Correct Answer: (b)
The definitive host is defined as the host in which the parasite undergoes sexual reproduction. For Plasmodium vivax, sexual reproduction occurs within the gut of the female Anopheles mosquito. Humans serve as the intermediate host where asexual reproduction (schizogony) occurs.
Q2. These are obligate intracellular parasites that lack mitochondria.
Correct Answer: (d) Microspora are unusual eukaryotes that lack mitochondria and microtubules; they are obligate intracellular parasites that were recently reclassified from protozoa to fungi. They cause various opportunistic infections in humans.
Q3. These are nonmotile parasites with special organelles for penetrating host tissue.
Correct Answer: (a) Apicomplexa are characterized by the presence of a complex of organelles at the tip (apex) of the cell, which contains enzymes used to penetrate host tissues. They are typically nonmotile in their mature forms and have complex life cycles.
Q4. Which of the following events follows cell fusion in an ascomycete?
Correct Answer: (d)
In the sexual cycle of an ascomycete, cell fusion (plasmogamy and karyogamy) results in a diploid nucleus within the ascus. This is followed by meiosis and mitosis to produce haploid ascospores. Thus, ascospore formation is the direct result of the sexual fusion process.
Q5. These photosynthetic organisms can cause paralytic shellfish poisoning.
Correct Answer: (c) Dinoflagellates are unicellular algae. Certain species, such as those in the genus Alexandrium, produce neurotoxins (saxitoxins). When mollusks eat these algae and are later consumed by humans, it results in paralytic shellfish poisoning (PSP).
Q6. If a snail is the first intermediate host of a parasite with these stages (metacercaria, redia, adult, miracidium, cercaria), which stage would be found in the snail?
Correct Answer: (b)
In the life cycle of a fluke, the snail is the first intermediate host. The miracidium (4) enters the snail and undergoes asexual reproduction to produce sporocysts and then rediae (2). Cercariae (5) are then produced within the rediae and subsequently leave the snail to find the next host. Therefore, the redia stage is found specifically developing within the snail.
Q7. How many phyla are represented in the following list of organisms: Echinococcus, Cyclospora, Aspergillus, Taenia, Toxoplasma, Trichinella?
Correct Answer: (d)
There are 4 phyla represented: 1. Platyhelminthes (flatworms): Echinococcus and Taenia. 2. Apicomplexa (protists, often categorized under the phylum Myzozoa or as a distinct group in older systems): Cyclospora and Toxoplasma. 3. Ascomycota (fungi): Aspergillus. 4. Nematoda (roundworms): Trichinella.
Q8. Use the following stages to answer the question: (1) metacercaria (2) redia (3) adult (4) miracidium (5) cercaria
Put the above stages in order of development, beginning with the egg.
Correct Answer: (b)
The typical life cycle of a trematode (fluke) starting from the egg is: Egg → Miracidium (4) which infects an intermediate host (snail) → Redia (2) or sporocyst produced within the snail → Cercaria (5) which leaves the snail → Metacercaria (1) which encysts on a second intermediate host or vegetation → Adult (3) in the definitive host. The correct sequence is 4, 2, 5, 1, 3.
Q9. Fleas are the intermediate host for Dipylidium caninum tapeworm, and dogs are the definitive host. Which stage of the parasite could be found in the flea?
Correct Answer: (a)
Fleas ingest the eggs of the tapeworm. Within the flea, the parasite develops into the larval stage known as a cysticercus (specifically a cysticercoid). The adult form, complete with a scolex and proglottids, develops only after a definitive host (dog or cat) ingests the infected flea.
Q10. Which of the following statements about yeasts are true? (1) Yeasts are fungi. (2) Yeasts can form pseudohyphae. (3) Yeasts reproduce asexually by budding. (4) Yeasts are facultatively anaerobic. (5) All yeasts are pathogenic. (6) All yeasts are dimorphic.
Correct Answer: (a)
Statements 1, 2, 3, and 4 are correct. Yeasts are unicellular fungi. Some species form pseudohyphae (chains of buds that do not separate). Budding is their primary asexual reproduction method, and many (like Saccharomyces) are facultative anaerobes used in fermentation. Statements 5 and 6 are false because the vast majority of yeasts are not pathogenic, and only a specific subset is dimorphic (changing between yeast and mold forms).
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