Which one of the following groups of animals reproduces only by sexual means? (a) Cnidaria (b) Porifera (c) Protozoa (d) Ctenophora
Option D In ctenophores, asexual reproduction is absent. They are monoecious and fertilization is generally external. In cnidaria, asexual reproduction (budding) is found in the polyps and sexual reproduction is found in the medusa form. Both asexual and sexual reproduction occur in porifera (sponges). Asexual reproduction occurs by budding and gemmules. In protozoa, asexual reproduction takes place by binary fission, budding etc. and sexual reproduction takes place by syngamy and conjugation
