(A) Plants $\rightarrow$ Deer $\rightarrow$ Lion In the given food chain, what will be the impact of removing all the organisms of second trophic level on the first and third trophic level? Will the impact be the same for the organisms of the third trophic level in the above food chain if they were present in a food web? Justify. OR (B) A gas 'X' which is a deadly poison is found at the higher levels of atmosphere and performs an essential function. Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?

(A) Impact of removing second trophic level (Deer):

1. First Trophic Level (Plants): The population of plants will increase significantly because there are no herbivores to consume them, potentially leading to overgrowth and competition for resources.
2. Third Trophic Level (Lion): The population of lions will decrease or they will die out due to starvation, as their primary food source (deer) is removed.

Food Web Justification: No, the impact would not be the same in a food web. In a food web, an organism usually has multiple food sources. If one species of prey is removed, the predator (lion) can consume other animals, making the ecosystem more stable and less prone to collapse.

OR

(B) Gas 'X' and Ozone Layer:

1. Name of Gas: Ozone ($O_3$).
2. Function: It shields the surface of the earth from harmful ultraviolet ($UV$) radiation from the sun, which can cause skin cancer and damage to organisms.
3. Chemical Linked to Decrease: Chlorofluorocarbons ($CFCs$), used in refrigerants and fire extinguishers.
4. International Measures: The United Nations Environment Programme (UNEP) succeeded in forging an agreement (Montreal Protocol) to freeze $CFC$ production at 1986 levels.