AP Biology Lecture Notes: Energy, Cells, Evolution, and Scientific Inquiry

Energy flows unidirectionally through ecosystems, originating from sunlight captured by producers, then moving through consumers, with much dissipated as heat. Matter, however, is recycled. Atmospheric CO₂ insulates, contributing to climate change, while fossil fuels, ancient solar energy, release excess carbon. The long-term energy outlook emphasizes efficient renewable sources like solar and wind, with nuclear fusion being a theoretical but challenging goal.

Structure and function are intrinsically linked across all biological levels; efficient structures, like lightweight bird bones or high-surface-area neurons/mitochondria, optimize performance. Cells are the fundamental units of life, categorized as simpler prokaryotes (no nucleus/organelles) or more complex eukaryotes (with nucleus/organelles). All cells contain DNA, which encodes heritable genetic information, central to reproduction, growth, and repair.

Continuity of life depends on DNA, organized into chromosomes, passed via genes. Meiosis in sexual reproduction creates haploid gametes, combining in fertilization to form a diploid zygote, thereby introducing genetic variation. Evolution, the unifying theme of biology, explains how populations change over billions of years through variation and differential survival. Humans are products of this long evolutionary history.

The Human Genome Project sequenced DNA, drastically reducing costs and time, and revolutionized medicine by enabling targeted therapies and drug development. Bioinformatics, combining biology and computer science, analyzes DNA sequences, a field increasingly aided by AI.

Biological regulation often uses negative feedback to maintain stability (homeostasis), for example, thermoregulation around 37°C. Positive feedback amplifies processes, seen in childbirth or fruit ripening via ethylene (chemical formula \mathrm{C2H4}), but generally requires more energy.

Evolution underpins biodiversity, currently estimated at 10 to 10^8 species, with taxonomy (hierarchical classification) and phylogeny (evolutionary relationships via genetic data) organizing this diversity.

Science is a problem-solving method using inquiry. Discovery science describes nature, while hypothesis-based science tests predictions from a hypothesis (a testable statement). A scientific theory is a well-supported, broadly applicable explanation, distinct from a common hypothesis. Deductive reasoning, using if-then logic to isolate variables, guides experiments.

These biological principles inform critical real-world issues, from climate policy and sustainable energy to targeted medicine, agricultural practices, and ethical considerations