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ISC Class 12 Biology Notes
ISC Class 12 Biology Notes
Comprehensive study guide for ISC Class 12 Biology
1. Reproduction in Organisms
- Asexual Reproduction: Binary fission, budding, spore formation.
- Sexual Reproduction: Gametogenesis, fertilization, zygote formation.
- Life Cycle: Alternation of generations, haplontic, diplontic, and haplodiplontic life cycles.
2. Sexual Reproduction in Flowering Plants
- Flower Structure: Male (stamen) and female (pistil) reproductive organs.
- Pollination: Types (self and cross), agents (wind, water, insects).
- Fertilization: Double fertilization process in angiosperms.
- Seed Development: Formation of seed and fruit post-fertilization.
3. Human Reproduction
- Male Reproductive System: Structure and function of testes, epididymis, vas deferens.
- Female Reproductive System: Structure and function of ovaries, fallopian tubes, uterus.
- Menstrual Cycle: Phases (menstrual, follicular, ovulatory, luteal).
- Fertilization and Pregnancy: Process of fertilization, implantation, and embryonic development.
4. Principles of Inheritance and Variation
- Mendelian Genetics: Laws of inheritance, monohybrid and dihybrid crosses.
- Chromosomal Theory: Chromosomal basis of inheritance.
- Genetic Disorders: Examples like sickle cell anemia, hemophilia.
5. Molecular Basis of Inheritance
- DNA Structure: Double helix model, nucleotides, base pairing.
- DNA Replication: Semi-conservative replication process.
- Genetic Code: Codons, start and stop codons.
- Protein Synthesis: Transcription and translation mechanisms.
6. Evolution
- Theories of Evolution: Lamarckism, Darwinism, Neo-Darwinism.
- Evidence of Evolution: Fossil records, comparative anatomy, embryology.
- Speciation: Mechanisms leading to the formation of new species.
7. Human Health and Disease
- Pathogens: Bacteria, viruses, fungi, and their modes of transmission.
- Immune System: Innate and adaptive immunity, antibodies, vaccines.
- Diseases: Examples like tuberculosis, malaria, AIDS, cancer.
8. Strategies for Enhancement in Food Production
- Animal Husbandry: Breeding, dairy farming, poultry farming.
- Plant Breeding: Hybridization, mutation breeding, tissue culture.
- Microbes in Agriculture: Biofertilizers, biopesticides.
9. Microbes in Human Welfare
- Microbial Products: Antibiotics, vaccines, enzymes.
- Microbial Decomposition: Role in recycling nutrients.
- Biotechnology Applications: Genetic engineering, bioremediation.
10. Biotechnology and Its Applications
- Recombinant DNA Technology: Gene cloning, vectors, restriction enzymes.
- Applications: Gene therapy, genetically modified organisms (GMOs), biopharming.
11. Organisms and Populations
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Reproduction in Organisms – ISC Biology Class 12 Reproduction in Organisms
Asexual Reproduction
- Binary Fission: Common in unicellular organisms like Amoeba and Paramecium. The parent cell divides into two identical daughter cells.
- Budding: Observed in Hydra and yeast. A small outgrowth (bud) forms on the parent which eventually detaches.
- Spore Formation: Seen in fungi (e.g., Rhizopus). Spores are produced in sporangia and dispersed to form new individuals.
Sexual Reproduction
- Gametogenesis: Formation of haploid male and female gametes through meiosis in the reproductive organs.
- Fertilization: Fusion of male and female gametes to form a diploid zygote. Can be internal or external.
- Zygote Formation: The zygote develops into a new individual through repeated mitotic divisions.
Life Cycle Patterns
- Haplontic: Dominant haploid stage (e.g., many algae). Zygote is the only diploid stage.
- Diplontic: Dominant diploid stage (e.g., humans, most animals). Gametes are the only haploid stage.
- Haplodiplontic: Alternation of haploid gametophyte and diploid sporophyte generations (e.g., ferns, mosses).
Sexual Reproduction in Flowering Plants – ISC Biology Sexual Reproduction in Flowering Plants
1. Structure of Flower
- Androecium (Stamens): Male reproductive part consisting of anther and filament. Produces pollen grains.
- Gynoecium (Carpels/Pistils): Female reproductive part consisting of stigma, style, and ovary.
- Ovule: Present inside the ovary, develops into seed after fertilization.
