1) Does the Earth's moon count as a "world"? 2) A "habitable" world is a world where there might possibly be

3) Are we only interested in intelligent life, or complex life, or any life?

4) Would fish be considered intelligent life, or complex life, or simple life?

The human eye contains a molecule called 11-cis-retinal that changes shape when struck with light of sufficient energy. the change in shape triggers a series of events that results in an electrical signal being sent to the brain that results in vision. the minimum energy required to change the conformation of 11-cis-retinal within the eye is about 164 kj/mol.