Questions & explanations
1. What prevents multiple sperms from entering the ovum during fertilisation?
- Acrosomal reaction
- Changes in the zona pellucida membrane induced by sperm contact
- Cortical reaction
- Formation of the second polar body
Answer: Changes in the zona pellucida membrane induced by sperm contact
When a sperm contacts the zona pellucida, it induces changes that block entry of additional sperms, ensuring monospermy. The acrosomal reaction helps the sperm penetrate, the cortical reaction also contributes to the block, but the question specifically mentions changes induced by sperm contact. Formation of the second polar body occurs after sperm entry.
2. Which of the following cells are responsible for the synthesis and secretion of androgens, mainly testosterone, in the male reproductive system?
- Sertoli cells
- Leydig cells
- Spermatogonia
- Germ cells
Answer: Leydig cells
Leydig cells, present in the interstitial space of the testes, produce and secrete androgens such as testosterone. Sertoli cells support spermatogenesis but do not secrete androgens. Spermatogonia are immature germ cells that undergo spermatogenesis. Germ cells are a general term for cells that develop into sperm, but they do not secrete hormones.
3. What is the function of the special tissue in the penis that helps in erection?
- To facilitate urination
- To facilitate insemination
- To produce sperm
- To secrete hormones
Answer: To facilitate insemination
The penis is made up of special erectile tissue that fills with blood during sexual arousal, causing an erection. This erection facilitates insemination by allowing the penis to enter the female reproductive tract. Urination is a separate function, sperm production occurs in the testes, and hormone secretion occurs in the testes and other glands.
4. Which duct leads from the epididymis and ascends into the abdomen to loop over the urinary bladder?
- Vas deferens
- Urethra
- Ejaculatory duct
- Vasa efferentia
Answer: Vas deferens
The epididymis leads to the vas deferens, which ascends to the abdomen and loops over the urinary bladder. The urethra is the tube that carries urine and semen out of the body. The ejaculatory duct is formed by the union of the vas deferens and the duct of the seminal vesicle. The vasa efferentia connect the testis to the epididymis.
5. The vas deferens receives a duct from which gland before opening into the urethra as the common ejaculatory duct?
- Prostate gland
- Seminal vesicle
- Bulbourethral gland
- Testis
Answer: Seminal vesicle
The vas deferens joins with the duct from the seminal vesicle to form the ejaculatory duct, which then opens into the urethra. The prostate gland and bulbourethral glands also contribute secretions but do not directly join the vas deferens. The testis produces sperm but does not have a duct that joins the vas deferens directly.
6. After leaving the testis, the vasa efferentia open into which structure?
- Rete testis
- Epididymis
- Vas deferens
- Seminal vesicle
Answer: Epididymis
The vasa efferentia leave the testis and open into the epididymis, which is located along the posterior surface of each testis. The rete testis is inside the testis. The vas deferens is the duct that continues from the epididymis. The seminal vesicle is an accessory gland that joins the vas deferens.
7. What is the process of fusion of a sperm with an ovum called?
- Implantation
- Fertilisation
- Gastrulation
- Ovulation
Answer: Fertilisation
Fertilisation is defined as the fusion of a sperm with an ovum, leading to the formation of a zygote. Implantation is the attachment of the blastocyst to the uterine wall, gastrulation is a stage in embryonic development, and ovulation is the release of an ovum from the ovary.
8. At which specific site in the female reproductive tract does fertilisation typically occur?
- Ampullary-isthmic junction of the fallopian tube
- Fundus of the uterus
- Cervical canal
- Fimbriae of the fallopian tube
Answer: Ampullary-isthmic junction of the fallopian tube
Fertilisation occurs when sperm and ovum meet at the ampullary-isthmic junction of the fallopian tube. The fundus is part of the uterus, the cervical canal is in the cervix, and fimbriae are finger-like projections that capture the ovum but are not the site of fertilisation.
9. The acrosomal reaction helps the sperm to penetrate which layers of the ovum?
- Zona pellucida and plasma membrane
- Corona radiata and zona pellucida
- Plasma membrane and cytoplasm
- Zona pellucida only
Answer: Corona radiata and zona pellucida
Acrosomal secretions enable the sperm to pass through the zona pellucida and the plasma membrane of the ovum. The corona radiata is the outer layer of cells, but the acrosomal reaction specifically aids in penetrating the zona pellucida and plasma membrane.
10. Which of the following correctly describes the structure of a mammalian ovum?
- It is surrounded by zona pellucida and corona radiata, contains nutritive yolk and a haploid nucleus.
- It is surrounded by corona radiata only, contains no yolk and a diploid nucleus.
- It is surrounded by zona pellucida only, contains abundant yolk and a haploid nucleus.
- It is surrounded by both zona pellucida and corona radiata, contains no yolk and a diploid nucleus.
Answer: It is surrounded by zona pellucida and corona radiata, contains nutritive yolk and a haploid nucleus.
The mammalian ovum is surrounded by an inner zona pellucida and an outer corona radiata. It contains a haploid nucleus (after meiosis) and nutritive yolk for early development. The other options incorrectly describe the layers, ploidy, or yolk content.
11. What event is triggered by the entry of the sperm into the secondary oocyte?
- Completion of the first meiotic division
- Completion of the second meiotic division
- Formation of the first polar body
- Immediate fusion of pronuclei
Answer: Completion of the second meiotic division
Sperm entry induces the secondary oocyte to complete its second meiotic division, forming a haploid ovum (ootid) and a second polar body. The first meiotic division and first polar body formation occur before ovulation. Pronuclear fusion occurs later.
12. Which of the following best describes the positive feedback mechanism during childbirth?
- Oxytocin inhibits uterine contractions to prevent premature birth
- Uterine contractions stimulate oxytocin release, which further strengthens contractions
- Oxytocin is released only after the baby is expelled
- The placenta produces oxytocin to initiate labor
Answer: Uterine contractions stimulate oxytocin release, which further strengthens contractions
During childbirth, uterine contractions stimulate the release of oxytocin from the posterior pituitary. Oxytocin then enhances the strength and frequency of contractions, creating a positive feedback loop that continues until the baby is delivered.