📘 BIOLOGY – LONG NOTES (Unit I–VII)
UNIT I: REPRODUCTION
Fertilization in angiosperms is a unique process called double fertilization. It begins with pollination, the transfer of pollen grains from anther to stigma. After pollination, the pollen grain germinates on the stigma and forms a pollen tube that grows through the style, guided by chemical attractants. The tube carries two male gametes into the ovule through the micropyle. Inside the embryo sac, one male gamete fuses with the egg cell to form the diploid zygote (syngamy). The second gamete fuses with two polar nuclei to form the triploid primary endosperm nucleus (PEN). This phenomenon is called double fertilization and is unique to flowering plants. The zygote develops into an embryo, while the PEN gives rise to the endosperm that nourishes the embryo. The ovule matures into a seed and the ovary into a fruit. Seed dispersal ensures survival of species.
UNIT II: GENETICS & EVOLUTION
The molecular basis of inheritance is primarily centered on the role of DNA. DNA is the genetic material in almost all organisms. Watson and Crick proposed the double helix model of DNA with two antiparallel strands held by complementary base pairs (A–T, G–C). DNA replication occurs semi-conservatively. Transcription is the process where DNA acts as a template to form RNA with the help of RNA polymerase. Translation occurs on ribosomes, where tRNA brings specific amino acids according to codons on mRNA. The genetic code is universal, triplet, and degenerate. Regulation of gene expression in prokaryotes was explained by Jacob and Monod in the lac operon model. DNA controls cellular functions by encoding proteins, ensuring continuity of life.
UNIT III: BIOLOGY IN HUMAN WELFARE
Microorganisms play a crucial role in daily life and industry. In households, lactic acid bacteria (Lactobacillus) convert milk into curd. Yeast (Saccharomyces cerevisiae) is used in baking industry for bread, idli, and dosa. In industries, microbes produce antibiotics (Penicillium → penicillin), ethanol (yeast), citric acid (Aspergillus niger), and enzymes. Microbes like Trichoderma are used as biocontrol agents. In sewage treatment, aerobic microbes form flocs and degrade organic matter, while anaerobic methanogens produce biogas. Microbes are indispensable for food, medicine, energy, and environment.
UNIT IV: BIOTECHNOLOGY
Recombinant DNA technology combines DNA from two sources to create genetically modified organisms. Key tools include restriction enzymes (cut DNA), ligase (joins DNA), and vectors (plasmids, bacteriophages). Techniques: DNA isolation, cutting, PCR amplification, vector insertion, transfer into host, and selection of transformed cells. Gel electrophoresis separates DNA fragments. Applications: human insulin, growth hormones, vaccines, transgenic plants like Bt cotton, gene therapy, and DNA fingerprinting for forensics.
UNIT V: ECOLOGY
An ecosystem is a functional unit where living organisms interact with each other and their environment. Components: abiotic (light, soil, water) and biotic (producers, consumers, decomposers). Energy flows sun → producers → consumers → decomposers (10% law). Ecological pyramids represent number, biomass, and energy. Nutrient cycles (carbon, nitrogen, phosphorus) maintain balance. Ecosystems ensure energy flow, material cycling, and stability of life on Earth.
UNIT VI: NEURAL CONTROL & COORDINATION
The human brain is protected by the skull and meninges. It consists of forebrain (cerebrum, thalamus, hypothalamus), midbrain, and hindbrain (cerebellum, pons, medulla). Cerebrum controls intelligence, memory, emotions, voluntary actions. Thalamus relays sensory info; hypothalamus regulates temperature, hunger, thirst, circadian rhythm, and pituitary. Midbrain controls visual & auditory reflexes. Cerebellum maintains balance, pons bridges brain parts, medulla controls heartbeat, respiration, blood pressure. Neurons transmit impulses via synapses.
UNIT VII: HUMAN HEALTH & DISEASE
Immunity is the ability to resist infection. Innate immunity is present at birth (physical barriers, physiological, cellular, cytokine-mediated). Acquired immunity develops after exposure or vaccination: active (antibody production, long-lasting) and passive (ready-made antibodies, short-lived). Acquired immunity can be humoral (B-lymphocytes) or cell-mediated (T-lymphocytes). Example: polio vaccine (active), maternal antibodies via placenta (passive). Immunological memory forms the basis of vaccines.
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