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SVT Terminale revision sheet: genetics, evolution, geology, plants, photosynthesis, nervous system, immunity, diabetes. French Bac 2026 program.
The Bac SVT exam lasts 3 hours 30 minutes (coefficient 16). Exercise 1 tests knowledge (6–7 points) and Exercise 2 tests scientific reasoning using documents (13–14 points).
Meiosis produces 4 haploid cells from one diploid cell through two divisions. Interchromosomal shuffling: random distribution of homologous pairs during anaphase 1 (2²³ ≈ 8.4 million combinations in humans). Intrachromosomal shuffling (crossing-over): exchange of chromatid segments during prophase 1, creating recombinant chromatids with new allele combinations.
Fertilisation restores diploidy and further amplifies genetic diversity. Each zygote is genetically unique.
Gene duplication (via unequal crossing-over) creates gene families. Copies accumulate independent mutations and may gain new functions. Example: globin family (α, β, γ, δ). Horizontal gene transfer: genetic material between unrelated organisms (common in bacteria via conjugation, transduction; also in eukaryotes via endosymbiosis).
The human lineage includes all species since the last common ancestor with chimpanzees. Criteria: bipedalism (centred foramen magnum, short wide pelvis), increasing cranial volume, reduced face, parabolic mandible, lithic industry. Human and chimp DNA are ~98.7% identical. Evolution is bushy: multiple species coexisted (e.g., Homo sapiens and Homo neanderthalensis, with 2–4% Neanderthal DNA in modern Europeans).
Relative dating: superposition (lower = older), cross-cutting (fault is younger), continuity, fossil identity. Absolute dating (radiochronology): N(t) = N₀e^(−λt), T₁/₂ = ln(2)/λ. Carbon-14 (T₁/₂ ≈ 5730 years, up to ~50 000 years). Potassium-Argon (⁴⁰K/⁴⁰Ar, T₁/₂ ≈ 1.25 billion years, for old igneous rocks).
Ophiolites: oceanic lithosphere fragments on continents, evidence of past ocean closure. HP-BT metamorphism: green schist → blue schist (glaucophane) → eclogite (jadeite + garnet), evidence of subduction.
Photosynthesis occurs in chloroplasts. Light phase (thylakoids): light energy splits water (2H₂O → O₂ + 4H⁺ + 4e⁻), producing ATP and NADPH. Calvin cycle (stroma): CO₂ fixation by RuBisCO onto RuBP, reduction using ATP and NADPH to form organic molecules. Overall: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Sap transport: xylem carries raw sap (water + minerals) upward via transpiration pull; phloem carries elaborated sap (sucrose) from source to sink organs.
Plant reproduction: pollination (anemophilous by wind, entomophilous by insects). Plant-pollinator coevolution: floral traits and pollinator traits evolved together. Seed dispersal: wind (anemochory), animals (zoochory), water (hydrochory).
Myotatic reflex: monosynaptic stretch reflex. Arc: sensory receptor (muscle spindle) → afferent neuron → spinal cord synapse → motor neuron → muscle contraction. Action potential: all-or-nothing signal encoded in frequency. Synapse: neurotransmitter release (e.g., acetylcholine) into synaptic cleft.
Voluntary movement: controlled by primary motor cortex (contralateral). Brain plasticity: synaptic connections modified by experience and learning.
Stress: acute stress activates sympathetic nervous system (adrenaline) and HPA axis (hypothalamus → CRH → pituitary → ACTH → cortisol). Negative feedback limits cortisol. Chronic stress: harmful effects (memory impairment, immunosuppression). Resilience depends on genetic, environmental, and psychological factors.
Blood glucose regulation: insulin (from β cells, lowers glucose) and glucagon (from α cells, raises glucose). Type 1 diabetes: autoimmune destruction of β cells, insulin injections needed. Type 2: insulin resistance ± insufficient secretion, linked to obesity and lifestyle.
Immune system: innate immunity (barriers, inflammation, phagocytosis via PRR/PAMP recognition) and adaptive immunity. B lymphocytes produce specific antibodies. CD8 T cells destroy infected cells. CD4 T cells coordinate the response via interleukins. Vaccination creates memory cells for faster secondary response.
Exercise 1: structured synthesis with introduction, organised argument, labelled diagrams, and conclusion. Exercise 2: analyse each document, cite data, link documents to each other and to your knowledge.