Question 1

What is the difference between positive and negative chemotaxis?

Accepted Answer

Positive chemotaxis is movement toward a chemical stimulus, while negative chemotaxis is movement away from it. Organisms use positive chemotaxis to move toward food sources or beneficial stimuli. Negative chemotaxis allows organisms to avoid harmful chemicals like heavy metals, acidic substances, or detergents that may be toxic.

Question 2

Why is age synchronization important when preparing C. elegans for a chemotaxis assay?

Accepted Answer

Age synchronization ensures all worms are at the same developmental stage, preventing differences in chemotaxis behavior from being artifacts of development rather than true responses to chemical stimuli. Using young adult worms of uniform age provides consistent, reliable data for accurate experimental results and supports studies of development and reproduction caenorhabditis elegans.

Question 3

How is the chemotactic index calculated and what do the values indicate?

Accepted Answer

The chemotactic index equals the number of worms in test quadrants minus worms in control quadrants, divided by total worms. A value close to +1 indicates strong attraction to the test chemical, while a value close to -1 indicates repulsion. Values near zero suggest the worms are neutral toward that chemical stimulus.

Question 4

What role does sodium azide play in a C. elegans chemotaxis assay?

Accepted Answer

Sodium azide is an anesthetic mixed with test and control solutions at 0.5 M concentration. When worms reach their destination on the chemotaxis plate, sodium azide paralyzes them, allowing researchers to count their final positions accurately without worms continuing to move during data collection.

Question 5

How can chemotaxis assays be used to study learning and memory in C. elegans?

Accepted Answer

Researchers condition starved worms by pairing a chemical stimulus like butanone with food. Worms are then placed on plates with food but without the chemical. A chemotaxis assay determines whether worms learned to associate the chemical with food, revealing genetic and neuronal mechanisms underlying learning and memory formation.

Question 6

What is olfactory adaptation and how does it affect chemotaxis assay results?

Accepted Answer

Olfactory adaptation occurs when sensory neurons decrease their response to a stimulus over time, allowing animals to focus on other stimuli. Wild-type C. elegans exposed to an odor will ignore it during a chemotaxis assay due to olfactory adaptation rather than being attracted to it, enabling genetic screens to identify regulatory genes like egl-4.

Question 7

How do chemotaxis assays help researchers study Alzheimer's disease using C. elegans?

Accepted Answer

Scientists express fluorescently tagged human amyloid beta peptide, a hallmark of Alzheimer's disease, in C. elegans neurons. Chemotaxis assays reveal that worms expressing amyloid beta show reduced chemotaxis toward chemo-attractants compared to controls, providing insights into how the disease affects neural function and potential therapeutic interventions.

ג. אלגנס Chemotaxis Assay - חידון הערכה