Class 12 Biology

An introduction to why reproduction is essential for species survival, the distinction between asexual and sexual reproduction, the role of flowers as reproductive organs in angiosperms, the pioneering contributions of Panchanan Maheshwari to plant embryology and tissue culture, the anatomy of a typical flower with its four whorls, the pre-fertilisation events that prepare a plant for reproduction, the detailed structure of the stamen, microsporangium wall layers, the process of microsporogenesis leading to pollen grain formation, the architecture, viability, and uses of pollen grains including sporopollenin, germ pores, the vegetative and generative cells, pollen allergies, and pollen banks, the gynoecium with its pistil structure, ovule anatomy (funicle, hilum, integuments, micropyle, chalaza, nucellus), and embryo sac as the female gametophyte, megasporogenesis from the megaspore mother cell through meiosis, monosporic development, the stepwise formation of the 7-celled, 8-nucleate embryo sac with its egg apparatus, antipodals, central cell, polar nuclei, and filiform apparatus, pollination as the mechanism to bring non-motile gametes together, the three types of pollination (autogamy, geitonogamy, xenogamy), chasmogamous versus cleistogamous flowers, the genetic consequences of each pollination type, the three agents of pollination (wind, water, and animals), adaptations of wind-pollinated flowers, the rarity of water pollination among angiosperms, surface and submerged pollination strategies in aquatic plants, why abiotic-pollinated flowers lack colour and nectar, animal pollination as the dominant biotic mechanism with floral adaptations for insects birds and bats, floral rewards including nectar pollen and safe egg-laying sites, obligate mutualism between Yucca and its moth, pollen and nectar robbers, the four outbreeding devices plants use to prevent self-pollination (timing mismatch physical separation self-incompatibility and unisexual flowers), monoecious versus dioecious conditions and their effects on autogamy and geitonogamy, the pollen-pistil chemical recognition system for accepting or rejecting pollen, the complete journey of the pollen tube from stigma through style to synergid via the micropyle and filiform apparatus, artificial hybridisation techniques including emasculation and bagging for crop improvement, double fertilisation where syngamy produces the diploid zygote and triple fusion produces the triploid primary endosperm nucleus, a phenomenon unique to angiosperms, the developmental stages of a dicot embryo from globular through heart-shaped to the mature embryo with cotyledons, plumule, radicle, and suspensor, the post-fertilisation events including endosperm development from the free-nuclear stage through cellularisation, the coconut as a living example of both endosperm stages, the two fates of endosperm in mature seeds, the detailed anatomy of dicot and monocot embryos including embryonal axis, epicotyl, hypocotyl, plumule, radicle, cotyledons, scutellum, coleoptile, and coleorrhiza, and the formation of seeds and fruits including seed structure with coat cotyledons and embryo axis, albuminous versus non-albuminous seeds, perisperm, the parallel transformation of ovary into fruit with pericarp, true fruits versus false fruits, parthenocarpy, the survival advantages seeds provide to angiosperms, the role of dormancy and dehydration in agriculture, remarkable records of seed viability, apomixis as seed production without fertilisation via diploid egg cell and nucellar embryony pathways, polyembryony in Citrus and Mango, and the significance of apomixis research for the hybrid seed industry

The male reproductive system including testes, accessory ducts, glands, and external genitalia, the female reproductive system with ovaries, oviducts, uterus, and mammary glands, gametogenesis covering spermatogenesis and oogenesis, the menstrual cycle and its hormonal regulation, fertilisation and implantation, pregnancy and embryonic development including placenta formation and foetal membranes, and parturition and lactation

