Reproductive System and Development

Question 13

What is the function of the reproductive system?

Answer 13

It generates new offspring from parent organisms, facilitating the survival of the species.

Some reproductive methods also increase genetic variation. This allows a species to adapt to changes in its environment.

Question 14

What is the difference between sexual and asexual reproduction?

Answer 14

• Sexual reproduction involves two organisms and results in offspring that genetically differs from both of them.
• Asexual reproduction is carried out by a single organism and produces genetically identical offspring.

All prokaryotes use asexual reproduction, though they have alternative methods of gene transfer. Eukaryotic species can reproduce sexually, asexually, or through both mechanisms.

Question 16

Define:

gamete

Answer 16

A haploid cell that combines with another gamete during sexual reproduction. Together, the fused cells form a zygote that develops into a new organism.

In humans, the male gamete is the sperm while the female gamete is the egg or ovum.

Question 17

Label the parts of the sperm cell below.

Answer 17

Question 18

What is spermatogenesis, and when and where does it begin?

Answer 18

It is the production of the male gametes, sperm, in the seminiferous tubules of the testes.

Spermatogenesis begins at puberty.

Question 20

Order the following terms from least to most mature: spermatid, spermatogonium, spermatozoon, secondary spermatocyte, primary spermatocyte.

Answer 20

1. Spermatogonium
2. Primary spermatocyte
3. Secondary spermatocyte
4. Spermatid
5. Spermatozoon

Both meiosis and mitosis are involved in this differentiation process.

Question 21

During which step of spermatogenesis do cells become haploid?

Answer 21

Meiosis I - the division from primary to secondary spermatocyte.

After this transition, the gamete will be haploid but with replicated chromosomes.

Meiosis II, on the other hand, refers to the division from secondary spermatocyte to spermatid. After this step, the gamete will be haploid with only one copy of each chromosome, as in its final state.

Question 22

Around what age in men does sperm production cease?

Answer 22

Spermatogenesis never ceases; it continues throughout a man’s adult life.

In contrast, oogenesis does not occur as a steady process. Virtually all of a woman’s eggs are partially differentiated by birth, and all differentiation ceases completely at menopause.

Question 23

What is oogenesis, and where and when does it begin?

Answer 23

It is the production of the female gametes, ova, in the ovaries.

Oogenesis begins before birth. Specifically, all of a female’s oocytes are produced and arrested at prophase I by the time she is born.

Question 25

Order the following terms from least to most mature: primary oocyte, ovum, oogonium, secondary oocyte.

Answer 25

1. Oogonium
2. Primary oocyte
3. Secondary oocyte
4. Ovum

Both meiosis and mitosis are involved in this differentiation process.

Question 26

Define:

polar body

Answer 26

A haploid cell produced by meiosis I or meiosis II of oogenesis.

Though they possess normal amounts of genetic material, polar bodies contain little cytosol and few organelles.

Oogenesis is thus characterized by uneven division of cytoplasm. Most of the cytoplasm is allocated to the functioning oocyte, while little is given to the polar body.

Question 27

How many cells are produced in the differentiation of one primary oocyte into one mature ovum?

Answer 27

Oogenesis produces three cells per primary oocyte:

• one ovum
• two polar bodies

In meiosis I, the primary oocyte divides into one secondary oocyte and one polar body. This first polar body generally does not divide further. If fertilized, the secondary oocyte undergoes meiosis II, where it divides into one ovum and a second polar body.

Question 28

From birth until puberty, all of a female’s oocytes are arrested at which stage of oogenesis?

Answer 28

All of a female’s oocytes are primary and are arrested in prophase I of meiosis.

Question 30

Meiosis I corresponds to which step of oogenesis?

Answer 30

Meiosis I involves the division of a primary into a secondary oocyte.

Meiosis II, which is only completed if the egg is fertilized, involves the division of this secondary oocyte into a mature ovum.

Question 31

Name two differences between spermatogenesis and oogenesis.

Answer 31

• Spermatogenesis produces four equally functional gametes; it takes place continuously from puberty to death.
• Oogenesis produces one mature ovum and two nonfunctional polar bodies; it begins before birth and ends at menopause.

