NCERT Solutions for Class 12 Biology Chapter Wise
Chapter 2 Sexual Reproduction in Flowering Plants
Chapter 3 Human Reproduction
Chapter 4 Reproductive Health
Chapter 5 Principles of Inheritance and Variation
Chapter 6 Molecular Basis of Inheritance
Chapter 7 Evolution
Chapter 8 Human Health and Diseases
Chapter 9 Strategies for Enhancement in Food Production
Chapter 10 Microbes in Human Welfare
Chapter 11 Biotechnology Principles and Processes
Chapter 12 Biotechnology: and its Application
Chapter 13 Organisms and Populations
Chapter 14 Ecosystem
Chapter 15 Biodiversity and Conservation
Chapter 16 Environmental Issues
Chapter 1: Reproduction in Organisms
The chapter, Reproduction in Organisms, explains how various organisms are able to procreate. Reproduction is an important biological process in which an organism gives rise to young ones similar to itself. There are two types of reproduction. When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual. When two parents (opposite sex) participate in the reproductive process and also involve the fusion of male and female gametes, it is called sexual reproduction. These concepts are elaborately explained with relevant diagrams and suitable examples.
Chapter 2: Sexual Reproduction in Flowering Plants
Sexual Reproduction in Flowering Plants explains the morphology, structure and the processes of sexual reproduction in angiosperms. It also elaborates on subtopics such as pre-fertilisation: Structure and Events, Double fertilisation, Post fertilisation: Structure and Events, Apomixis and Polyembryony.
Chapter 3: Human Reproduction
Reproductive events in humans include the formation of gametes (gametogenesis), i.e., sperms in males and ovum in females. Humans reach sexual maturity after attaining a certain age – this is called puberty. There are remarkable differences between the reproductive events in the male and in the female. In this chapter, you will examine the male and female reproductive systems in humans. The subtopics covered in this chapter are the male reproductive system, the female reproductive system, gametogenesis, menstrual cycle, fertilisation and implantation, pregnancy and embryonic development, parturition and lactation.
Chapter 4: Reproductive Health
In the previous chapter, you have learnt about the human reproductive system and its functions. This chapter discusses a closely related topic – reproductive health. The term simply refers to healthy reproductive organs with normal functions. According to the World Health Organisation (WHO), reproductive health means total well-being in all the aspects of reproduction, i.e., physical, emotional, behavioural and social. It covers subtopics such as Reproductive health –Problems and Strategies, Population Explosion and Birth Control, Medical Termination of Pregnancy, Sexually Transmitted Diseases, Infertility.
Chapter 5: Principles of Inheritance and Variation
Genetics is a branch of Biology that deals with inheritance, as well as the variation of characters from parents to offspring. Inheritance is the process by which the characters are passed on from parent to progeny; it is the basis of heredity. Variation is the degree by which progeny differ from their parents. The chapter covers subtopics such as Mendel’s Laws of Inheritance, Inheritance of One Gene, Inheritance of Two Genes, Sex Determination, Mutation, Genetic Disorders.
Chapter 6: Molecular Basis of Inheritance
In the previous chapter, you have learnt the inheritance patterns and the genetic basis of such patterns. At the time of Mendel, the nature of those ‘factors’ regulating the pattern of inheritance was not clear. Over the next hundred years, the nature of the putative genetic material was investigated culminating in the realisation that DNA – deoxyribonucleic acid – is the genetic material, at least for the majority of organisms. In Class XI you have learnt that nucleic acids are polymers of nucleotides. It also includes subtopics such as The DNA, The Search for Genetic Material, RNA World, Replication, Transcription, Genetic Code, Translation, Regulation of Gene Expression, Human Genome Project and DNA Fingerprinting.
Chapter 7: Evolution
Evolutionary Biology is the study of history of life forms on earth. It covers subtopics such as Origin of Life, Evolution of Life Forms – A Theory, What are the Evidences for Evolution? What is Adaptive Radiation? Biological Evolution, Mechanism of Evolution, Hardy – Weinberg Principle, A Brief Account of Evolution, Origin and Evolution of Man related to Evolution, which is important for the students to study.
Chapter 8: Human Health and Diseases
Health, for a long time, was considered as a state of body and mind where there was a balance of certain humor. Health is affected by – (i) genetic disorders – deficiencies with which a child is born and deficiencies/defects which the child inherits from parents from birth; (ii) infections and (iii) lifestyle including food and water we take, rest and exercise we give to our bodies, habits that we have or lack, etc. The chapter also includes subtopics such as Common Diseases in Humans, Immunity, AIDS, Cancer, Drugs and Alcohol Abuse.
