You Take Absorbance Readings on a Spectrophotometer Across a 6-Hour

question 16

Multiple Choice

You take absorbance readings on a spectrophotometer across a 6-hour culture of

• A)Clearly,something is wrong with the spectrophotometer and it isn't measuring the correct values.Perhaps something is on the detector,making it register falsely high absorbance numbers.
• B)When we establish a growth curve,we should actually plot the log of the number of viable cells vs.time.However,a spectrophotometer can only measure absorbance.Absorbance is NOT the same as the number of viable cells.Many of the cells in the tube are most likely dead,but the machine can't discriminate between a live cell and a dead one.This keeps the absorbance high even into the death phase.
• C)It'll happen-E.coli just grow slowly.We haven't gotten to the end of the stationary phase yet.Be patient!
• D)Perhaps there's a big smudge of something on the tube that is blocking some of the light.This would lead to an elevated reading for every timepoint after the smudge was placed on the tube.
• E)coli cells growing in tryptic soy broth (TSB).Your absorbance readings clearly indicate a lag phase,a log phase,and a stationary phase.You come back in and take readings at 8,10,12,14,and 16 hours,but the absorbance number remains the same.Shouldn't it start coming down as the closed batch culture enters death phase? What's the most likely thing that is happening?

---

Definitions:

Glial Cell

Non-neuronal cells in the central nervous system that support, protect, and nourish neurons, playing a crucial role in maintaining homeostasis and forming myelin.

Neurons

Specialized cells in the nervous system that transmit information to other nerve cells, muscle, or gland cells.

Waste Products

Materials that are not useful or consumed during a process and are subsequently discarded.

Terminal Buttons

Terminal buttons are the small knobs at the end of an axon that release chemicals called neurotransmitters, which convey signals across synapses to other neurons.