Why Do Organisms Look The Way They Do?

This unit uses investigations of organisms (including people) to raise questions about how similarities and differences between individuals and populations are influenced by inheritance of traits. Students investigate inheritance in plants they grow in class, and investigate pedigrees that document inheritance of human traits, developing a Mendelian model of inheritance to account for the patterns they uncover. Students use this model to explain the source of variation within a population, and why organisms of the same species exhibit many common characteristics. Students examine how changing environmental conditions can influence variation in a population. Through investigations of several data-rich scenarios of population change, students develop a model of how changing environmental conditions can lead to organisms with some variations of traits being more likely to survive and produce offspring, resulting in shifted distributions of those traits in future generations. Students generalize their explanations to develop a model of natural selection as defined by naturally occurring variation in inherited traits, changing environmental conditions and differential survival, addressing most notably the crosscutting concepts of patterns, and of stability and change in systems.