The process by which a stimulus produces a response that opposes the original stimulus

1. efficient use of space

2. elimination of groundwater contamination

3. energy generation

4. lower carbon footprint

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.