Q5. Distinguish between intracellular and extracellular digestion. (NCERT Exercise Q4)
In intracellular digestion food is digested inside cells, as in sponges, where digestion is intracellular (NCERT page 40). In extracellular digestion food is digested outside the cells, in a cavity such as the gastro-vascular cavity of cnidarians, which show both kinds (page 41); ctenophores also show both (page 42). The alimentary canal of animals with a complete digestive system, from roundworms (page 43) to chordates, is also a site of extracellular digestion. Beyond the NCERT text: in extracellular digestion, enzymes are secreted into the cavity and the digested products are then absorbed.
Q6. What is the difference between direct and indirect development? (NCERT Exercise Q5)
In direct development the young ones resemble the adult (NCERT page 43), as in bony fishes, reptiles, birds and mammals (pages 48–51). In indirect development there is a larval stage that is morphologically distinct from the adult, as in sponges (page 40), echinoderms (page 45) and amphibians (page 48).
Q7. What reasons can you think of for the arthropods being the largest group of the animal kingdom? (NCERT Exercise Q7)
NCERT asks for your reasoning. Features it gives that help: a chitinous exoskeleton, jointed appendages, several kinds of respiratory organs (gills, book gills, book lungs, tracheae) and sense organs such as compound eyes and statocysts (page 44). Beyond the NCERT text: these let arthropods live on land and in water, and insects fly, and their usually small size and many young let them fill a great many habitats.
Q8. Could the number of eggs or young produced by an oviparous and a viviparous mother be equal? Why? (NCERT Exercise Q12)
Yes, their numbers could be equal: egg-laying versus live birth does not uniquely determine clutch or litter size. A tendency towards more offspring where individual survival is lower can help explain differences, but offspring size, parental care and ecology also matter. Egg-laying animals do not invariably produce more young, and live-bearing animals do not invariably produce fewer.
Q9. List some animals that are parasitic on human beings. (NCERT Exercise Q15)
From NCERT: the tapeworm Taenia (page 42); the roundworm Ascaris, the filaria worm Wuchereria and the hookworm Ancylostoma (page 43). Entamoeba, Trypanosoma and Plasmodium (NCERT Chapter 2, page 16) are human parasites too, but they are protists, not animals.
Q10. In amphibians, into which chamber do the alimentary canal, urinary and reproductive tracts open?
The cloaca, which opens to the exterior (NCERT page 48). Beyond the NCERT text: reptiles, birds and cartilaginous fishes also have one.
Q11. Name a living fossil, a gregarious pest and three mosquito vectors from NCERT’s arthropod examples.
Limulus (king crab); Locusta (locust); Anopheles, Culex and Aedes (NCERT page 44).
Q12. In which annelid are the sexes separate, and which annelids are monoecious?
Nereis is dioecious; earthworms and leeches are monoecious (NCERT page 43).