Question

The life cycle of Saccharomyces ludwigii is
(a) Haplobiontic
(b) Haplodiplobiontic
(c) Diplobiontic
(d) All of the above

Answer 1

Hint: There is a dominant diploid phase represented by somatic cells and a short haploid phase represented by the ascospores. These ascospores copulate within the ascus in place of getting dispersed.

Complete answer:
In Saccharomyces ludwigii, somatic cells are diploid and these cells reproduce asexually by two methods – budding and fission. This type of life cycle is termed as a diplobiontic life cycle. Here, each diploid somatic cell is capable of functioning as an ascus and thus each somatic cell produces four haploid ascospores by undergoing a meiotic division. The ascospores represent the only haploid phase in the life cycle of these organisms and the ascospores do not get dispersed immediately. Instead, the ascospores fuse inside the ascus in pairs and thus there is the formation of two diploid cells known as zygotes. Now, a germ tube is formed and it pierces the ascus wall and acts like a sprout mycelium helping in the germination of diploid cells. Further development of diploid cells occurs through budding form this sprout mycelium. These buds are the diplobiontic vegetative cells. Here, both the phases i.e. the diploid phase and the haploid phase are multicellular.
So, the correct answer is ‘Diplobiontic’.
Note:
Hplobiontic life cycle is shown by Schizosaccharomyces Octosporus and not by Saccharomyces ludwigii. Somatic cells in the former are haploid and thus the diploid phase is very short and represented by the zygote. The diploid zygote cells act as ascus and undergo meiotic divisions followed by mitosis to form haploid ascospores that further germinate.