Final answer:
Basophils are granular leukocytes with a dark granular, bilobed nucleus that release histamines and heparin, often associated with allergic reactions and certain health conditions.
Step-by-step explanation:
The characteristics of a basophil include being granular with large granules that stain dark blue to purple. Basophils are known for having a dark granular nucleus, specifically a bilobed nucleus that might be obscured by the large granules. These cells are involved in allergic reactions and inflammatory processes and help to combat infections. They release histamines, which contribute to inflammation, and heparin, which prevents blood clotting. High counts of basophils can be associated with allergies, parasitic infections, and certain conditions such as hypothyroidism.