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| Non-Rationalised Science NCERT Notes and Solutions (Class 12th) | ||||||||||||||
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Class 12th Biology NCERT Notes and Solutions (Non-Rationalised)
1. Reproduction In Organisms
This chapter provides a foundational overview of reproduction, the biological process that ensures the continuity of a species. It introduces and contrasts the two major modes of reproduction. Asexual reproduction, involving a single parent, results in offspring that are genetically identical clones, with methods including binary fission, budding, spore formation, and vegetative propagation. In contrast, sexual reproduction involves the formation and fusion of male and female gametes, usually from two different parents, leading to genetic variation. The chapter outlines the key events in sexual reproduction: pre-fertilisation (gametogenesis and gamete transfer), fertilisation (syngamy), and post-fertilisation (embryogenesis), setting the stage for more detailed discussions in subsequent chapters.
2. Sexual Reproduction In Flowering Plants
This chapter provides a detailed exploration of sexual reproduction in angiosperms. It begins with the structure of a flower, detailing the male reproductive whorl (androecium) and female reproductive whorl (gynoecium). Key processes covered include microsporogenesis (formation of pollen grains) and megasporogenesis (formation of the embryo sac). The chapter explains the agents and mechanisms of pollination, followed by pollen-pistil interaction. A central focus is on double fertilisation, a unique event in flowering plants involving both syngamy and triple fusion, which leads to the development of the diploid zygote and the triploid primary endosperm nucleus (PEN). The chapter concludes with post-fertilisation events, including the development of the endosperm, embryo, seed, and fruit, and special modes like apomixis and polyembryony.
3. Human Reproduction
This chapter offers a comprehensive account of the human reproductive process. It details the anatomy and physiology of the male and female reproductive systems. The process of gamete formation, spermatogenesis in males and oogenesis in females, is explained, along with the hormonal control of the menstrual cycle in females. The chapter follows the journey from intercourse and insemination to fertilisation in the fallopian tube, the formation of the zygote, and its development into a blastocyst. The process of implantation in the uterine wall, pregnancy, and embryonic development (gestation) are discussed. Finally, it covers parturition (childbirth) and lactation, the production of milk by the mammary glands.
4. Reproductive Health
This chapter addresses the crucial topic of reproductive health, defined as total well-being in all aspects of reproduction. It discusses the problems and strategies related to reproductive health in India, including the need for population control. A major focus is on various contraceptive methods (natural, barrier, IUDs, oral, injectable, and surgical methods). The chapter also covers medical termination of pregnancy (MTP), the causes and prevention of Sexually Transmitted Infections (STIs) like AIDS and Gonorrhoea, and the issue of infertility. It introduces Assisted Reproductive Technologies (ARTs) such as In-Vitro Fertilisation (IVF), Zygote Intra Fallopian Transfer (ZIFT), and Gamete Intra Fallopian Transfer (GIFT) as solutions for infertile couples.
5. Principles Of Inheritance And Variation
This foundational genetics chapter explores heredity and variation. It is built upon the pioneering work of Gregor Mendel and his experiments on pea plants, leading to his three Laws of Inheritance: the Law of Dominance, the Law of Segregation, and the Law of Independent Assortment. The chapter explains monohybrid and dihybrid crosses. It also delves into deviations from Mendelian inheritance, such as incomplete dominance, co-dominance, and multiple alleles (e.g., ABO blood grouping). The Chromosomal Theory of Inheritance, linkage, recombination, and mechanisms of sex determination are discussed. The chapter concludes with an overview of genetic disorders, including Mendelian disorders like sickle-cell anaemia and chromosomal disorders like Down's syndrome.
6. Molecular Basis Of Inheritance
This chapter delves into the molecular world of genetics, establishing DNA as the genetic material through classic experiments. It details the double helix structure of DNA as proposed by Watson and Crick and discusses the structure of RNA. The chapter explains the central dogma of molecular biology: DNA replication (the semi-conservative model), transcription (synthesis of RNA from DNA), and translation (protein synthesis from the mRNA template). Key concepts like the genetic code, with its salient features, are elucidated. The chapter also covers gene regulation, using the lac operon as a model, and provides an overview of the landmark Human Genome Project (HGP) and DNA fingerprinting.
7. Evolution
This chapter traces the history of life on Earth through the process of evolution. It discusses theories on the origin of life, from the Big Bang to the chemical evolution proposed by Oparin and Haldane. It presents compelling evidence for evolution from paleontology (fossils), comparative anatomy (homologous and analogous structures), and molecular biology. The cornerstone of the chapter is Darwin's theory of evolution by natural selection. It explains the mechanisms of evolution, including mutation and the Hardy-Weinberg principle. Concepts like adaptive radiation (e.g., Darwin's Finches), speciation, and a brief account of human evolution are explored to illustrate the gradual emergence of diverse life forms.