2. Microsporogenesis
- Formation of microspores (pollen grains) from microspore mother cells (MMC) by meiosis inside the anther.
- Pollen grains are two-celled (vegetative and generative cells) and form the male gametophyte.
3. Megasporogenesis
- Formation of megaspore from megaspore mother cell (MMC) in the ovule by meiosis.
- One functional megaspore develops into the female gametophyte (embryo sac).
4. Pollination
- Types:
- Autogamy: Self-pollination (same flower).
- Geitonogamy: Pollination between different flowers of the same plant.
- Xenogamy: Cross-pollination (different plants).
- Agents: Wind, water, insects, birds (anemophily, hydrophily, entomophily, ornithophily).
- Pollen-pistil interaction: Recognition and compatibility check before fertilization.
5. Fertilization
- Double fertilization: One male gamete fuses with egg (syngamy), the other fuses with two polar nuclei (triple fusion) to form endosperm.
- Unique feature of angiosperms.
6. Post-Fertilization Events
- Zygote: Develops into embryo.
- Endosperm: Nourishes developing embryo (especially in monocots).
- Ovule: Becomes seed.
- Ovary: Becomes fruit.
7. Seed and Fruit Formation
- Seed: Has seed coat, embryo, and stored food.
- Types: Albuminous (with endosperm), Exalbuminous (without endosperm).
- Fruit: True fruits from ovary, false fruits may include other floral parts.
Human Reproduction – ISC Biology Human Reproduction
1. Male Reproductive System
- Testes: Located in the scrotum; produce sperm and testosterone. Each testis has seminiferous tubules where spermatogenesis occurs.
- Epididymis: Stores and matures sperm. Sperm gain motility here.
- Vas deferens: Transports sperm from epididymis to the urethra via the ejaculatory duct.
- Accessory glands (seminal vesicle, prostate, bulbourethral) add fluid to sperm to form semen.
2. Female Reproductive System
- Ovaries: Produce ova and female hormones (estrogen and progesterone). Oogenesis occurs here.
- Fallopian Tubes (Oviducts): Site of fertilization. Transport ovum from ovary to uterus.
- Uterus: Muscular organ where implantation and fetal development occur.
- Cervix and Vagina: Cervix connects uterus to vagina, which serves as the birth canal.
3. Menstrual Cycle
- Menstrual Phase (Days 1–5): Shedding of uterine lining due to drop in hormones.
- Follicular Phase (Days 6–13): Follicle grows; estrogen levels rise, endometrium regenerates.
- Ovulation (Day 14): LH surge triggers release of mature ovum from ovary.
- Luteal Phase (Days 15–28): Corpus luteum secretes progesterone; prepares endometrium for implantation. If no fertilization, cycle restarts.
4. Fertilization and Pregnancy
- Fertilization: Occurs in the ampulla of fallopian tube. Sperm fuses with ovum to form diploid zygote.
- Implantation: Blastocyst attaches to and embeds in the endometrium of uterus.
- Embryonic Development: Zygote → Morula → Blastocyst → Embryo. Placenta forms to nourish the embryo.
Principles of Inheritance and Variation – ISC Biology Principles of Inheritance and Variation
1. Mendelian Genetics
- Gregor Mendel: Father of genetics; experimented on pea plants.
- Law of Dominance: In a heterozygote, only the dominant allele is expressed.
- Law of Segregation: Alleles separate during gamete formation.
- Law of Independent Assortment: Alleles of different genes assort independently during gamete formation.
- Monohybrid Cross: Cross between individuals with one pair of contrasting traits (e.g., tall × dwarf).
- Dihybrid Cross: Cross involving two different traits (e.g., seed shape and color); results in 9:3:3:1 ratio.
2. Chromosomal Theory of Inheritance
- Proposed by Sutton and Boveri in 1902.
- States that genes are located on chromosomes and are inherited through gametes.
- Evidence from Thomas Hunt Morgan’s experiments on fruit flies (Drosophila melanogaster).
- Linkage: Genes located on the same chromosome tend to be inherited together.
- Recombination: Exchange of genetic material between homologous chromosomes during meiosis.
3. Genetic Disorders
- Mendelian Disorders: Caused by mutation in a single gene; inherited according to Mendel’s laws.
