South 고등학교 3학년 Life Science II
Chapters: 6
1. History of life science
Development of life science · Key discoveries
- History of Science: How Our Ideas About Nature Changed – Science grew slowly over 5,000 years. Early civilisations watched the sky to make calendars. Greek thinkers asked why things happen and used reason. Indian and Islamic scholars gave us zero, algebra and careful experiments. In the Scientific Revolution, Copernicus, Galileo and Newton replaced the Earth-centred model with a Sun-centred one and tested ideas by experiment. Modern science brought atoms, evolution, relativity and quantum theory. Each step shows the same lesson: good evidence can overturn old ideas.
2. Cell characteristics
Levels of organisation · Biomolecules · Prokaryotic vs eukaryotic cells · Organelles working together · Membrane transport · Enzymes and activation energy
- Levels of Organisation: From Cell to Biosphere – Life is built in levels, like a set of boxes inside boxes. Cells join into tissues, tissues into organs, organs into organ systems, and organ systems into a whole organism. Organisms of one species form a population; many populations form a community; a community plus its non-living surroundings is an ecosystem; all ecosystems together make the biosphere. Each level is made of the level below it and can do things the lower level cannot.
- Biomolecules – A cell is mostly water, plus four big families of carbon compounds: proteins, carbohydrates, lipids and nucleic acids. Grinding tissue in acid separates small molecules (acid-soluble pool) from big ones – proteins, polysaccharides and nucleic acids (acid-insoluble pool). Proteins are chains of amino acids folded into four levels of structure. Polysaccharides are chains of sugars; lipids are fatty acids on glycerol; nucleic acids are chains of nucleotides. Enzymes are protein catalysts that bind a substrate at the active site, lower the activation energy, and are affected by temperature, pH, substrate level and inhibitors.
- Cell: The Unit of Life – Every living thing is made of cells, and every new cell comes from an old cell. Prokaryotic cells (bacteria) have no nuclear envelope and no membrane-bound organelles; eukaryotic cells have a true nucleus and many organelles. The membrane is a fluid mosaic of lipids and proteins; plants add a cellulose wall. ER, Golgi, lysosomes and vacuoles form the endomembrane system. Mitochondria and plastids make energy and food, ribosomes make proteins, the cytoskeleton, cilia, flagella and centrioles give shape and movement, and the nucleus holds the DNA.
- Membrane Transport: How Things Get In and Out of a Cell – The cell membrane is a thin double layer of fat-like molecules with proteins in it. It lets some substances through and stops others (selectively permeable). Diffusion moves particles from high to low concentration with no energy. Facilitated diffusion does the same through protein channels. Osmosis is the diffusion of water through a partially permeable membrane. Active transport uses ATP and a protein pump to move particles from low to high concentration. Very large things enter and leave in bubbles (endocytosis and exocytosis).
3. Respiration and photosynthesis
Mitochondria and chloroplasts · Respiration and photosynthesis compared · Aerobic respiration vs fermentation · Light reactions · Electron transport chains
- Cell: The Unit of Life – Every living thing is made of cells, and every new cell comes from an old cell. Prokaryotic cells (bacteria) have no nuclear envelope and no membrane-bound organelles; eukaryotic cells have a true nucleus and many organelles. The membrane is a fluid mosaic of lipids and proteins; plants add a cellulose wall. ER, Golgi, lysosomes and vacuoles form the endomembrane system. Mitochondria and plastids make energy and food, ribosomes make proteins, the cytoskeleton, cilia, flagella and centrioles give shape and movement, and the nucleus holds the DNA.
- Respiration in Plants – Respiration breaks food like glucose to release energy stored as ATP. Plants take in O₂ through stomata and lenticels. Glycolysis in the cytoplasm splits glucose into two pyruvates. Without O₂, pyruvate is fermented to ethanol or lactic acid. With O₂, pyruvate enters the mitochondrion, runs the Krebs cycle, and the electron transport system uses O₂ to make most of the ATP: up to 38 per glucose. The same path also builds molecules (amphibolic). RQ = CO₂ given out ÷ O₂ taken in.
- Photosynthesis in Higher Plants – Green plants make sugar from carbon dioxide and water using light. It happens in chloroplasts. The light reaction in the thylakoids splits water, gives out oxygen and makes ATP and NADPH. The Calvin cycle in the stroma uses that ATP and NADPH to fix CO₂ into sugar. C₄ plants add a CO₂ pump that stops the wasteful photorespiration. The slowest factor, such as light, CO₂ or temperature, sets the rate.
4. Gene expression and control
Gene structure · DNA replication · Transcription and translation · Genetic code · Control of transcription · Development and differentiation
- Gene Structure: What Is Inside a Gene? – A gene is a stretch of DNA that carries the instructions to make a functional product, usually a protein (sometimes an RNA). A typical gene has a promoter (where RNA polymerase binds and transcription starts), a coding region (the message) and a terminator (where transcription stops). The template strand is read; the coding strand has the same sequence as the mRNA (with T instead of U). In prokaryotes, genes are continuous (no introns) and related genes are often grouped in an operon under one promoter, making one polycistronic mRNA. In eukaryotes, genes are split: coding exons are separated by non-coding introns. The whole gene is copied into pre-mRNA; then introns are removed and exons joined (splicing), a cap and a poly-A tail are added, and the mature mRNA leaves the nucleus. Alternative splicing lets one gene make several proteins. The genome is all the DNA of an organism; in humans only about 1–2% codes for protein.
