Topic 4 Reproduction And Development Review Questions Answer Key

Reproduction and development, cornerstones of life itself, involve intricate processes that ensure the continuation of species. Understanding these processes requires a thorough exploration of various concepts, from gametogenesis to organogenesis. This comprehensive review delves into essential questions concerning reproduction and development, providing detailed answers and explanations to solidify your understanding.

Fundamentals of Reproduction

What are the primary modes of reproduction?

The primary modes of reproduction are sexual and asexual reproduction.

• Sexual reproduction involves the fusion of gametes (sex cells) from two parents, resulting in offspring with genetic variation.
• Asexual reproduction involves a single parent and produces offspring that are genetically identical to the parent.

What are the advantages and disadvantages of sexual vs. asexual reproduction?

Sexual Reproduction:

• Advantages:
  • Genetic variation: Increases the adaptability of a population to changing environments.
  • Disease resistance: Genetic diversity can lead to increased resistance to pathogens.
• Disadvantages:
  • Slower reproduction: Requires finding a mate and the development period is longer.
  • Energy intensive: Requires more energy to produce gametes and find mates.

Asexual Reproduction:

• Advantages:
  • Rapid reproduction: Allows for quick colonization of new environments.
  • Energy efficient: Requires less energy since there is no need to find a mate.
• Disadvantages:
  • Lack of genetic variation: Makes the population vulnerable to environmental changes and diseases.
  • Limited adaptability: Offspring are genetically identical, reducing the ability to adapt.

What is gametogenesis and where does it occur in males and females?

Gametogenesis is the process of forming gametes (sex cells) through meiosis. In males, it is called spermatogenesis and occurs in the seminiferous tubules of the testes. In females, it is called oogenesis and occurs in the ovaries.

Describe the process of spermatogenesis.

Spermatogenesis is the process of sperm production. It involves the following steps:

1. Spermatogonia: These are diploid stem cells in the seminiferous tubules.
2. Primary spermatocytes: Spermatogonia undergo mitosis to produce primary spermatocytes.
3. Meiosis I: Primary spermatocytes undergo meiosis I to form two haploid secondary spermatocytes.
4. Meiosis II: Secondary spermatocytes undergo meiosis II to form four haploid spermatids.
5. Spermiogenesis: Spermatids differentiate into mature spermatozoa (sperm cells).

Describe the process of oogenesis.

Oogenesis is the process of egg production. It involves the following steps:

1. Oogonia: These are diploid stem cells in the ovaries.
2. Primary oocytes: Oogonia undergo mitosis to produce primary oocytes.
3. Meiosis I: Primary oocytes begin meiosis I but arrest in prophase I until puberty.
4. First polar body: After puberty, one primary oocyte completes meiosis I, producing a secondary oocyte and a first polar body (which usually degenerates).
5. Meiosis II: The secondary oocyte begins meiosis II but arrests in metaphase II.
6. Ovulation: If the secondary oocyte is fertilized, it completes meiosis II, producing a mature ovum (egg) and a second polar body.

What are the key differences between spermatogenesis and oogenesis?

The key differences between spermatogenesis and oogenesis are:

• Timing: Spermatogenesis begins at puberty and continues throughout life, while oogenesis begins before birth, arrests until puberty, and ends at menopause.
• Number of gametes: Spermatogenesis produces four functional sperm cells from each primary spermatocyte, while oogenesis produces only one functional egg cell from each primary oocyte (and polar bodies).
• Cytokinesis: In oogenesis, cytokinesis is unequal, resulting in one large ovum and smaller polar bodies, ensuring the ovum has sufficient nutrients for the developing embryo.

Fertilization and Early Development

What is fertilization and where does it typically occur in humans?

Fertilization is the fusion of a sperm cell and an egg cell to form a diploid zygote. In humans, fertilization typically occurs in the oviduct (fallopian tube).

Describe the steps involved in fertilization.

