Answer:
space between gas molecules
Explanation:
as the altitude increases the air density decrease because of weaker gravity and these led to more distant of air molecule and the space between gas is increased
That statement is false
The plants still have to undergo a fierce competition in order to obtain sunlight. The taller trees will obtain more sunlight while overshadowing the smaller one.
Meanwhile , even though there are a lot of food resources in the rain forest, it also have many animals that compete for the same food.
Plankton is the answer to your question.