(i) Pyramid of number can look inverted in a tree ecosystem,where the single tree is the producer (first trophic level) and a number of insects are feeding on that tree (primary consumers or second trophic level).
(ii) Pyramid of biomass in a sea is generally inverted because the biomass of fishes far exceeds those of the phytoplankton,which are microscopic organisms.

Role of organisms
1. The roots of plants absorb the minute quantities of phosphates found dissolved in the soil solution.
2. The consumers obtain this element either directly (herbivores) or indirectly (carnivores) from plants.
3. The organic wastes from the living organisms and the dead organisms are decomposed and the phosphate-solubilising bacteria release phosphorus.

(a) Removal of all producer reduce primary production in the ecosystem. Hence, no biomass will be available to the successive/higher trophic level or heterotrophic organisms.
(b) Elimination of all organisms of herbivore level results into an increase in primary productivity and biomass of producer and carnivorous animal will not survive due to availability of food due to elimination of herbivores.
(c) Removal of top carnivores also disturb the ecosystem as it will result in huge increase in number of herbivores which will finish plants (producers) creating desertification.

Green algae are not likely to be found in the deepest strata of sea because the environment is perpectually dark and sun as source of energy not available.

Grazing food chain:
Autotrophs ---> herbivores ---> primary carnivores ---> secondary carnivores
Detritus food chain:
Decay and ---> decomposer ---> soil animal
Excretory organism which consume Materials other soil from the organisms. grazing food.

Many organisms occupy different positions in different food chains, several food chains get interconnected to form the food web.