Life Sciences
Core Concepts
Know cell theory: all living things are made of cells, cells arise from existing cells, and the cell is the basic unit of life. Distinguish prokaryotic (no nucleus) from eukaryotic (nucleus) cells, and plant from animal cells (chloroplasts, cell wall). Understand DNA → RNA → protein as the flow of genetic information, and that genes are inherited units. Know natural selection: variation, heritability, differential reproduction, and adaptation over generations. Understand ecosystems: producers, consumers, decomposers, food webs, and energy flow (about 90% lost between trophic levels). Recognize homeostasis as maintaining stable internal conditions.
Traps
Questions often imply that individual organisms "adapt" during their lifetime in an evolutionary sense; populations evolve, not individuals. Another trap is confusing mitosis (growth, identical cells) with meiosis (gametes, genetic variation). Watch for claims that evolution is "goal-directed" or that dominant traits are more common.
Rule of Thumb
When asked why a trait spread in a population, check for three ingredients: variation, heritability, and a reproductive advantage.
Worked Example
A beetle population has green and brown individuals. Birds more easily spot green beetles on brown soil, so brown beetles survive and reproduce more. Over generations, brown beetles become more common. This is natural selection: the environment acts on existing variation, not on the beetles' intentions.