What are the three unifying characteristics of chordates?

a) dorsal nerve chord, radial symmetry, three layers of cells

b) water vascular system, backbone, gill slits

c) exoskeleton, notochord, lungs

d) notochord, gill slits, dorsal nerve cord

D) Notochord, gill slits, dorsal nerve cord

Explanation:

Notochord:  is an embryonic midline structure common to all members of the phylum Chordata. It provides rigid support. It is flexible rodlike structure of mesodermal cells.

Gill slits: In most land- living chordates, the "gill slits" are present only in embryonic stages.In fishes and some amphibians, the slits bear gills and are used for gas exchange.

Dorsal nerve cord: The dorsal hollow nerve cord is a hollow cord dorsal to the notochord. It is formed from a part of the ectoderm. It develops into the central nervous system: the brain and spine.

hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

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