12th Zoology Important 1 Mark Questions Chapter Wise (Samacheer Kalvi)

The one-mark questions in Class 12 Zoology come directly from the textbook's key facts: named structures, hormones, scientists, diseases and technical terms. Below is a chapter-by-chapter list of what the book back questions ask.

Unit 1: Reproduction in Organisms

• Arrhenotoky is parthenogenesis that produces only males
• Bacteria reproduce sexually by conjugation
• Variations appear in sexual reproduction
• In a bee colony, drones are haploid because they develop by parthenogenesis

Unit 2: Human Reproduction

• Mature sperms are stored in the epididymis
• Leydig cells secrete testosterone; Sertoli cells produce androgen binding protein
• The seminal vesicle produces the largest share of semen
• The allantois forms the basis of the umbilical cord; implantation happens in the uterus
• Prolactin initiates and maintains lactation; colostrum is rich in IgA
• Sperm undergo capacitation before penetrating the ovum; the mammalian egg is alecithal and non-cleidoic
• Painful menstruation is dysmenorrhoea; absence of menstruation is amenorrhoea

Unit 3: Reproductive Health

• Syphilis, chlamydiasis and gonorrhoea are the bacterial STDs
• Contraceptive pills prevent ovulation by inhibiting FSH and LH
• Diaphragms, cervical caps and vaults are mechanical barriers, not chemical ones
• Multiload-375 is a copper releasing IUD, LNG-20 is hormone releasing, Lippes loop is non-medicated and Saheli is a mini pill

Unit 4: Principles of Inheritance and Variation

• Haemophilia is a recessive trait carried on the X chromosome
• The ABO blood group is controlled by multiple alleles, which occupy the same locus
• O is the universal donor and AB the universal recipient; AB shows co-dominance
• Down's syndrome is trisomy 21, Patau's syndrome is trisomy 13 and Klinefelter's syndrome is XXY
• XO and XY systems show male heterogamety; the ZW-ZZ system is found in birds, some reptiles and fishes
• Francis Galton founded the eugenics movement; euphenics deals with inborn errors of metabolism

Unit 5: Molecular Genetics

• Hershey and Chase showed that DNA is the genetic material
• Meselson and Stahl proved that DNA replication is semi-conservative
• mRNA is produced by transcription; the central dogma runs replication, transcription, translation
• DNA polymerase adds nucleotides only at the 3' end; eukaryotic replication starts at many origins
• UUU, coding for phenylalanine, was the first codon deciphered
• An operon is a cluster of structural genes with related functions

Unit 6: Evolution

• Darwin published On the Origin of Species in 1859; Hugo de Vries proposed the mutation theory; Weismann proposed the germplasm theory
• Industrial melanism demonstrates natural selection; Darwin's finches show adaptive radiation
• Fossils are found in sedimentary rocks and dated by carbon dating
• The Mesozoic was the golden age of reptiles and the Devonian the age of fishes; modern man belongs to the Quaternary
• Selective mating breaks Hardy-Weinberg equilibrium

Unit 7: Human Health and Diseases

• Malaria spreads through mosquito bites; exo-erythrocytic schizogony takes place in the liver
• Sporozoites form from oocysts and are present in the saliva of the female Anopheles mosquito
• Shigella dysenteriae causes bloody diarrhoea; chicken pox spreads through droplet nuclei
• Amphetamines are stimulants; barbiturates are CNS depressants; Datura yields a hallucinogen
• Athlete's foot is caused by fungi; cirrhosis follows chronic alcohol intake

Unit 8: Immunology

• Colostrum gives naturally acquired passive immunity
• The paratope is the antigen binding site; allergy involves IgE
• The AIDS virus has single stranded RNA; the thymus is not a peripheral lymphoid organ
• T cells carry out cell-mediated immunity and B cells humoral immunity; plasma cells release antibodies
• Interferons inhibit viral replication; spread of cancer cells is metastasis

Unit 9: Microbes in Human Welfare

• Aspergillus niger produces citric acid; Saccharomyces cerevisiae produces ethanol from molasses
• Cyclosporin A comes from Trichoderma polysporum
• Lactate fermentation releases no CO2; biological waste water treatment reduces BOD

Unit 10: Applications of Biotechnology

• The first clinical gene therapy treated SCID; Dolly was cloned by nuclear transfer
• Insulin's A chain has 21 amino acids and its B chain 30
• PCR runs denaturation, annealing and synthesis, using a DNA polymerase that stays active at high temperature
• ELISA detects pathogens; GEAC stands for Genetic Engineering Approval Committee

Unit 11: Organisms and Populations

• Eurytherms tolerate a wide range of temperatures
• Predation and parasitism are (+, −) interactions; sucker fish and shark show commensalism
• Insects are r-selected: many small offspring
• Catadromous animals move from fresh water to the sea

Unit 12: Biodiversity and Its Conservation

• Tropical forests have the maximum biodiversity
• In-situ conservation is within natural habitats; a zoological park is ex-situ
• IUCN publishes the Red List; Walter Rosen introduced the term biodiversity
• The Amazon rainforest is called the lungs of the planet; amphibians are at high risk from habitat destruction

Unit 13: Environmental Issues

• The right to clean water falls under Article 21
• Ozone thickness is measured in Dobson units
• Bioremediation uses microorganisms to remove pollutants; ozonisation disinfects waste water
• Energy always decreases across trophic levels; copper is the most abundant metal in mobile phone e-waste
• Excess fluoride causes fluorosis

How to revise this section

Zoology facts fade quickly if you only read them. Cover each list, recall as many facts as you can, then check. The full solved sets, with explanations, are on the Class 12 Zoology section, and every chapter has a practice test you can time.