Spain 4º ESO Biology and Geology

Chapters: 5

1. Scientific project

Scientific hypotheses and questions · Searching and communicating science · Reliable scientific sources · Experimental controls · Experiments and fieldwork · Modelling natural processes · Observing and collecting data · Analysing results · Scientists and their work · History of scientific knowledge

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.
Research Skills: From a Question to a Finished Project – Research is a careful way of finding an answer. You ask a clear, focused question, plan how to answer it, find information and check that each source can be trusted, collect and analyse your own data, draw a conclusion that the evidence supports, and share it while crediting every source you used.
Computer Simulation – A model is a simplified description of a real system that keeps only what matters. A computer simulation runs that model step by step in time to see what would happen. It has variables (the state), rules (how the state changes), parameters (numbers we can set) and often randomness, so we repeat runs and average. We check a simulation against real data (validation). Simulations are used for weather, traffic, disease spread, flight training and design, because they are cheaper, safer and faster than real tests, but they are only as good as their model and data.
Collection of Data: Primary and Secondary Sources, Sampling, Census of India and NSSO – Data can be primary (collected first-hand by you) or secondary (already collected by someone else). Primary data comes from personal interviews, mailed questionnaires or telephone interviews. We may study everyone (census) or a small part (sample). Samples can be random or non-random. Results can have sampling errors and non-sampling errors. In India, the Census counts everyone every 10 years, and the NSSO (now NSO) runs sample surveys.
Data: Source and Compilation (Class 12 Geography Practical) – Data are numbers or facts about places and people. We get them from primary sources (our own field work), secondary sources (published by others) and unpublished records. Raw data are messy, so we tabulate them in a clear table, group them into equal classes and count the frequency of each class. A frequency polygon joins the midpoints of the classes to show the shape of the data.
Data Analysis – Data analysis means turning raw data into answers. It follows a cycle: ask a question, collect data, clean it (remove errors, repeats and blanks), organise and transform it, analyse it with summaries such as mean, median, range and patterns, show it with a good chart, and draw a careful conclusion. Watch for outliers, small samples and bias, and remember that a correlation between two things does not prove that one causes the other. Data must also be stored safely and used with permission.
Nature of Science: How Scientific Knowledge Is Built and Changed – Science is a way of knowing that rests on evidence anyone can check. Scientists observe, infer, test ideas that could be proved wrong, and let other experts check their work. Laws describe what happens; theories explain why. Scientific knowledge is reliable but always open to change, and sometimes a whole way of seeing (a paradigm) is replaced.

2. Geology

Relief and landscape · Geosphere structure and dynamics · Plate tectonics · Geological processes and hazards · Geological cross-sections

Landforms: How the Earth's Surface is Shaped – The Earth has layers: crust, mantle, outer core and inner core. The crust is broken into plates that move slowly. When plates push, pull or slide, they make mountains, valleys, earthquakes and volcanoes. On the surface, weathering breaks rocks and agents like rivers, wind, glaciers and waves carry the pieces away (erosion) and drop them (deposition). Sudden events like earthquakes, landslides, avalanches, GLOFs and duststorms are natural hazards we can prepare for.
Interior of the Earth: Earthquake Waves, Layers and Volcanoes – Nobody can dig to the centre of the Earth, so we learn about the inside from direct sources (mine rocks, deep drilling, lava) and indirect sources (heat and pressure with depth, meteors, gravity, magnetism and, above all, earthquake waves). P-waves travel through solids and liquids; S-waves only through solids. Where the waves do not arrive, we get shadow zones, which prove the outer core is liquid. Earthquakes are measured by magnitude (Richter) and intensity (Mercalli). The Earth has a thin crust, a thick mantle with a soft asthenosphere, a liquid outer core and a solid inner core. Magma that reaches the surface builds volcanoes; magma that cools inside forms intrusive landforms like batholiths, sills and dykes.
Distribution of Oceans and Continents: Drift, Spreading and Plates – In 1912 Alfred Wegener said all continents were once one landmass, Pangaea, surrounded by one ocean, Panthalassa, and that they drifted apart. Matching coastlines, rocks, fossils, glacier deposits and placer gold supported him, but he could not explain the force. Mapping the ocean floor showed ridges, plains and trenches; Harry Hess then proposed sea-floor spreading: new crust forms at mid-ocean ridges and old crust sinks at trenches. This led to plate tectonics: the lithosphere is broken into rigid plates that move on the soft asthenosphere and meet at divergent, convergent and transform boundaries. The Indian plate broke away from the south, moved north, and collided with Asia to raise the Himalayas.
Natural Hazards – A natural hazard is a natural event that can harm people and property, such as an earthquake, volcano, landslide, flood, drought or cyclone. It becomes a disaster when it hits people who are not ready. Geological hazards come from inside the Earth; meteorological (weather) hazards come from the air and water. Risk = hazard × vulnerability ÷ capacity to cope, so warning systems, strong buildings and trained people cut the damage.

