Question 1

Cytoplasmic contents in the fertilized egg move along microtubule networks.What kinds of proteins would you predict would facilitate these movements?

Accepted Answer

Kinesins are motor proteins that move along microtubule networks and are responsible for various cellular movements, including the transport of cytoplasmic contents during fertilization. Enzymes (A), tubulins (C), keratins (D), and collagens (E) do not have a direct role in facilitating these movements.

Question 2

Which of the following directors of embryonic development can be found in the unfertilized egg?

Accepted Answer

Cytoplasmic determinants, which are maternal RNAs and proteins, are present in the unfertilized egg and play a crucial role in directing embryonic development.

Question 3

If microtubule formation were disrupted experimentally by the use of drugs,the effects might include all of the following EXCEPT

Accepted Answer

Microtubules are involved in cell division, intracellular transport, and maintaining cell shape. Disruption of microtubules would affect processes like organizer formation and gastrulation, but translation of cytoplasmic RNAs into proteins is primarily a function of ribosomes and not directly dependent on microtubules.

Question 4

In many animal embryos,the eye is the first organ to develop.The Pax6 protein is important to eye development;its absence may prevent the formation of eyes in mice and humans.Pax6 probably acts as a(n)

Accepted Answer

Pax6 is a transcription factor that regulates the expression of genes necessary for eye development, including those involved in the formation of photoreceptors.

Question 5

During gastrulation in amphibians,the presumptive mesoderm moves into the interior of the embryo by following fibrils of fibronectin.The fibronectin is probably secreted by which cells?

Accepted Answer

The fibronectin is secreted by the ectodermal cells that line the inside of the blastocoel.

Question 6

The function of the acrosomal complex during fertilization is

Accepted Answer

The acrosomal complex contains enzymes that help dissolve the protective coating surrounding the egg, allowing the sperm to penetrate and fertilize the egg.

Question 7

Which of the following is the most basic process in the developing embryo because all of the other processes listed can occur only after or in conjunction with it?

Accepted Answer

Mitosis is the most basic process in the developing embryo as it is the process by which cells divide and multiply, leading to the formation of all the different tissues and organs in the body. Organogenesis, cell differentiation, morphogenesis, and germ layer formation all occur after mitosis has taken place.

Question 8

What is a major difference between the development of Drosophila or Xenopus and that of humans?

Accepted Answer

Drosophila and Xenopus undergo metamorphosis as part of their development, whereas humans do not undergo metamorphosis.

Question 9

Scientists using RNA hybridization techniques found that a transcription factor called macho-1 localized to some cells during early cleavage,but not others.Descendents of these cells produce mesodermal derivatives.Which structures might not be found in embryos depleted of macho-1?

Accepted Answer

Macho-1 localized to cells that give rise to mesodermal derivatives. Somites, which are mesodermal structures, are likely to be affected in embryos that are depleted of macho-1. The neural tube and digestive system are derived from different germ layers and are unlikely to be affected by macho-1 depletion. Similarly, the skin is also derived from a different layer and is unlikely to be affected. Hence, the best choice is B) somites.

Question 10

In mammals,the zona pellucida is digested during the process of fertilization.This structure is probably similar to

Accepted Answer

The zona pellucida in mammals is similar to the vitelline envelope in sea urchins, as both serve as protective layers surrounding the egg and are involved in sperm binding and fertilization.

Question 11

Chordin is an organizer protein found only in the dorsal regions of Xenopus laevis embryos.An antibody to chordin might disrupt the determination of which structure?

Accepted Answer

Chordin is important in regulating dorsal-ventral patterning in Xenopus embryos, which is critical for the formation of the central nervous system. Therefore, an antibody to chordin would most likely disrupt the determination of the central nervous system.

Question 12

Many amphibian species release their sperm and eggs directly into a watery environment.All of the following mechanisms might ensure species-specific fertilization in these populations EXCEPT

Accepted Answer

Blocking of non-species-specific mRNA sequences is not a mechanism that ensures species-specific fertilization in amphibians. The other options (acrosomal complexes in sperm, complex coverings of the egg, specific protein binding between sperm and egg, and fertilization envelopes) all play a role in ensuring that the sperm of one species can successfully fertilize the eggs of that same species.

Question 13

Suppose an antibody to bindin was introduced into a chamber containing sea urchin sperm and eggs.What might be the result of this experiment?

Accepted Answer

Bindin is a protein found on the surface of sea urchin sperm that is responsible for binding to the egg surface. If an antibody to bindin was introduced into the chamber, it would likely prevent the sperm from being attracted to the egg surface, as the antibody would bind to and neutralize the bindin protein. This would result in fertilization being inhibited, as the sperm would not be able to reach the eggs to fertilize them.

Question 14

One difference between early development in humans and in Xenopus is that

Accepted Answer

In humans, the blastocyst implants into the uterine wall, which is a critical step in early development. In contrast, Xenopus embryos develop externally in water and do not undergo implantation.

Question 15

In Xenopus embryos,which developmental sequence is correct?

Accepted Answer

In Xenopus embryos, the correct developmental sequence is cleavage, blastula, gastrula, and then neurula. Cleavage is the initial series of cell divisions, forming the blastula. Gastrulation follows, forming the three germ layers, and neurulation is the development of the nervous system.

Question 16

Where do you suppose the first microtubules will be observed in the fertilized egg?

Accepted Answer

Microtubules are initially formed at the centrosomes, where the sperm centriole is located after fertilization. Therefore, the first microtubules will be observed at the site of sperm entry.

Question 17

During early cleavage in animal embryos,minimal growth of the embryo is observed,even though rapid cell division is taking place.How might this lack of growth be most easily measured without destroying the embryo?

Accepted Answer

The answer of During early cleavage in animal embryos,minimal growth...

Question 18

During organogenesis,the first organ system to begin forming in animal embryos is

Accepted Answer

The nervous system is the first organ system to begin forming in animal embryos during organogenesis. This is because the development and functioning of all other organ systems depend on the presence and proper functioning of the nervous system.

Question 19

What happens during gastrulation?

Accepted Answer

Gastrulation is the process by which massive movements of cells occur, making the primary body axes visible and organizing the three embryonic tissues (endoderm, mesoderm, and ectoderm). During this process, the blastula develops into a gastrula, and the formation of structures such as the notochord and neural tube begins. Therefore, option D is the correct answer. Option A is incorrect because the formation of the neural tube occurs during neurulation, not gastrulation. Option B is incorrect as it refers to the formation of the embryonic suspensor in flowering plants, while option C is also incorrect as it describes cleavage rather than gastrulation.

Question 20

What happens during cleavage?

Accepted Answer

During cleavage, the fertilized egg undergoes multiple rapid cell divisions without any growth, resulting in a ball of cells known as a blastula.

Note: options A, B, and D describe events that occur later in embryonic development after cleavage.

Quiz 22: An Introduction to Animal Development