If you could mark the ectoderm of a mouse embryo so that all tissues and organs descended from ectoderm were easily identifiable, where would you expect to find the marker?

Ectoderm refers to one of the three primary germ layers found in the initial phase of an embryo. The other two layers are the endoderm (the most proximal layer) and the mesoderm (the middle layer), the ectoderm is the most distal or the exterior layer. It originates from the external layer of germ cells.  

Generally, ectoderm in vertebrates further develops into the brain and the nervous system, and into the parts of the skin. So, in the given case of the mouse, one would easily find the marker in the nervous system and in the epidermis.  

the index of refraction of the second medium is higher. i just took the test trust me !

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.