The 15 one-mark questions from the March 2025 12th Standard Zoology public exam, in paper order, with the correct option marked and a short explanation.
Q1
A person is injured and got swelling. The swelling, due to the infection of tissue is an example of :
- A. Phagocytosis
- B. Mechanical barrier
- C. InflammationCorrect
- D. Physiological barrier
Explanation. Swelling, redness, heat and pain at the site of tissue injury or infection form the inflammatory response, a part of innate immunity.
Q2
The first codon to be deciphered was __________ which codes for __________.
- A. UUU, PhenylalanineCorrect
- B. AAA, Proline
- C. TTT, Arginine
- D. GGG, Alanine
Explanation. Nirenberg and Matthaei used poly-U synthetic RNA, which produced polyphenylalanine; so UUU, coding for phenylalanine, was the first codon deciphered.
Q3
Find out the wrongly matched pair.
- A. Klinefelter’s Syndrome - XXY FemaleCorrect
- B. Down’s Syndrome - Trisomy-21
- C. Turner’s Syndrome - XO Female
- D. Patau’s Syndrome - Trisomy-13
Explanation. Klinefelter’s syndrome (44A + XXY) occurs in males, not females; the other three pairs are correct.
Q4
The Neanderthal man had the brain capacity of :
- A. 900 cc
- B. 650-800 cc
- C. 1400 ccCorrect
- D. 1200 cc
Explanation. Neanderthal man had a brain capacity of about 1400 cc; 650-800 cc is Homo habilis and about 900 cc is Homo erectus.
Q5
Which one of the following groups includes sexually transmitted diseases caused by bacteria only ?
- A. Syphilis, gonorrhoea and trichomoniasis
- B. Syphilis, gonorrhoea and candidiasis
- C. Syphilis, trichomoniasis and pediculosis
- D. Syphilis, chlamydiasis and gonorrhoeaCorrect
Explanation. Syphilis (Treponema pallidum), chlamydiasis (Chlamydia trachomatis) and gonorrhoea (Neisseria gonorrhoeae) are all bacterial; trichomoniasis is protozoan, candidiasis fungal and pediculosis caused by lice.
Q6
ELISA is mainly used for :
- A. Selecting animals having desired traits
- B. Detection of mutations
- C. Selecting plants having desired traits
- D. Detection of pathogensCorrect
Explanation. ELISA (Enzyme Linked Immunosorbent Assay) detects antigens or antibodies, so it is mainly used to diagnose infections by detecting pathogens such as HIV.
Q7
The most important hormone in initiating and maintaining lactation after birth is :
- A. ProlactinCorrect
- B. Oestrogen
- C. Oxytocin
- D. FSH
Explanation. Prolactin from the anterior pituitary initiates and maintains milk secretion (lactation); oxytocin only causes milk ejection.
Q8
Assertion : The Environmental conditions of the Tropics are favourable for speciation and diversity of organisms.
Reason : The climate seasons, temperature, humidity and photo period are more or less stable and congenial.
- A. Assertion is true, but Reason is false.
- B. Both Assertion and Reason are true and Reason explains Assertion correctly.Correct
- C. Both Assertion and Reason are false.
- D. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Explanation. Tropical regions have stable, congenial seasons, temperature, humidity and photoperiod, which promote niche specialisation and speciation; so both statements are true and the reason explains the assertion.
Q9
The figure given below is a diagrammatic representation of response of organisms to abiotic factors. What do A, B and C represent respectively ?
- A. A - Partial Regulator, B - Regulator, C - Conformer
- B. A - Conformer, B - Regulator, C - Partial RegulatorCorrect
- C. A - Regulator, B - Conformer, C - Partial Regulator
- D. A - Regulator, B - Partial Regulator, C - Conformer
Explanation. In A the internal level rises with the external level (conformer); in B the internal level stays constant (regulator); C conforms up to a point and then regulates (partial regulator).
Q10
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 exchanged between two cells through conjugation, which is regarded as their sexual mode of reproduction.
Q11
The headquarters of the National Biodiversity Authority is situated in __________.
- A. Delhi
- B. Mumbai
- C. Kolkata
- D. ChennaiCorrect
Explanation. The National Biodiversity Authority, set up in 2003 under the Biological Diversity Act, 2002, has its headquarters in Chennai.
Q12
The clusters of gene with related functions are called as __________.
- A. Recons
- B. Mutons
- C. OperonsCorrect
- D. Cistrons
Explanation. An operon is a cluster of functionally related structural genes controlled together by a common promoter and operator, e.g. the lac operon.
Q13
Which of the following micro-organisms is used for production of citric acid in Industries ?
- A. Aspergillus nigerCorrect
- B. Lactobacillus bulgaricus
- C. Rhizopus nigricans
- D. Penicillium citrinum
Explanation. The fungus Aspergillus niger is used for the industrial production of citric acid.
Q14
The ‘thickness’ of Stratospheric Ozone layer is measured in :
- A. Melson units
- B. Sieverts units
- C. Beaufort scale
- D. Dobson unitsCorrect
Explanation. The thickness of the ozone layer is expressed in Dobson units (DU); 1 DU is a 0.01 mm thick layer of pure ozone at standard temperature and pressure.
Q15
Haemozoin is :
- A. A toxin from Plasmodium speciesCorrect
- B. A precursor of haemoglobin
- C. A toxin from Haemophilus species
- D. A toxin from Streptococcus
Explanation. When RBCs infected by Plasmodium rupture, the toxin haemozoin is released, causing the chill and high fever of malaria.