Question 32

Which gamete contributes mitochondria to the developing zygote?

Answer 32

A zygote’s mitochondria are contributed by the ovum.

While sperm contain mitochondria, they are destroyed by the ovum shortly after fertilization. As a result, mitochondrial diseases are inherited maternally.

Question 33

Define:

gonads

Answer 33

These are endocrine organs that produce gametes.

The female gonads are the ovaries while the male gonads are the testes.

Question 34

What is an androgen?

Answer 34

It is a general term for a hormone that influences male development.

The most important androgen to know is testosterone, a steroid hormone.

Question 36

Name the major male and female sex hormones.

Answer 36

• testosterone in males
• estrogen and progesterone in females.

While these hormones are steroids, their production is closely related to that of the peptides FSH and LH.

Question 38

Give two structural differences between the male and female reproductive systems.

Answer 38

Male

• reproductive organs are mainly found outside of the body
• the urethra serves both reproductive and urinary purposes

Female:

• reproductive organs are located internally
• the urethra solely involved in urination

Question 40

Define:

puberty

Answer 40

The period of the human lifespan during which the reproductive system becomes mature.

In females, this process is marked by menarche, or the first menstrual period. In males, spermatogenesis begins at puberty.

Question 42

In females, which process involves a decrease in sex hormones and the halting of ovulation?

Answer 42

menopause

Specifically, menopause is the period when menstrual cycles stop occurring and a female can no longer become pregnant.

Question 43

On the diagram below, label the ovaries, Fallopian tubes, uterus, and vagina.

Answer 43

Question 44

What is another term used for the Fallopian tubes?

Answer 44

oviducts

Each Fallopian tube connects a single ovary to the uterus.

Question 45

What are follicles, and in which female reproductive structure are they located?

Answer 45

These are multicellular structures located within the ovaries. Each follicle surrounds and nourishes a single oocyte.

During ovulation, the follicle bursts and develops into the corpus luteum.

Question 46

Once every 28 days, one follicle ruptures inside the ovary, releasing an oocyte into the Fallopian tube. What term is used to refer to this process?

Answer 46

ovulation

Question 47

In which structure of the female reproductive system does the fertilized zygote implant?

Answer 47

The endometrium (lining) of the uterus.

Immediately after ovulation, this lining begins to thicken to provide a favorable environment for the potential zygote.

Question 48

How many sperm cells typically fertilize a single ovum?

Answer 48

One sperm fertilizes each ovum, assuming fertilization occurs at all.

Ova use specific mechanisms to avoid polyspermy, or fertilization by multiple sperm. It is important to know that polyspermy inevitably causes the death of the zygote.

Question 49

What is the length of an average menstrual cycle?

Answer 49

28 days

Question 50

Name the two simultaneous cyclical processes involved in the menstrual cycle.

Answer 50

1. ovarian cycle
2. uterine cycle

In general, the ovarian cycle relates to the development of the follicle within the ovary. The uterine cycle describes the buildup and degradation of the endometrial lining.

Question 51

What are the phases of the ovarian cycle?

Answer 51

1. follicular
2. ovulation
3. luteal

The follicular phase roughly corresponds to the first half of the menstrual cycle, with the luteal phase comprising the other half. Ovulation occurs between these two phases.

Question 52

What physiological changes occur during the follicular phase?

Answer 52

Both LH and FSH are released at fairly high levels, stimulating the development of the follicle. The follicle itself starts to secrete estrogen.

Remember, both LH (luteinizing hormone) and FSH (follicle-stimulating hormone) are peptides released from the anterior pituitary.

Question 53

Describe the conditions that trigger ovulation.

Answer 53

Estrogen levels increase due to its release from the follicle. At this time only, estrogen exerts a positive feedback effect on LH secretion, causing a spike known as the LH surge. The follicle then ruptures, releasing the oocyte.

Question 54

Prior to ovulation, what type(s) of feedback is/are exhibited by estrogen?

Answer 54

Estrogen exhibits positive feedback, triggering the LH surge.

