List three structural changes that must occur in young, unmodified plant cells as they develop into xylem tissue.

Classify the structures as homologous or analogous, depending on their structure and function.

Drag each tile to the correct box. the body monitors the levels of oxygen in the blood to regulate breathing. isabel is running in a marathon and is near the finish line. she feels out of breath. how will her nervous system work to generate a reaction? arrange the tiles in chronological order. isabel's breathing rate increases. sensory receptors in the arteries detect low oxygen levels. the brain sends signals through motor neurons. sensory neurons generate an impulse. the central nervous system relays an impulse to certain brain regions.

Natural selection changes allele frequencies because some survive and reproduce more successfully than others.