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SVT Seconde revision sheet: cell biology, DNA, metabolism, biodiversity, geology, soils, human body, microbiome, health. French program 2026.
The Seconde SVT (Life and Earth Sciences) curriculum provides a solid scientific foundation. It is built around three themes: Life and the Organisation of Living Things, Contemporary Issues of the Planet, and The Human Body and Health.
All living things are made of cells. Eukaryotic cells (animals, plants, fungi) have a membrane-bound nucleus containing DNA, cytoplasm, and organelles (mitochondria for respiration, chloroplasts for photosynthesis in plants). Plant cells also have a cellulose wall and a large vacuole. Prokaryotic cells (bacteria) lack a nucleus; their circular DNA floats freely in the cytoplasm. They are much smaller (1–10 μm vs 10–100 μm).
DNA is a double helix of two nucleotide strands linked by hydrogen bonds between complementary bases: A–T and C–G. A gene is a DNA segment coding for a protein. Alleles are gene variants arising from mutations (substitution, insertion, deletion). Diploid organisms carry two alleles per gene (homozygous if identical, heterozygous if different).
Autotrophs synthesise organic matter from mineral matter. Photosynthesis (in chloroplasts): 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, using light energy. Heterotrophs use organic matter from other organisms. Cellular respiration (in mitochondria): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. Fermentation (anaerobic): alcoholic (yeast → ethanol + CO₂) or lactic (bacteria → lactic acid), producing less ATP than respiration.
Three levels: genetic (allele diversity within a species), species (number of species in an ecosystem), ecosystem (variety of habitats). An ecosystem = biotope (physical environment) + biocoenosis (living organisms). Trophic networks describe feeding relationships. Human activities threaten biodiversity: habitat destruction, pollution, overexploitation, climate change.
Rocks undergo physical (freeze-thaw, wind, water), chemical (dissolution), and biological erosion. Products are transported by water, wind, or glaciers and deposited as sediments when energy decreases. Over time, sediments become sedimentary rocks through compaction and cementation (diagenesis). The rock cycle connects sedimentary, igneous, and metamorphic rocks.
Soil is a living interface composed of: mineral fraction (sand, silt, clay from bedrock weathering), organic matter (litter, humus), living organisms (billions of bacteria per gram, earthworms, fungi), water, and air. Soil formation is extremely slow (~1 cm per century). Degradation through intensive farming, deforestation, and pollution is a major environmental concern.
Natural ecosystems have high biodiversity and closed nutrient cycles. Agroecosystems are human-modified: reduced biodiversity (monoculture), matter exported via harvest, requiring external inputs (fertilisers N-P-K, pesticides, irrigation). Environmental impacts: water pollution (eutrophication), soil degradation, greenhouse gas emissions. Sustainable agriculture aims to balance productivity and environmental protection.
The heart is a double pump. Right side: deoxygenated blood → lungs (pulmonary circulation). Left side: oxygenated blood → body (systemic circulation). Blood pressure: systolic/diastolic, normal ~120/80 mmHg. Hypertension (>140/90) is a cardiovascular risk factor.
Bacteria: prokaryotic; treated with antibiotics. Viruses: non-cellular, obligate intracellular parasites (DNA or RNA + capsid). Parasites: eukaryotic organisms (e.g., Plasmodium causing malaria). Transmission: direct (contact, droplets) or indirect (water, food, vectors).
The gut microbiome (~10¹³ bacteria) aids digestion (fibre breakdown), supports immunity, and acts as a barrier against pathogens. A diverse microbiome is linked to good health; dysbiosis is associated with inflammatory diseases, obesity, and allergies.
During exercise, heart rate and breathing increase to supply muscles with O₂ and glucose. Regular exercise improves cardiovascular health, prevents obesity and type 2 diabetes, and enhances mental well-being. Maximum heart rate ≈ 220 − age.
Male system: testes produce sperm and testosterone. Female system: ovaries produce oocytes, oestrogen, and progesterone. Menstrual cycle (~28 days): follicular phase → ovulation (day ~14, LH surge) → luteal phase. Contraception: hormonal (pill, implant), mechanical (condom — the only method also protecting against STIs; IUD), emergency (morning-after pill within 72 h).