12th Standard Zoology March 2024: Online Practice Test

Explanation. Colostrum, the first milk secreted after childbirth, is rich in IgA antibodies, which give the newborn passive immunity.

Explanation. UV radiation kills microbes in treated waste water without adding any chemical or leaving residues, so it does not change the water quality, unlike chlorination or ozonisation.

Explanation. Each ovary is held to the pelvic wall and uterus by a ligament called the mesovarium. Myometrium is the muscular layer of the uterus, and ovarian stroma and tunica albuginea are parts of the ovary itself.

Explanation. B cells are activated when their receptors bind a specific antigen; they then form plasma cells that secrete antibodies. Antibodies are the product, not the activator.

Explanation. mRNA is synthesised from a DNA template by RNA polymerase in transcription. Replication copies DNA and translation uses mRNA to make protein.

Explanation. A normal foetal heart rate, monitored with a foetoscope, lies between 120 and 160 beats per minute.

Explanation. Wings of birds and butterflies do the same job (flight) but have different origins and structures; such analogous organs arise by convergent evolution.

Explanation. Modern man (Homo sapiens) appeared in the Quaternary period of the Cenozoic era; the other periods belong to the Palaeozoic and Mesozoic eras.

Explanation. Sugarcane molasses, a cheap sugar-rich by-product, is fermented by yeast (Saccharomyces cerevisiae) to produce ethanol in distilleries.

Explanation. GEAC is the Genetic Engineering Approval (now Appraisal) Committee of the Government of India, which decides on the use of genetically modified organisms.

Explanation. Leishmania donovani causes kala-azar, Wuchereria bancrofti causes filariasis, Trypanosoma gambiense causes sleeping sickness and Entamoeba histolytica causes amoebiasis: A-ii, B-iv, C-iii, D-i.

Explanation. r-species are small, short-lived organisms that produce many offspring with little parental care, such as insects. Rhinoceros, humans and whales are K-species.

Explanation. The ABO blood group is governed by one gene (I) with three alleles, I^A, I^B and i, so it is an example of multiple alleles.

Explanation. The International Union for Conservation of Nature (IUCN) maintains and publishes the Red List of threatened species.

Explanation. In sexual reproduction, crossing over during meiosis and fusion of gametes from two parents create new gene combinations, so offspring show variations. Asexual reproduction and parthenogenesis give offspring like the single parent.