France Première Life and Earth Sciences (specialty)
Chapters: 3
1. Earth, life and organisation
Cell division, mutation and gene expression · Earth’s internal dynamics
- 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.
- 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.
2. Contemporary issues
Ecosystems and ecosystem services
- Ecosystem, Food Chains and Energy Flow – An ecosystem is all the living things in a place plus the non-living things around them, working together. Energy enters as sunlight, passes one way up a food chain, and only about 10% moves to each next level.
3. Human body and health
Genetic variation and health · The human immune system
- Genetic Disorders – A genetic disorder is a health problem caused by a change in a gene or in the number or shape of chromosomes. Single-gene disorders can be recessive (cystic fibrosis, sickle cell anaemia: you need two faulty copies), dominant (Huntington disease: one faulty copy is enough) or X-linked (haemophilia, colour blindness: mostly boys). Chromosome disorders such as Down syndrome (an extra chromosome 21) come from a mistake when egg or sperm cells form. Punnett squares predict the chance of each outcome, and genetic testing, counselling and gene therapy help families.
- 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.