Gametogenesis and Fertilization Practice Exam Quiz
What is the process of gamete formation called?
a) Mitosis
b) Meiosis
c) Gametogenesis
d) Fertilization
Which of the following occurs in meiosis but not in mitosis?
a) DNA replication
b) Chromosome alignment at the metaphase plate
c) Crossing over
d) Cytokinesis
What is the primary function of the Sertoli cells in spermatogenesis?
a) Produce testosterone
b) Support and nourish developing sperm
c) Store sperm
d) Trigger ovulation
Where does oogenesis primarily occur?
a) Fallopian tubes
b) Ovary
c) Uterus
d) Endometrium
What is the haploid number of chromosomes in humans?
a) 46
b) 22
c) 23
d) 44
In females, at what stage of meiosis are oocytes arrested at birth?
a) Prophase I
b) Metaphase I
c) Anaphase II
d) Telophase II
When does the second meiotic division of the oocyte complete?
a) During ovulation
b) At puberty
c) After fertilization
d) During menstruation
What is the end product of spermatogenesis?
a) 2 diploid spermatocytes
b) 4 haploid sperm cells
c) 1 haploid sperm cell
d) 4 diploid spermatocytes
What triggers ovulation in the female reproductive cycle?
a) Estrogen surge
b) Follicle-stimulating hormone (FSH)
c) Luteinizing hormone (LH) surge
d) Progesterone decline
How is meiosis in males different from meiosis in females?
a) Meiosis in males produces four gametes; females produce one.
b) Crossing over occurs only in males.
c) Males produce diploid gametes.
d) Females skip prophase I.
Where does fertilization typically occur in humans?
a) Ovary
b) Uterus
c) Fallopian tube
d) Cervix
Which structure in the sperm helps penetrate the egg?
a) Acrosome
b) Midpiece
c) Tail
d) Nucleus
What prevents polyspermy after fertilization?
a) Zona pellucida hardening
b) Increased motility of sperm
c) Multiple sperm fusion
d) Slow block mechanism
What is the role of calcium ions during fertilization?
a) Stimulate meiosis in the oocyte
b) Activate sperm motility
c) Trigger cortical granule reaction
d) Inhibit zona pellucida formation
How long does the sperm remain viable in the female reproductive tract?
a) 12 hours
b) 24 hours
c) 48–72 hours
d) 7 days
What is the first cell formed after fertilization called?
a) Blastula
b) Morula
c) Zygote
d) Embryo
How many chromosomes are present in a zygote?
a) 23
b) 46
c) 22
d) 44
Which hormone maintains the uterine lining after fertilization?
a) Estrogen
b) Progesterone
c) Oxytocin
d) Prolactin
Which term describes the fusion of male and female pronuclei?
a) Syngamy
b) Plasmalemma fusion
c) Cleavage
d) Fertilization reaction
What prevents the fertilized egg from implanting in the fallopian tube?
a) Ciliary movement
b) Fertilization membrane
c) Zona pellucida degradation
d) Amniotic fluid
What is the final stage of gametogenesis in males?
a) Spermatogonia differentiation
b) Spermiogenesis
c) Formation of Leydig cells
d) Acrosome reaction
What is the role of follicle-stimulating hormone (FSH) in females?
a) Trigger ovulation
b) Stimulate the growth of ovarian follicles
c) Maintain the corpus luteum
d) Promote fertilization
How many mature eggs are typically produced during oogenesis?
a) 1
b) 2
c) 3
d) 4
What stage of the fertilized egg implants in the uterus?
a) Zygote
b) Morula
c) Blastocyst
d) Gastrula
What happens to the polar bodies formed during oogenesis?
a) Fertilize other eggs
b) Degenerate
c) Convert into sperm
d) Participate in embryogenesis
Which hormone primarily regulates spermatogenesis?
a) Testosterone
b) Progesterone
c) Prolactin
d) Oxytocin
What is the main purpose of the zona pellucida?
a) Provide nutrients to the embryo
b) Prevent premature fertilization
c) Facilitate sperm binding
d) Guide the embryo to the uterus
What stage of meiosis is completed upon fertilization?
a) Metaphase II
b) Prophase II
c) Telophase I
d) Anaphase II
Which organelle in the sperm provides energy for motility?
