Plant biology, perhaps the oldest branch of science, is driven by a combination of curiosity and need curiosity about how plants work need to apply this knowledge judiciously to feed, clothe, and house a burgeoning human population.

 Growth toward or away from a stimulus Gravitropism (Gravity) Phototropism (Light) Thigmotropism (Touch)

 The stems of plants raised in the dark elongate much more rapidly than normal, a phenomenon called etiolation.

CELL WALL CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay molecules Activation of cellular responses Hormone or environmental stimulus Plasma membrane

 Are chemical signals that coordinate the different parts of an organism  Help coordinate growth, development, and responses to stimuli

 The relative lengths of night and day  The environmental stimulus plants use most often to detect the time of year