HefeZellen

Hefezellen (yeast cells) are unicellular fungi that convert sugars into energy and by-products. The best-known is Saccharomyces cerevisiae, widely used in baking, brewing, and winemaking. They inhabit natural environments such as fruit surfaces and soil, and can be cultured in labs and industrial processes.

Morphology and reproduction. They are typically small oval cells about 3 to 5 micrometers in diameter. They reproduce primarily by budding, in which a daughter cell forms a protrusion on the parent, grows, and detaches. Under certain conditions they may form pseudohyphae or true hyphae. They are facultative anaerobes, able to ferment in the absence of oxygen but also respire aerobically.

Metabolism. In the presence of sugars, yeast cells metabolize glucose via glycolysis; under anaerobic conditions they ferment to ethanol and carbon dioxide; this fermentation is exploited in bread dough (CO2 makes dough rise) and alcoholic beverages; respiration yields more ATP but requires oxygen.

Cell biology. Yeast have a defining cell wall composed largely of glucans and mannan, with chitin in certain places; membranes contain ergosterol. Internal organelles include nucleus, mitochondria, vacuoles; genetic material is in chromosomes; widely used in molecular biology as a model organism because many cellular pathways are conserved with higher eukaryotes.

Applications and context. Beyond food production, yeast serves as a model organism for genetics and cell biology, with extensive genetic tools and a fully sequenced genome. Industrial strains are engineered for higher fermentation efficiency, tolerance to alcohol, or production of specific compounds. Safety and regulation consider strains are typically food-grade.