What stimulates the ribosome to move down one codon?

The chain moves from the 5' - 3' direction caused by the use of GTP and several protein-enzyme complexes. As the polypeptide chain is produced the t-RNA move from site A to site P, and then are released into the cytoplasm. The polypeptide chain continues to grow, and is held to the ribosome by the t-RNA at the P site.

Explanation:

one would be wind another would be water density

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?