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| Classwise Science MCQ Questions with Solutions (Class 12th) | ||||||||||||||
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Class 12th Biology MCQ Questions
1. Reproduction In Organisms
This chapter introduces **reproduction** as a vital process enabling the continuation of life and species. It discusses the lifespan of organisms and different modes of reproduction observed across the living world. The chapter categorizes reproduction into **asexual reproduction** (involving a single parent, producing genetically identical offspring, e.g., binary fission, budding, vegetative propagation) and **sexual reproduction** (involving two parents, fusion of gametes, leading to genetic variation). Understanding these basic modes provides context for the detailed study of reproduction in plants and humans in subsequent chapters.
2. Sexual Reproduction In Flowering Plants
This chapter focuses specifically on **sexual reproduction in angiosperms** or flowering plants. It describes the structure of the flower, which is the site of reproduction. It covers **gametogenesis** (formation of pollen and ovules), **pollination** (transfer of pollen), and the crucial event of **fertilisation** (fusion of male and female gametes), including the unique **double fertilisation** process. Post-fertilisation events leading to the development of the embryo, endosperm, seed, and fruit are explained. Special mechanisms like apomixis and polyembryony are also briefly discussed, highlighting the intricacies of plant reproduction.
3. Human Reproduction
This chapter provides a detailed account of **human reproduction**. It describes the structure and functions of the **male and female reproductive systems**. The processes of **gametogenesis** (**spermatogenesis** in males and **oogenesis** in females) are explained. The menstrual cycle in females is discussed. Key events like **fertilisation** (fusion of sperm and egg), **implantation** of the embryo in the uterus, embryonic development (**pregnancy**) with its different stages, and ultimately **parturition** (childbirth) are covered. Basic concepts of lactation and reproductive hormones are also introduced, giving a comprehensive overview of human reproductive biology.
4. Reproductive Health
This chapter addresses the important topic of **reproductive health**, encompassing physical, emotional, behavioral, and social well-being related to the reproductive system. It discusses major issues facing society, such as rapid population growth and strategies for control, including various **contraceptive methods** (barrier, chemical, surgical). Prevention of **sexually transmitted infections (STIs)**, common STIs, and their symptoms are covered. Infertility and **assisted reproductive technologies (ARTs)** like IVF, ZIFT, and GIFT are also discussed. The chapter highlights challenges and government initiatives in India regarding reproductive health awareness, promoting responsible reproductive behaviour for a healthy society.
5. Principles Of Inheritance And Variation
This foundational genetics chapter explores how traits are passed from one generation to the next (**heredity**) and the differences observed among individuals (**variation**). It details **Mendel's experiments** with pea plants and his fundamental **Laws of Inheritance** (Dominance, Segregation, Independent Assortment). Deviations from Mendelian inheritance, such as incomplete dominance, codominance, multiple alleles, and polygenic inheritance, are discussed. Concepts like the **chromosomal theory of inheritance**, linkage, crossing over, **sex determination** (e.g., in humans, birds), and common mendelian disorders (e.g., colour blindness, sickle-cell anaemia) are also covered, explaining the mechanisms behind heredity.
6. Molecular Basis Of Inheritance
This chapter delves into the molecular mechanisms underlying heredity. It describes the structure of **DNA** and **RNA**, identifying DNA as the primary genetic material through experimental evidence. Processes like **DNA replication** (copying DNA), **transcription** (synthesizing RNA from DNA template), and **translation** (synthesizing protein from mRNA template) are explained in detail. The **genetic code**, gene regulation (e.g., **lac operon**), and the **Human Genome Project** are discussed, providing a deep understanding of how genetic information is stored, expressed, and transmitted at the molecular level, forming the core of modern genetics.
7. Evolution
This chapter explores the process of **evolution**, the gradual change in life forms over vast periods of time, leading to the diversity of organisms on Earth. It discusses theories on the origin of life (e.g., Oparin-Haldane hypothesis). Various lines of **evidence for evolution** are presented, including fossils (paleontology), comparative anatomy, embryology, and molecular evidence. **Darwin's theory of natural selection** is explained as a key mechanism of evolution. Concepts like adaptive radiation, genetic drift, gene flow, Hardy-Weinberg principle, and the evolutionary history of man are also covered, illustrating how life has diversified and adapted.
8. Human Health And Diseases
This chapter focuses on factors affecting **human health** and the common diseases. It differentiates between health and disease. Causes of diseases are discussed, primarily focusing on **infectious diseases** caused by pathogens (bacteria, viruses, fungi, protozoans, helminths) like typhoid, pneumonia, common cold, malaria, amoebiasis, ascariasis, filariasis, ringworm, AIDS, and cancer. The **human immune system**, different types of immunity (innate and acquired), vaccination, allergy, autoimmunity, and the harmful effects of **drug and alcohol abuse** are also covered, emphasizing disease prevention and maintaining good health.