a) Acrosome
b) Nucleus
c) Mitochondria
d) Golgi apparatus
What is the main function of cortical granules during fertilization?
a) Release enzymes to block polyspermy
b) Enhance sperm motility
c) Guide the zygote to the uterus
d) Provide nutrients to the embryo
What is the first stage of spermatogenesis?
a) Spermiogenesis
b) Formation of spermatogonia
c) Meiosis II
d) Formation of polar bodies
What structure is responsible for producing testosterone in males?
a) Sertoli cells
b) Leydig cells
c) Epididymis
d) Vas deferens
What is the name of the process where the oocyte is released from the follicle?
a) Fertilization
b) Ovulation
c) Implantation
d) Meiosis I
What is the chromosome number in a primary spermatocyte?
a) 23
b) 46
c) 92
d) 44
Which hormone stimulates the production of sperm?
a) Progesterone
b) Follicle-stimulating hormone (FSH)
c) Oxytocin
d) Human chorionic gonadotropin (hCG)
What is the name of the follicle that ruptures during ovulation?
a) Graafian follicle
b) Primordial follicle
c) Antral follicle
d) Secondary follicle
At what stage is the oocyte released during ovulation?
a) Primary oocyte
b) Secondary oocyte
c) Polar body
d) Zygote
What is the name of the connective tissue capsule surrounding the testis?
a) Tunica albuginea
b) Seminiferous tubule
c) Epididymis
d) Scrotal sac
Which cell type is haploid?
a) Primary spermatocyte
b) Secondary oocyte
c) Spermatogonia
d) Zygote
What happens to the follicle after ovulation?
a) It degenerates immediately
b) It becomes the corpus luteum
c) It remains as a Graafian follicle
d) It undergoes meiosis
What is the term for the chemical signal that attracts sperm to the egg?
a) Acrosomal reaction
b) Chemotaxis
c) Cortical reaction
d) Capacitation
What is the final step of sperm maturation that occurs within the female reproductive tract?
a) Spermiogenesis
b) Acrosome reaction
c) Capacitation
d) Syngamy
What is the term for the fertilized egg dividing into multiple cells?
a) Fertilization
b) Cleavage
c) Gastrulation
d) Implantation
Which structure prevents the zygote from adhering to the fallopian tube wall?
a) Zona pellucida
b) Endometrium
c) Peristalsis
d) Cilia in the fallopian tube
What structure forms from the fusion of the egg and sperm plasma membranes?
a) Pronuclei
b) Zygote membrane
c) Fertilization envelope
d) Cytoplasmic bridge
Which of the following is a product of meiosis II in oogenesis?
a) Primary oocyte
b) Secondary oocyte
c) First polar body
d) Second polar body
Which of the following structures gives rise to the male gametes?
a) Sertoli cells
b) Spermatogonia
c) Leydig cells
d) Spermatids
What phase of meiosis is paused in a primary oocyte until ovulation?
a) Prophase I
b) Metaphase I
c) Metaphase II
d) Anaphase II
What is the genetic makeup of a secondary spermatocyte?
a) 23 chromosomes, haploid
b) 46 chromosomes, diploid
c) 92 chromosomes, diploid
d) 23 pairs of chromosomes, diploid
How many mature sperms are formed from one spermatogonium?
a) 1
b) 2
c) 4
d) 8
The first meiotic division in oogenesis results in the formation of:
a) Two secondary oocytes
b) A secondary oocyte and a polar body
c) Two primary oocytes
d) Four polar bodies
Which organelle in the sperm provides energy for motility?
a) Nucleus
b) Acrosome
c) Mitochondria
d) Endoplasmic reticulum
What phase of meiosis is completed only after fertilization?
a) Prophase I
b) Metaphase II
c) Anaphase II
d) Telophase II
Which of the following hormones directly triggers ovulation?
a) FSH
b) LH
c) Progesterone
d) Estrogen
In the seminiferous tubules, spermatogonia are located:
a) In the lumen
b) Closest to the basement membrane
c) Near the Sertoli cells
d) Inside the epididymis
Which reaction ensures that only one sperm fertilizes the egg?
a) Acrosome reaction
b) Cortical reaction
c) Zona reaction
d) Sperm capacitation
What is the significance of the acrosomal enzymes in fertilization?
