Saccharomyces cerevisiae can exist

Saccharomyces cerevisiae can exist in two different forms: haploid or diploid. It is usually found in the diploid form. The diploid form is ellipsoid-shaped with a diameter of 5-6um, while the haploid form is more spherical with a diameter of 4um. In exponential phase, haploid cells reproduce more than diploid cells. Haploid and diploid cells can reproduce asexually in a process called budding, where the daughter cell protrudes off a parent cell. The buds of haploid cells are adjacent to each other, while the buds of diploid cells are located in opposite poles. Additionally, diploid cells can exhibit pseudohyphal growth if it is growing on a poor carbon source, exposed to heat or high osmolarity. Activated by cAMP, newly developed cells remain attached to the parent cell through a septum.
In addition to budding, diploid cells can undergo a meiotic process called sporulation to produce four haploid spores. Haploid spores can be one of two mating type, a or α. These spores can also undergo budding to produce more haploid cells. a and α cells can also mate and fuse together, producing a diploid cell. S. cerevisiae strains are further distinguished by differences in the haploid stage. In heterothallic strains, the spores resulting from sporulation cannot undergo budding, and their mating type cannot be changed. . However, in homothallic strains, the presence of a HO gene allows the spores to change mating type as they grow. Sporulation can be induced if the yeast is exposed to either a poor carbon or nitrogen source or lack of a nitrogen source. Spores also have a higher tolerance to conditions such as high temperature.
As a eukaryote, S. cerevisiae contains membrane-bound organelles. Its chromosomes are located in the nucleus, and it uses mitochondria to conduct cellular respiration. Like all other fungi, the cell's shape is based on its cell wall. The cell wall protects the cell from its environment as well as from any changes in osmotic pressure. The inner cell wall has a high concentration of β-glucans, while the outer cell wall has a high concentration of mannoprotein. Chitin is usually located in the septum.
S cerevisiae can live in both aerobic as well as anaerobic conditions. In the presence of oxygen, yeast can undergo aerobic respiration, where glucose is broken to CO2 and ATP is produced by protons falling down their gradient to an ATPase. When oxygen is lacking, yeast only get their energy from glycolysis and the sugar is instead converted into ethanol, a less efficient process than aerobic respiration. The main source of carbon and energy is glucose, and when glucose concentrations are high enough, gene expression of enzumes used in respiration are repressed and fermentation takes over respiration. However, yeast can also use other sugars as a carbon source. Sucrose can be converted into glucose and fructose by using an enzyme called invertase, and maltose can be converted into two molecules of glucose by using the enzyme mannase