Question

1. what is a dorsal notochord?

part of the nervous system in both vertebrates and invertebrates
part of most chordate embryos that develops into a spinal column (vertebrae)
part of mammals only that develops into the spinal column
part of chordates that protects the circulatory system

Explanation:

1. Analyze the first option: The dorsal notochord is not part of the nervous system in invertebrates (chordates are a specific group, and invertebrates here would be non - chordate, and the notochord is a chordate feature, not part of the nervous system in the way described). So this option is incorrect.
2. Analyze the second option: Chordates have a dorsal notochord in their embryos. In vertebrate chordates, the notochord typically develops into the vertebral column (spinal column made of vertebrae). This matches the definition of the dorsal notochord.
3. Analyze the third option: The notochord is a feature of all chordates (not just mammals), including non - mammalian chordates like fish and amphibians in their embryonic stages. So this option is incorrect.
4. Analyze the fourth option: The notochord's main role is related to the development of the axial skeleton (spinal column in vertebrates), not to protect the circulatory system. So this option is incorrect.

Answer:

B. part of most chordate embryos that develops into a spinal column (vertebrae)