Question

Which of these statements is true? a. Sperm are not motile until they pass through the epididymis. b. Sperm require capacitation in the female reproductive tract before they can fertilize an ovum. c. A secondary oocyte does not complete meiotic division until it has been fertilized. d. All of these are true.

Short answer

The correct answer is d. All of these are true. Sperm are not motile until they pass through the epididymis, they require capacitation in the female reproductive tract before they can fertilize an ovum, and a secondary oocyte does not complete meiotic division until it has been fertilized.

Step-by-step solution

Understand statement a

Sperm are not motile until they pass through the epididymis. This statement is true. Sperm are produced in the testes and then move to the epididymis, where they mature and gain the ability to swim. They are not motile until they have passed through the epididymis.

Understand statement b

Sperm require capacitation in the female reproductive tract before they can fertilize an ovum. This statement is true. Capacitation is a series of changes that sperm undergo within the female reproductive tract that prepares them to penetrate and fertilize the ovum. Sperm must undergo capacitation before they are capable of fertilizing an egg.

Understand statement c

A secondary oocyte does not complete meiotic division until it has been fertilized. This statement is true. A secondary oocyte is formed during the first meiotic division of oogenesis. It remains in a state of suspended animation until it is fertilized by a sperm. Once fertilized, a secondary oocyte completes its second meiotic division, resulting in a haploid ovum and an additional polar body.

Determine the true statement(s)

All three statements (a, b, and c) are true. Therefore, the correct answer is: d. All of these are true.

Key concepts

Epididymis Function

The epididymis, a coiled tube located at the back of the testes, plays a critical role in male fertility. Its primary function is to store and mature sperm cells that are produced in the testes.

When sperm are first produced, they lack the ability to move effectively and are considered immotile. As they pass through the epididymis, they undergo essential physical and chemical changes that lead to the development of motility. This maturation process can take several days and includes the gain of forward motility and the ability to navigate the female reproductive system.

Moreover, the epididymis also contributes to the concentration of sperm by absorbing excess fluid, and it adds important substances to the seminal fluid that facilitate sperm motility and longevity. Thus, the epididymis is vital for ensuring that sperm are motile and capable of reaching and fertilizing an egg during reproduction.

Sperm Capacitation

Sperm capacitation is an essential physiological process that sperm undergo once inside the female reproductive tract. This process involves the removal of proteins and lipids from the sperm plasma membrane and alterations in the sperm’s motility and signaling pathways.

Capacitation is a prerequisite for sperm to acquire the ability to penetrate the protective layers surrounding the ovum, allowing them to reach and fertilize the egg. During this time, sperm exhibit hyperactivated motility, a distinct swimming pattern that assists them in navigating through the cervical mucus and the uterine cavity to reach the ovum in the fallopian tube.

The alterations in membrane fluidity and ion channel regulation also prepare sperm for the acrosome reaction, an enzymatic process that occurs just prior to fertilization and is pivotal for the sperm to penetrate the ovum. Without capacitation, sperm would be unable to fertilize an egg, highlighting its significance in the fertilization process.

Meiotic Division of Oocytes

The meiotic division of oocytes, or female gametes, is a specialized form of cell division that results in the formation of haploid cells. Unlike the continual process of spermatogenesis in males, oogenesis in females is a cyclical event resulting in one ovum per cycle.

The primary oocyte begins meiosis during the female's embryonic development, but the process is arrested in prophase I until puberty. After puberty, during each menstrual cycle, hormonal changes trigger the continuation of meiosis in a primary oocyte, which then completes Meiosis I, giving rise to a secondary oocyte and a smaller polar body.

The secondary oocyte progresses to metaphase of Meiosis II but arrests again and is only completed when fertilization by a sperm occurs. This second division leads to the formation of a haploid ovum and an additional polar body, which ensures the correct distribution of genetic material in preparation for fertilization.

Oogenesis

Oogenesis is the process through which ova (eggs) are produced in the female ovaries. This process begins prenatally, when a finite number of oocytes are created and then enter a stalled phase of development. At birth, females possess their lifetime supply of oocytes, which remains dormant until puberty.

Unlike males who produce sperm continuously throughout their lives, females undergo a cyclical process of oogenesis. Each cycle typically matures one follicle, containing an oocyte, which will be released during ovulation. However, not all oocytes will complete maturation and ovulation; most will degenerate over time in a process called atresia.

Oogenesis is crucial for sexual reproduction because it provides a mechanism to decrease the chromosome number by half, allowing the combination of genetic material from both parents without causing an increase in the number of chromosomes. This reductive division is also the process by which genetic variability is increased, contributing to the genetic diversity of a population.