investigate The Growth Of The Yeast Using Agar Plates And Controls Control Flashcards
Name the plant you used during this experiment.
Oak, ash, or sycamore leaves.
To which kingdom do yeasts belong?
Fungi.
Yeasts are eukaryotic organisms – what does this mean?
Yeast cells have a nucleus and membrane-bound organelles.
Distinguish between aseptic and sterile techniques in microbiology.
Aseptic techniques: Methods used to prevent contamination (e.g., disinfecting surfaces, washing hands).
Sterile techniques: Methods used to completely remove all microorganisms (e.g., heating equipment, using sterile agar plates).
Describe how you collected the leaf sample.
Picked healthy, undamaged leaves from a tree in a clean outdoor area. Chose leaves from low-pollution environments (e.g., away from busy roads).
What part of the leaf provided the spores?
The underside (lower epidermis) of the leaf, where yeast spores are released.
How did you ensure that the samples were all of similar size?
Used a cork borer or scissors to cut uniformly sized leaf discs.
Agar on its own has no nutrient value. What nutrient was in the agar that you used?
Malt extract agar, which provides carbohydrates to support yeast growth.
Describe how you transferred the yeast to the nutrient medium.
Opened the petri dish as little as possible to prevent contamination. Attached the leaf (underside facing down) to the lid of the petri dish.
Give three precautions you took to prevent contamination of the dishes while setting up the leaves in the dishes.
(a) Worked near a Bunsen burner flame to reduce airborne contamination.
(b) Flamed the forceps before use to sterilize them.
(c) Kept petri dish lids closed as much as possible.
How did you attach the leaves to the lid of the dish?
Used vaseline, tape, or forceps to secure the leaf inside the lid.
What surface of the leaf faced the nutrient agar? Why?
The underside (lower epidermis) faced the agar because this is where yeast spores are released.
Describe what you did after attaching the leaves to the lid.
Inverted the petri dish (lid facing down) to allow yeast spores to fall onto the agar. Incubated the plates at 25°C for several days to allow yeast growth.
After incubation, what did you observe in the control dish?
No yeast colonies (since no leaf was present to release spores).
Give two words to describe the yeast you observed.
Creamy, Circular.
Yeasts are sensitive to air pollution. If sample A came from a clean air environment and sample B came from a busy town, which sample would you expect to yield fewer colonies and why?
Sample B (from the busy town) would have fewer yeast colonies. Air pollution (e.g., sulfur dioxide from cars) kills yeast spores or prevents them from growing.
How would you safely dispose of the used petri dishes from the above experiment?
Soak in disinfectant before disposal. Autoclave (heat at 121°C) or place in a biohazard bag for safe disposal.
The petri dishes that you used are not opened to view the colonies. Why?
To prevent exposure to potentially harmful microorganisms that may have grown alongside the yeast.
