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

Identify the stage of hydrarch succession shown in the figure.

Assertion $A$: As a result of evolution,plant species have migrated from aquatic habitats to terrestrial habitats.
Reason $R$: Plants have undergone developmental changes while passing through various stages of succession.
Which option is correct for Assertion $A$ and Reason $R$?

In hydrarch succession,the reed swamp stage is preceded by

Find an incorrect statement for $DFC$ (Detritus Food Chain).

If all the green plants were to disappear from the earth,what would happen?