Categorise the following plants into hydrophytes, halophytes, mesophytes and xerophytes. Give reasons for your answers.

$(a)$ Salvinia    $(b)$ Opuntia     $(c)$ Rhizophora    $(d)$ Mangifera

Population density of terrestrial organisms is measured in terms of individuals per

Species are considered as

Assertion : Tropical rain forests are disappearing fast from developing countries such as India.

Reason : No value is attached to these forests because these are poor in biodiversity.

Presence of plants arranged into well defined vertical layers depending on their height can be seen best in