South 고등학교 3학년 Life Science I
Chapters: 5
1. Understanding life science
Characteristics of life · Integrated nature of life science · Methods of inquiry
- Characteristics of Life – Living things share a set of signs: they are made of cells, use energy (metabolism), respond to their surroundings, keep their inside steady (homeostasis), grow, reproduce, and as groups adapt over generations. Something is called alive only if it shows all of these. Viruses sit on the border because they copy themselves only inside a host cell.
- The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.
2. Human metabolism
Energy from metabolism · Wastes and organ systems · Metabolic diseases
- Metabolism: How Cells Build, Break and Use Energy – Metabolism is the full set of chemical reactions inside a living thing. Breaking big molecules into small ones is catabolism; it gives out energy. Building big molecules from small ones is anabolism; it uses energy. ATP carries the energy between the two, like a rechargeable battery. Each reaction is sped up by its own enzyme, and the reactions link into chains called metabolic pathways.
- Human Body Systems – Your body is organised in levels: cells make tissues, tissues make organs, organs make organ systems, and all systems together make you, the organism. Each system has a main job: skeletal (frame), muscular (movement), circulatory (transport), respiratory (gas exchange), digestive (food), excretory (waste), nervous and endocrine (control), immune (defence), integumentary (skin, hair, nails) and reproductive. No system works alone: during exercise the muscles, heart, lungs and nerves all change together to keep the inside of the body steady (homeostasis).
- Metabolic Diseases: Diabetes and Blood Sugar – Metabolic diseases happen when the body cannot handle energy and nutrients properly. In diabetes, blood sugar (glucose) stays too high, either because the body makes too little insulin (type 1) or because cells stop answering insulin (type 2). Food, exercise and medicine help keep sugar steady.
3. Homeostasis and control
Nerve impulses · Muscle contraction · Central and peripheral nervous systems · Hormones · Homeostasis · Diseases and defences · Vaccines
- Neural Control and Coordination – Coordination means organs working together. The nervous system does this fast, using neurons. A neuron has a cell body, dendrites and an axon; many axons have a myelin sheath with nodes of Ranvier. The central nervous system (brain and spinal cord) processes information; the peripheral nervous system (nerves) carries it. The PNS has a somatic part (skeletal muscles) and an autonomic part (sympathetic and parasympathetic) for internal organs, the visceral system. At rest the axon is polarised: inside −, outside +, about −70 mV. A stimulus lets Na+ rush in, creating an action potential that travels along the axon. At a synapse, neurotransmitters carry the signal to the next neuron.
- Locomotion and Movement – Movement is a change in position of a body part; locomotion is moving the whole body from place to place. Cells move in three ways: amoeboid, ciliary and flagellar. Humans use muscular movement. Muscles are skeletal, visceral or cardiac. A skeletal muscle is made of fibres, each packed with myofibrils made of repeating sarcomeres of actin and myosin. A nerve signal releases Ca2+, myosin heads pull actin using ATP, and the sarcomere shortens (sliding filament theory). The skeleton has 206 bones. Joints can be fibrous, cartilaginous or synovial (ball and socket, hinge, pivot, gliding, saddle). Disorders include myasthenia gravis, tetany, muscular dystrophy, arthritis, osteoporosis and gout.
- Chemical Coordination and Integration – Hormones are chemical messengers made in tiny amounts by ductless (endocrine) glands. They travel in blood and act on target cells that have the right receptor. The hypothalamus controls the pituitary, which controls many other glands; negative feedback keeps levels steady. Main glands: pineal, pituitary, thyroid, parathyroid, thymus, adrenal, pancreas (islets), testis and ovary. The heart, kidney and gut also make hormones. Protein hormones act through membrane receptors and second messengers like cAMP; steroid and thyroid hormones enter the cell and change gene expression. Too little (hypo-secretion) or too much (hyper-secretion) of a hormone causes disorders like dwarfism, gigantism, goitre, diabetes, Addison's disease and Cushing's syndrome.
- Homeostasis – Homeostasis is how the body keeps its internal environment (blood and tissue fluid) steady even when the outside world changes. It controls body temperature (about 37 °C), blood glucose (about 4–6 mmol/L), water and salt, and blood pH (about 7.4). It mostly uses negative feedback: a receptor senses a change, a control centre decides, and an effector brings the level back to its set point.
