Which of the following statements about Spirogyra is correct?
A. Lateral conjugation takes place in homothallic species.
B. Scalariform conjugation takes place in homothallic species.
C. Lateral conjugation takes place in heterothallic species.
D. The type of conjugation is unrelated to homothallic and heterothallic species.

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Hint:Conjugation, a type of Spirogyra sexual reproduction. The conjugation tubes between the two filaments of algae make it possible to combine the contents of one cell with those of the other, forming a zygote. Clearly visible are the typical spiral chloroplasts.

Complete answer:Sexual reproduction takes place via the conjugation process in Spirogyra. The conjugation process in Spirogyra may consist of two types: scalariform conjugation and lateral conjugation. In heterothallic animals, scalariform conjugation occurs. Lateral conjugation occurs between the adjacent cells of Spirogyra homothallic species with the same filament. There are two forms of lateral conjugation. They are indirect (chain type) lateral conjugation and direct lateral conjugation.
Lateral Conjugation: Here, inside the same filament, conjugation occurs between adjacent cells. Protuberances are produced by the cells involved in conjugation. Cellular matter from one cell fuses with the other as these protuberances increase. Such conjugation contributes to the creation of a zygospore diploid. This kind of conjugation is often referred to as chain-like conjugation.

Scalariform Conjugation: Two filaments come together in scalariform conjugation and ultimately lie together. The resulting structure can be compared to that of a ladder. Some of the features of this reproduction include -
Male and female gametes combine, leaving one vacant and one full of zygotes.
The fusion occurs via the forming of conjugation canals between the two cells next to each cell.
After the latter decays, zygotes escape from the parent filament. These zygotes germinate after escaping when conditions are favorable.
Hence, option A- Lateral conjugation takes place in homothallic species is the correct answer.

Note: Fragmentation is also a type of reproduction that takes place in Spirogyra where it simply undergoes intercalary cell division to expand the length of the new filaments. Scalariform conjugation involves the association, either partially or throughout its length, of two or more separate filaments lined side by side.
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