Question 1

Which of the following is the diffusible extracellular element in the process of vulval cell differentiation?

Accepted Answer

The EGF ligand is the diffusible extracellular element involved in the process of vulval cell differentiation. It binds to the EGF receptor on the vulval precursor cells and initiates a signaling cascade that leads to their differentiation into vulval cells. The Notch pathway also plays a role in this process, but it is mediated by direct cell-to-cell contact rather than a diffusible ligand.

Question 2

Shown here are four ligands (M, H, K, and L) and their corresponding receptors along with three genes (U, V, and W) whose activity the receptor controls through signal transduction. The arrows indicate gene activation, the T-bars indicate gene repression.  If either U or V is required to activate W, which ligand (or ligands) result in W being active?

Accepted Answer

The answer of Shown here are four ligands (M, H,...

Question 3

Consider a gene affected by two transcription factors, U and V. Transcription of the gene takes place in the presence of U alone or of V alone, but when U and V are present together transcription is repressed. This is an example of:

Accepted Answer

This scenario describes combinatorial control, where the presence of different transcription factors can lead to different or opposing effects on gene expression. In this case, U and V can activate transcription individually, but when they are both present, they inhibit transcription. This is a common mechanism for regulating gene expression in complex organisms.

Question 4

During the development of the vulva in Caenorhabditis elegans, binding of _____ to its receptor initiates development of the cell into _____ cell.

Accepted Answer

The answer of During the development of the vulva in...

Question 5

During the development of the vulva in Caenorhabditis elegans, when the Notch ligand binds a Notch receptor on a progenitor cell:

Accepted Answer

The answer of During the development of the vulva in...

Question 6

All transcription factors-like Pax6-are normally transcriptional activators; only mutated forms of transcription factors act as transcriptional repressors.

Accepted Answer

While some transcription factors like Pax6 are known to function as transcriptional activators, many others can act as repressors in certain contexts. Mutations can indeed affect the activity of transcription factors, but not all mutations necessarily lead to a switch from activator to repressor function.

Question 7

A mutation is found in C. elegans that causes the organism to have no vulval opening cells or any vulval supporting cells. What could this mutation be?

Accepted Answer

The answer of A mutation is found in C. elegans...

Question 8

What is the consequence of inactivating the Notch receptor in the type 2 progenitor cell?

Accepted Answer

Inactivating the Notch receptor in the type 2 progenitor cell will prevent the downstream signaling necessary for the progenitor to complete its differentiation into a type 2 cell.

Question 9

Imagine that a researcher is looking at a mutant Arabidopsis plant that only produces carpels and sepals; stamens and petals are absent. Which of the following statements must be TRUE regarding this plant?

Accepted Answer

The answer of Imagine that a researcher is looking at...

Question 10

Which of the following statements is TRUE regarding AP2, AP3, PI, and AG?

Accepted Answer

AP2, AP3, PI, and AG are all transcription factors that interact with specific cis-regulatory elements of genes involved in plant flower development. They do not function independently, but often form heterodimers and interact with other transcription factors to regulate gene expression in a combinatorial manner.

Question 11

Signal transduction is the process by which:

Accepted Answer

Signal transduction refers to the process by which an extracellular molecule, such as a hormone or neurotransmitter, binds to a receptor on the cell membrane. This binding activates a series of intracellular signaling molecules, which eventually lead to a cellular response. Thus, option D correctly describes the process of signal transduction. Option A is referring to gene regulation, while option B describes the role of transcription factors in determining cell fate. Option C describes a simplified version of a signaling pathway, but it is not specific enough to be considered the best choice. Option E is incorrect because there is a correct answer option.

Question 12

Review Figure 20.19. Which floral organ develops from whorl 1 in Arabidopsis?

Accepted Answer

Whorl 1 in Arabidopsis develops into sepals, as indicated by the label on the diagram.

Question 13

Which of the following statements is TRUE regarding Arabidopsis?

Accepted Answer

All of these statements are true regarding Arabidopsis. Arabidopsis is a model plant used to study plant development, and its floral development is well-characterized. It has four cell whorls in its floral meristem, and the combinatorial control of transcription by AP2, AP3, PI, and AG in Arabidopsis leads to the development of different plant structures, such as carpels, stamens, petals, and sepals.

Question 14

In the roundworm Caenorhabditis elegans, development of the vulva begins when the _____ cell secretes _____, which then bind(s) to _____ on a(n) _____ cell.

Accepted Answer

In the roundworm Caenorhabditis elegans, the development of the vulva begins when the anchor cell secretes EGF (Epidermal Growth Factor), which then binds to the EGF receptor on a progenitor cell. This signaling pathway is crucial for the proper development of the vulva in C. elegans.

Question 15

A constitutively active receptor will do what in the presence of its ligand?

Accepted Answer

A constitutively active receptor is already in an active state in the absence of its ligand. Therefore, it will remain activated in the presence of its ligand.

Question 16

Consider Figure 20.25. Imagine that there is a mutation in the gene for the Notch receptor in the progenitor cell. How does mutation affect vulva development?

Accepted Answer

The Notch receptor plays a role in promoting the differentiation of the progenitor cell into a type 2 cell, which then induces neighboring cells to adopt a type 1 fate. A mutation in the Notch receptor gene would prevent this differentiation, causing the progenitor cell to remain a type 1 cell, and disrupting normal vulva development. The other answer options are not directly related to the function of the Notch receptor in this pathway.

Question 17

Review the ABC model for flower development in Arabidopsis shown below. Which of the following statements about the ABC model is INCORRECT?

Accepted Answer

The answer of Review the ABC model for flower development...

Question 18

The progenitor cell that is closest to the anchor cell:

Accepted Answer

The progenitor cell closest to the anchor cell receives the largest dose of EGF, activates genes for differentiation into a type 1 cell, prevents adjacent cells from differentiating into a type 1 cell, and induces adjacent cells to differentiate into type 2 cells. This is a classic example of lateral inhibition and cell signaling in developmental biology, where the proximity to a signaling source (the anchor cell) determines the fate of progenitor cells.

Question 19

Which of the following statements is TRUE regarding AP3 and PI (the protein products of APETALA-3 and PISTILLATA, respectively)?

Accepted Answer

Both AP3 and PI are involved in stamen/petal development, and they bind to one another to form a heterodimer. This complex is necessary for the induction of B activity, which controls the development of petals and stamens.

Question 20

Review the ABC model for flower development in Arabidopsis shown below. If additional B activity were expressed in all four whorls, what floral organs would develop from each whorl?

Accepted Answer