Question

4. Define the terms monogenetic and digenetic. Of the three organisms discussed which are monogenetic and which are digenetic?

5. Gregarines are not often studied because they do not parasitize vertebrates, and seem to

cause not so serious damage to their invertebrate hosts. Gregarines are species-specific

parasites of a wide range of invertebrates from phyla Arthropoda (including crustaceans,

insects, myriapods), Annelida (including polychaetes, oligochaetes and leeches),

Nemertea, Mollusca, Echinodermata, and Urochordata.

The gregarines that you worked with infects the organism ________________________.

It is a __________________________ (vertebrate or invertebrate). This organism belongs

to the phylum _________________

Answer 1

4. Both monogenetic and digenetic terms are used for parasites. Parasite is an organism which depends on the other organism (host) for its survivial. This relationship called parasitism.

Monogenetic are those parasite which completes their life cycle in a single host organism. No intermediate asexual generation present in such mode of life cycle means these parasites have only one generation in their life cycle. parasites of fish, amphibians are monogenetic. Example-  Entamoeba histolytica a protozoan parasite in the large intestine of humans causes disease amoebiasis. it does not require any intermediate host so Its life cycle is monogenetic.

Digenetic are those parasite which completes their life cycle in two host organisms. Parasite larvae develops in one host and the adult develops in another host organism. these parasites exibited both sexual and asexual life forms. Example- Plasmodium, Taenia solium and  Fasciola hepatica

Plasmodium is a protozoan parasite having digenetic life cycle. it requires two hosts- human & mosquito.

Fasciola hepatica (liver fluke) also exibited digenetic life cycle in which female lays eggs in the liver of an infected human.and eggs are taken out through feces and the larvae develop outside the host.

Taenia solium (tapeworm)- requires two hosts- humans and cattle. Eggs are produced in humans and taken out with feces then ingested by cattle where they hatch.

5. The gregarines that you worked with infects the organism which are invertebrates. It is a Protozoan. This organism belongs to the phylum Apicomplexa.

Gregarine are the large protozoans belongs to sporozoan class Gregarinidea. Gregarines are parasites of invertebrates (not found in any vertebrates). They are single-celled parasites with monogenetic life cycle i,e they required only one host.

Protozoa are single-celled eukaryotes, and invertebrates as well as vertebrates are multicellular. So, Gregarine is a protozoa. phylum Apicomplexa contains the unicellular and spore-forming parasites having a type of plastid called an apicoplast which helps in penetration of a host cell.