Evolution and Evolutionary Theory
Core concepts
Know the evidence for evolution: fossils, comparative anatomy (homologous and analogous structures), embryology, molecular biology, and biogeography. Understand Darwin's mechanism: variation, inheritance, differential reproduction, and natural selection. Know the modern synthesis, genetic drift, gene flow, mutation, and non-random mating as evolutionary forces. Know speciation types (allopatric, sympatric) and isolating mechanisms. Understand adaptation, fitness, and the concept of a species. Know the major transitions in the history of life.
Traps
Natural selection acts on phenotypes, not directly on genotypes. Individuals do not evolve; populations do. Homologous structures share ancestry; analogous structures share function but not ancestry. Fitness means reproductive success, not strength. Evolution is not a ladder of progress. Do not confuse Lamarckian inheritance with Darwinian selection. Genetic drift is random and strongest in small populations.
Worked example / rule of thumb
Rule of thumb: "variation plus selection equals change in allele frequency." Worked example: a beetle population with colour variation; birds eat the most visible beetles, so darker beetles survive and reproduce more, and the dark allele frequency rises. If a question asks why two species cannot interbreed, answer reproductive isolation (prezygotic or postzygotic).
Ecology
Core concepts
Know the levels of ecological organization: organism, population, community, ecosystem, biosphere. Understand population dynamics: birth and death rates, immigration and emigration, carrying capacity, and growth models. Know species interactions: competition, predation, parasitism, mutualism, commensalism. Understand food chains, food webs, trophic levels, and energy flow (10% rule). Know biogeochemical cycles (carbon, nitrogen, water) and ecological succession (primary and secondary). Know the factors affecting ecosystems: abiotic and biotic.
Traps
Energy decreases at each trophic level; only about 10% transfers. Decomposers are not a trophic level in the same sense as producers and consumers but recycle nutrients. Primary succession starts on bare rock; secondary succession starts on disturbed soil. A niche is not the same as a habitat. Carrying capacity is not fixed. Do not confuse a food chain with a food web.
Worked example / rule of thumb
Rule of thumb: "energy flows, nutrients cycle." Worked example: if producers fix 10,000 kcal, primary consumers receive about 1,000 kcal, secondary consumers about 100 kcal, and tertiary consumers about 10 kcal. If a question asks why food chains are short, answer energy loss at each level.
Biosphere and Environmental Protection
Core concepts
Know the biosphere as the global system of life and its boundaries (atmosphere, hydrosphere, lithosphere). Understand biodiversity levels: genetic, species, ecosystem. Know the causes of biodiversity loss: habitat destruction, pollution, overexploitation, invasive species, climate change. Understand conservation strategies: protected areas, sustainable use, restoration, and international cooperation. Know pollution types (air, water, soil) and their effects. Understand the greenhouse effect, ozone depletion, and acid rain. Know renewable and non-renewable resources and the principles of sustainable development.
Traps
The greenhouse effect is natural and necessary; its enhancement by human activity is the problem. Ozone depletion and global warming are different issues with different causes. Biodiversity is not just species count; it includes genetic and ecosystem diversity. Conservation is not only about protected areas; it includes sustainable resource use. Do not confuse pollution with habitat loss as the leading cause of biodiversity decline.
Worked example / rule of thumb
Rule of thumb: "reduce, reuse, recycle, restore; protect the habitat first." Worked example: a wetland that filters water and hosts migratory birds provides ecosystem services; draining it removes both the service and the habitat. If a question asks the most effective way to protect biodiversity, answer habitat protection and restoration, supported by sustainable use.