Human Health and Disease — Questions & Answers

Sample questions from Human Health and Disease

1. Q1. Although the human is where Plasmodium produces most of its clinical effects, the female Anopheles mosquito is regarded as the definitive host of the parasite. This classification is based on the fact that:

   • A.The mosquito lives longer than the parasite stages in the human body
   • B.Sporozoites are the only stage found in the mosquito
   • C.The parasite feeds on the mosquito's blood rather than on human blood
   • D.Fertilisation and the sexual phase of the life cycle occur in the mosquito✓
   Solution

   The host in which a parasite reproduces sexually is termed the definitive host. Gametocytes taken up by the mosquito fuse to form a zygote in its gut, so the sexual phase (fertilisation and development) occurs in the mosquito, making it the definitive host while humans serve as the intermediate host.

2. Q2. A tumour is found to have an activated cellular oncogene. Which statement about such genes is correct?

   • A.They are normal genes of the host cell, called proto-oncogenes, which under certain conditions become activated and cause oncogenic transformation✓
   • B.They are foreign genes introduced only by oncogenic viruses
   • C.They are genes that produce alpha-interferon and thereby kill the tumour
   • D.They are present only in benign tumours and disappear after metastasis
   Solution

   Several genes called cellular oncogenes or proto-oncogenes are present in normal cells; when activated under particular conditions they can lead to oncogenic transformation of the cell. Viral oncogenes, by contrast, are carried by cancer-causing viruses, so the two categories must not be confused.

3. Q3. Primary lymphoid organs, where lymphocytes are produced and/or mature before becoming immunocompetent, include:

   • A.Bone marrow and thymus✓
   • B.Spleen and lymph nodes only
   • C.Tonsils and appendix only
   • D.Skin and mucous membranes
   Solution

   Bone marrow and thymus are classified as primary lymphoid organs since this is where lymphocytes are produced and mature into antigen-sensitive but naive immunocompetent cells, distinct from secondary lymphoid organs (like spleen and lymph nodes) where mature lymphocytes encounter antigens.

4. Q4. Comparing amoebiasis and ascariasis, both diseases share which common epidemiological feature relevant to their prevention?

   • A.Both are transmitted through contaminated food/water and can be reduced through improved sanitation and hygiene✓
   • B.Both require an insect vector for transmission
   • C.Both are exclusively airborne diseases
   • D.Neither can be prevented by any hygiene measure
   Solution

   Both amoebiasis (Entamoeba histolytica) and ascariasis (Ascaris lumbricoides) are transmitted via ingestion of contaminated food or water (faecal-oral route), meaning improved sanitation, safe water supply, and personal hygiene are effective shared prevention strategies for both diseases.

5. Q5. Within the gut of the female Anopheles mosquito, Plasmodium gametocytes (taken up from an infected human's blood meal) undergo which type of reproduction?

   • A.Sexual reproduction, forming a zygote that develops into sporozoites✓
   • B.Only mitotic asexual division identical to the human liver stage
   • C.Binary fission with no fusion of gametes
   • D.No reproduction occurs within the mosquito
   Solution

   Inside the mosquito gut, male and female Plasmodium gametocytes fuse to form a zygote (sexual reproduction), which develops into an ookinete and eventually an oocyst, ultimately producing sporozoites that migrate to the mosquito's salivary glands for transmission to a new human host.

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