Week 1 Wed Flashcards
What is Saccharomyces cerevisiae?
Unicellular fungus (Eukaryote) commonly known as “bakers yeast” or “brewers yeast”
How does Saccharomyces cerevisiae reproduce?
by “budding” from pre-existing cell (asexual or via mating (sexual)
How many stages of yeast growth are there?
Four
How are the different stages of yeast growth characterized?
by different cell behavior
Yeast cells tend to intake ___ during the log phase of growth.
DNA
What are the four stages of yeast growth?
Lag phase, Log (exponential) phase, Stationary phase, death (decline) phase
How can the number of cells present be determined?
Optical Density, Direct plating of cells (CFU)
What happens during Optical Density?
a spectrophotometer is used to transmit light through a culture so that the number of cells present can be measured
What are the advantages and limitations of using the optical density method?
Advantages: speed, non-invasive
Disadvantages: Indirect measurement, not good at different extremes (low and high cell count), does differentiate between live, dead, and viable cells.
How do you determine the number of cells present using direct plating of cells?
Plate a sample on a petri dish with agar. Plate a diluted sample on a petri dish with agar and then back-calculate the number of cells in the original culture.
What are the advantages and limitations of direct plating of cells
Advantages: only viable cells are shown, different plate media can be used to only plate specific cells, gives an absolute count of visible cells, versitle, only need basic equipment
Disadvantages: Time consuming, cell clumping can occur, selective conditions ma not allow some organisms to grow, might not detect low concentrations
What is the formula for working concentration?
Working concentration= stock concentration/ dilution factor
What happens during the log phase of yeast growth?
yeast produces more ethanol
What happens during the stationary phase of yeast growth?
the yeast thicken their cell walls
