Answer:
[ANSWER]
Explanation:
When a molecule moves down its concentration gradient is it participating in passive transport; moving up the concentration gradient requires energy making it active transport.
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Answer: It's not blocked
https://www.khanacademy.org/science/high-school-biology/hs-human-body-systems/hs-body-structure-and-homeostasis/a/tissues-organs-organ-systems
The answer is Echinoderms.
According to the Embryological studies, the most ancient chordates were closely related to the ancestors of the echinoderms. Echinoderms are members of the group Phylum Echinodermata of marine animals. Some known echinoderms are starfish, and sea cucumbers.
