1. Roots are totally absent in Wolffia and Salvinia or poorly developed in Hydrilla or well developed in Ranunculus.
2. The root caps are replaced by root pockets. Example: Eichhornia

Amensalism is an interspecific interaction in which one species is inhibited while the other species is neither benefitted nor harmed. The inhibition is achieved by the secretion of certain chemicals called allelopathic substances. Amensalism is also called antibiosis.

Commensalism is an interaction between two organisms in which one is benefitted and the other is neither benefitted nor harmed. The species that derives benefit is called the commensal, while the other species is called the host.

Mutualism is an interaction between two species of organisms in which both are benefitted from the obligate association. E.g: Lichens (alga with fungus).

Edaphic factors are the abiotic factors related to soil, include the physical and chemical composition of the soil formed in a particular area.

Pyronema confluens is a fungus which grow on the soil of burnt or fire disturbed areas. Hence it is called as indicator of fire.

Raunkiaer classified the world's vegetation into the following four types. They are megatherms, mesotherms, microtherms and hekistotherms.

Heliophytes - Light loving plants. Example: Angiosperms.
Sciophytes - Shade loving plants. Example: Bryophytes and Pteridophytes

The interaction of organisms with their environment results in the establishment of grouping of organisms which is called ecological hierarchy.

Earnest Haeckel defined "Ecology is the study of the reciprocal relationship between living organisms and their environment."

A desert has little or no plant life without plants, there is no organic horizon in the soil leading to a low level of water retention that is unsuitable for plant growth.

The blue green light have short wavelength & penetrates into the water. Green algae is unable to use that component of light. Blue light can penetrate up to 500 ft depth therefore algae are unlikely to survive below that depth.

Taxonomically different species occupying similar habitats (Niches) in different geographical regions are called Ecological equivalents.
E.g: Certain species of epiphytic orchids of Western Ghats of India differ from the epiphytic orchids of South America. But they are epiphytes.

The interaction of organisms with their environment results in the establishment of grouping of organisms
Levels of ecological hierarchy

Aerosols with small particles is reflecting the solar radiation entering the atmosphere. This is known as Albedo effect.
Effects:
1. It reduces the temperature limits, photosynthesis & respiration.
2. The sulphur compounds are responsible for acid rain due to acidification of rain water and destroy the ozone.