At other times, however, estrogen negatively feeds back on LH and FSH production.

Estrogen’s activity prior to ovulation is one of the few examples of positive feedback. Less common examples include thrombin’s role in blood clotting and the effect of oxytocin during labor.

Question 55

The active ingredients of many birth control medications include synthetic estrogen and progesterone. What effect would such medications have on ovulation?

Answer 55

Ovulation would be inhibited.

The presence of both estrogen and progesterone mimics the condition of pregnancy, in which FSH and LH are inhibited. Without these hormones, no LH surge can be initiated and ovulation cannot occur. In pregnancy, this effect is important to prevent multiple pregnancies from simultaneously occurring.

Question 56

What physiological changes occur during the luteal phase?

Answer 56

The follicle, now called the corpus luteum, begins to secrete progesterone. LH and FSH fall to very low levels.

If fertilization occurs, implantation of the zygote would occur during this phase. Menstrual cycles, then, would temporarily cease due to pregnancy.

Question 57

What are the three phases of the uterine cycle, and what major events do they contain?

Answer 57

1. Menstruation is marked by the degeneration of the endometrial lining.
2. Proliferative phase is involve in regrowth of the endometrium, promoted by estrogen.
3. Secretory phase is affected by progesterone from the corpus luteum. This causes the uterine lining to release nutrients.

Question 58

How do the phases of the uterine cycle match up with the ovarian cycle?

Answer 58

The follicular phase encompasses both menstruation and the proliferative phase, while the luteal phase aligns perfectly with the secretory phase.

Question 59

Define:

corpus luteum

Answer 59

The structure that arises from the burst follicle after ovulation.

If the ovum is not fertilized, it is degraded; otherwise, it persists during early pregnancy.

Since the corpus luteum secretes progesterone, it technically functions as an endocrine gland.

Question 60

Which hormone, commonly detected in pregnancy tests, prevents the corpus luteum from degrading after implantation?

Answer 60

Human chorionic gonadotropin, a classic sign of pregnancy; it maintains the corpus luteum.

(hCG)

Note that hCG is a peptide hormone.

Question 61

Define:

placenta

Answer 61

The organ through which a fetus obtains nutrients and performs gas exchange.

The placenta also performs endocrine functions, secreting estrogen, progesterone, and hCG.

Question 62

A woman is midway through her second trimester of pregnancy. Which of her hormones will be present at high levels?

Answer 62

• Estrogen
• progesterone
• hCG

In early pregnancy, progesterone and some estrogen are secreted by the corpus luteum. Within the third month, the placenta becomes the main source of these hormones, as well as hCG.

Question 63

The end of pregnancy is marked by a series of uterine contractions, leading to the expulsion of the fetus through the birth canal. Which two interchangeable terms describe this process?

Answer 63

Parturition or birth

The repeated contractions that lead to the birth of the fetus are known as labor.

Question 64

Which hormone, released from the anterior pituitary, promotes lactation after birth?

Answer 64

prolactin

Question 65

On the diagram below, label the testes, epididymis, vas deferens, prostate gland, and urethra.

Answer 65

Question 66

What is the function of the scrotum?

Answer 66

It holds the testes, sits outside the body. This keeps the testes at a temperature slightly lower than 37º C, facilitating spermatogenesis.

Question 67

What process occurs in the epididymis?

Answer 67

The sperm become fully mature and motile. This structure also stores sperm after they are made.

Question 68

Name two male reproductive glands and describe their functions.

Answer 68

• Prostate gland secretes a basic solution that protects the sperm from acidic conditions.
• Bulbourethral or Cowper’s glands produce a lubricating fluid prior to ejaculation.

Question 69

Define:

zygote

Answer 69

It is the diploid cell created when a sperm cell fertilizes an ovum.

Note that a zygote is single-celled; once it undergoes a single division, it will be called an embryo.

Question 70

Trace the path of a zygote from the point of fertilization to the point of implantation. What structures does it encounter?

Answer 70

Fertilization occurs in the Fallopian tubes. From there, the zygote travels directly to the uterus and implants in the endometrium, or uterine lining.

