9i6 



TEST QUESTIONS FOR STUDENTS 



animals they are specialised white blood corpuscles (leucocytes), but 

 !hey are often active outside the blood, and they occur in animals that 

 have no blood.] 



10. What is meant by commensalism ? Give an example. [A 

 mutually beneficial external partnership between two organisms of 

 different kinds, e.g. hermit-crab and partner sea-anemones.] 



11. What is meant by corals? Distinguish different kinds. [A 

 general name for Coelentera with calcareous skeletons, (a) Hydroid 

 corals— millepores and stylasters ; (&) Madrepore corals— reef-building 

 and solitary, related to sea-anemones ; (c) Alcyonarian corals, such as 

 organ-pipe coral and precious coral ; {d) the divergent blue-coral, 

 Heliopora, also Alcyonarian. Black corals, Antipatharia, are related 

 to sea-anemones, but not calcareous.] 



12. Why should a cell divide at its limit of growth ? [A physiological 

 instabihty sets in, to some extent probably connected with the fact 

 that increase of surface does not keep pace with increase of volume— 

 in spheres, the former increases as the square of the radius, the latter as 

 the cube ; and with the fact that a normal ratio between nucleoplasm 

 and cytoplasm has to be sustained.] 



13. Distinguish the two modes of digestion observed in Hydra. 

 [Intra-cellular, as in Protozoa, sponges, some other Coelentera, and 

 some simple worms. Also extra-cellular as in some other Coelentera 

 and all higher forms.] 



14. What is meant by alternation of generations ? Give three quite 

 different examples. [The alternate occurrence in one hfe-history of 

 two (or more) different forms differently produced. The fixed asexual 

 hydroid colony, developing from a fertilised ovum, buds off a sexual 

 medusoid. The fertilised ovum of the jellyfish Aurelia develops into 

 a hydra-tuba which forms a strobila liberating Ephyrae which grow into 

 sexual medusae. Other examples : — Liver-fluke, salps.] 



15. Give three good reasons why a hydroid colony or zoophyte 

 cannot be regarded as a plant. 



16. Compare in parallel columns the three classes of parasitic worms 

 represented in man, and give two examples of each class, stating in 

 what part of man's body they occur. 



17. Name two entirely different kinds of animal parasites sometimes 

 found in the blood of man, and explain how they find entrance into the 

 blood. 



18. Explain why the egg of a liver-fluke gives rise to a miracidium, 

 whereas the egg of a tapeworm gives rise usually to a hexacanth or 

 oncosphere. 



19. In what respects are tapeworms suited to their mode of life? 

 [A large surface for absorption ; suckers and sometimes hooks and 

 a proboscis fixing the animal to the wall of its host's intestine ; very 

 prolific reproduction, the chances against successful development being 

 great ; an anti-body is said to counteract the digestive juices of the 

 host ; and so on.] 



20. Give a reason why Tcenia echinococcus has a bladderworm stage 

 with very numerous heads or scolices, while an ordinary tapeworm, like 

 TcBuia sagifiata, has a bladderworm with only one head. 



21. A common parasite of man, Ascaris lumhricoides, has a general 



