The Living World 8th Edition by George Johnson

تمرين 19

Living things can be distinguished from nonliving things because they have
A) complexity.
B) movement.
C) cellular organization.
D) response to a stimulus.
In Fred Hoyle's science fiction novel The Black Cloud , the earth is approached by a large interstellar cloud of gas. As the cloud orients around the sun, scientists discover that the cloud is feeding, absorbing the sun's energy through the excitation of electrons in the outer energy levels of cloud molecules, a process similar to the photosynthesis that occurs on earth. Different portions of the cloud are isolated from each other by associations of ions created by this excitation. Electron currents pass between these sectors, much as they do on the surface of the human brain, and endow the cloud with self-awareness, memory, and the ability to reason. Using electricity produced by static discharges, the cloud is able to communicate with human beings and to describe its history. The cloud tells our scientists that it once was smaller but has grown by absorbing molecules and energy from stars like our sun, on which it has been grazing. Eventually the cloud moves off in search of other stars. Is the cloud alive? Explain.