Question

In spirogyra, ladder like structure is formed in
A. Lateral conjugation
B. Fragmentation
C. Palmella stage
D. Scalariform conjugation

Answer 1

Hint:Spirogyra is also called water silk due to its filamentous thread like structure. It is common in freshwater habitats. More than 400 species of spirogyra are found in the world.

Complete answer:
In spirogyra, ladder-like structure is formed in Scalariform conjugation. Spirogyra is an alga that belongs to the division Charophyta and is of the class Zygnematophyceae. It is very common in clear eutrophic water developing slimy filamentous matter. The structure of spirogyra possesses a cell wall, nucleus, pyrenoid and spiral chloroplast. Chloroplast is found in the leaves of plants. It has the presence of pigmentosus structure called chlorophyll which is green in color and takes part in the preparation of food material that is known as photosynthesis.

The process of sexual reproduction occurs in spirogyra by the means of conjugation. The two types of conjugation are Lateral conjugation and scalariform conjugation. Scalariform conjugation is the most common mode method in spirogyra. The cytoplasmic content is rounded up and leads to formation of gametes. The ladder-like structure is formed by the conjugation of many cells.
In scalariform conjugation, conjugation occurs between two filamentous structures and in the lateral conjugation, conjugation takes place between two adjacent cells. Lateral conjugation takes place in monoecious or homothallic species.

Therefore, the correct answer is option (D) Scalariform conjugation.

Note: Spirogyra derived its name from the spiral shape of the chloroplast possessed by the genus. Spirogyra is commonly found in the clean water and due to the presence of the chloroplast, it has the ability to photosynthesise its food material. It is also called 'scum' as they are found floating slimy masses in the summer season.