Question

Explain the life cycle of Saccharomyces cerevisiae (yeast) by illustrating with diagram.

 

 

Answer 1

• LIFE CYCLE OF SACCHAROMYCES CEREVISIAE (YEAST):
  
  The yeast is a one-celled ascomycete fungus which includes in its life cycle two morphologically identical diploid and haploid generations that alternate with each other.
• The diploid adult usually multiplies by budding in which the nuclei divide by mitosis, but under certain environmental conditions they undergo meiosis to form four monoploid meiospores or ascospores within the old cell wall which now called ascus.
• The ascospores are liberated from the ascus and each ascospore germinates into a monoploid adult cell.
• Out of four ascospores two develop into adults of + mating type, while rest two develop into adults of-mating type.
• Sometime two yeast cells of opposite strains contact and an inter-cellular cytoplasmic bridge is formed between the two cells.
• Both cells ultimately fuse (plasmogamy) and their nuclei also fuse to form a diploid nucleus (karyogamy).
• The resultant vegetative cell repeats the same life cycle.

Saccharomyces cerevisiae :

• This is a species of yeast.
• This species has been instrumental in winemaking, baking, and brewing since ancient times.
• It is originally isolated from the skin of grapes.