Q5. What difficulties would you face in classifying animals if common fundamental features were not taken into account? (NCERT Exercise Q1)
With over a million described species, grouping by chance resemblances or by a few superficial features would separate related animals and lump unrelated ones together, and a newly described species could not be given a systematic position. NCERT bases classification on fundamental features shared by many animals: arrangement of cells, symmetry, coelom, and the patterns of the digestive, circulatory and reproductive systems (page 37).
Q6. Segmentation in the body is first observed in which of these: (a) Platyhelminthes, (b) Aschelminthes, (c) Annelida, (d) Arthropoda? (NCERT Exercise Q13)
(c) Annelida, which NCERT describes as metamerically segmented (page 43). Arthropods are also segmented (page 44), but in NCERT’s sequence of phyla annelids come first; Platyhelminthes and Aschelminthes are not described as segmented.
Q7. At which level of organisation are Platyhelminthes, and at which are annelids?
Platyhelminthes show the organ level, and annelids the organ system level (NCERT pages 37–38).
Q8. What is a notochord, and which animals lack it?
A mesodermally derived rod-like structure formed on the dorsal side during embryonic development; non-chordates, from Porifera to Echinodermata and Hemichordata, do not form it (NCERT pages 39 and 45).
Q9. Name the undifferentiated layer between the ectoderm and endoderm of diploblastic animals.
The mesoglea (NCERT page 38).
Q10. Assertion: Aschelminthes are pseudocoelomates. Reason: their body cavity lacks a complete mesodermal lining. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: the defining contrast is absence of a complete mesodermal lining around the pseudocoelom (NCERT page 39; clarification of its simplified wording).
Q11. Which animals show radial symmetry, and what does NCERT note about echinoderms?
Coelenterates, ctenophores and echinoderms (page 38); echinoderms show radial or bilateral symmetry depending on the stage (NCERT Figure 4.4 note, page 40).
Q12. Which has a complete digestive system: Platyhelminthes or Aschelminthes?
Aschelminthes (NCERT page 43); the typical flatworm gut has one opening (page 38), while tapeworms lack an alimentary canal altogether.