12th Standard Zoology March 2026: Online Practice Test

Explanation. In arrhenotoky, unfertilised eggs develop only into males (e.g. drones of honey bees). Thelytoky gives only females and amphitoky gives both sexes.

Explanation. Surgical removal of the testes (castration) is called orchidectomy, so Statement I is correct. Removing the testes affects sperm and testosterone production, not the passage of urine, so Statement II is not correct.

Explanation. Hormonal pills taken by women inhibit ovulation, change cervical mucus to hinder sperm and make the endometrium unsuitable for implantation. They do not act on spermatogenesis, which occurs in males.

Explanation. Twins are shown by two lines from one point; the horizontal bar joining the two individuals denotes identical (monozygotic) twins. Without the bar the symbol means dizygotic twins.

Explanation. Phages with 32P-labelled DNA passed radioactivity into the bacteria, while 35S-labelled protein coats stayed outside. So DNA, not protein, is the genetic material.

Explanation. The Human Genome Project found that the Y chromosome has the fewest genes (231), chromosome 1 the most (2968) and dystrophin is the largest gene (2.4 million bases). The human genome has about 3 billion bases, not 300.

Explanation. Wings of birds and butterflies have different origins and structure but perform the same function (flight). Such analogous organs are an example of convergent evolution.

Explanation. Small pox, polio, diphtheria and tetanus all have effective vaccines and have been controlled through immunisation and awareness. There are no routine vaccines for amoebiasis, AIDS or common cold.

Explanation. In allergy, IgE antibodies bind to mast cells and basophils; on re-exposure to the allergen they trigger release of histamine and other mediators.

Explanation. Molasses, the by-product of sugarcane factories, is rich in sugars and is the most common substrate fermented by yeast in distilleries to produce ethanol.

Explanation. Asexual reproduction involves a single parent and no fusion of gametes, so the offspring are genetically identical to the parent, i.e. clones. Hence the Reason correctly explains the Assertion.

Explanation. The sucker fish (Remora) attaches to the shark and gets transport and food scraps, while the shark is neither benefited nor harmed. This is commensalism.

Explanation. According to the textbook, Charles Elton (1927) was the first ecologist to use the term niche to describe the functional role of an organism in its community.

Explanation. Amphibians depend on both water and land, have moist permeable skin and limited dispersal, so habitat loss affects them most; they are the most threatened vertebrate group.

Explanation. Ozone is a powerful oxidant that kills pathogens, including chlorine-resistant ones, and breaks down to oxygen without leaving harmful residues, so ozonisation is the ideal disinfectant for waste water.