December 3, 2015

Junior Intermediate Zoology Unit - V Important Questions for 4 Marks

Q: Describe the process of longitudinal binary fission in Euglena.
A: Longitudinal binary fission takes place in Euglena during favourable conditions.
The division of nucleus during binary fission is known as karyokinesis and that of cytoplasm is called cytokinesis.

Euglena is a common protozoan in fresh water bodies and is green in colour due to
presence of chromatophores containing chlorophyll. Euglena is a spindle shaped individual having two flagellae in the anterior end arising from two basal granules
besides cytostome, cytopharynx, reservoir, contractile vacuole, stigma, paraflagellar
body etc. Almost in the middle of the body, there is a nucleus.

a. During binary fission, nucleus divides by mitosis.
b. Then the basal granules and chromatophores also divide.
c. A constriction appears in the anterior end, grow deep dividing the parent Euglena into two daughter Euglenae.
d. The basal granules and flagellae are retained by one daughter and the other acquires new flagellae from the newly formed basal granules.
e. Stigma, paraflagellar body and contractile vacuole of the parent disappear and new
structures are formed in both daughter Euglenae.
f. As the daughter Euglenae formed after longitudinal binary fission are like mirror
images, the binary fission in Euglena is also called symmetrogenic division.

Q: Write short notes on multiple fission.

A: Division of the parent individual into many daughter individuals is known as multiple fission. Generally, multiple fission takes place during unfavourable conditions. In multiple fission, nucleus of the parent individual divides many times by mitosis. Thus many nuclei are formed. Each nucleus is surrounded by a bit of cytoplasm and thus many small daughter individuals are formed. When the body covering of the parent ruptures, all the daughter individuals are liberated out and each one develops into a complete organism.

Eg: Multiple fission in Plasmodium is described as schizogony, male gametogony
and sporogony.
Multiple fission in Amoeba is known as sporulation.

Q: Draw neat labelled diagram of Euglena.

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