BACE - Biotechnician Assistant Credentialing Cell Culture Fundamentals Questions and Answers 1 — Questions and Answers
Question 1: A technician is passaging an adherent mammalian cell line. Which of the following reagents is commonly used to enzymatically detach the cells from the surface of the culture flask?
- Trypsin-EDTA (Correct answer)
- Phosphate-Buffered Saline (PBS)
- Fetal Bovine Serum (FBS)
- Dimethyl sulfoxide (DMSO)
Correct answer: Trypsin-EDTA
Trypsin is a proteolytic enzyme that cleaves the proteins cells use to attach to the flask surface. EDTA is a chelating agent that binds calcium and magnesium ions, which further disrupts cell adhesion.
Question 2: A technician observes that a flask of cell culture medium, which was clear and pink the previous day, is now turbid (cloudy) and has turned a distinct yellow color. What is the most likely cause of this change?
- The cells have become over-confluent.
- Bacterial contamination. (Correct answer)
- Fungal contamination.
- The CO2 level in the incubator is too low.
Correct answer: Bacterial contamination.
Rapid turbidity (cloudiness) and a sharp drop in pH are classic signs of bacterial contamination. The bacteria grow quickly and produce acidic byproducts, causing the phenol red pH indicator in the medium to change from pink/red to yellow.
Question 3: What is the primary function of providing a 5% CO2 atmosphere in a standard mammalian cell culture incubator?
- To provide a direct carbon source for cell metabolism.
- To prevent anaerobic bacteria from growing.
- To work with the bicarbonate buffer system in the medium to maintain a stable pH. (Correct answer)
- To increase the dissolved oxygen levels in the culture medium.
Correct answer: To work with the bicarbonate buffer system in the medium to maintain a stable pH.
The CO2 gas in the incubator dissolves in the cell culture medium and forms a bicarbonate buffer system. This system is crucial for maintaining a stable, physiological pH (typically around 7.2-7.4), which is essential for cell viability and growth.
Question 4: A biotechnician is preparing to cryopreserve a cell line. What is the primary role of adding dimethyl sulfoxide (DMSO) to the freezing medium?
- It acts as a primary nutrient source for the cells while frozen.
- It serves as a selective agent to kill any contaminating cells.
- It triggers the cells to enter a state of suspended animation.
- It prevents the formation of large intracellular ice crystals that can damage cell membranes. (Correct answer)
Correct answer: It prevents the formation of large intracellular ice crystals that can damage cell membranes.
DMSO is a cryoprotectant that lowers the freezing point and, most importantly, prevents the formation of large, damaging ice crystals inside the cells during the freezing process. This action is critical for preserving cell integrity and viability upon thawing.
Question 5: A technician performs a cell count using a hemocytometer and Trypan Blue exclusion staining. In a specific counted volume, they observe 120 live (unstained) cells and 30 dead (blue-stained) cells. What is the percent viability of the culture?
- 75%
- 80% (Correct answer)
- 25%
- 100%
Correct answer: 80%
Percent viability is calculated by dividing the number of live cells by the total number of cells (live + dead), then multiplying by 100. The calculation is: [120 / (120 + 30)] * 100 = [120 / 150] * 100 = 0.8 * 100 = 80%.
Question 6: When working with cell cultures in a Class II Biological Safety Cabinet (BSC), which of the following is a critical aseptic technique to prevent contamination?
- Wiping the outside of all media bottles and flasks with 70% ethanol before placing them in the cabinet. (Correct answer)
- Wearing two pairs of gloves for extra protection.
- Keeping the UV light on while working to sterilize the air.
- Moving hands and arms rapidly to create a sterile vortex.
Correct answer: Wiping the outside of all media bottles and flasks with 70% ethanol before placing them in the cabinet.
A fundamental principle of aseptic technique is to decontaminate the surface of all items before they enter the sterile field of the BSC. Wiping items with 70% ethanol kills microorganisms on the container surface, preventing their introduction into the cabinet and subsequent contamination of cultures.
BACE - Biotechnician Assistant Credentialing Cell Culture Fundamentals Questions and Answers 1
A technician is passaging an adherent mammalian cell line.
Which of the following reagents is commonly used to enzymatically detach the cells from the surface of the culture flask?