Solution

Parthenium hysterophorus is common invasive weed and causes damage to the wheat crop. Its infection causes dermatitis and respiratory disorders in human and dermatitis in cattle. Stratification is the key character of the ecosystem and refers to the arrangement of flora and fauna in vertical layers. Parenchyma with large intercellular spaces filled with air are termed as aerenchyma which serves to maintain buoyancy of aquatic plants in aquatic medium and allow them to float; Opuntia is xerophyte plant. Age pyramid represents distribution of organisms of a population in different age groups.
Therefore, the correct answer is option A.