The steps involved in fertilization are:

1. Sperm penetration: Sperm cells penetrate the corona radiata and zona pellucida surrounding the egg.
2. Acrosomal reaction: Enzymes in the acrosome of the sperm break down the zona pellucida, allowing the sperm to reach the egg's plasma membrane.
3. Fusion of membranes: The sperm and egg plasma membranes fuse, and the sperm nucleus enters the egg.
4. Cortical reaction: The egg releases cortical granules, which cause the zona pellucida to harden and prevent polyspermy (fertilization by multiple sperm).
5. Completion of meiosis II: The egg completes meiosis II, forming the mature ovum and a second polar body.
6. Fusion of nuclei: The sperm and egg nuclei fuse, forming a diploid zygote.

What is cleavage and what is its significance?

Cleavage is a series of rapid cell divisions that occur after fertilization, without significant cell growth. Its significance lies in increasing the number of cells in the embryo while maintaining the overall size, preparing the embryo for further development.

What are the stages of early embryonic development?

The stages of early embryonic development include:

1. Zygote: The single-celled fertilized egg.
2. Cleavage: Rapid cell divisions resulting in a morula.
3. Morula: A solid ball of cells.
4. Blastocyst: A hollow ball of cells with an inner cell mass (which will become the embryo) and an outer layer called the trophoblast (which will contribute to the placenta).
5. Gastrulation: The process by which the three primary germ layers (ectoderm, mesoderm, and endoderm) are formed.

What is gastrulation and what are the three primary germ layers formed during this process?

Gastrulation is a crucial stage in embryonic development where the single-layered blastula is reorganized into a multi-layered structure known as the gastrula. This process establishes the three primary germ layers:

• Ectoderm: The outermost layer, which gives rise to the epidermis (skin), nervous system, and sensory organs.
• Mesoderm: The middle layer, which gives rise to muscles, bones, circulatory system, reproductive system, and excretory system.
• Endoderm: The innermost layer, which gives rise to the lining of the digestive tract, respiratory system, and associated organs.

Organogenesis and Development

What is organogenesis and when does it occur?

Organogenesis is the process of organ formation. It occurs after gastrulation, during the first trimester of pregnancy in humans.

What are some of the key developmental processes that occur during organogenesis?

Key developmental processes during organogenesis include:

• Cell differentiation: Cells become specialized in structure and function.
• Morphogenesis: The development of the form and structure of organs and tissues.
• Apoptosis: Programmed cell death, which is essential for shaping developing structures.

Describe the role of the notochord in vertebrate development.

The notochord is a flexible rod-shaped structure derived from the mesoderm. It plays a crucial role in vertebrate development by:

• Providing structural support to the developing embryo.
• Inducing the formation of the neural tube (precursor to the brain and spinal cord) from the ectoderm.
• Contributing to the formation of the vertebral column.

What is neuralation and how does it occur?

Neuralation is the process of forming the neural tube, which will develop into the central nervous system (brain and spinal cord). It occurs through the following steps:

1. Notochord formation: The notochord signals the ectoderm above it to thicken and form the neural plate.
2. Neural plate folding: The edges of the neural plate fold upward, forming the neural folds.
3. Neural tube closure: The neural folds fuse together to form the neural tube.
4. Neural crest cells: Cells at the tips of the neural folds migrate away and form various structures, including parts of the peripheral nervous system, pigment cells, and some skeletal and connective tissues.

What are neural crest cells and what do they give rise to?

Neural crest cells are a unique population of migratory cells that arise from the edges of the neural folds during neuralation. They give rise to a wide variety of structures, including:

• Peripheral nervous system: Sensory ganglia, autonomic ganglia, and Schwann cells.
• Pigment cells: Melanocytes in the skin.
• Skeletal and connective tissues: Cartilage and bone of the face and skull.
• Adrenal medulla: Hormone-producing cells of the adrenal gland.

Extraembryonic Membranes

What are the four extraembryonic membranes and what are their functions?