a) They help the sperm swim faster
b) They prevent polyspermy
c) They digest the zona pellucida
d) They assist in pronucleus formation
What is the term for the process where sperm binds to the zona pellucida?
a) Acrosome reaction
b) Sperm capacitation
c) Zona binding
d) Cleavage
What is the genetic composition of a zygote?
a) Haploid
b) Diploid
c) Triploid
d) Tetraploid
What structure facilitates the movement of the zygote toward the uterus?
a) Zona pellucida
b) Cilia in the fallopian tubes
c) Corpus luteum
d) Blastocyst
What is the main role of Sertoli cells in the testes?
a) Produce testosterone
b) Provide nutrients and support for spermatogenesis
c) Store mature sperm
d) Secrete follicle-stimulating hormone
How many chromosomes are present in a human spermatid?
a) 46
b) 92
c) 23
d) 44
What type of division produces primary spermatocytes from spermatogonia?
a) Mitosis
b) Meiosis I
c) Meiosis II
d) Binary fission
What is the function of the midpiece of the sperm?
a) Stores genetic material
b) Generates energy for movement
c) Aids in egg penetration
d) Helps in capacitation
During which phase of the ovarian cycle does the corpus luteum form?
a) Follicular phase
b) Ovulation
c) Luteal phase
d) Menstrual phase
Which structure houses developing oocytes in the ovary?
a) Graafian follicle
b) Endometrium
c) Corpus albicans
d) Zona pellucida
Which hormone maintains the corpus luteum if fertilization occurs?
a) Estrogen
b) Progesterone
c) Human chorionic gonadotropin (hCG)
d) Luteinizing hormone (LH)
What is the purpose of the zona pellucida?
a) Protect the egg and regulate sperm entry
b) Nourish the zygote
c) Aid in egg implantation
d) Stimulate the corpus luteum
What cell type initiates spermatogenesis?
a) Leydig cells
b) Spermatogonia
c) Primary spermatocyte
d) Spermatids
Which phase of meiosis reduces the chromosome number by half?
a) Prophase I
b) Metaphase I
c) Anaphase I
d) Telophase I
What is the term for the fusion of sperm and egg pronuclei?
a) Fertilization
b) Zygote formation
c) Syngamy
d) Cortical reaction
Which layer of the egg is penetrated first by the sperm?
a) Corona radiata
b) Zona pellucida
c) Plasma membrane
d) Perivitelline space
What prevents polyspermy after fertilization?
a) Capacitation
b) Acrosomal reaction
c) Cortical granules release
d) Flagella movement of sperm
Which event marks the completion of fertilization?
a) Release of the second polar body
b) Activation of the egg
c) Fusion of male and female pronuclei
d) Formation of the zona pellucida
What happens to the zona pellucida after fertilization?
a) It thickens to prevent polyspermy
b) It dissolves completely
c) It fuses with the sperm
d) It becomes part of the embryo
What structure in the testes is the site of spermatogenesis?
a) Vas deferens
b) Epididymis
c) Seminiferous tubules
d) Prostate gland
What happens to the secondary oocyte if it is not fertilized?
a) It completes meiosis II
b) It forms a polar body
c) It degenerates during menstruation
d) It becomes a zygote
Which hormone stimulates spermatogenesis?
a) Testosterone
b) Follicle-stimulating hormone (FSH)
c) Progesterone
d) Prolactin
During which stage of meiosis does crossing-over occur?
a) Prophase I
b) Metaphase I
c) Anaphase II
d) Telophase II
What is the fate of the polar bodies formed during oogenesis?
a) They develop into secondary oocytes
b) They degenerate and are reabsorbed
c) They provide nutrients for the zygote
d) They form the placenta
Which of the following is true about spermatogenesis?
a) It produces one viable sperm per spermatogonium
b) It begins during embryonic development
c) It produces four viable sperm from one primary spermatocyte
d) It halts after puberty
Which phase of meiosis is paused in a fertilized secondary oocyte?
a) Prophase I
b) Metaphase II
c) Anaphase I
d) Telophase I
What cell type is directly formed by meiosis I in spermatogenesis?
a) Primary spermatocyte
b) Secondary spermatocyte
c) Spermatid
d) Spermatozoon
Which cell type in the ovary secretes estrogen during follicular development?