9. Strategies For Enhancement In Food Production
Addressing the challenge of feeding a large population, this chapter explores strategies to increase and improve the quantity and quality of **food production** to meet the growing needs, especially crucial in India. It covers **plant breeding** techniques for developing high-yielding, disease-resistant, and improved quality crop varieties (e.g., Green Revolution). **Tissue culture** and micropropagation for rapid plant multiplication are discussed. **Animal husbandry** practices, including the management of farms for cattle (dairy), poultry (eggs, meat), fisheries (pisciculture), and apiculture (beekeeping), are explained as ways to enhance livestock production, promoting efficient and scientific methods for food security.
10. Microbes In Human Welfare
This chapter highlights the many beneficial roles that **microorganisms** play in human life and the environment, moving beyond their disease-causing potential. It discusses their use in household products (e.g., making curd, bread, cheese), industrial production (e.g., antibiotics like penicillin, beverages, organic acids, enzymes), **sewage treatment** for wastewater purification, production of **biogas** ($\textsf{CH}_4$), and as **biocontrol agents** (using microbes to control pests) and **biofertilisers** (enhancing soil fertility). The chapter showcases the significant positive contributions of microbes in various sectors, contributing to sustainable development.
11. Biotechnology : Principles And Processes
This foundational chapter introduces **biotechnology**, defining it as the use of biological processes, organisms, or systems to create useful products or services. It focuses on the core principles of **genetic engineering**, which involves manipulating genetic material (**recombinant DNA technology**). Key tools used in genetic engineering are discussed, such as restriction enzymes (molecular scissors), cloning vectors (plasmids, viruses), and competent host cells. The basic processes involved in rDNA technology, including isolation of genetic material, gene cloning, and gene transfer methods, are explained, providing the technical basis for modern biotechnological applications.
12. Biotechnology And Its Applications
Building upon the principles, this chapter explores the diverse and impactful **applications of biotechnology** in various fields. It discusses applications in **agriculture**, such as developing genetically modified (GM) crops for improved yield, pest resistance (e.g., Bt cotton), herbicide tolerance, or enhanced nutritional value (e.g., Golden Rice). Applications in **medicine** include the production of therapeutic proteins (e.g., recombinant insulin), vaccines, gene therapy for treating genetic disorders, and molecular diagnosis. The chapter also touches upon ethical issues and biosafety concerns related to biotechnology and GM organisms, reflecting the societal implications.
13. Organisms And Populations
This ecology chapter introduces the study of individual organisms and their interactions with their environment, as well as the dynamics of **populations** (groups of individuals of the same species). It discusses how organisms respond to various **environmental factors** (temperature, water, light, soil) through **adaptations** (morphological, physiological, behavioural). **Population ecology** explores population attributes like size, density, birth rate, death rate, age distribution, sex ratio, and growth models (exponential and logistic). Different types of **interspecific interactions** (mutualism, competition, predation, parasitism, commensalism, amensalism) are also explained, highlighting the complex web of relationships in nature.
14. Ecosystem
This chapter introduces the concept of an **ecosystem** as a structural and functional unit of nature comprising interacting **biotic** (living) and **abiotic** (non-living) components. It discusses the structure of an ecosystem (species composition, stratification). Key **ecosystem functions** are explored: **productivity** (rate of biomass production), **decomposition** (breakdown of organic matter), **energy flow** through different trophic levels in **food chains** and **food webs** (following the 10% law), and **nutrient cycling** (biogeochemical cycles like carbon, phosphorus, nitrogen). Ecological succession and ecosystem services are also discussed, highlighting the interconnectedness and vital roles of ecosystems in sustaining life.
15. Biodiversity And Conservation
This chapter emphasizes the importance of **biodiversity**, the variety of life at all levels (genetic, species, ecological). It discusses patterns of biodiversity (latitudinal gradients, species-area relationship) and its significance for ecosystem stability, human survival, and well-being. Major threats to biodiversity, collectively known as the "Evil Quartet" (habitat loss/fragmentation, over-exploitation, alien species invasion, co-extinctions), are explained. Strategies for **conservation** are discussed, including **in-situ conservation** (protecting species in their natural habitats like national parks, wildlife sanctuaries, biosphere reserves, sacred groves in India) and **ex-situ conservation** (protecting species outside natural habitats like zoos, botanical gardens, seed banks), stressing the urgent need to protect Earth's rich biodiversity.
16. Environmental Issues
This chapter addresses major **environmental issues** arising from human activities and their impact on the planet. Topics include air pollution (causes, effects, control), water pollution (sources, effects, sewage treatment), soil pollution, and solid waste management. It discusses the effects of deforestation, **climate change** (global warming), **ozone layer depletion**, and degradation of natural resources. The chapter emphasizes the need for sustainable practices, waste reduction, and environmental protection measures, encouraging responsible actions at individual and societal levels to mitigate these issues and ensure a healthier environment, relevant to addressing environmental challenges in India.