This strengthens the argument by helping to establish a connection between chlorophyll and moving to that shade of red.

This is consistent with the author’s hypothesis. Because those other shades don’t produce energy as effectively, the bacteria tends not to move to those areas.

This strengthens the argument by eliminating the alternate explanation that the bacteria are moving to the areas that are warmer rather than because of the greater energy produced by their chlorophyll.

This presents evidence inconsistent with the author’s hypothesis. If the bacteria don’t move to areas lit in blue, even if those areas produce as much energy as the areas lit in the particular shade of red, this suggests the bacteria isn’t moving due to its chlorophyll’s energy.

Other bacteria might move toward other lights for other reasons besides chlorophyll. The author never suggested that no bacteria can ever move to any lights through other methods. The conclusion is just that this particular bacteria detects the red light through chlorophyll.