Question -
Answer -
The euglenoid flagellates are the most interesting organisms having a mixture of animal and plant characteristics. The characteristic features are:
(i) They are unicellular flagellates.
(ii)These protists lack a definite cellulose cell wall. Instead the cells are covered by
a thin membrane known as pellicle. The pellicle is composed of protein, lipid and carbohydrates.
(iii)One or two flagella which help these protists in active swimming are present. If two flagella are present, then one is long and other is short. They are tinsel – shaped i.e., with two longitudinal rows of fine hairs. Each flagellum has its own basal granule. The two flagella join with each other at a swelling, called paraflagellar body and finally only one long flagellum emerges out through the cytostome.
(iv)Cell at the anterior end possesses an eccentric mouth or cytostome which leads into a flask-shaped cavity viz. gullet or cytopharynx. Gullet opens into a large basal reservoir.
(v) At one end of the reservoir, the cytoplasm contains an orange red stigma (eye spot). The eye spot is a curved plate with orange-red granules and contains red pigment astaxanthin. Both paraflagellar body and eye spot act as photoreceptors.
(vi)Just below the reservoir is found a contractile vacuole having many feeding canals. The contractile vacuole takes part in osmoregulation. It expands and pumps its fluid contents in the reservoir.
(vii)The mode of nutrition in euglenoids is holophytic or photoautotrophic. Some euglenoids show mixotrophic nutrition (both holophytic as well as saprobic mode).
(viii)Cytoplasm is differentiated into ectoplasm and endoplasm. Nucleus is large and occurs roughly in middle. The envelope and nucleolus persist during cell division.
(ix)Each chloroplast is composed of a granular matrix traversed by 10-45 dense bands and is covered by 3-membraned envelope. They contain the photo¬synthetic pigments-chlorophyll – n, b. They store carbohydrates as paramylon bodies, scattered throughout the cytoplasm.
(x) Asexual reproduction occurs by longitudinal binary fission. The flagellum is duplicated before cell division.
(xi)Under unfavourable condition the euglenoids form cysts to perennate the dry period.
(xii)Sexual reproduction is not observed.