Comparative Embryology Quiz 1

Chemotaxis is the movement of organisms in response to chemical stimuli in their environment. In aquatic organisms, such as bacteria or plankton, chemotaxis is crucial for their survival and finding food sources. They can detect and move towards or away from specific chemicals in the water, helping them locate nutrients, avoid toxins, or find suitable habitats. Therefore, chemotaxis is indeed particularly important in aquatic organisms.

In sea urchins, the bindin-bindin receptor matching (recognition) occurs when the sperm contacts the vitelline envelope. This means that when a sea urchin sperm comes into contact with the vitelline envelope of an egg, the bindin protein on the sperm binds to the bindin receptor on the egg's envelope. This binding is crucial for successful fertilization to occur. Therefore, the statement "True" is correct as it accurately describes the process of bindin-bindin receptor matching in sea urchins.

The fertilization membrane actually develops during the second half of fertilization. This membrane forms as a result of the fusion of the egg and sperm membranes, creating a barrier that prevents additional sperm from entering the egg. Therefore, the correct answer is False.

The last step listed among the given options is "binding to the oocyte cell membrane". This step occurs after the acrosomal reaction, penetration of the jelly layer, and chemotaxis. Once the sperm has reached the oocyte, it binds to the oocyte cell membrane, allowing for fertilization to occur.

Cortical granules are not found in mature sperm cells. These granules are present in the oocyte, or egg cell, and are responsible for preventing multiple sperm from fertilizing the same egg. They release their contents upon fertilization, creating a fertilization envelope that blocks the entry of additional sperm. Therefore, mature sperm cells do not possess cortical granules.

The contact between oocyte and sperm cell membranes has the latest control because it occurs after the acrosome reaction, bindin-bindin receptor recognition, and chemotaxis have taken place. This contact is the final step in the fertilization process and requires precise coordination and control to ensure successful fusion of the sperm and oocyte membranes.

During the first half of fertilization, both the sperm cell finding the egg and the sperm cell penetrating the barriers occur. This means that the sperm cell successfully locates the egg and then manages to penetrate the protective layers surrounding the egg. Therefore, options "a and b above" are correct.

The cumulus layer is not part of a sea urchin egg. The cumulus layer is a layer of cells that surrounds the egg in some animals, such as mammals, but it is not present in sea urchin eggs. Sea urchin eggs have a vitelline envelope, which is a protective layer surrounding the egg, a cell membrane that separates the inside of the egg from the outside environment, cortical granules that are involved in fertilization, and a nucleus that contains the genetic material of the egg.

Bindin receptors are needed for a highly species-specific step on the surface of the vitelline envelope, which is responsible for attracting the sea urchin sperm toward the egg. This means that both options "a" and "b" are correct. The bindin receptors play a crucial role in ensuring that only sperm from the same species can successfully fertilize the egg, promoting reproductive isolation and maintaining species integrity.

The correct answer is "all of the above". The acrosomal reaction refers to a series of biochemical changes that occur in the sperm's acrosome, a specialized structure at the tip of the sperm. It occurs in sea urchins and other organisms. During the acrosomal reaction, the acrosome releases enzymes that help penetrate the vitelline envelope, which is the protective layer surrounding the egg. This reaction allows the sperm to pass through the oocyte cell membrane and fertilize the egg. Therefore, all of the given statements are true about the acrosomal reaction.