Samacheer Kalvi 12th Zoology Book Back Answers: All 13 Chapters
Class 12 Zoology covers reproduction, genetics, evolution, health, biotechnology and ecology in thirteen chapters. Its book back MCQs are more varied than in most subjects: alongside straight recall there are assertion-reason questions, match-the-following sets and genetics problems that need a quick cross. This page collects the answers for every chapter, each with an explanation.
All 13 chapters of 12th Zoology
Each chapter also has additional MCQs and a timed practice test on the 12th Zoology chapter list.
Where the book back questions concentrate
The number of book back MCQs varies a lot between chapters, which is a useful guide to where detail matters:
- Principles of Inheritance and Variation has the largest set. It covers blood groups, sex-linked inheritance, sex determination, chromosomal disorders and eugenics, and several questions are small genetics problems.
- Human Reproduction tests exact structures and hormones: where sperm are stored, which cells secrete testosterone, which gland makes most of the semen.
- Evolution and Molecular Genetics test who proved what: Hershey and Chase, Meselson and Stahl, Darwin, Hugo de Vries, August Weismann.
- Human Health and Diseases and Immunology test pathogens, drugs and antibodies, often through match-the-following questions.
How to handle the harder question types
- Assertion-reason. Judge each statement on its own first, as true or false. Only if both are true, ask whether the reason actually explains the assertion. For example, the assertion that ovulation releases the ovum from the Graafian follicle is true, but the reason that it happens during the follicular phase is false, because it occurs at the end of that phase.
- Match the following. Start with the pair you are surest of, then eliminate options that don't contain it. One certain pair often leaves a single option standing.
- Genetics problems. Write the parents' genotypes, list the gametes, and draw the cross. Don't try to do it in your head. Our blood group and sex-linked inheritance guide works through every pattern.
Common traps in 12th Zoology MCQs
- Leydig versus Sertoli cells. Leydig cells secrete testosterone; Sertoli cells produce androgen binding protein.
- Pathogen versus disease. HIV is a pathogen, while hepatitis B, gonorrhoea and trichomoniasis are diseases.
- Vasectomy. It blocks sperm transport but does not stop sperm production. The option saying it "prevents spermatogenesis" is the incorrect action.
- Convergent evolution. The wings of birds and butterflies do the same job but have different origins. That makes them analogous, an example of convergent evolution.
- Primary lymphoid organs. The thymus is primary, so it is the answer to "all are peripheral lymphoid organs except".
- ZW-ZZ sex determination. Here females are heterogametic (ZW) and males are homogametic (ZZ), the reverse of humans.
Where to practise
Revise by theme, not by chapter number
The thirteen chapters form four themes, and revising a theme in one sitting helps you connect facts the MCQs deliberately set side by side:
- Reproduction (Units 1–3). Modes of reproduction, the human reproductive system and hormones, and contraception and STDs. Colostrum, for example, appears here and again in Immunology.
- Genetics and evolution (Units 4–6). Inheritance, molecular genetics and evolution. This theme holds most of the scientist-and-experiment questions.
- Health and biotechnology (Units 7–10). Diseases, immunity, useful microbes and biotechnology applications. Match-the-following questions on pathogens, drugs and products are common here.
- Ecology (Units 11–13). Populations and interactions, biodiversity and conservation, and environmental issues. These are mostly direct recall and suit quick daily revision.
Take a chapter's timed test straight after revising its answers on the Class 12 Zoology section, and keep a single page of the facts you get wrong. That page is your revision in the final week.