What are ecosystem services?

What is an incomplete ecosystem? Explain with the help of a suitable example.

Phytoplankton $\rightarrow$ Submerged plant stage $\rightarrow$ Floating plant stage $\rightarrow$ Reed-swamp stage $\rightarrow$ Marsh-meadow stage $\rightarrow$ Scrub $\rightarrow$ Forest. What type of succession does this sequence represent?

Both hydrarch and xerarch successions lead to ..........

Choose the correct identification for the given stage of succession and the stage by which it is followed,respectively.

In a pond,we see plants which are free-floating; rooted-submerged; rooted-emergent; and rooted with floating leaves. Identify the type of plant for each of the following:

Plant Name	Type
$(1)$ Hydrilla	....................
$(2)$ Typha	....................
$(3)$ Nymphaea	....................
$(4)$ Lemna	....................
$(5)$ Vallisneria	....................