Which of these describes the most widely held scientific theory on what catastrophic events led to the cretaceous–tertiary extinction about 65.5 million years ago, which eventually led to the extinction of dinosaurs?

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.

sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.