Genetic diversity is the measure of

What is the total number of species of orchids in the world (in $,000$)?

At which level is ecological diversity observed?

Tropical regions show the greatest level of species richness because:
$A$. Tropical latitudes have remained relatively undisturbed for millions of years,hence more time was available for species diversification.
$B$. Tropical environments are more seasonal.
$C$. More solar energy is available in the tropics.
$D$. Constant environments promote niche specialization.
$E$. Tropical environments are constant and predictable.
Choose the correct answer from the options given below.

Approximately $.........$ plant species are used by indigenous people around the world in traditional medicines. (in $,000$)

Among the classes of invertebrates that represent global biodiversity, which are the most abundant?