If a single plant species is removed from a food web,then most likely

The following chart shows the phosphorus cycle in a terrestrial ecosystem. Select the correct option for the four labels $a, b, c$ and $d$ shown in the diagram.
$a$ - $b$ - $c$ - $d$

Consider the following statements concerning food chains.
$I$. Removal of $80\; \%$ tigers from an area resulted in greatly increased growth of vegetation.
$II.$ Removal of most of the carnivores resulted in an increased population of deers.
$III.$ The length of food chains is generally limited to $3$ to $4$ trophic levels due to energy loss.
$IV.$ The length of food chains may vary from $2$ to $8$ trophic levels.
Which two of the above statements are correct?

Which of the following is an example of a man-made ecosystem?

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

Phosphorus of the ocean becomes available to land plants due to: