Maximum photosynthesis occurs through .......

Which of the following is $NOT$ a gaseous biogeochemical cycle in an ecosystem?

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

Maximum biomass and variable organisms are found in

Assertion : In tropical rain forests,$O-$ horizon and $A-$ horizon of soil profile are shallow and nutrient-poor.
Reason : Excessive growth of micro-organisms in the soil depletes its organic content.

Zooplanktonic forms are