One, that we're sure of; Earth. There's a very slight chance that some life might exist elsewhere, but at this point, it doesn't seem likely.
There is a vague chance that life might exist on one or more of Jupiter's or Saturn's moons.
I would think exobiology is the study of living things on other planets, though we still have not found living things on other planets.
No, planets are not living things. They are celestial bodies that orbit around a star like the sun. Living things are characterized by biological processes such as growth, reproduction, and response to stimuli, which planets do not exhibit.
depending on the planet there cannot be living things on other planets
Earth is the only planet known to have an atmosphere rich in gases like oxygen and nitrogen, which are essential for supporting life as we know it. Other planets in our solar system have atmospheres with different compositions that would not support life as we know it.
There are no planets of our knowledge that contain living creatures.
Earth, Apart from ours no other planets been proved to have living things !
An ecosystem
It is highly unlikely that any other planet in our solar system will. That does not preclude the possibility of life being elsewhere in the universe.
So far yes, but scientists are still searching for other life forms on planets such as Mars.
Every planet in our solar system has a direct line of sight to the Sun, but Earth is the only one where there are living things to look up at it.
Planets cannot like things, they are not living.
No. The metric system (and the Imperial system and any other system like them) is a system of measurement. In so far as all living things occupy a volume, have a mass and experience time, the system measures characteristics that living things experience but these are not, in themselves, characteristics of the living things.