Part (A):
Plants → Deer → Lion
In this food chain, the elimination of the second trophic level (Deer) profoundly affects the first and third trophic levels.
Impact on the First Trophic Level (Plants):
Plants (producers) would be indirectly affected. With the removal of herbivores (Deer), fewer organisms would consume plants, potentially leading to an overpopulation of plants. This imbalance could, however, harm plant species diversity and overall ecosystem health.
Impact on the Third Trophic Level (Lion):
The removal of deer (secondary consumers) directly impacts lions (tertiary consumers) as deer are their primary food source. Without this prey, lions would face starvation, potentially reducing their population or forcing a dietary shift to other species, which could cause further ecological disruption.
Impact in a Food Web:
The impact would differ if lions were part of a food web. In a food web, organisms typically have multiple food sources. Lions might have alternative prey species available to compensate for the absence of deer. This dietary redundancy in food webs enhances ecosystem resilience to species loss, unlike in a simple food chain where species are more dependent on specific trophic levels.
Part (B):
The gas 'X' mentioned is Ozone (O₃).
Function of Ozone:
Ozone plays a crucial role by absorbing most of the Sun's damaging ultraviolet (UV) radiation, thereby shielding life on Earth from these harmful rays.
Chemical Linked to Ozone Decrease:
Chlorofluorocarbons (CFCs) are the chemicals associated with the depletion of the ozone layer. These compounds degrade ozone molecules in the stratosphere, causing the ozone layer to thin.
Measures by International Organizations:
The Montreal Protocol, established in 1987, is an international agreement designed to phase out the production and use of ozone-depleting substances, including CFCs. This protocol has resulted in a substantial global decrease in the use of such chemicals.