- Sickle Cell Anemia: Caused by a mutation in the gene coding for hemoglobin; results in sickle-shaped RBCs.
- Hemophilia: X-linked recessive disorder; affects blood clotting ability. More common in males.
- Thalassemia: Inherited blood disorder affecting hemoglobin production.
- Phenylketonuria (PKU): Inability to break down phenylalanine; leads to brain damage if untreated.
Molecular Basis of Inheritance – ISC Biology Molecular Basis of Inheritance
1. DNA Structure
- Double Helix Model: Proposed by Watson and Crick. Two strands coiled around each other.
- Nucleotides: Each consists of a phosphate group, deoxyribose sugar, and nitrogenous base (A, T, G, C).
- Base Pairing: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C) via hydrogen bonds.
2. DNA Replication
- Semi-Conservative Process: Each daughter DNA contains one original and one new strand.
- Enzymes Involved: Helicase (unzips), DNA polymerase (adds nucleotides), Ligase (joins fragments).
- Replication begins at origins and proceeds bidirectionally in eukaryotes.
3. Genetic Code
- Codons: Triplet sequences of nucleotides on mRNA that code for specific amino acids.
- Start Codon: AUG (codes for Methionine).
- Stop Codons: UAA, UAG, UGA (signal termination of translation).
- The code is universal, unambiguous, and degenerate (multiple codons can code for one amino acid).
4. Protein Synthesis
- Transcription: DNA → mRNA. Occurs in the nucleus. RNA polymerase synthesizes mRNA using DNA template.
- Translation: mRNA → Protein. Occurs in the cytoplasm on ribosomes.
- tRNA: Brings specific amino acids to the ribosome according to the codon on mRNA.
- Ribosomes: Facilitate the formation of peptide bonds between amino acids, creating a polypeptide chain.
Evolution – ISC Biology Evolution
1. Theories of Evolution
- Lamarckism: Proposed by Jean-Baptiste Lamarck. Suggested that acquired traits are inherited (e.g., long neck of giraffe).
- Darwinism: Proposed by Charles Darwin. Based on natural selection — survival of the fittest.
- Neo-Darwinism: Modern synthesis of Darwin’s theory with genetics. Includes mutation, genetic recombination, gene flow, and natural selection.
2. Evidence of Evolution
- Fossil Records: Provide chronological evidence of organismal change over time. Example: Archaeopteryx as a link between reptiles and birds.
- Comparative Anatomy:
- Homologous Organs: Same origin, different functions (e.g., forelimbs of humans and bats).
- Analogous Organs: Different origin, similar functions (e.g., wings of birds and insects).
- Embryology: Similar embryonic stages in vertebrates suggest common ancestry.
- Molecular Evidence: Similar DNA and protein sequences in related species.
3. Speciation
- Speciation: Formation of new species from pre-existing species.
- Types of Speciation:
- Allopatric: Due to geographic isolation.
- Sympatric: Without physical separation; may involve genetic divergence or behavioral changes.
- Mechanisms: Mutation, natural selection, genetic drift, reproductive isolation.
Human Health and Disease – ISC Biology Human Health and Disease
1. Pathogens
- Bacteria: Unicellular prokaryotes (e.g., Mycobacterium tuberculosis causes TB).
- Viruses: Non-living outside host (e.g., HIV causes AIDS).
- Fungi: Eukaryotic organisms; may cause skin infections (e.g., ringworm).
- Transmission Modes:
- Airborne (e.g., TB, flu)
- Waterborne (e.g., cholera)
- Vector-borne (e.g., malaria via mosquitoes)
- Direct contact (e.g., fungal infections)
2. Immune System
- Innate Immunity: Non-specific, present from birth (e.g., skin, mucus, phagocytes).
- Adaptive Immunity: Specific, acquired over time; includes:
- Humoral Immunity: B-cells produce antibodies.
- Cell-Mediated Immunity: T-cells destroy infected cells.
- Antibodies: Protein molecules that neutralize pathogens.
- Vaccines: Provide artificial immunity by stimulating antibody production.
3. Common Diseases
- Tuberculosis (TB): Bacterial infection affecting lungs; caused by Mycobacterium tuberculosis.
- Malaria: Protozoan disease caused by Plasmodium; spread by female Anopheles mosquito.
- AIDS (Acquired Immuno Deficiency Syndrome): Caused by HIV; attacks immune cells (especially CD4+ T cells).
