Organismal Biology
What to know
Organismal biology spans structure, function, and physiology across the diversity of life. Review the levels of organization from cells to tissues to organs to organ systems, and the major plant and animal systems. In plants, understand vascular tissue (xylem carries water upward, phloem carries sugars), transpiration and stomatal control, photosynthesis, and the alternation of generations. In animals, focus on circulation, gas exchange, digestion, osmoregulation, nervous signaling, and hormonal regulation, plus homeostasis as a unifying theme.
Know the principles of classification and phylogeny: the domains Bacteria, Archaea, and Eukarya; the kingdoms within Eukarya; binomial nomenclature; and how to read a cladogram based on shared derived characters. Understand the major evolutionary mechanisms: natural selection, mutation, gene flow, genetic drift, and the concept of fitness. Also review the evidence for evolution (fossils, homologous and analogous structures, molecular similarities).
Traps
Questions often reverse the direction of xylem and phloem flow, or confuse homologous structures (shared ancestry) with analogous structures (shared function, different origin). Watch for items that treat individual organisms as evolving; populations evolve, not individuals. Distractors also swap positive and negative feedback, or claim that dominant species are always most numerous.
Worked example
Two species share a similar wing shape. If their wing bones derive from the same ancestral structure, the wings are homologous; if they evolved independently, they are analogous. Rule of thumb: homology reflects common ancestry (structure), analogy reflects common function (convergent evolution).