Question 71

By which process does an embryo increase its number of cells, but not its overall size?

Answer 71

The early divisions of the embryo are referred to as cleavage. In this process, the cells divide very quickly without growing between divisions.

The regular cell cycle includes two rest or “gap” phases, G₁ and G₂. During cleavage, dividing cells skip these phases.

Question 72

Define:

morula

Answer 72

The name given to the embryo after multiple cleavage divisions. This structure is extremely dense.

The morula later develops into the blastula.

Question 73

What is a blastocyst, and from what other structure does it arise?

Answer 73

A hollow cell arrangement that develops from the morula. A blastocyst contains a central blastocoel, a dense inner cell mass, and a surrounding trophoblast.

Question 74

What is gastrulation, and which germ cell layers does it produce?

Answer 74

It is the differentiation of the blastula into three distinct layers: the ectoderm, the mesoderm, and the endoderm.

Question 75

Define:

ectoderm

Answer 75

It is the outermost germ layer formed during development.

Structures arising from the ectoderm include the eyes, skin, hair, nails, and nervous system.

Question 76

Define:

mesoderm

Answer 76

It is the middle germ layer formed during development.

Structures arising from the mesoderm include blood vessels, gonads, and the muscular and skeletal systems. Note that the kidneys also derive from mesoderm, not endoderm.

Question 77

Define:

endoderm

Answer 77

It is the innermost germ layer formed during development.

Structures arising from the endoderm include internal organs such as the pancreas and urinary bladder. The endoderm also gives rise to the linings of the digestive tract and lungs.

Question 78

A student asserts that the endoderm gives rise to internal organs like the pancreas, lungs, kidneys, and urinary bladder. About which structure was the student incorrect?

Answer 78

The student was wrong about the kidneys, which develop from the mesoderm.

The remaining organs (pancreas, lungs, and urinary bladder) do arise from the endoderm.

Question 79

What process involves the differentiation of ectodermal tissue into the structures that will become the nervous system?

Answer 79

neurulation

The final product of neurulation is the neural tube, which develops into the central nervous system. Peripheral nervous structures arise from cells of the neural crest.

Question 80

Briefly describe the steps involved in neurulation.

Answer 80

1. The notochord, a long, cylindrical structure related to the backbone, forms.
2. The neural plate (ectoderm lying above the notochord) begins pinching inward to create neural folds.
3. The neural folds meet, forming the neural tube.
4. Neural crest cells move away to form peripheral structures.

Question 81

After what amount of time has the zygote progressed into an embryo? Into a fetus?

Answer 81

The zygote is considered an embryo after its first cell division. The embryo is classified as a fetus the beginning of the third month of pregnancy, specifically after the eighth week following fertilization.

Estrogen’s activity prior to ovulation is one of the few examples of positive feedback. Less common examples include thrombin’s role in blood clotting and the effect of oxytocin during labor.

Question 82

With regard to development, what is determination?

Answer 82

It refers to the limitation of a cell’s potential fate in the body.

Determination does not actually change cells into a specific tissue type; it simply restricts what these cells can be.

Question 83

With regard to development, what is differentiation?

Answer 83

It refers to actual changes in a cell’s gene expression that cause it to assume a specific cell type.

For example, the differentiation of a muscle cell might involve changes in cell size, protein production, and responsiveness to signals.

Question 84

Define:

stem cell

Answer 84

An undifferentiated cell that can either develop into a variety of cell types itself, or produce other cells that can then differentiate further.

Question 85

Which cell is more restricted in its development: a pluripotent or a multipotent cell?

Answer 85

multipotent cell

Pluripotent cells can develop into any cell type, such as muscle, epithelial, or nervous tissue. These differentiate into multipotent stem cells, which can only give rise to cells of a particular type.

Question 86

In which situations might a cell undergo apoptosis?

Answer 86

Apoptosis, or programmed cell death, generally occurs in damaged cells. However, it can also serve as a normal part of development.

Viral infection, UV-induced damage, and hypoxia can all induce apoptosis.