Life cycle in Spirogyra is haplontic as dominant phase in life cycle is haploid (n) and diploid phase is represented by only zygospore and it undergoes meiosis.

Usually most of the algae belongs to haplontic life cycle.As spirogyra is an algae having dominant gametophyte and zygotic meiosis, absence of free living sporophyte.This charcterises spirogyra having haplontic life cycle

Spirogyra has a Haplontic life cycle

Haplontic life cycle is a type of life cycle that is characterized by a dominant haploid phase. In this life cycle, the organism spends most of its life in the haploid phase and the diploid phase is relatively short-lived.

Spirogyra is a filamentous green algae that belongs to the division Chlorophyta. It is commonly found in freshwater habitats, such as ponds and streams. The life cycle of Spirogyra is characterized by alternation of generations, with the haploid phase being dominant.

1. Haplontic life cycle:
The haplontic life cycle begins with the haploid gametophyte phase. In Spirogyra, the haploid gametophyte is the filamentous green alga that we commonly observe. The filaments of Spirogyra consist of individual cells, each containing a single haploid nucleus.

2. Gametogenesis:
During the haploid phase, specialized reproductive structures called gametangia are formed. These gametangia produce gametes through the process of gametogenesis. In Spirogyra, the gametangia are called conjugation tubes. Each conjugation tube contains a single haploid nucleus, which undergoes mitosis to produce gametes.

3. Conjugation:
The gametes are released from the gametangia and are capable of moving through the water. When two compatible gametes meet, they fuse together in a process called conjugation. This results in the formation of a zygote, which is diploid.

4. Zygospore formation:
The zygote undergoes mitotic divisions and develops into a thick-walled structure called a zygospore. The zygospore is a dormant stage that protects the developing diploid cells from adverse conditions, such as desiccation or extreme temperatures.

5. Germination:
Under favorable conditions, the zygospore germinates and gives rise to a new filamentous haploid individual, thus completing the life cycle. The haploid individual grows and undergoes mitotic divisions to form new filaments, which can then produce gametangia and gametes.

In conclusion, Spirogyra exhibits a haplontic life cycle, where the haploid phase is dominant and the diploid phase is short-lived. This life cycle allows for genetic diversity through the fusion of gametes and the formation of zygospores.