Which structures regulate blood flow to certain tissues by closing off pathways and opening them back up? ?
A)Arterioles
B)Pre-Capillary Sphincters
C)Venules
D)Post-Capillary Sphnicters

Sydney drew a flow chart to illustrate the nitrogen cycle. which labels best complete the flow chart? x: producers undergo photosynthesis. y: nitrogen compounds are released into the air. x: nitrogen compounds are released into the air. y: producers undergo photosynthesis. x: free nitrogen is in the atmosphere. y: producers absorb nitrogen compounds through their roots. x: producers absorb nitrogen compounds through their roots. y: free nitrogen is in the atmosphere.

The kind of fertilization found in the majority of aquatic animals is (internal or external) fertilization.

This rapid change in species that rarely leaves behind fossil evidence is referred to as