The plant produces oxygen which the animals need (may also be food source), and the animals produce waste products and carbon dioxide which the plants need, so theoratically the system can be left on its own without external support(self sustaining).
Physical
When something is cooling it isn’t changing it’s chemical composition so it’s physical
Answer:
Velocity is vector quantity. So it needs <em>direction</em> in addoition to <em>speed</em>.
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of its speed and direction of motion.
By increasing Atomic number