a) Granulosa cells
b) Theca cells
c) Corpus luteum
d) Germinal epithelium
Which of the following is a characteristic of primary oocytes?
a) They are haploid
b) They complete meiosis II before ovulation
c) They are arrested in prophase I
d) They are formed after puberty
What triggers the completion of meiosis II in the oocyte?
a) Hormonal stimulation
b) Fertilization by sperm
c) Ovulation
d) Cortical reaction
Which of the following ensures species-specific fertilization in mammals?
a) Corona radiata
b) Zona pellucida proteins
c) Cortical granules
d) Acrosomal enzymes
The zona pellucida hardens after fertilization to prevent:
a) Egg activation
b) Sperm capacitation
c) Polyspermy
d) Pronuclei fusion
Which step in fertilization involves the release of enzymes from the sperm acrosome?
a) Binding to the egg membrane
b) Penetration of the zona pellucida
c) Formation of the pronuclei
d) Sperm capacitation
Which part of the sperm enters the oocyte during fertilization?
a) Entire sperm
b) Nucleus and mitochondria
c) Nucleus and centrioles
d) Nucleus only
What is the main function of the Leydig cells in the testes?
a) To secrete testosterone
b) To support spermatogenesis
c) To produce sperm
d) To store sperm
Which of the following is produced during the second meiotic division of oogenesis?
a) Two secondary oocytes
b) One secondary oocyte and one polar body
c) One ovum and three polar bodies
d) One ovum and two polar bodies
What is the first stage of sperm development in spermatogenesis?
a) Spermatid
b) Spermatogonium
c) Secondary spermatocyte
d) Primary spermatocyte
Which of the following is true about the process of spermatogenesis?
a) It is completed before birth
b) It produces haploid cells
c) It results in the production of one sperm from each spermatogonium
d) It occurs in the uterus
Which hormone stimulates the production of testosterone in males?
a) Follicle-stimulating hormone (FSH)
b) Luteinizing hormone (LH)
c) Prolactin
d) Estrogen
How many polar bodies are formed during oogenesis in humans?
a) One
b) Two
c) Three
d) Four
Which of the following occurs during the luteal phase of the ovarian cycle?
a) Ovulation occurs
b) The corpus luteum forms and secretes progesterone
c) Estrogen levels peak
d) Menstruation begins
At which stage is an oocyte arrested in meiosis before ovulation?
a) Prophase II
b) Metaphase II
c) Anaphase I
d) Telophase I
Which of the following best describes the chromosome number in spermatogonia?
a) Diploid
b) Haploid
c) Triploid
d) Tetraploid
What process in the seminiferous tubules results in the production of spermatozoa?
a) Mitosis
b) Spermiogenesis
c) Spermatogenesis
d) Meiosis
Which of the following is responsible for the release of enzymes that help the sperm penetrate the egg?
a) Acrosome
b) Nucleus
c) Flagellum
d) Midpiece
What is the function of the cortical granules released during fertilization?
a) To destroy the sperm head
b) To promote cell division
c) To block further sperm entry
d) To activate the egg
What event marks the transition from a zygote to an embryo?
a) Fertilization
b) Cleavage
c) Blastulation
d) Gastrulation
Which of the following occurs immediately after the sperm penetrates the egg?
a) The egg activates its metabolism
b) The sperm’s mitochondria enter the egg
c) The egg’s plasma membrane fuses with the sperm
d) The zona pellucida disintegrates
In fertilization, the sperm’s contribution to the zygote’s genetic material includes:
a) Only the nucleus
b) The nucleus and mitochondria
c) The nucleus, mitochondria, and centrioles
d) Only the flagellum
Which part of the sperm enters the egg during fertilization?
a) Tail
b) Acrosome
c) Nucleus
d) Midpiece
Which structure is responsible for blocking polyspermy during fertilization?
a) The sperm’s acrosome
b) The zona pellucida
c) The egg’s plasma membrane
d) Cortical granules
In which part of the female reproductive tract does fertilization typically occur?
a) Uterus
b) Fallopian tube
c) Ovaries
d) Cervix
Which event immediately follows the fusion of the egg and sperm nuclei?
a) Formation of the blastocyst
b) Completion of meiosis II in the oocyte
c) Fertilization membrane formation
d) Zygote formation
What is the purpose of the sperm’s journey through the female reproductive tract?