8. Human Health And Disease
This chapter focuses on maintaining human health and understanding common diseases. It distinguishes between infectious and non-infectious diseases and discusses common pathogens. The chapter provides a detailed explanation of the immune system, our body's defence mechanism, covering innate immunity and acquired immunity (humoral and cell-mediated). The principles of vaccination and immunisation are explained. It describes specific diseases like malaria, typhoid, and pneumonia, and provides a detailed account of AIDS (caused by HIV) and cancer. The chapter also addresses the societal issues of drug and alcohol abuse and their effects on health.
9. Strategies For Enhancement In Food Production
This chapter addresses the challenge of feeding an ever-growing population by exploring scientific strategies to enhance food production. It covers modern animal husbandry practices, including dairy farm management and poultry farm management. A major focus is on plant breeding techniques aimed at developing high-yielding and disease-resistant crop varieties, which were central to the Green Revolution. The chapter also discusses advanced methods like tissue culture and single-cell protein (SCP) production as innovative approaches to increase food quantity and quality and meet future demands.
10. Microbes In Human Welfare
This chapter highlights the crucial and beneficial roles of microorganisms in our daily lives and industries. It discusses the use of microbes in household food production (Lactobacillus for curd), and industrial fermentation to produce beverages and antibiotics. The role of microbes in sewage treatment plants (STPs) to reduce pollution and in the production of biogas (methane) is detailed. The chapter also explores their application in agriculture as biocontrol agents (to control pests naturally, e.g., Bacillus thuringiensis) and as biofertilisers (to enrich soil fertility, e.g., Rhizobium), showcasing their immense contribution to a sustainable environment.
11. Biotechnology : Principles And Processes
This chapter introduces the core principles of biotechnology, focusing on modern genetic engineering. It explains the two foundational techniques: genetic engineering and the maintenance of a sterile environment. A key focus is on the tools of recombinant DNA technology, including restriction enzymes (molecular scissors), cloning vectors (like plasmids), and DNA ligase. The chapter outlines the process of creating recombinant DNA (rDNA) and inserting it into a host organism. It also details the powerful technique of Polymerase Chain Reaction (PCR) for amplifying DNA and explains the processes of separating DNA fragments and using bioreactors for large-scale production.
12. Biotechnology And Its Applications
This chapter explores the practical applications of biotechnology across various fields. In agriculture, it discusses the development of genetically modified (GM) crops, such as pest-resistant Bt cotton and nutritionally enhanced "Golden Rice." In medicine, it highlights the production of therapeutic proteins like human insulin using rDNA technology, the development of vaccines, and the revolutionary potential of gene therapy and molecular diagnosis (using PCR and ELISA). The chapter also touches upon the use of transgenic animals and addresses the important ethical issues related to biotechnological advancements.
13. Organisms And Populations
This chapter marks the beginning of the ecology unit, focusing on the interactions between organisms and their environment. It defines ecology and discusses the effects of major abiotic factors (temperature, water, light, soil) on organisms. It explores how organisms adapt and respond to these factors. The chapter then shifts to the population level, defining population attributes like birth rate, death rate, and age distribution. It describes population growth models (exponential and logistic growth) and explains the various types of population interactions, including predation, competition, parasitism, commensalism, and mutualism, with relevant examples.
14. Ecosystem
This chapter describes an ecosystem as the functional unit of nature where living organisms interact among themselves and also with the surrounding physical environment. It explains the structure and components of an ecosystem. The chapter focuses on four key functional aspects: productivity (rate of biomass production), decomposition, energy flow through different trophic levels (explained via food chains and food webs), and nutrient cycling. It details the concept of ecological pyramids and introduces major biogeochemical cycles, such as the carbon and phosphorus cycles. The chapter concludes with the concept of ecological succession, the gradual change in species composition over time.
15. Biodiversity And Conservation
This chapter highlights the importance of the immense variety of life on Earth, known as biodiversity, at the genetic, species, and ecosystem levels. It discusses the patterns of biodiversity, such as latitudinal gradients, and its significance for ecosystem health and human well-being. The chapter addresses the alarming rate of biodiversity loss, identifying the "Evil Quartet" (habitat loss, over-exploitation, alien species invasion, and co-extinctions) as the primary causes. It strongly advocates for biodiversity conservation, detailing the two main strategies: in-situ conservation (protecting species in their natural habitats, e.g., national parks, wildlife sanctuaries, and biodiversity hotspots) and ex-situ conservation (protecting species outside their natural habitats, e.g., zoos, botanical gardens).
16. Environmental Issues
This chapter focuses on the detrimental effects of human activities on our environment and the strategies to mitigate them. It discusses major forms of pollution, including air pollution (and its control), water pollution (and the importance of sewage treatment), and the management of solid and electronic wastes. It provides a detailed account of major global environmental issues, such as the greenhouse effect and global warming, and the depletion of the stratospheric ozone layer. The chapter emphasizes the importance of laws, individual responsibility, and sustainable practices to address these pressing environmental challenges.