Question 1

Which of the following best describes the dauer stage in the life cycle of Caenorhabditis elegans?

Accepted Answer

A developmental arrest stage that allows survival under harsh environmental conditions.

Question 2

During the laboratory experiment, why is bleaching used in the preparation of C. elegans cultures?

Accepted Answer

To synchronize the population by killing all adults and larvae, leaving only eggs.

Question 3

Which buffer is commonly used for pouring NGM agar plates in C. elegans experiments, and what is its primary function?

Accepted Answer

M9 buffer; it maintains osmotic balance and is used for washing worms.

Question 4

In the development of Xenopus laevis, which stage is characterized by the formation of three germ layers?

Accepted Answer

Gastrula stage

Question 5

Which of the following best explains the role of seam cells in C. elegans development?

Accepted Answer

They are stem-like cells that divide asymmetrically and contribute to epidermal development.

Question 6

A student is quantifying RNA isolated from Xenopus laevis using UV/VIS spectroscopy. Which equation should be used to calculate RNA concentration from absorbance at 260 nm?

Accepted Answer

$$C = \frac{A_{260}}{\epsilon \cdot l}$$

Question 7

During reverse transcription in gene expression analysis, which enzyme is responsible for synthesizing cDNA from RNA?

Accepted Answer

Reverse transcriptase

Question 8

In a qPCR experiment to measure gene expression in Xenopus laevis, which formula is used to calculate the relative expression of a target gene using the comparative Ct method?

Accepted Answer

$$2^{-\Delta \Delta Ct}$$

Question 9

Which of the following is a correct sequence of developmental stages in C. elegans from fertilization to adulthood?

Accepted Answer

Egg → L1 → L2 → L3 → L4 → Adult

Question 10

A researcher observes that C. elegans larvae enter the dauer stage when exposed to high population density and low food availability. What is the most likely biological advantage of this response?

Accepted Answer

It allows the organism to survive unfavorable conditions until the environment improves.

Question 11

Which statement best describes the purpose of using non-ruled, non-squared white paper for drawings in the lab book?

Accepted Answer

It ensures clarity and accuracy in scientific illustrations without visual distractions.

Question 12

In the context of gene expression analysis, what is the main reason for isolating RNA before performing reverse transcription?

Accepted Answer

To obtain a template for synthesizing complementary DNA (cDNA).

Question 13

Which of the following is a critical step in the evaluation of developmental stages in Xenopus laevis embryos?

Accepted Answer

Microscopic observation and drawing until the blastula stage.

Question 14

A student is asked to collect one oocyte/embryo per experiment during the Xenopus laevis development lab. What is the most likely reason for this protocol?

Accepted Answer

To allow for individual analysis and minimize cross-contamination.

Question 15

Which of the following best describes the function of the seam cells in C. elegans as visualized in Figure 2?

Accepted Answer

They form a polarized epithelium with stem-like divisions.

Question 16

If a C. elegans population is maintained at 22°C, how long does it typically take for an egg to develop into an adult under optimal conditions?

Accepted Answer

Approximately 3 days

Question 17

Which of the following is a correct statement regarding the use of qPCR in gene expression analysis?

Accepted Answer

qPCR quantifies the amount of specific DNA sequences amplified from cDNA.

Question 18

A student performs RNA quantification using UV/VIS spectroscopy and obtains an $$A_{260}/A_{280}$$ ratio of 1.2. What does this result most likely indicate?

Accepted Answer

The RNA sample is contaminated with protein.

Developmental Biology Laboratory: C. elegans and Xenopus laevis

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