The main cause of water blooms observed in rivers,lakes,and seas is .......

Which organism is considered a connecting link between plants and animals?

Describe briefly the four major groups of Protozoa.

The given statements are some characters of a particular group of Kingdom $Protista$.
$(i)$ Most of them are freshwater organisms found in standing water.
$(ii)$ They have a protein-rich layer (called pellicle) which makes their body flexible.
$(iii)$ They have two flagella,a short and a long one.
$(iv)$ Though they are photosynthetic in the presence of sunlight,but in the absence of sunlight they behave like heterotrophs by predating on other smaller organisms.
Identify the correct group on the basis of these characters.

$Entamoeba$ $gingivalis$ lives in the

Which one of the following shows bioluminescence?