Organismal Biology: Structure, Function, and Diversity
What to know
This domain covers the relationship between structure and function across major groups: plants, animals, fungi, protists, and prokaryotes. Know plant tissues and organs (roots, stems, leaves; xylem and phloem; stomata and transpiration), animal systems (circulation, respiration, digestion, nervous, endocrine, immune, excretory), and homeostasis as regulation of internal conditions. Understand levels of organization (cell, tissue, organ, organ system, organism). Know major taxonomic groupings and distinguishing features, and how body plans reflect environment and lifestyle. Recognize feedback loops: negative feedback stabilizes, positive feedback amplifies.
Traps
Questions often test the direction of transport in xylem (water and minerals upward from roots) versus phloem (sugars to sinks, both directions). Another trap is confusing negative and positive feedback: most homeostatic regulation is negative feedback. Watch for questions asking which structure performs a function in a specific group (e.g., gills vs. lungs vs. tracheae). Also be careful not to assume all organisms share the same organ systems; compare analogous functions across taxa.
Worked example
During exercise, body temperature rises; sensors detect the change and the body sweats, cooling down and returning temperature toward a set point. This is negative feedback because the response counteracts the initial change. Rule of thumb: if the response reduces the deviation, it is negative feedback; if it increases the deviation, it is positive feedback.
Rule of thumb
For any structure-function question, identify the environment the organism lives in and the function the structure must serve.