It lies below 2000 m and complete darkness persists here.

These are poor in nutrients and phosphates and are generally deep, e.g. Sambhar Lake which is a salty lake.

These are tropical lakes and are characterised by overturning of water once in a year.

A shallow water region of the marginal slope with light penetration.

It is a greenhouse gas produced by paddy fields.

It is the movement of any of the natural circulation pathways of the essential elements of living matter.

It is an oxygen carrier and a hemoprotein found in the nitrogen-fixing root nodules of leguminous plants.

Temperate or tepid latitudes of the globe lie between the tropics and the polar regions. Deciduous forests are found here.

Potamogeton is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae.

A psammosere is a seral community, an ecological succession that began life on newly exposed coastal sand.

The tropical evergreen forests usually occur in areas receiving more than 200 cm of rainfall and having a temperature of 15 to 30 degrees Celsius. 

The collection of minute or microscopic organisms that inhabit the surface layer of a body of water

The limnetic zone is the well-lit, open surface waters in a lake, away from the shore.

Lotic refers to free fresh flowing water.

Fusion of male and female gametes in plants, called as fertilization. It does not require sunlight.