3. The cell

Cell cycle phases · Mitosis and meiosis · Observing mitosis

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.

4. Genetics and evolution

DNA and RNA structure · DNA extraction · Gene expression and genetic code · Mutations and their effects · Theories of evolution · Phenotype and genotype · Simple inheritance problems · Complex inheritance problems

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.
Protein Synthesis: From Gene to Protein – A gene is a stretch of DNA that holds the recipe for one protein. In transcription, the cell copies the gene into messenger RNA (mRNA) inside the nucleus; U replaces T. The mRNA goes to a ribosome in the cytoplasm. In translation, the ribosome reads the mRNA three bases at a time (a codon). Each codon matches one amino acid, carried in by a transfer RNA (tRNA). The amino acids join into a chain that folds into a protein. A change in the DNA (a mutation) can change the protein.
Mutations – A mutation is a sudden, lasting change in the DNA. Gene (point) mutations change one or a few bases: substitution, insertion or deletion. Insertions and deletions shift the reading frame. Chromosome mutations change big pieces or the number of chromosomes. Mutations happen by chance or because of mutagens such as UV light, X-rays and some chemicals. They can be harmful, neutral or useful, and they are the first source of all genetic variation.
Evolution: How New Kinds of Living Things Arise – Variations arise during reproduction. Nature selects those that help survival, so over many generations populations change: this is evolution. Only inherited (DNA) changes pass on; acquired changes do not. Separated populations can become new species. Homologous organs, analogous organs and fossils help us trace who is related to whom, and complex organs evolved step by step.
Heredity and Mendel's Laws – Heredity is the passing of traits from parents to children through genes. Each parent gives one copy of every gene. A dominant copy hides a recessive one, which is why Mendel saw 3:1 in a monohybrid cross and 9:3:3:1 in a dihybrid cross. Genes are pieces of DNA that make proteins, and proteins build the trait.
Sex-Linked Inheritance – Some genes sit on the X chromosome and have no partner on the short Y chromosome. Such X-linked genes pass from parents to children in a special pattern. A man (XY) has only one X, so one faulty recessive allele shows up in him. A woman (XX) needs two faulty copies; with one she is a healthy carrier. Red-green colour blindness and haemophilia follow this X-linked recessive pattern.

5. Earth in the universe

Origin of universe and solar system · Solar system components · Origin of life hypotheses · Astrobiology research

Cosmology: The Expanding Universe and the Big Bang – Cosmology is the study of the whole universe: its structure, history and future. Galaxies gather in groups, clusters and filaments around huge voids. Distant galaxies are moving away from us, faster the farther they are (Hubble's law, v = H₀d), because space itself is expanding. Running the expansion backwards leads to a hot, dense beginning about 13.8 billion years ago, the Big Bang. The main evidence is redshift, the cosmic microwave background and the amounts of hydrogen and helium. Most of the universe is dark matter and dark energy.
The Solar System – The Solar System is the Sun and everything its gravity holds: 8 planets, their moons, dwarf planets, asteroids, comets and dust. The inner four planets (Mercury, Venus, Earth, Mars) are small and rocky. After the asteroid belt come the giants: gas giants Jupiter and Saturn, ice giants Uranus and Neptune. Gravity pulls planets towards the Sun while they move sideways, so they travel in orbits; closer planets move faster and have shorter years. It all formed about 4.6 billion years ago from a spinning cloud of gas and dust.
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.
Space Exploration – Space exploration means sending rockets, satellites, probes and people beyond Earth's air. Rockets rise by pushing gas down (action–reaction). At about 7.9 km/s sideways a craft keeps falling around Earth in orbit; at 11.2 km/s it escapes. Since 1957 space has been a place of rivalry and cooperation, and it gives us weather forecasts, navigation, communication and new science.