERT states clearly: 'Digestion is intracellular' in Porifera. This is a very common NEET one-liner, so remember Porifera = intracellular only.
Two phyla in the Animal Kingdom chapter show both: Coelenterata (Cnidaria, like Hydra and jellyfish) and Ctenophora (comb jellies). In these animals, food is first partly broken down OUTSIDE the cells in a central gastro-vascular cavity (extracellular part), and then the small pieces are taken into the lining cells and finished off INSIDE the cells (intracellular part). NCERT says for both Coelenterata and Ctenophora: 'Digestion is extracellular and intracellular.' This 'both' point is a favourite NEET trap.
Hydra is a coelenterate (Cnidaria), so it shows BOTH. Hydra has a gastro-vascular cavity with only one opening (the mouth on the hypostome). Food is caught by tentacles, pushed into this cavity, and enzymes start breaking it down there (extracellular). The gastrodermis cells then engulf the food particles and finish digestion inside food vacuoles (intracellular). So the correct answer for Hydra is 'both', not 'only intracellular'.
In higher animals like humans, frogs, birds and echinoderms, digestion is mainly EXTRACELLULAR. Food is broken down in a complete gut (mouth to anus) by digestive enzymes, and only the small soluble molecules are absorbed into the cells. This is more efficient because the animal can eat large food and digest it in a tube. NCERT describes a complete digestive system with two openings (mouth and anus) in echinoderms and vertebrates, where digestion is extracellular.
Simpler animals with a cellular level of organisation (sponges) can only do intracellular digestion because they have no digestive cavity. Animals with a tissue level and a gastro-vascular cavity (Coelenterata, Ctenophora) can do both. Animals with an organ-system level and a real gut (from higher worms up to mammals) do extracellular digestion. So as body organisation becomes higher, digestion shifts from intracellular to extracellular. This trend helps you answer many match-the-column questions.
Select the correct statements: A. Platyhelminthes are triploblastic pseudocoelomate and bilaterally symmetrical organisms. B. Ctenophores reproduce only sexually and fertilization is external. C. In tapeworm, fertilization is internal but sexes are not separate. D. Ctenophores are exclusively marine, diploblastic and bioluminescent organisms. E. In sponges, fertilization is external and development is direct.
Select the incorrect statements from the following: A. Digestive system in Platyhelminthes is incomplete. B. Bilateral symmetry is a characteristic feature of adult Echinoderms. C. Pseudocoelom is possessed by Aschelminthes. D. Notochord is persistent throughout life in the class Chondrichthyes. E. Members of class Reptilia maintain a constant body temperature.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Intracellular digestion happens inside the cell in food vacuoles. Extracellular digestion happens outside the cells, in a cavity or gut, and only the digested pieces are absorbed. Think INside the cell vs EXternal to the cell.
Porifera (sponges) show only intracellular digestion. Coelenterata and Ctenophora show intracellular digestion together with extracellular digestion.
Extracellular digestion lets an animal eat large food and break it down in a gut using enzymes, then absorb small molecules. This is more efficient than the cell-by-cell intracellular method, so higher animals use it.
They are related. Inside the cell, food vacuoles fuse with lysosomes whose hydrolytic enzymes digest the food. So intracellular digestion in animals like sponges uses this lysosome-based breakdown inside the cell.
Usually yes. A complete digestive system has two openings, mouth and anus, and digestion in it is extracellular. NCERT notes echinoderms and vertebrates have a complete gut with extracellular digestion.