a) To avoid immune recognition
b) To find an egg for fertilization
c) To increase the sperm count
d) To undergo capacitation
What is the primary function of the cortical reaction during fertilization?
a) To enable the sperm to enter the egg
b) To block additional sperm from entering the egg
c) To start the egg’s metabolism
d) To prevent the egg from undergoing meiosis II
Which of the following hormones is responsible for the final maturation of the oocyte before ovulation?
a) Estrogen
b) Progesterone
c) Luteinizing hormone (LH)
d) Follicle-stimulating hormone (FSH)
What is the fate of the secondary oocyte if fertilization does not occur?
a) It completes meiosis II and becomes an ovum
b) It degenerates and is expelled during menstruation
c) It continues to develop into a zygote
d) It undergoes apoptosis in the ovary
Which phase of spermatogenesis involves the transformation of spermatids into spermatozoa?
a) Spermiogenesis
b) Spermatocytogenesis
c) Spermatogenesis
d) Spermatogonium phase
Which of the following statements about the male gamete (sperm) is correct?
a) It is produced in the ovaries
b) It is haploid and contains half the number of chromosomes
c) It contains two sets of chromosomes
d) It does not undergo meiosis
Which of the following is the result of the first meiotic division in oogenesis?
a) One secondary oocyte and one polar body
b) Two secondary oocytes
c) One ovum and two polar bodies
d) One egg and three polar bodies
Where does the majority of sperm maturation occur in males?
a) Epididymis
b) Testes
c) Seminal vesicles
d) Prostate gland
Which of the following occurs during the luteal phase of the menstrual cycle?
a) Ovulation
b) Corpus luteum formation
c) Menstruation
d) Endometrial shedding
During oogenesis, what is the chromosome number in the primary oocyte?
a) Haploid
b) Diploid
c) Triploid
d) Tetraploid
At what stage of development is a male gamete considered mature?
a) Spermatogonium
b) Spermatocyte
c) Spermatid
d) Spermatozoon
Which of the following is true about oogenesis in females?
a) It produces four viable eggs
b) Oocytes are produced after puberty only
c) Meiosis I begins during fetal development and is completed after puberty
d) It results in the production of one egg per year
Fertilization
Which structure of the sperm fuses with the egg’s plasma membrane during fertilization?
a) Head
b) Tail
c) Acrosome
d) Midpiece
Which of the following occurs first after sperm fertilizes the egg?
a) Fusion of the egg and sperm pronuclei
b) Activation of the egg’s metabolic processes
c) Formation of the fertilization membrane
d) Cleavage of the zygote
What is the role of the zona pellucida in fertilization?
a) To help sperm swim toward the egg
b) To activate the egg’s metabolism
c) To prevent polyspermy
d) To provide nutrients to the sperm
What is the immediate consequence of the sperm’s acrosomal reaction during fertilization?
a) The sperm enters the egg’s cytoplasm
b) The sperm’s nucleus fuses with the egg’s nucleus
c) The egg’s zona pellucida hardens
d) The egg’s metaphase plate is formed
What is the term for the fusion of sperm and egg nuclei?
a) Fertilization
b) Zygote formation
c) Pronuclear fusion
d) Cleavage
Which structure forms the fertilization membrane to block additional sperm entry?
a) Acrosome
b) Cortical granules
c) Zona pellucida
d) Egg membrane
Which event happens immediately after sperm penetration of the egg?
a) Meiosis II in the egg is completed
b) The zygote divides into two cells
c) The sperm loses its tail
d) The egg activates its metabolism
Which of the following best describes the role of the sperm tail in fertilization?
a) It helps the sperm attach to the egg
b) It carries the sperm’s DNA to the egg
c) It provides energy for the sperm to swim
d) It fuses with the egg’s plasma membrane
What happens to the egg immediately after fertilization in humans?
a) It begins the process of cleavage
b) It undergoes meiosis I
c) It forms a blastocyst
d) It becomes a morula
Short Questions and Answers for Study Guide
Explain the process of spermatogenesis, including the stages involved and the final product.
Answer:
Spermatogenesis is the process through which male gametes (sperm) are produced in the testes. It occurs in the seminiferous tubules and consists of three main stages:
- Spermatogonial phase: This is the starting point, where spermatogonia (diploid stem cells) undergo mitosis to produce primary spermatocytes.
