France Terminale Life and Earth Sciences (specialty)
Chapters: 5
1. Genetics and evolution
Origin of genotype: meiosis and mixing · Genome complexification · Evolution of genomes in populations · Other sources of diversity
- 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.
- Genome Evolution: How Genomes Become More Complex – Genomes do not only change by small mutations. They can also gain whole genes. Horizontal gene transfer moves genes between unrelated cells, for example between bacteria. Viruses can carry genes from one cell to another and leave copies in the host DNA. Endosymbiosis made mitochondria and chloroplasts from engulfed bacteria that stayed inside a host cell and kept some of their own DNA. Gene and genome duplications give extra copies that are free to change and take new jobs. These events add genes quickly and are a major source of new functions.
- 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.
2. Earth’s geological past
Relative and absolute dating · Traces of Earth’s past
- Radiometric Dating – Relative dating puts rocks and fossils in order (lower layers are usually older). Absolute (radiometric) dating gives an age in years. A rock crystal traps radioactive parent atoms that decay at a fixed rate into daughter atoms. After each half-life, half of the parent atoms are left. Measuring the daughter-to-parent ratio gives the age: t = T½ × log₂(1 + D/P).
- 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.
3. From wild to domesticated plants
Functional organisation of flowering plants · Plants make organic matter · Plant reproduction · Plant domestication
- How a Flowering Plant Works – A flowering plant cannot move, so it is built to collect: roots with millions of hairs take water and minerals from the soil, and wide leaves take carbon dioxide and light. Xylem carries raw sap (water + minerals) up, pulled by evaporation from leaves. Phloem carries elaborated sap (sugars) from leaves to roots, fruits and growing tips. Hormones control growth, chemical and physical defences protect it, and its shape changes with the environment.
- Life Processes and Photosynthesis – Life processes are the jobs every living body must keep doing to stay alive: nutrition, respiration, transport and excretion. Green plants do nutrition by photosynthesis: using sunlight and chlorophyll, they turn carbon dioxide and water into glucose and give out oxygen.
- Sexual Reproduction in Flowering Plants – A flower is the sex organ of a plant. The stamen makes pollen grains (male gametophytes). The ovule holds the embryo sac (female gametophyte, 7 cells, 8 nuclei). Pollination brings pollen to the stigma; the pistil checks it; a pollen tube carries two male gametes to the embryo sac. One fuses with the egg (zygote, 2n) and the other with two polar nuclei (primary endosperm nucleus, 3n). This is double fertilisation. The ovule becomes the seed and the ovary becomes the fruit.
- Plant Domestication: From Wild Plants to Crops – Domestication means people slowly changed wild plants into crops by always keeping seeds from the best plants. Chosen traits: seeds that stay on the plant, bigger grains, less bitterness, even ripening. The price is lost genetic diversity: fields of one variety can all fall to one disease. Hybridisation joins good traits of two parents, and genetic engineering moves a single gene into a crop.
4. Contemporary planetary issues
Past and future climates
- Climate Change and the Greenhouse Effect – Climate is the average weather of a place over about 30 years. Greenhouse gases like carbon dioxide and methane trap some of the heat the Earth gives off. Humans have added a lot more of these gases by burning fossil fuels and cutting forests, so the Earth is warming. This causes melting ice, rising seas and more extreme weather. We can cut emissions (mitigation) and prepare for changes (adaptation).
5. Human body and health
Behaviour, movement and nervous system · Producing movement: muscle contraction and energy supply · Stress response
- Nervous System, Reflex Action and the Human Brain – Nerve cells (neurons) carry messages as electric impulses and pass them to the next cell with chemicals across a gap called a synapse. Quick safety responses (reflexes) are handled by the spinal cord; thinking and control come from the brain, which is guarded by the skull and a fluid cushion.
- Muscle Physiology: How Muscles Contract – A skeletal muscle is made of long cells called fibres. Each fibre holds chains of tiny units called sarcomeres. In a sarcomere, thin actin filaments and thick myosin filaments overlap. A nerve signal releases calcium, myosin heads grab actin and pull it to the middle, and the muscle shortens. Every pull uses ATP. ATP comes from creatine phosphate (seconds), fermentation that makes lactate (up to about two minutes) and aerobic respiration (long exercise). When ATP runs low the muscle tires.
- Stress Hormones: Adrenaline, Cortisol and Feedback – Danger wakes the brain's alarm centre. A fast nerve signal (autonomic nervous system) makes the adrenal glands release adrenaline, so the heart pumps more blood. A slower hormone chain releases cortisol, which keeps sugar high. Cortisol then returns to the brain and switches the alarm off by negative feedback. If stress never stops, the brake weakens, cortisol stays high, and body and memory are harmed.