The four extraembryonic membranes are:

1. Yolk sac: Provides nutrients to the developing embryo (especially in birds and reptiles) and is the site of early blood cell formation in mammals.
2. Amnion: Encloses the embryo in a fluid-filled amniotic cavity, providing a protective cushion and preventing desiccation.
3. Chorion: The outermost membrane, which contributes to the formation of the placenta and facilitates gas exchange.
4. Allantois: Stores waste products and contributes to the formation of the umbilical cord and the urinary bladder.

How does the placenta form and what are its functions?

The placenta forms from the chorion of the embryo and the endometrium (lining) of the mother's uterus. Its functions include:

• Nutrient and gas exchange: Facilitates the transfer of oxygen, nutrients, and waste products between the mother and the fetus.
• Hormone production: Produces hormones (such as human chorionic gonadotropin, estrogen, and progesterone) that maintain the pregnancy.
• Immune protection: Transfers antibodies from the mother to the fetus, providing passive immunity.

Human Reproductive System

What are the main organs of the male reproductive system and what are their functions?

The main organs of the male reproductive system and their functions are:

• Testes: Produce sperm and testosterone.
• Epididymis: Stores and matures sperm.
• Vas deferens: Transports sperm from the epididymis to the ejaculatory duct.
• Seminal vesicles: Secrete a fluid rich in fructose, which provides energy for sperm.
• Prostate gland: Secretes an alkaline fluid that helps neutralize the acidity of the female reproductive tract.
• Bulbourethral glands: Secrete a lubricating mucus that neutralizes acidic urine in the urethra.
• Urethra: Transports sperm and urine out of the body.
• Penis: Delivers sperm to the female reproductive tract.

What are the main organs of the female reproductive system and what are their functions?

The main organs of the female reproductive system and their functions are:

• Ovaries: Produce eggs and estrogen and progesterone.
• Oviducts (fallopian tubes): Transport eggs from the ovaries to the uterus and are the site of fertilization.
• Uterus: Provides a site for implantation and development of the embryo.
• Cervix: The lower part of the uterus that connects to the vagina.
• Vagina: Receives sperm during intercourse and serves as the birth canal.
• Mammary glands: Produce milk for nourishing the infant.

Describe the menstrual cycle and the hormones that regulate it.

The menstrual cycle is a recurring series of changes in the female reproductive system that occur approximately every 28 days. It is regulated by hormones from the hypothalamus, pituitary gland, and ovaries:

1. Follicular phase:
   • Hypothalamus: Releases gonadotropin-releasing hormone (GnRH).
   • Pituitary gland: GnRH stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
   • Ovaries: FSH stimulates the growth of ovarian follicles, which produce estrogen. Estrogen levels rise, inhibiting the release of FSH and LH (negative feedback).
2. Ovulation:
   • A surge in LH triggers ovulation, the release of a mature egg from the ovary.
3. Luteal phase:
   • The ruptured follicle develops into the corpus luteum, which secretes progesterone and estrogen. Progesterone prepares the uterus for implantation of the embryo.
   • High levels of progesterone and estrogen inhibit the release of FSH and LH (negative feedback).
4. Menstruation:
   • If fertilization does not occur, the corpus luteum degenerates, and progesterone and estrogen levels decline.
   • The drop in hormone levels causes the uterine lining to shed, resulting in menstruation.
   • The cycle then repeats.

What is fertilization in vitro (IVF) and when is it used?

Fertilization in vitro (IVF) is a process in which eggs are fertilized by sperm outside the body, in a laboratory dish. The resulting embryos are then transferred to the woman's uterus. IVF is used to treat infertility caused by various factors, including:

• Blocked or damaged fallopian tubes
• Low sperm count or motility
• Ovulation disorders
• Endometriosis
• Unexplained infertility

Developmental Abnormalities

What are some common causes of developmental abnormalities?

