Question

In an examination Raj drew diagrams of four stages of binary fission in Amoeba as shown below. However, he was not awarded full marks as one of the stages was incorrectly drawn. The incorrectly drawn stage is:

A. I
B. II
C. III
D. IV

Answer 1

Hint: As we all know that Amoeba is an irregular shaped organism but it tries to attain a spherical shape when it engulfs its pseudopodia and then further events take place like the mitotic division and then formation of two daughter cells.

Complete answer:
Amoeba is a unicellular organism with a unique ability to change its regular shape by extending and retracting its pseudopodia (false-feet) which is an arm-like or finger-like projection. It does not possess a cell wall that allows it to move freely. It mainly reproduces by Binary fission which is an asexual mode of reproduction. Amoeba eats by stretching its pseudopodia around the food and pulls it inside the rest of the body.
This process begins when the parent cell pulls its pseudopodia inside to reach a spherical shape.
After mitotic cell division, the nucleus and cytoplasm get constricted.
The cytoplasm starts dividing and results in the formation of two daughter cells.

Therefore, the correct option is (B) i.e. image II needs to be spherical.

Note:
Sometimes, Amoeba can also use the multiple fission mode of reproduction when the conditions are not suitable and the environment is unable to provide the necessary nutrients. When the pseudopodia is pulled inside amoeba attains a more spherical shape and forms a protective wall-like covering around itself to form a cyst to survive in such hostile conditions. Mitotic division takes place inside the cyst and a number of daughter cells are produced inside it and when the conditions are favourable the cyst ruptures and daughter cells are released.