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Sponges represent one of the simplest animal body plans. Their bodies lack true tissues and organs. Which feature of sponge cells supports its classification under the animal kingdom? (i) Absence of mitochondria (ii) Ability to photosynthesise (iii) Presence of a cell membrane (iv) Presence of a cell wall
The Kingdom Animalia is characterised by eukaryotic cells that have a cell membrane but no cell wall, are heterotrophic, and contain mitochondria.
Evaluate each option:
(i) Absence of mitochondria — Incorrect. All eukaryotes, including sponges and other animals, have mitochondria. Absence of mitochondria would disqualify a cell from being eukaryotic.
(ii) Ability to photosynthesise — Incorrect. Animals are heterotrophic and cannot photosynthesise. This ability would classify the organism in Kingdom Plantae or Protista, not Animalia.
(iii) Presence of a cell membrane — Correct. All animal cells are bounded by a cell membrane and notably lack a cell wall. The absence of a cell wall combined with the presence of a cell membrane is a key feature that places organisms in Animalia, distinguishing them from plants and fungi (which have cell walls).
(iv) Presence of a cell wall — Incorrect. Animal cells do not have a cell wall. If sponge cells had a cell wall, they would be excluded from the animal kingdom.
The correct option is (iii): Presence of a cell membrane.
Answer: (iii) Presence of a cell membrane. Animal cells possess a cell membrane but no cell wall. The absence of a cell wall is a fundamental criterion that places sponges (and all animals) in Kingdom Animalia, distinguishing them from plants, fungi, and most prokaryotes.