The movement of an organism (specially the plants) as a response to the gravity of earth is called geotropism.
The roots of the plant exhibit positive geotropism as they move towards the gravity of earth while growing downward.
On the other hand , the shoot /stem of the plant show negative geotropism as they move away from the gravity of earth while growing in upward direction.
When a molecule moves down its concentration gradient is it participating in passive transport; moving up the concentration gradient requires energy making it active transport.
