Question

Roots obtain oxygen from air in the soil for respiration. In the absence or deficiency of $O_2$, root growth is restricted or completely stopped. How do the plants growing in marsh lands or swamps obtain their $O_2$ required for root respiration?

Answer 1

The roots of the plants (e.g., Rhizophora) growing in marshy/swamp areas become negatively geotropic. They grow vertically upwards in air, above the soil level and respire so called respiratory roots or pneumatophores.