The meaning and scope of reproductive health as defined by WHO, India's pioneering role in national family planning and RCH programmes, strategies for spreading awareness through media, education, and community involvement, the infrastructure needed for medical support in reproduction-related problems, the procedure and ethical regulation of amniocentesis, indicators of improved reproductive health in society, population stabilisation measures, detailed contraceptive methods including natural, barrier, IUD-based, oral hormonal, injectable, implant-based, and surgical approaches, emergency contraception, the importance of medical guidance and awareness of side effects, medical termination of pregnancy including the legal framework under the MTP Act 1971 and the 2017 amendment, the dangers of illegal abortions, misuse of amniocentesis for sex-selective female foeticide, the role of counselling and healthcare access, sexually transmitted infections including gonorrhoea, syphilis, genital herpes, chlamydiasis, genital warts, trichomoniasis, hepatitis-B, and HIV/AIDS, non-sexual routes of STI transmission, curable versus incurable STIs, early symptoms, complications of untreated infections, preventive measures, infertility and its causes in both males and females, assisted reproductive technologies including IVF, ZIFT, IUT, GIFT, ICSI, and artificial insemination, limitations and social barriers to ART adoption, and legal adoption as a meaningful alternative

Introduction to genetics, inheritance, heredity, and variation, ancient selective breeding, key molecular biologists and Watson-Crick biography, Mendel's seven-year hybridisation experiments on garden peas (1856-1863), true-breeding lines, seven pairs of contrasting traits, artificial cross-pollination technique including emasculation, monohybrid cross between tall and dwarf pea plants, key genetics terminology (genes, alleles, genotype, phenotype, homozygous, heterozygous, dominant, recessive), Punnett Square, Law of Segregation, binomial expression for genotypic ratios, the test cross, the formal Laws of Dominance and Segregation with their postulates, incomplete dominance in snapdragons with 1:2:1 phenotypic ratio, the molecular basis of dominance through enzyme function, co-dominance in ABO blood grouping with six genotypes and four phenotypes, multiple alleles in populations, pleiotropy showing how one gene affects multiple traits with the starch synthesis example, the dihybrid cross tracking seed colour and seed shape simultaneously with the 4x4 Punnett square producing the 9:3:3:1 phenotypic ratio, the Law of Independent Assortment showing that two gene pairs segregate independently during gamete formation with the combination series derivation and nine distinct F2 genotypes, the chromosomal theory of inheritance by Sutton and Boveri linking chromosome behaviour during meiosis to Mendel's laws, the 35-year gap between Mendel's publication and its 1900 rediscovery by de Vries Correns and von Tschermak, independent orientation of chromosome pairs at metaphase I as the physical basis for independent assortment, Morgan's use of Drosophila melanogaster to experimentally verify the chromosomal theory, linkage as the physical association of genes on the same chromosome deviating from independent assortment, recombination as the generation of non-parental gene combinations through crossing over, tight linkage (1.3% recombination for yellow-white) versus loose linkage (37.2% for white-miniature), Sturtevant's construction of the first genetic map using recombination frequency, the role of genetic maps in the Human Genome Sequencing Project, polygenic inheritance where three or more genes with additive allelic effects produce continuous phenotypic variation such as human skin colour and height, the role of environment in shaping polygenic traits, pleiotropy through the phenylketonuria example showing how a single gene mutation in phenylalanine hydroxylase causes both mental retardation and reduced