The 15 one-mark questions from the May 2022 12th Standard Zoology public exam, in paper order, with the correct option marked and a short explanation.
Q1
Radioactive wastes can be disposed off by ________.
- A. composting
- B. burning
- C. surface impoundments
- D. a deep geological repositoryCorrect
Explanation. Radioactive wastes remain hazardous for thousands of years, so they are sealed and stored in deep geological repositories far below the earth's surface.
Q2
In which mode of reproduction are variations seen?
- A. Asexual
- B. Parthenogenesis
- C. SexualCorrect
- D. Both (a) and (b)
Explanation. Sexual reproduction involves meiosis (crossing over) and fusion of gametes from two parents, producing offspring with variations; asexual reproduction and parthenogenesis give genetically similar offspring.
Q3
Which one of the following are at high risk of extinction due to habitat destruction?
- A. AmphibiansCorrect
- B. Mammals
- C. Echinoderms
- D. Birds
Explanation. Amphibians depend on both aquatic and terrestrial habitats and have moist, permeable skin, so habitat loss and degradation put them at the highest risk of extinction.
Q4
When a Drosophila body cells contain 3 sets of autosomes and 2 X chromosomes, what will be the sex of the fly?
- A. metamale
- B. male
- C. intersexCorrect
- D. female
Explanation. By the genic balance theory, sex index X/A = 2/3 = 0.67, which lies between 0.5 (male) and 1.0 (female), so the fly is an intersex.
Q5
The total number of nitrogenous bases in human genome is estimated to be about ________.
- A. 35 million
- B. 3.5 million
- C. 3.1 billionCorrect
- D. 35,000
Explanation. The Human Genome Project showed that the human genome contains about 3.1 billion (3164.7 million) nucleotide bases.
Q6
A contraceptive pill prevents ovulation by:
- A. stimulating release of FSH and LH
- B. blocking fallopian tube
- C. causing immediate degeneration of released ovum
- D. inhibiting release of FSH and LHCorrect
Explanation. Oral pills contain synthetic progesterone and estrogen, which inhibit the secretion of FSH and LH from the pituitary, so ovulation does not occur.
Q7
Organisms which can survive a wide range of temperature are called ________.
- A. Endotherms
- B. Ectotherms
- C. Stenotherms
- D. EurythermsCorrect
Explanation. Eurytherms tolerate a wide range of temperature, whereas stenotherms can tolerate only a narrow range.
Q8
B-lymphocytes are activated by:
- A. Interferon
- B. Antibiotics
- C. AntigenCorrect
- D. Antibody
Explanation. When a specific antigen binds to receptors on a B-lymphocyte, the cell is activated and multiplies into plasma cells that secrete antibodies; the antibody is the product, not the activator.
Q9
The most common substrate used in distilleries for the production of ethanol is:
- A. MolassesCorrect
- B. Soyameal
- C. Corn meal
- D. Groundgram
Explanation. Molasses, the cheap sugar-rich by-product of sugarcane mills, is fermented by Saccharomyces cerevisiae to produce ethanol in distilleries.
Q10
Which is the correct order of action?
- A. FSH → LH → Inhibin → Spermatogenesis
- B. LH → Leydig cells → Testosterone → SpermatogenesisCorrect
- C. TSH → FSH → Sertoli cells → Spermatogenesis
- D. LTH → Sertoli cells → Androgen → Spermatogenesis
Explanation. LH acts on the Leydig (interstitial) cells, which secrete testosterone, and testosterone stimulates spermatogenesis.
Q11
A population will not exist in Hardy Weinberg equilibrium, if:
- A. There is no migration
- B. Individuals mate selectivelyCorrect
- C. The population is large
- D. There are no mutations
Explanation. Hardy-Weinberg equilibrium requires random mating, a large population, and no migration, mutation or selection; selective (non-random) mating disturbs it.
Q12
ABO blood group in man is controlled by:
- A. Sex-linked genes
- B. Multiple allelesCorrect
- C. Y-linked genes
- D. Lethal genes
Explanation. The ABO blood group is controlled by gene I, which has three alleles (IA, IB, i), an example of multiple alleles.
Q13
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.
Q14
Which one of the following is a suitable adaptation to overcome food and water scarcity?
- A. A short reproductive period
- B. Winter sleep
- C. Migration
- D. Summer sleepCorrect
Explanation. Aestivation (summer sleep) is a dormant state with lowered metabolism that lets animals such as lungfishes and snails survive hot, dry periods when food and water are scarce.
Q15
The purpose of biological treatment of waste water is to ________.
- A. Reduce sedimentation
- B. Reduce BODCorrect
- C. Increase sedimentation
- D. Increase BOD
Explanation. In secondary (biological) treatment, aerobic microbes digest the organic matter in sewage, which significantly reduces its BOD.