- Cancer: Uncontrolled cell division; may be triggered by mutations, carcinogens, or viruses. Treated via surgery, chemotherapy, and radiation.
Strategies for Enhancement in Food Production – ISC Biology Strategies for Enhancement in Food Production
1. Animal Husbandry
- Breeding: Improving genetic quality of livestock through selective breeding and cross-breeding.
- Dairy Farming: Management of animals for milk production. Involves nutrition, housing, and disease control.
- Poultry Farming: Rearing of birds (chicken, ducks, etc.) for eggs and meat. Layers (egg-laying) and broilers (meat-yielding) are bred selectively.
2. Plant Breeding
- Hybridization: Crossing two genetically different plants to produce improved offspring with desirable traits.
- Mutation Breeding: Inducing mutations using chemicals or radiation to create varieties with better yield or disease resistance.
- Tissue Culture: Growing plants from a small tissue in a nutrient medium. Enables mass production of disease-free plants (micropropagation).
3. Microbes in Agriculture
- Biofertilizers: Microorganisms like Rhizobium, Azospirillum, and cyanobacteria that enrich the soil with nutrients.
- Biopesticides: Biological agents such as Bacillus thuringiensis (Bt) used to control pests without harming the environment.
Microbes in Human Welfare – ISC Biology Microbes in Human Welfare
1. Microbial Products
- Antibiotics: Substances produced by microbes that kill or inhibit other microbes. Example: Penicillin from Penicillium notatum.
- Vaccines: Microbe-derived products that provide immunity by stimulating the immune system. Example: BCG vaccine for tuberculosis.
- Enzymes: Microbes like Streptococcus and Aspergillus produce enzymes used in detergents, food, and medicine industries.
2. Microbial Decomposition
- Decomposers: Fungi and bacteria break down organic matter, recycling essential nutrients like nitrogen and carbon back into the environment.
- Sewage Treatment: Utilizes aerobic and anaerobic bacteria to clean waste water.
- Composting: Organic waste converted into nutrient-rich compost by microbes.
3. Biotechnology Applications
- Genetic Engineering: Use of microbes like E. coli in recombinant DNA technology for producing insulin, growth hormones, etc.
- Bioremediation: Use of microbes to clean up pollutants from the environment. Example: Oil spill cleanup by Pseudomonas putida.
- Bio-control: Use of living organisms to control pests (e.g., Trichoderma fungus against plant pathogens).
Biotechnology and Its Applications – ISC Biology Biotechnology and Its Applications
1. Recombinant DNA Technology
- Gene Cloning: Producing multiple copies of a gene by inserting it into a host organism.
- Vectors: DNA molecules (like plasmids and bacteriophages) used to carry foreign DNA into host cells.
- Restriction Enzymes: Molecular scissors that cut DNA at specific sequences enabling gene splicing.
2. Applications of Biotechnology
- Gene Therapy: Correcting defective genes responsible for disease development by inserting normal genes.
- Genetically Modified Organisms (GMOs): Organisms with altered genomes for desirable traits, e.g., pest-resistant crops.
- Biopharming: Using genetically modified plants and animals to produce pharmaceuticals like insulin, vaccines, and antibodies.
Organisms and Populations – ISC Biology Organisms and Populations
1. Organism and Its Environment
- Ecology: Study of interactions among organisms and their environment.
- Abiotic Factors: Temperature, water, light, and soil affect organisms’ survival and reproduction.
- Adaptations: Morphological, physiological, and behavioral changes that help organisms survive (e.g., camels in deserts, penguins in cold).
2. Population
- Population: Group of individuals of a species living in a specific area at a given time.
- Attributes: Birth rate, death rate, sex ratio, age distribution, and population density.
- Growth Models:
- Exponential Growth: Unlimited resources, J-shaped curve.
- Logistic Growth: Limited resources, S-shaped curve with carrying capacity (K).
- Population Interactions:
- Mutualism (+/+): Both species benefit (e.g., pollination).
- Competition (-/-): Compete for resources (e.g., lion and tiger).
- Predation (+/-): One kills and eats the other (e.g., lion and deer).
- Parasitism (+/-): Parasite lives on/in the host and harms it (e.g., lice on humans).
- Commensalism (+/0): One benefits, other unaffected (e.g., orchids on trees).