pigmentation, chromosomal sex determination covering Henking's 1891 discovery of the X body, the XO mechanism in grasshoppers, the XY mechanism in humans and Drosophila, male heterogamety, the ZW system of female heterogamety in birds, sex determination in humans with 22 autosome pairs plus XX/XY sex chromosomes and the father's sperm deciding child's sex with 50% probability for either sex, and the haplodiploid sex-determination system in honey bees where fertilised eggs produce diploid females and unfertilised eggs produce haploid males via parthenogenesis with sperm produced by mitosis, mutation as alteration of DNA sequences leading to changes in genotype and phenotype, chromosomal aberrations from deletions and insertions/duplications commonly observed in cancer cells, point mutations with sickle cell anaemia as the classic example, frame-shift mutations caused by base pair insertions or deletions, and mutagens as the physical and chemical agents that induce mutations including UV radiation, pedigree analysis as the tool for studying human inheritance where controlled crosses are impossible, standard pedigree symbols for males females affected individuals matings consanguinity and unspecified sex, reading family trees across generations and birth order, determining dominant versus recessive and autosomal versus sex-linked inheritance from pedigree patterns, and the connection between mutations in genes or chromosomes and human genetic disorders, the two broad categories of genetic disorders (Mendelian and chromosomal), Mendelian disorders as single-gene mutations following Mendel's inheritance principles, recognising autosomal dominant pedigree patterns (affected every generation as in myotonic dystrophy) versus autosomal recessive patterns (trait skips generations as in sickle-cell anaemia), colour blindness as a sex-linked recessive disorder caused by defective red or green cone genes on the X chromosome affecting 8% of males but only 0.4% of females, inheritance scenarios for carrier mothers and colour blind daughters, haemophilia as a sex-linked recessive disorder affecting blood clotting proteins with carrier-mother-to-son transmission, why female haemophiliacs are extremely rare, and Queen Victoria's pedigree as a landmark case study, sickle-cell anaemia as an autosomal recessive disorder caused by substitution of glutamic acid by valine at the sixth position of the beta-globin chain due to a single base change from GAG to GUG causing haemoglobin polymerisation and sickle-shaped RBCs, the three genotypes (HbA HbA normal, HbA HbS carrier with sickle-cell trait and 50% transmission probability, HbS HbS affected), phenylketonuria as an autosomal recessive inborn error of metabolism where the missing enzyme fails to convert phenylalanine to tyrosine causing accumulation of phenylpyruvic acid leading to mental retardation and urinary excretion, thalassemia as an autosomal recessive blood disease caused by mutation or deletion reducing globin chain synthesis, alpha thalassemia controlled by HBA1 and HBA2 genes on chromosome 16 with severity scaling by number of affected genes out of four copies, beta thalassemia controlled by single gene HBB on chromosome 11, and the key distinction that thalassemia is a quantitative defect (too few globin molecules) while sickle-cell anaemia is a qualitative defect (incorrectly functioning globin), chromosomal disorders caused by absence excess or abnormal arrangement of chromosomes, aneuploidy from failed chromatid segregation and polyploidy from failed cytokinesis, trisomy and monosomy, Down's syndrome (trisomy 21) first described by Langdon Down in 1866 with characteristic features including short stature small round head furrowed tongue broad palm with palm crease and retarded physical psychomotor and mental development, Klinefelter's syndrome (47 XXY) with masculine development plus gynaecomastia and sterility, and Turner's syndrome (45 X0) with rudimentary ovaries sterility and lack of secondary sexual characters

