Only $2.99/month

Need to memorize (K)

Key Concepts:

Terms in this set (186)

C. Zona pellucida
The correct answer is [C]. Vitelline is a similar component in the egg cells of sea urchins, and is responsible for much of the same function. Progesterone plays a role in leading the sperm to the egg, but not in the binding. The zona pellucida is the outer layer of the egg that is responsible for the initial binding of the sperm to the egg. The ZP3 protein is responsible for the species-specific binding of the sperm to the egg, but is more important for helping galactosyltransferase (GaIT) activate the acrosome reaction. Without it, the sperm will not be able to bind to the egg. Once the egg has undergone the acrosome reaction and fused with the sperm, it can then bind to the uterine wall.

A. Vitelline membrane
Choosing the vitelline membrane is at first a tempting answer, as it is an oocyte component that functions in the binding of sperm. However, the vitelline membrane (or vitelline layer) is the term used to describe this structure in non-mammals (for example, a common model used to describe the process of egg fertilization is the sea urchin - the sea urchin egg would be said to have a surrounding vitelline membrane); therefore the answer choice is incorrect.

C. Zona pellucida
The zona pellucida (specifically the ZP3 protein) is the component of the oocyte responsible for the binding of sperm in mammalian fertilization, so the answer choice is correct. The zona pellucida is a glycoprotein membrane that surrounds the oocyte. It binds sperm, and is required to initiate the acrosome reaction (the sperm releases the contents of its acrosome as it approaches the egg which contributes to charge-based fast block of polyspermy). Other zona glycoproteins include ZP2, which helps in oocyte-sperm recognition and in the prevention of polyspermy, and ZP1, which cross-links ZP3 and ZP2. Without ZP1, the zona pellucida cannot form.
C. Tight junctions

Tight junctions prevent the passage of materials between digestive tract cells in animals. This way, the body must absorb the food through intracellular space. Desmosomes are a type of anchoring junctions that provide mechanical stability and are often seen in animal skin cells. They consist of the protein keratin to bind adjacent cells together. Gap junctions are narrow protein channels between animal cells that allow for the exchange of ions and small molecules, but not cytoplasm. They are often used in cell-to-cell communication by the exchange of materials or electrical impulse. Plasmodesmata are narrow protein channels between plant cells.

Tight junctions are junctions that completely encircle the sides of each cell, providing a seal that prevents passage of material between cells. This junction is characteristic of cells lining the digestive tract where materials are required to pass through cells into blood. They prevent the passage of molecules and ions through the space between cells so that materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue.

Gap junctions are junctions that form narrow tunnels between cells via proteins called connexins. These junctions prevent the cytoplasms of each cell from mixing, but allow for the passage of ions and small molecules between cells. These junctions are found in tissues like the heart, which pass electrical impulses across many cells.

Anchor junctions (consisting of desmosomes - for additional detail see answer A's explanation) provide strong mechanical stability and are present in tissues subject to mechanical stress (such as the cervix and outer layer of the skin).
B. totipotent cell.
Two types of cleavage can occur. Indeterminate cleavage produces a blastomere that can individually complete normal development. This is how identical twins are born. Pluripotent cells cannot form an entire individual, but they can differentiate into any of the three primary germ layers (ectoderm, mesoderm, endoderm).
A totipotent cell can give rise to any and all human cells, and even an entire functional organism. Similarly, in indeterminate cleavage, if blastomeres are separated from the rest of the embryo, both will individually complete normal development. The product of an indeterminate cleavage can be thought of as a totipotent cell due to its ability to form a new organism, so the answer choice is correct.
C. pluripotent cell.
A pluripotent cell can give rise to all tissue types, but not an entirely new organism. In contrast, the product of indeterminate cleavage is able to fully complete development into a new organism; therefore the answer choice is incorrect. Once an embryo develops from a morula to a blastula, it loses its totipotency and becomes pluripotent.
E. multipotent cell.
A multipotent cell can give rise to a limited range of cells within a tissue type. In contrast, the product of indeterminate cleavage is able to fully complete development into a new organism; therefore the answer choice is incorrect. A multipotent stem cell that could give rise to new brain cells, for example, would be unable to differentiate to form new muscle cells (as these organs in embryonic origins and tissue type).