$A$: The soil of tropical rain forests has a low base content.
$R$: Such soil shows less percolation and leaching.

Read the given statements and determine how many of them are correct.
$(1)$ Secondary succession depends on the condition of the soil and the availability of water.
$(2)$ Air,water,and land are abiotic factors of an ecosystem.
$(3)$ The structure of an ecosystem includes the cycling of nutrients and the unidirectional flow of energy.
$(4)$ The primary source of energy in an ecosystem is the sun.

Which one of the following is not a functional unit of an ecosystem?

Which one of the following animals may occupy more than one trophic levels in the same ecosystem at the same time?

The changes that occur in successive seral stages to reach a climax community are:
$I.$ Changes in the diversity of species of organisms.
$II.$ Increase in the number of species and organisms.
$III.$ Increase in the total biomass.
Choose the correct option.

The process of evapo-transpiration and precipitation is known as