The 15 one-mark questions from the March 2023 12th Standard Zoology public exam, in paper order, with the correct option marked and a short explanation.
Q1
Competition between species leads to :
- A. Amensalism
- B. ExtinctionCorrect
- C. Symbiosis
- D. Mutation
Explanation. Interspecific competition for the same limited resources can eliminate the weaker competitor, so it can lead to the extinction of a species.
Q2
________ is used to lower blood cholesterol level.
- A. StatinsCorrect
- B. Clot buster
- C. Tetracycline
- D. Cyclosporin A
Explanation. Statins, produced by the yeast Monascus purpureus, inhibit the enzyme that synthesises cholesterol and so lower blood cholesterol.
Q3
Which one of the following is true to gastrulation ?
- A. Formation of three germ layer embryo from single layer embryo.Correct
- B. Formation of multicellular structure from zygote.
- C. Attachment of blastocyst to the uterine wall.
- D. Formation of specific organs from Primary germ layers.
Explanation. Gastrulation converts the single-layered blastocyst (blastula) into a gastrula with three primary germ layers: ectoderm, mesoderm and endoderm. Attachment to the uterine wall is implantation and organ formation is organogenesis.
Q4
Which of the following Codon codes for methionine ?
- A. UUU
- B. AUGCorrect
- C. AUC
- D. UAA
Explanation. AUG is the initiation codon and codes for methionine. UUU codes for phenylalanine, AUC for isoleucine and UAA is a stop codon.
Q5
ZW-ZZ system of sex determination occurs in :
- A. Reptiles
- B. Birds
- C. Fishes
- D. All of the aboveCorrect
Explanation. In the ZW-ZZ system the female is heterogametic (ZW) and the male homogametic (ZZ). It is found in birds and also in some reptiles and fishes (and butterflies and moths), so all of the above.
Q6
The golden age of reptiles was :
- A. Paleozoic era
- B. Mesozoic eraCorrect
- C. Proterozoic era
- D. Cenozoic era
Explanation. Reptiles, including the dinosaurs, dominated the Earth during the Mesozoic era, which is therefore called the golden age of reptiles.
Q7
________ was the first human like being.
- A. Ramapithecus
- B. Homo erectus
- C. HominidsCorrect
- D. Australopithecus
Explanation. The textbook states that the first human-like being was the hominid (Homo habilis). Ramapithecus was a man-like primate (ape), while Australopithecus and Homo erectus are separate stages of the line.
Q8
Animals that can move from Fresh water to Sea water :
- A. CatadromousCorrect
- B. Stenothermal
- C. Anadromous
- D. Eurythermal
Explanation. Catadromous fishes (e.g. eels) migrate from fresh water to the sea to breed; anadromous fishes (e.g. salmon) move from sea to fresh water. Stenothermal and eurythermal refer to temperature tolerance.
Q9
The first ejaculation of the semen is ________.
- A. Orchidectomy
- B. Infertility
- C. SpermarcheCorrect
- D. Azoospermia
Explanation. Spermarche is the first ejaculation of semen at puberty. Orchidectomy is removal of testes and azoospermia is absence of sperm in semen.
Q10
Exo-erythrocytic schizogony of Plasmodium takes place in :
- A. Stomach
- B. RBC
- C. LiverCorrect
- D. Leucocytes
Explanation. Sporozoites injected by the mosquito first multiply asexually in the liver cells; this is exo-erythrocytic schizogony. Schizogony inside RBCs is the erythrocytic cycle.
Q11
The male sex hormone testosterone is secreted from :
- A. Epididymis
- B. Sertoli cells
- C. Prostate gland
- D. Leydig cellCorrect
Explanation. The interstitial Leydig cells of the testis secrete testosterone. Sertoli cells nourish developing sperms.
Q12
Dodo, Passenger pigeon and Steller's sea cow have become extinct due to ________.
- A. Habitat Loss
- B. Over exploitationCorrect
- C. Shifting cultivation
- D. Habitat fragmentation
Explanation. Dodo, passenger pigeon and Steller's sea cow were hunted excessively by humans; over exploitation drove them to extinction.
Q13
Allergy involves :
- A. IgA
- B. IgECorrect
- C. IgM
- D. IgG
Explanation. Allergens stimulate production of IgE antibodies, which bind to mast cells and cause release of histamine, producing allergic symptoms.
Q14
The highest DDT concentration in aquatic food chain shall occur in :
- A. Cell
- B. Seagull (Fish eating birds)Correct
- C. Phytoplankton
- D. Crab
Explanation. DDT is not degraded or excreted, so its concentration increases at each trophic level (biomagnification). Fish-eating birds such as seagulls, at the top of the aquatic food chain, have the highest concentration.
Q15
The mode of sexual reproduction in bacteria is by :
- A. ConjugationCorrect
- B. Formation of gametes
- C. Zoospore formation
- D. Endospore formation
Explanation. Bacteria do not form gametes; genetic material is transferred from donor to recipient cell through a conjugation tube, which is considered their mode of sexual reproduction.
