AP Biology : Systems Physiology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #331 : Systems Physiology

Which of the following is not one of the changes that take place in sperm cells just after ejaculation?

Possible Answers:

Increase in intracellular calcium levels

Loss of certain membrane proteins to facilitate binding to the oocyte

Initiation of the acrosomal reaction

Change in sperm tail beating pattern 

Correct answer:

Initiation of the acrosomal reaction

Explanation:

After ejaculation into the female vagina, capacitation of sperm cells takes place. During this process, sperm undergo molecular and biochemical changes that allow them to fertilize the oocyte. In this final stage of maturation, sperm cells lose many membrane proteins (including glycoproteins and steroids to ease binding to the oocyte), undergo an influx of intracellular calcium, and change their tail movement pattern. The changes that occur during sperm activation put the sperm cells into a state of hyperactivity, or heightened motility that aids fertilization.

Example Question #332 : Systems Physiology

Which of the following components of acrosomal content aids the sperm cell's approach towards the oocyte?

Possible Answers:

Digestive enzymes

Glycoproteins

Calcium ions

Steroids

Correct answer:

Digestive enzymes

Explanation:

The acrosome of sperm cells is a cap on the anterior end of the cell that contains digestive enzymes (i.e. acrosin and hyaluronidase) and surface antigens. During the acrosomal reaction, the acrosome fuses with the sperm’s plasma membrane and releases the acrosomal contents from the cell. The digestive enzymes break down the layers surrounding the oocyte and allow the sperm cell to approach the oocyte plasma membrane.

Example Question #333 : Systems Physiology

Which of the following best describes where fertilization takes place in “in vitro” fertilization (IVF)?

Possible Answers:

Outside of the human body

Inside the uterus

In the ovaries 

Inside the fallopian tubes

Correct answer:

Outside of the human body

Explanation:

“In vitro” fertilization, or IVF, is the fertilization of the oocyte outside of the human body in a culture. In this process, an oocyte is extracted from a female and exposed to ejaculate containing sperm cells. The fertilization, therefore, occurs outside of the female reproductive system. The zygote is then implanted in a female uterus for gestation and development. IVF is a process used in cases of infertility, surrogacy, and other cases of reproductive difficulties.

Example Question #334 : Systems Physiology

Which of the following ions are intracellularly released during the fertilized egg’s cortical reaction?

Possible Answers:

Potassium ions

Sodium ions

Chlorine ions

Calcium ions

Correct answer:

Calcium ions

Explanation:

After fertilization and sperm cell penetration of the oocyte, the cortical reaction takes place. During the cortical reaction, a release of intracellular calcium ions triggers the exocytosis of cortical granules. Cortical granules are vesicles in the cortex of the oocyte that contain enzymes that prevent polyspermy. Exocytosis of the cortical granules releases their contents into the extracellular matrix—the zona pellucida in mammals—creating changes to prevent further sperm penetration.

Example Question #335 : Systems Physiology

Which of the following best explains the changes that result from the release of contents of the cortical granule into the oocyte’s extracellular matrix?

Possible Answers:

Formation of the hyaline layer

All of these

Slow block to polyspermy 

Water attraction into the perivitelline space

Correct answer:

All of these

Explanation:

Penetration of the oocyte by a sperm cell leads to an intracellular calcium release, trigging the exocytosis of cortical granules. The cortical granules release their contents—including proteases, peroxidases, and carbohydrates—into the extracellular matrix. These contents untether the perivitelline membrane and attract water into the perivitelline space, expanding it to form the hyaline layer. This is known as the slow block to polyspermy because it creates a permanent barrier to other sperm.

Example Question #336 : Systems Physiology

Which of the following changes to the zona pellucida that prevent polyspermy are made in mammalian cortical reactions?

Possible Answers:

Extracellular increase of calcium ions

Proteolytic cleavage of glycoproteins that bind to sperm cells

Modification of vitelline envelope tethering 

Shrinking of perivitelline space 

Correct answer:

Proteolytic cleavage of glycoproteins that bind to sperm cells

Explanation:

In mammals, the cortical reaction involves a very similar influx of intracellular calcium ions and exocytosis of cortical granules. The exocytosis releases the contents into the zona pellucida, where glycoproteins are cleaved to prevent further sperm cell binding. The hyaline layer then forms around the fertilized egg.

Example Question #31 : Understanding Other Reproductive Physiology

Which of the following processes allows for the fusion of the genetic material of the sperm and egg?

Possible Answers:

Mitosis

All of meiosis

Meiosis I

Meiosis II

Correct answer:

Mitosis

Explanation:

After sperm cell and oocyte plasma membrane fusion, the sperm pronucleus moves into the oocyte cytoplasm. The sperm and egg pronuclei migrate towards the center of the cell while performing DNA replication, where both nuclear membranes dissolve. The chromosomes are prevented from dispersing by a mitotic spindle that tethers the maternal and paternal genetic material together. The cell then begins mitosis, which fuses the genetic material into a single diploid genome.

Example Question #32 : Understanding Other Reproductive Physiology

Which of the following features of egg activation releases the egg from the metaphase II meiotic arrest?

Possible Answers:

Fusion of sperm and oocyte plasma membrane 

Intracellular calcium release 

Cortical granule exocytosis

Hyaline layer formation

Correct answer:

Intracellular calcium release 

Explanation:

During oogenesis, specifically ootidogenesis, the secondary oocyte halts development and arrests its growth at metaphase II of meiosis. This arrest is maintained through ovulation until fertilization in the fallopian tube. During fertilization, the cortical reaction in the oocyte acts as the slow block to polyspermy and starts with the release of intracellular calcium. This release of calcium ions allows the egg to resume meiosis and ends the metaphase II arrest. 

Example Question #33 : Understanding Other Reproductive Physiology

Which of the following characteristics is not true regarding the fast block to polyspermy?

Possible Answers:

There is an influx of calcium ions

It is an electrical block

The egg develops a positive charge

It is a faster block for the many sperm surrounding the egg

Correct answer:

There is an influx of calcium ions

Explanation:

The fast block to polyspermy is the initial method that prevents polyspermy by the large number of sperm cells surrounding the egg. The fast block is triggered by sperm binding, which initiates a change in membrane potential. There is a large influx of sodium ions into the egg, creating a depolarization event that prevents further sperm penetration.

Example Question #337 : Systems Physiology

Which of the following best represents a difference between the fast and slow blocks to polyspermy?

Possible Answers:

Sperm cells can overcome the fast block to polyspermy but not the slow block

The fast block involves an increase in intracellular ion concentration and the slow block does not

None of these

Fast block involves sodium ion transport and the slow block involves calcium ion transport

Correct answer:

Fast block involves sodium ion transport and the slow block involves calcium ion transport

Explanation:

Both the fast and slow blocks to polyspermy prevent the penetration of a second sperm cell into the oocyte. The fast block to polyspermy is the initial and immediate block upon sperm binding. The fast block is an electrical block caused when oocyte membrane depolarization is started by an influx of calcium ions. The slow block is characterized by a change in zona pellucida makeup through the cortical reaction, which prevents sperm cell binding. The cortical reaction is triggered by the release of intracellular calcium.

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