Chapter 9: Strategies for Enhancement in Food Production
With ever-increasing population of the world, enhancement of food production is a major necessity. Biological principles, as applied to animal husbandry and plant breeding have a major role in our efforts to increase food production. Several new techniques like embryo transfer technology and tissue culture techniques are going to play a pivotal role in further enhancing food production. Subtopics that are explained in this chapter are Animal Husbandry, Plant Breeding, Single Cell Proteins and Tissue Culture.
Chapter 10: Microbes in Human Welfare
Besides macroscopic plants and animals, microbes are the major components of biological systems on this earth. You have studied about the diversity of living organisms in Class XI. Microbes are diverse–protozoa, bacteria, fungi and microscopic animal and plant viruses, viroids and also prions that are proteinaceous infectious agents. Microbes like bacteria and many fungi can be grown on nutritive media to form colonies that can be seen with the naked eyes. Such cultures are useful in studies on micro-organisms. Few of the subtopics are Microbes in Household Products, Microbes in Industrial Products, Microbes in Sewage Treatment, Microbes in Production of Biogas, Microbes as Biocontrol Agents and Microbes as Biofertilisers.
Chapter 11: Biotechnology Principles and Processes
Biotechnology deals with technique of using live organisms or enzymes from organisms to produce products and processes useful to humans. The European Federation of Biotechnology (EFB) has given a definition of biotechnology that encompasses both traditional view and modern molecular biotechnology. The definition given by EFB is as follows: ‘The integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services’. Some of the subtopics mentioned in the chapter are Principles of Biotechnology, Tools of Recombinant DNA Technology and Processes of Recombinant DNA Technology.
Chapter 12: Biotechnology: and its Application
Biotechnology, as you would have learnt from the previous chapter, essentially deals with the industrial-scale production of biopharmaceuticals and biologicals using genetically modified microbes, fungi, plants and animals. The applications of biotechnology include therapeutics, diagnostics, genetically modified crops for agriculture, processed food, bioremediation, waste treatment and energy production. The chapter also includes topics such as Biotechnological Applications in Agriculture, Biotechnological Applications in Medicine, Transgenic Animals and Ethical Issues.
Chapter 13: Organisms and Populations
You have already learnt in the previous classes that Ecology is a subject which studies the interactions among organisms and between the organism and its physical (abiotic) environment. Ecology is basically concerned with four levels of biological organisation – organisms, populations, communities and biomes. In this chapter, we explore ecology at organismic and population levels. It also includes subtopics such as Organism and Its Environment, Populations.
Chapter 14: Ecosystem
An ecosystem can be visualised as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. In this chapter, we will first look at the structure of the ecosystem, in order to appreciate the input (productivity), transfer of energy (food chain/web, nutrient cycling) and the output (degradation and energy loss). We will also look at the relationships – cycles, chains, webs – that are created as a result of these energy flows within the system and their inter- relationship. It includes subtopics such as Ecosystem–Structure and Function, Productivity, Decomposition, Energy Flow, Ecological Pyramids, Ecological Succession, Nutrient Cycling and Ecosystem Services.
Chapter 15: Biodiversity and Conservation
Biodiversity and Conservations consist of topics like Genetic diversity, Species diversity, Ecological diversity, Different types of Species, Patterns of Diversity, Loss of Biodiversity, Biodiversity Conservation, etc. Biodiversity conservation may be in situ as well as ex situ. In in situ conservation, the endangered species are protected in their natural habitat so that the entire ecosystem is protected. Ex situ conservation methods include protective maintenance of threatened species in zoological parks and botanical gardens, in vitro fertilisation, tissue culture propagation and cryopreservation of gametes.
Chapter 16: Environmental Issues
Human population size has grown enormously over the last hundred years. This means the increase in demand for food, water, home, electricity, roads, automobiles and numerous other commodities. Pollution is any undesirable change in physical, chemical or biological characteristics of air, land, water or soil. The agents that bring about such an undesirable change are called pollutants. The other subtopics students will study in this chapter are Air Pollution and Its Control, Water Pollution and Its Control, Solid Wastes, Agrochemicals and their Effects, Radioactive Wastes, Greenhouse Effect and Global Warming, Ozone Depletion in the Stratosphere, Degradation by Improper Resource Utilisation and Maintenance, Deforestation.
सजीव की संरचना सुसंगिठत होती है , उनमऊतक होतेहैऊतकोंमकोिशकाएं होती है। कोिशकाओंमछोटेघटक होतेहै। सजीव की यह संगिठत एवं सुवथत संरचना समय के साथ पयावरण भाव के कारण वघिटत होनेलगती है। यिद यह वथा टूटती हैतो जीव और अिधक समय तक जीिवत नहींरह पायेगा ।