- Meiotic phase: The primary spermatocytes enter meiosis I to form two secondary spermatocytes, which are haploid. These secondary spermatocytes then undergo meiosis II to produce four spermatids, which are also haploid.
- Spermiogenesis: The spermatids undergo morphological changes to become mature spermatozoa (sperm). This includes the formation of the acrosome, condensation of the nucleus, and the development of the flagellum (tail). The final product of spermatogenesis is four functional sperm cells, each carrying half the number of chromosomes (haploid), ready for fertilization.
Discuss the stages of oogenesis and how it differs from spermatogenesis.
Answer:
Oogenesis is the process of egg (ovum) formation in females and occurs in the ovaries. It has distinct stages compared to spermatogenesis:
- Fetal Development: During fetal development, all the primary oocytes are formed. These oocytes are arrested in prophase I of meiosis until puberty.
- At Puberty: Each menstrual cycle, some primary oocytes complete meiosis I, resulting in a secondary oocyte and a smaller polar body.
- Meiosis II (Only if Fertilized): The secondary oocyte enters meiosis II but arrests at metaphase II. If fertilization occurs, the oocyte completes meiosis II, resulting in a mature ovum and a second polar body.
Unlike spermatogenesis, which produces four viable sperm from one primary spermatocyte, oogenesis produces one viable egg and two (or three) non-functional polar bodies. Additionally, oogenesis begins before birth and continues throughout a female’s reproductive life, while spermatogenesis is a continuous process starting at puberty.
Describe the process of fertilization in humans, detailing the key events that lead to the formation of a zygote.
Answer:
Fertilization in humans is a complex process that involves the fusion of the sperm and egg to form a zygote. The key events in fertilization include:
- Sperm Capacitation: Upon entering the female reproductive tract, sperm undergo capacitation, which involves biochemical changes that allow the sperm to penetrate the egg.
- Acrosomal Reaction: The sperm’s acrosome releases enzymes that help the sperm penetrate the egg’s outer layer, the zona pellucida.
- Sperm-Egg Fusion: The sperm’s head binds to the egg’s plasma membrane. The sperm’s nucleus enters the egg, and the egg’s plasma membrane depolarizes to prevent polyspermy (entry of multiple sperm).
- Cortical Reaction: The egg releases cortical granules into the space between the egg membrane and the zona pellucida, causing a hardening of the zona pellucida, which prevents further sperm from entering.
- Completion of Meiosis II: The egg completes meiosis II and forms a mature ovum and a second polar body.
- Pronuclear Fusion: The sperm and egg nuclei fuse to form a diploid zygote, restoring the full set of chromosomes (46 in humans).
The zygote then begins to divide through cleavage, initiating embryonic development.
Discuss the hormonal regulation of gametogenesis in both males and females.
Answer:
The regulation of gametogenesis in both males and females is controlled by a series of hormones released by the hypothalamus, pituitary gland, and gonads:
- In Males:
- The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
- LH stimulates the Leydig cells in the testes to produce testosterone, which is essential for spermatogenesis.
- FSH acts on Sertoli cells in the testes to support sperm production and maturation.
- Testosterone provides negative feedback to the hypothalamus and pituitary to regulate hormone levels.
- In Females:
- GnRH from the hypothalamus stimulates the release of LH and FSH from the anterior pituitary.
- FSH stimulates the growth of ovarian follicles, and LH triggers ovulation when the mature follicle ruptures.
- Estrogen is produced by the developing follicles and plays a key role in the regulation of the menstrual cycle and in preparing the endometrium for possible pregnancy.
- After ovulation, the corpus luteum forms and secretes progesterone, which maintains the uterine lining for implantation. If fertilization does not occur, progesterone levels drop, leading to menstruation.
Explain the significance of the acrosomal reaction during fertilization and how it contributes to the successful fusion of sperm and egg.
Answer:
The acrosomal reaction is a critical event in fertilization that enables sperm to penetrate the egg’s protective layers. The acrosome is a cap-like structure on the head of the sperm, containing enzymes such as hyaluronidase and acrosin. These enzymes are crucial for breaking down the zona pellucida, the glycoprotein layer surrounding the egg. The acrosomal reaction begins when the sperm contacts the zona pellucida, triggering the release of these enzymes.