Introduction to DNA and nucleic acids, DNA as the genetic material in most organisms, RNA as genetic material in some viruses and its four functional roles (messenger, adapter, structural, catalytic), DNA as a long polymer of deoxyribonucleotides, measurement of DNA length in nucleotides and base pairs, DNA content across organisms from bacteriophage phi-X-174 (5,386 nucleotides) through E. coli (4.6 million bp) to human haploid DNA (3.3 billion bp), the chemical structure of nucleotides (nitrogenous base, pentose sugar, phosphate group), purines and pyrimidines, nucleoside and nucleotide formation, the polynucleotide chain with 3-prime-5-prime phosphodiester bonds and 5-prime/3-prime polarity, Watson and Crick's double helix model built on X-ray diffraction data and Chargaff's base pairing rules, the five salient features of the double helix (anti-parallel strands, hydrogen-bonded base pairing, helical dimensions, base stacking), complementarity and the Central Dogma of molecular biology, how cells package over two metres of DNA into a microscopic nucleus using histones, nucleosomes, chromatin organisation, the functional distinction between euchromatin and heterochromatin, the search for genetic material through Griffith's transformation experiment with Streptococcus pneumoniae and the biochemical proof by Avery MacLeod and McCarty using enzyme digestion tests that DNA is the transforming principle, the four criteria for genetic material with a comparison of DNA versus RNA in terms of stability, mutation rate, and ability to express traits, the RNA World hypothesis with RNA as the first genetic material and catalyst (ribozymes), how DNA evolved from RNA with chemical modifications for stability, Watson and Crick's semiconservative model of DNA replication where each strand serves as a template producing daughter molecules with one parental and one new strand, the experimental proof of semiconservative replication by Meselson and Stahl (1958) using heavy nitrogen labelling and CsCl density gradient centrifugation in E. coli with results across generations ruling out conservative and dispersive models and confirmation in eukaryotic chromosomes by Taylor and colleagues using radioactive thymidine in Vicia faba, the replication machinery including DNA-dependent DNA polymerase and its extraordinary speed (approximately 2000 bp per second in E. coli) and accuracy requirements, deoxyribonucleoside triphosphates as dual-purpose substrates and energy sources, the replication fork as the localised site of active copying, continuous and discontinuous synthesis on antiparallel template strands with Okazaki fragments joined by DNA ligase, the origin of replication and vectors in recombinant DNA work, coordination of replication with S-phase of the eukaryotic cell cycle and the consequence of polyploidy from failed cell division, transcription as the process of copying genetic information from one strand of DNA into RNA governed by complementary base pairing with uracil replacing thymine, why only a specific segment and one strand is copied unlike replication which duplicates the entire genome, the need for boundary signals to define the transcribed region and strand, the two reasons both strands cannot be templates simultaneously (different proteins from different RNA sequences and complementary RNAs forming untranslatable double-stranded RNA), the three regions of a transcription unit (promoter, structural gene, terminator) and the naming convention for template and coding strands, the concept of cistrons and monocistronic versus polycistronic genes, the split-gene arrangement of exons and introns in eukaryotes and how it complicates the definition of a gene, how the triplet genetic code was proposed and deciphered by Gamow, Khorana, Nirenberg, and Ochoa, the complete codon table mapping 64 codons to amino acids and stop signals, the six key properties of the genetic code including degeneracy, universality, and the dual role of AUG, the process of translation including tRNA charging, ribosome structure, translational units with UTRs, and the three stages of initiation, elongation, and termination, the salient features of the human genome including total size (3164.7 million bp), estimated gene count (~30,000), less than 2% protein-coding DNA, repetitive sequences, gene distribution across chromosomes, SNPs, and how whole-genome data is transforming biological research, regulation of gene expression at four eukaryotic levels (transcriptional, processing, transport, translational) and prokaryotic gene control through promoters operators activators and repressors, the lac operon as the first transcriptionally regulated system elucidated by Jacob and Monod with one regulatory gene (i gene for repressor) and three structural genes (z for beta-galactosidase, y for permease, a for transacetylase), lactose as inducer that inactivates the repressor to allow transcription, negative regulation, the launch and scope of the Human Genome Project as a 13-year international mega project to sequence all 3 billion base pairs of human DNA with goals including gene identification and database building and addressing ethical legal and social issues (ELSI) and the rise of bioinformatics and parallel sequencing of model organisms, the methodologies of the Human Genome Project including Expressed Sequence Tags (ESTs) and Sequence Annotation approaches, DNA fragmentation and cloning into BAC and YAC vectors, automated Sanger sequencing, computer-assisted assembly of overlapping fragments, completion of Chromosome 1 in May 2006, and genetic and physical mapping using restriction site polymorphism and microsatellites, and DNA fingerprinting using repetitive DNA polymorphisms, VNTR probes, and Southern blot hybridisation for forensic identification, paternity testing, and population genetics