Common causes of developmental abnormalities include:

• Genetic factors: Inherited genetic mutations or chromosomal abnormalities (e.g., Down syndrome).
• Environmental factors: Exposure to teratogens (substances that can cause birth defects), such as alcohol, drugs, radiation, and certain infections.
• Nutritional deficiencies: Lack of essential nutrients, such as folic acid.
• Maternal health conditions: Diseases such as diabetes, high blood pressure, and autoimmune disorders.

What are some examples of teratogens and how do they affect development?

Teratogens are substances that can cause birth defects. Examples include:

• Alcohol: Can cause fetal alcohol syndrome, characterized by facial abnormalities, growth deficiencies, and intellectual disabilities.
• Thalidomide: Caused limb deformities when taken by pregnant women in the 1950s and 1960s.
• Rubella virus: Can cause deafness, blindness, heart defects, and intellectual disabilities if a woman is infected during pregnancy.
• Radiation: Can cause various birth defects, including microcephaly and intellectual disabilities.
• Certain medications: Such as some acne medications (e.g., isotretinoin) and anticonvulsants.

What are some techniques used for prenatal diagnosis of genetic disorders?

Techniques used for prenatal diagnosis of genetic disorders include:

• Amniocentesis: A sample of amniotic fluid is taken from the amniotic sac and analyzed for chromosomal abnormalities and genetic mutations.
• Chorionic villus sampling (CVS): A sample of chorionic villi (tissue from the placenta) is taken and analyzed for chromosomal abnormalities and genetic mutations.
• Ultrasound: Uses sound waves to create an image of the fetus, which can detect some structural abnormalities.
• Non-invasive prenatal testing (NIPT): A sample of the mother's blood is analyzed for fetal DNA, which can detect some chromosomal abnormalities.

Review Questions and Answers

Question 1: Explain the significance of the acrosomal reaction during fertilization.

The acrosomal reaction is essential for fertilization because it allows the sperm to penetrate the zona pellucida, a protective layer surrounding the egg. Enzymes released from the acrosome break down the zona pellucida, enabling the sperm to reach the egg's plasma membrane and initiate fusion.

Question 2: Describe the process of gastrulation and its importance in embryonic development.

Gastrulation is the process by which the single-layered blastula is transformed into a multi-layered gastrula. This process establishes the three primary germ layers: ectoderm, mesoderm, and endoderm. Gastrulation is crucial because these germ layers give rise to all the tissues and organs of the body.

Question 3: How do the extraembryonic membranes contribute to the development of a terrestrial vertebrate embryo?

The extraembryonic membranes provide essential support for the developing embryo. The yolk sac provides nutrients, the amnion protects the embryo in a fluid-filled cavity, the chorion facilitates gas exchange, and the allantois stores waste products. These membranes create a self-contained environment that allows the embryo to develop independently of the external environment.

Question 4: Explain the role of hormones in regulating the menstrual cycle.

Hormones from the hypothalamus, pituitary gland, and ovaries regulate the menstrual cycle. GnRH from the hypothalamus stimulates the pituitary to release FSH and LH. FSH stimulates follicle growth and estrogen production in the ovaries. LH triggers ovulation. Progesterone and estrogen from the corpus luteum prepare the uterus for implantation. Fluctuations in these hormone levels control the cyclical changes in the uterus and ovaries.

Question 5: What are some potential consequences of exposure to teratogens during pregnancy?

Exposure to teratogens during pregnancy can cause a wide range of developmental abnormalities, including structural defects, functional deficits, and even death of the embryo or fetus. The specific effects depend on the type of teratogen, the dose, and the timing of exposure during development.

Conclusion

Reproduction and development are complex and fascinating processes that are essential for the continuation of life. Understanding the mechanisms involved in gametogenesis, fertilization, early development, organogenesis, and the role of extraembryonic membranes provides a solid foundation for comprehending the intricacies of life's beginnings. Moreover, awareness of potential developmental abnormalities and their causes is crucial for promoting healthy pregnancies and preventing birth defects. By mastering these concepts, you gain a deeper appreciation for the miracle of life and the delicate balance that ensures its continuity.