Heartwood. In contrast to sapwood, a term for the dead, clogged xylem cells near the center of a tree. Heartwood is the tree's main column of support.
In facilitated diffusion molecules only move with the aid of a protein in the membrane. Normal diffusion requires molecules to move through a special doorway
Answer:
Reptiles
Explanation:
Vertebrate paleontology covers everything from the tiny, fish-like creatures, to the salamander-like ancestors of all land vertebrates, to dinosaurs, mammals, flying and swimming reptiles, etc.
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