Origin of life on earth from chemical evolution through Oparin-Haldane hypothesis and Miller's experiment, Darwin's theory of evolution by natural selection and the voyage of HMS Beagle, evidences for evolution from palaeontology, comparative anatomy (homologous and analogous organs), embryology and molecular biology, industrial melanism as observed natural selection in action, adaptive radiation illustrated by Darwin's finches and Australian marsupials, biological evolution from simple cellular forms to the present biodiversity, mechanism of evolution including Hugo de Vries' mutation theory, Hardy-Weinberg principle and the five forces that disturb genetic equilibrium (gene migration, genetic drift, mutation, recombination, natural selection), a brief chronological account of evolution from first cellular forms through invertebrates, jawless fish, amphibians, reptiles, dinosaurs, birds, and mammals, and the origin and evolution of humans from early primates through Australopithecines, Homo habilis, Homo erectus, Neanderthals, and Homo sapiens

Understanding health as complete physical, mental and social well-being, common infectious diseases caused by bacteria, viruses, protozoans and helminths along with their symptoms, transmission and prevention, the immune system including innate and adaptive immunity with humoral and cell-mediated responses, vaccination and immunisation, allergies, autoimmune diseases and immunodeficiency, AIDS caused by HIV and its replication cycle, modes of transmission and prevention, cancer as uncontrolled cell growth involving oncogenes and tumour suppressor genes with detection and treatment methods, drug and alcohol abuse covering opioids, cannabinoids, stimulants and their effects on health and society, and adolescence as a vulnerable period for substance abuse with addiction, tolerance, dependence, and withdrawal syndrome

The diversity and ubiquity of microbes, their role in household products like curd, bread, cheese, and fermented foods, industrial applications including fermented beverages, antibiotics, and chemicals, sewage treatment through primary and secondary biological processes, biogas production by methanogenic bacteria, their use as biocontrol agents including Bacillus thuringiensis and Trichoderma, and their role as biofertilisers through nitrogen-fixing bacteria, mycorrhizal fungi, and cyanobacteria

The meaning and scope of biotechnology from traditional microbe-mediated processes to modern genetic engineering, the two core techniques that define modern biotechnology (genetic engineering and bioprocess engineering), the tools of recombinant DNA technology including restriction enzymes, cloning vectors, and host organisms, the step-by-step processes of recombinant DNA technology from isolation of DNA through gene cloning and expression in host cells, PCR amplification of genes using Taq polymerase, insertion of recombinant DNA into host cells using competent cell preparation and selectable markers, obtaining the foreign gene product as recombinant proteins using bioreactors for large-scale production, and downstream processing including separation, purification, formulation, clinical trials, and quality control

How biotechnology is applied in agriculture through tissue culture, micro-propagation, meristem culture for virus-free plants, and somatic hybridisation, how genetically modified organisms are created and used for pest resistance, nutritional enhancement, and industrial purposes, how biotechnology serves medicine through genetically engineered insulin, gene therapy, and molecular diagnostics including ELISA and PCR, the creation and uses of transgenic animals in research, medicine, and industry, and the ethical issues surrounding genetic modification, biopiracy, and patenting of biological resources

How organisms interact with their abiotic environment and with each other at the population level, covering ecology's scope, levels of biological organisation, foundational questions, population attributes, the four processes that drive population growth, the exponential and logistic mathematical models of population growth, life history variation in reproductive strategies, the six types of interspecific interactions in biological communities, predation including energy transfer, ecosystem regulation, prey defences, and plant defences against herbivores, interspecific competition including exploitation and interference competition, Gause's Competitive Exclusion Principle, competitive release, and resource partitioning, parasitism including host-specificity, co-evolution, ectoparasites, endoparasites, complex life cycles with intermediate hosts and vectors, and brood parasitism in birds, commensalism with examples of epiphytes, barnacles, cattle egrets, and clown fish, and mutualism including lichens, mycorrhizae, plant-pollinator co-evolution, fig-wasp partnerships, and orchid pollination strategies including the sexual deceit of Ophrys

Understanding ecosystems as functional units of nature: their structure (species composition, stratification, biotic and abiotic components), the four core functional processes (productivity, decomposition, energy flow, and nutrient cycling), illustrated through the pond ecosystem model, a detailed look at ecosystem productivity including GPP, NPP, secondary productivity, and global biomass production patterns, how dead organic matter is recycled through the five steps of decomposition, how energy flows unidirectionally through trophic levels governed by the 10 per cent law, and how trophic level relationships are visualised as ecological pyramids of number, biomass, and energy, including inverted pyramids in special cases and the limitations of the pyramid model

Understanding biodiversity at genetic, species, and ecological levels, the patterns and significance of Earth's biological wealth, and the principles and strategies behind conserving it