Ques. 1AIPMT 2000
Which of the following animals have scattered cells with cell-tissue grade organisation?
- Sponge
- Hydra
- Liver fluke
- Ascaris
Answer
(2) Hydra
Solution
As per NCERT, sponges show cellular level of organisation; coelenterates (cnidarians) show tissue level of organisation; Platyhelminthes and Aschelminthes show organ / organ-system level.
⇒ In Hydra (a cnidarian) many cells, such as interstitial and nerve cells, lie scattered among the two body layers, and only a few are organised into tissues — the cell-tissue grade.
∵ Liver fluke and Ascaris have organs and organ systems, while sponges have only loose cell aggregates.
∴ Hydra shows the cell-tissue grade of organisation.
Answer: (2)