As the enzymes degrade the zona pellucida, the sperm is able to move through it and reach the egg’s plasma membrane. This process allows the sperm to bind to the egg’s surface and ultimately fuse with it. The fusion of sperm and egg membranes results in the entry of the sperm’s nucleus into the egg, leading to the formation of a zygote. The acrosomal reaction ensures that only one sperm is able to penetrate the egg, preventing polyspermy and ensuring the correct genetic contribution from both parents.
Compare and contrast the processes of spermatogenesis and oogenesis.
Answer:
Spermatogenesis and oogenesis are both processes that produce gametes (sperm and eggs, respectively), but they differ in several key aspects:
- Location: Spermatogenesis occurs in the testes, while oogenesis takes place in the ovaries.
- Timing: Spermatogenesis begins at puberty and continues throughout a male’s life. In contrast, oogenesis begins during fetal development, with the primary oocytes arrested in prophase I until puberty. Oogenesis is a cyclic process that continues until menopause.
- End Products: Spermatogenesis produces four functional sperm from one primary spermatocyte. Oogenesis, however, produces one viable ovum and three non-functional polar bodies.
- Duration: Spermatogenesis is a continuous process, whereas oogenesis has long periods of arrest (e.g., primary oocytes are arrested in prophase I, and secondary oocytes are arrested in metaphase II).
- Meiosis: Both processes involve meiosis, but in oogenesis, the two meiotic divisions are unequal, with most of the cytoplasm going to the ovum and very little retained in the polar bodies. In spermatogenesis, the cytoplasm is evenly divided among the four sperm cells.
Explain the significance of meiosis in gametogenesis and its role in maintaining genetic diversity.
Answer:
Meiosis is a type of cell division that reduces the chromosome number by half and is essential for gametogenesis. It consists of two rounds of division: meiosis I and meiosis II. During meiosis I, homologous chromosomes are separated into different cells, and genetic recombination (crossing over) occurs between non-sister chromatids, allowing for genetic diversity. In meiosis II, the sister chromatids are separated, resulting in four non-identical haploid gametes, each with half the number of chromosomes of the original cell.
Meiosis plays a crucial role in maintaining genetic diversity through two mechanisms:
- Independent Assortment: Chromosomes are randomly distributed to the gametes, leading to different combinations of maternal and paternal chromosomes.
- Crossing Over: This process results in the exchange of genetic material between homologous chromosomes, creating new combinations of genes.
These mechanisms ensure that gametes are genetically unique, which contributes to the diversity seen in offspring.
Describe the roles of estrogen and progesterone in the female reproductive system during the menstrual cycle and their influence on oogenesis.
Answer:
Estrogen and progesterone are key hormones in regulating the menstrual cycle and oogenesis in females.
- Estrogen: At the beginning of the menstrual cycle, estrogen levels rise due to the maturation of ovarian follicles. Estrogen promotes the growth of the endometrial lining, preparing it for potential implantation. It also stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary, which is crucial for ovulation. Estrogen also aids in the maturation of the oocyte within the follicle.
- Progesterone: After ovulation, the ruptured follicle becomes the corpus luteum, which secretes progesterone. Progesterone maintains the uterine lining, making it receptive to a fertilized egg. If pregnancy does not occur, progesterone levels drop, triggering the shedding of the endometrial lining (menstruation).
Both hormones are vital for regulating the menstrual cycle and ensuring that oogenesis occurs in sync with the preparation of the uterus for possible pregnancy.
What is the role of the zona pellucida in fertilization, and how does it contribute to species-specific recognition?
Answer:
The zona pellucida is a glycoprotein layer surrounding the egg (oocyte) that plays an important role in fertilization. It serves several functions:
- Protection: The zona pellucida protects the egg from mechanical damage and prevents polyspermy (fertilization by multiple sperm).
- Sperm Binding: The zona pellucida contains specific receptors that allow for sperm binding. The sperm’s acrosomal enzymes help it penetrate the zona pellucida, but only after binding to the specific receptors present on this layer.
- Species-Specific Recognition: The zona pellucida is species-specific, meaning that only sperm from the same species can bind to it effectively. This ensures that fertilization occurs between gametes of the same species, preventing interspecies fertilization.