- Molecular Basis of Inheritance – DNA is the genetic material in most living things (some viruses use RNA). It is a double helix: two antiparallel strands of nucleotides, A pairs with T by 2 hydrogen bonds and G with C by 3. Long DNA is packed on histones into nucleosomes and then chromatin. DNA copies itself semi-conservatively (Meselson–Stahl). The central dogma says DNA → RNA → protein. Transcription makes RNA from one strand; in eukaryotes the hnRNA is capped, tailed and spliced. The genetic code is a triplet, has 64 codons (61 for amino acids, 3 stops), starts with AUG, is nearly universal and degenerate. Ribosomes translate mRNA into protein with tRNA adaptors. Genes are switched on and off; the lac operon is the classic example. The Human and Rice Genome Projects read whole genomes, and DNA fingerprinting uses repeat DNA (VNTRs) to identify people.
- Gene Regulation: How Cells Switch Genes On and Off – Every cell carries the same DNA but uses only some genes. Cells control mostly at transcription. In bacteria, the lac operon is a set of genes under one promoter and one operator: a repressor blocks it when there is no lactose; lactose removes the repressor and the genes are read (an inducible operon). In eukaryotes, transcription factors, enhancers and silencers control each gene, and epigenetic marks (DNA methylation, histone packing) can keep genes off without changing the DNA code. Different on/off patterns make different cell types (differentiation).
- Development: From One Cell to a Whole Body – Development (ontogenesis) is the life story of one organism. The zygote divides by cleavage into a ball of cells, the blastula. In gastrulation cells move inwards and make three germ layers: ectoderm, mesoderm and endoderm. Cells then differentiate: every cell has the same genes, but each type switches on a different set. Signals between cells (induction) and master genes such as Hox genes decide where each part forms. After birth or hatching the organism grows, develops directly or by metamorphosis, ages and can sometimes regenerate.
5. Evolution and diversity
Origin of first cells · Major transitions · Three domains, six kingdoms · Features of phyla · Evidence for evolution · Speciation
- Evolution: Origin of Life, Mechanisms and Human Evolution – Life began on the early Earth from simple chemicals: Oparin and Haldane proposed it and Miller made amino acids in a flask. Evidence of evolution comes from fossils, homologous and analogous organs, embryos, molecules and changes we can watch (industrial melanism, drug resistance). Darwin explained it by natural selection acting on variation in populations; the modern synthetic theory adds genes: mutation, recombination, gene flow, genetic drift and natural selection change allele frequencies. If none of these act, frequencies stay constant: Hardy–Weinberg, p² + 2pq + q² = 1. Selection can be stabilising, directional or disruptive. One ancestor spreading into many habitats gives adaptive radiation (Darwin’s finches, Australian marsupials). Humans evolved from Dryopithecus-like apes through Australopithecus, Homo habilis, Homo erectus and Neanderthals to Homo sapiens.
- Biological Classification – Whittaker (1969) sorted living things into five kingdoms, Monera, Protista, Fungi, Plantae and Animalia, using cell type, cell wall, body plan, mode of nutrition, reproduction and relationships. Monera are prokaryotes (bacteria, archaebacteria, cyanobacteria, mycoplasma). Protista are one-celled eukaryotes in five groups. Fungi are heterotrophs with chitin walls in four classes. Lichens are an alga and a fungus living together. Viruses, viroids and prions are not placed in any kingdom.
- Diversity and Classification of Living Organisms – Earth has millions of kinds of living things, and India is one of the richest places. To study them, we sort them into groups by asking simple questions about their bodies: Is there a nucleus? One cell or many? Can it make its own food? This gives five kingdoms: Monera, Protista, Fungi, Plantae and Animalia. Animals split into invertebrates and vertebrates. Every species gets a two-part scientific name. Viruses are not cells, so they fit in no kingdom.
6. Biotechnology and life
Recombinant DNA · Cloning, tissue culture, fusion · Antibodies, gene therapy, stem cells · LMOs · Bioethics
- Biotechnology: Principles and Processes (Recombinant DNA Technology) – Genetic engineering means changing the genes of a living thing on purpose. We cut the gene we want with restriction enzymes (molecular scissors), paste it into a carrier DNA called a vector using DNA ligase (molecular glue), put it into a host cell, pick out the cells that took it, and grow them in big tanks (bioreactors) to collect the product. PCR makes millions of copies of a gene, and gel electrophoresis sorts DNA pieces by size.
- Biotechnology and its Applications – The tools of genetic engineering are used in medicine, farming and research. Bacteria make human insulin; yeast makes safe vaccine proteins. Stem cells can become many cell types. Gene therapy puts a correct gene into a patient's cells. GM crops like Bt cotton carry a gene for a protein that kills pests. Transgenic animals carry foreign genes to help study disease or make medicines. Because these are powerful, India controls them through GEAC, and laws guard against biopiracy and unfair patents.
- Bioethics: Deciding What Is Right in Biology and Medicine – Bioethics asks whether we should do what biology and medicine now let us do. It uses four principles: autonomy (respect choice), beneficence (do good), non-maleficence (do no harm) and justice (fairness). Human dignity means a person is never only a means to an end, so informed consent is needed. Therapeutic cloning may be allowed under strict rules; reproductive human cloning is banned in most countries. Start-of-life and end-of-life questions are weighed as benefits against risks and values.