- Human Health and Disease – Health means the body, mind and social life all work well. Diseases can be caused by germs (pathogens) like bacteria, viruses, protozoa, worms and fungi. Our body fights them with two kinds of immunity: innate (we are born with it) and acquired (it learns and remembers). Vaccines use this memory. HIV destroys helper T cells and causes AIDS. Cancer is cells dividing without control. Drugs and alcohol harm the body and mind, especially in teenagers.
4. Heredity
Chromosomes, genome, genes · Meiosis · Human pedigrees · Chromosome and gene disorders
- Chromosomes, Genes, Alleles and Polygenic Inheritance – Each cell nucleus holds chromosomes made of DNA. All the DNA of an organism is its genome. A gene is a stretch of DNA at a fixed place on a chromosome; its different forms are alleles. Chromosomes come in pairs, one from each parent. Meiosis puts one chromosome of each pair into each gamete, and fertilisation restores the pairs. Some traits, like height, depend on many genes together (polygenic) and so show a smooth range. All living things use the same four-letter DNA code.
- Cell Cycle and Cell Division – A cell grows, copies its DNA and splits in a fixed order called the cell cycle: interphase (G1, S, G2) and M phase. In S phase the DNA doubles (2C → 4C) but the chromosome number stays the same. Mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis give two cells identical to the parent – it is an equational division used for growth and repair. Meiosis has two divisions; in meiosis I homologous chromosomes pair, cross over and separate, halving the chromosome number (2n → n). It makes four haploid cells for gametes and creates variation.
- Principles of Inheritance and Variation – Genes come in pairs (alleles). Each parent passes one allele of each pair to the child. Mendel showed dominance (3 : 1), segregation and independent assortment (9 : 3 : 3 : 1). Real life has twists: incomplete dominance (1 : 2 : 1), co-dominance (AB blood), multiple alleles, pleiotropy (one gene, many effects) and polygenic traits (many genes, one trait). Genes sit on chromosomes, so genes on the same chromosome are linked and are separated only by crossing over. Sex chromosomes decide sex (XX-XY in humans, ZW in birds, haplo-diploid in honeybees) and carry sex-linked genes (haemophilia, colour blindness). Mistakes in genes cause Mendelian disorders (thalassemia, sickle-cell) and mistakes in chromosome number cause Down, Turner and Klinefelter syndromes.
5. Ecosystems and interactions
Ecosystem levels · Populations and communities · Importance values and dominance · Succession · Energy flow and cycles · Biodiversity
- Ecosystem: Structure, Productivity, Energy Flow and Pyramids – An ecosystem is a working unit of nature where living things (biotic) and non-living things (abiotic) interact. Plants make food at a rate called productivity: gross (GPP) minus respiration gives net (NPP = GPP − R). Dead matter is broken down in five steps: fragmentation, leaching, catabolism, humification and mineralisation. Energy enters as sunlight, flows one way through trophic levels and only about 10% passes on each time. Ecological pyramids of number, biomass and energy show this; number and biomass pyramids can be inverted, but the energy pyramid is always upright.
- Organisms and Populations: Growth and Interactions – A population is a group of the same species living in one area at one time. It has features that a single organism does not have: density, birth rate, death rate, sex ratio and age structure. N grows by births and immigration and shrinks by deaths and emigration. With unlimited food it grows fast (J-curve, dN/dt = rN); with limited food it slows and stops at the carrying capacity K (S-curve, dN/dt = rN(1 − N/K)). Different species affect each other: mutualism (+/+), competition (−/−), predation and parasitism (+/−), commensalism (+/0) and amensalism (−/0).
- Biodiversity and its Conservation – Biodiversity is the variety of life at three levels: genetic, species and ecological. It is highest near the equator and grows with area (log S = log C + Z log A). Every species matters, like rivets on a plane. We are losing species fast because of the 'evil quartet': habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinction. The IUCN Red List (Red Data Book) ranks species from Least Concern to Extinct. We protect life in situ (hotspots, national parks, sanctuaries, biosphere reserves, sacred groves, Ramsar wetlands) and ex situ (zoos, botanical gardens, seed and gene banks).