Once the sperm binds to the zona pellucida, it triggers the acrosomal reaction, allowing the sperm to penetrate the zona pellucida and fuse with the egg’s plasma membrane, leading to fertilization.
Discuss the importance of the cortical reaction in preventing polyspermy during fertilization.
Answer:
The cortical reaction is a crucial mechanism that prevents polyspermy, the fertilization of an egg by multiple sperm, which would result in an abnormal number of chromosomes and developmental issues. The cortical reaction occurs after the sperm fuses with the egg’s plasma membrane. Here’s how it works:
- Activation of Cortical Granules: Upon sperm entry, calcium ions are released within the egg, triggering the activation of cortical granules, which are stored in the egg’s cytoplasm.
- Release of Enzymes: The cortical granules release enzymes into the space between the egg membrane and the zona pellucida.
- Hardening of the Zona Pellucida: The enzymes modify the zona pellucida, causing it to harden and prevent other sperm from penetrating the egg.
- Membrane Depolarization: The egg’s plasma membrane also depolarizes, creating an electrical barrier that further prevents additional sperm from fusing with the egg.
These mechanisms ensure that only one sperm fertilizes the egg, leading to the formation of a viable zygote with the correct number of chromosomes.
What is the role of the sperm’s mitochondria in fertilization, and how does it contribute to the embryo’s energy needs?
Answer:
The mitochondria in sperm provide energy required for their motility and are vital for the fertilization process. The mitochondria are located in the sperm’s midpiece and are responsible for producing ATP through oxidative phosphorylation, which powers the sperm’s flagellum for swimming toward the egg.
Once fertilization occurs, the sperm’s mitochondria do not contribute to the mitochondrial population of the embryo. The mitochondria in the egg are the sole source of mitochondrial inheritance in the offspring. This phenomenon is called maternal inheritance, where mitochondria are passed on exclusively from the mother. The energy provided by the sperm’s mitochondria is critical during the journey to the egg, but once fertilization is complete, the egg’s mitochondria take over to meet the embryo’s energy needs as it begins to divide and develop.
Explain the process of the second meiotic division in oogenesis and its significance in the formation of the mature ovum.
Answer:
The second meiotic division in oogenesis is completed only after fertilization. It occurs as follows:
- Arrest in Meiosis II: After ovulation, the secondary oocyte enters meiosis II but arrests at metaphase II. At this stage, it is not yet a mature ovum.
- Completion After Fertilization: When sperm fertilizes the secondary oocyte, the entry of the sperm triggers the completion of meiosis II. The oocyte divides asymmetrically, producing one mature ovum and a second polar body.
- Significance of Unequal Cytokinesis: The division of cytoplasm is unequal, with the majority of the cytoplasm retained in the mature ovum. This ensures that the egg has sufficient resources for early embryonic development.
- Formation of a Zygote: The fusion of the egg and sperm nuclei results in the restoration of the diploid chromosome number and the formation of a zygote. The polar body, which is much smaller and contains little cytoplasm, degenerates.
The completion of meiosis II ensures that the ovum is ready for development after fertilization, contributing to the proper chromosomal makeup of the zygote.
How do hormonal changes during the menstrual cycle affect the development of the ovarian follicle and the release of the egg?
Answer:
The menstrual cycle is controlled by hormonal fluctuations that regulate the development of ovarian follicles and the release of the egg. The cycle is divided into three phases:
- Follicular Phase (Days 1–14): At the beginning of the cycle, low levels of estrogen and progesterone stimulate the release of follicle-stimulating hormone (FSH) from the pituitary gland. FSH promotes the growth and maturation of ovarian follicles. The developing follicles secrete estrogen, which further stimulates the growth of the endometrial lining and the production of more FSH and LH.
- Ovulation (Day 14): A surge in luteinizing hormone (LH), triggered by the rising estrogen levels, induces ovulation. The mature follicle ruptures, releasing the egg (secondary oocyte) into the fallopian tube.
- Luteal Phase (Days 15–28): After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone. Progesterone helps maintain the uterine lining for potential implantation. If pregnancy does not occur, the corpus luteum degenerates, progesterone levels drop, and menstruation begins. These hormonal changes are essential for the maturation of the egg and the preparation of the uterus for a possible pregnancy.