12th Standard Zoology May 2022: Online Practice Test

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.

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.

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.

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.

Explanation. The Human Genome Project showed that the human genome contains about 3.1 billion (3164.7 million) nucleotide bases.

Explanation. Oral pills contain synthetic progesterone and estrogen, which inhibit the secretion of FSH and LH from the pituitary, so ovulation does not occur.

Explanation. Eurytherms tolerate a wide range of temperature, whereas stenotherms can tolerate only a narrow range.

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.

Explanation. Molasses, the cheap sugar-rich by-product of sugarcane mills, is fermented by Saccharomyces cerevisiae to produce ethanol in distilleries.

Explanation. LH acts on the Leydig (interstitial) cells, which secrete testosterone, and testosterone stimulates spermatogenesis.

Explanation. Hardy-Weinberg equilibrium requires random mating, a large population, and no migration, mutation or selection; selective (non-random) mating disturbs it.

Explanation. The ABO blood group is controlled by gene I, which has three alleles (I^A, I^B, i), an example of multiple alleles.

Explanation. When RBCs infected by Plasmodium rupture, the toxin haemozoin is released, causing the chill and high fever of malaria.

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.

Explanation. In secondary (biological) treatment, aerobic microbes digest the organic matter in sewage, which significantly reduces its BOD.