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Questions and Answers

What are germ cells primarily responsible for?

  • Producing energy for the organism
  • Carrying genetic mutations
  • Forming somatic cells
  • Ensuring reproductive function (correct)

    • What happens to the volume of a frog egg during cleavage?

  • It stays the same (correct)
  • It decreases slightly
  • It doubles in size
  • It increases significantly

    • Where do germ cells migrate to for differentiation?

  • The skin
  • The stomach
  • The brain
  • The gonads (correct)

    • How do most frog species fertilize their eggs?

    <p>Externally, while in the water</p> Signup and view all the answers

    What is one effect of environmental factors on frog life cycles?

    <p>Tadpoles wouldn't survive if they hatched in fall</p> Signup and view all the answers

    What type of cells are formed from somatic cells?

    <p>Muscle cells</p> Signup and view all the answers

    What facilitates the anchoring of frog eggs in certain species?

    <p>Egg jelly sticking to plants</p> Signup and view all the answers

    What is the primary function of gametogenesis?

    <p>To produce gametes for reproduction</p> Signup and view all the answers

    What initiates the process of gametogenesis and fertilization in frogs?

    <p>Pituitary gland signaling due to photoperiod and temperature</p> Signup and view all the answers

    What is the primary function of fertilization in frogs?

    <p>To ensure genetic recombination and reproduction</p> Signup and view all the answers

    What role does the ectoderm play during frog development?

    <p>Acts as a precursor for the epidermis and nervous system</p> Signup and view all the answers

    What marks the future dorsal side of the embryo in frogs during gastrulation?

    <p>The appearance of the blastopore</p> Signup and view all the answers

    Which germ layer is responsible for developing into connective tissues and muscles?

    <p>Mesoderm</p> Signup and view all the answers

    What triggers the movement of cytoplasm inside the fertilized egg?

    <p>The entry of the sperm</p> Signup and view all the answers

    During organogenesis, what is the function of the notochord?

    <p>To release signals that affect ectodermal cells</p> Signup and view all the answers

    What does the endoderm develop into in frogs?

    <p>Gut lining and respiratory systems</p> Signup and view all the answers

    What are the three germ layers identified by Christian Pander in the chick embryo?

    <p>Ectoderm, Mesoderm, Endoderm</p> Signup and view all the answers

    What is the primary role of the ectoderm in embryonic development?

    <p>Generates the outer layer of the embryo</p> Signup and view all the answers

    Which cell movement is NOT one of the five basic movements of gastrulation described by Pander?

    <p>Ectodermation</p> Signup and view all the answers

    What does the endoderm mainly contribute to in the developing embryo?

    <p>Epithelial lining of internal organs</p> Signup and view all the answers

    Which principle is essential for the proper development of germ layers according to Pander's findings?

    <p>Induction</p> Signup and view all the answers

    What significant contribution did Karl Ernst von Baer make to the understanding of vertebrate embryonic development?

    <p>Proposed that all vertebrate embryos follow a common pattern</p> Signup and view all the answers

    What is the function of the mesoderm during embryonic development?

    <p>Creating blood, heart, and connective tissues</p> Signup and view all the answers

    Which of the following is NOT produced by the ectoderm?

    <p>Digestive organs</p> Signup and view all the answers

    What role do fate maps play in embryology?

    <p>They provide a diagram mapping larval or adult structures to the embryo.</p> Signup and view all the answers

    What does preformationism suggest about the development of organisms?

    <p>Organisms have all structure prefigured in the sperm or egg.</p> Signup and view all the answers

    Which of the following correctly describes cell migration during development?

    <p>Cells must move to appropriate locations for proper development.</p> Signup and view all the answers

    What concept did Johann Friedrich Blumenbach introduce to support preformationism?

    <p>Bildungstrieb (developmental force)</p> Signup and view all the answers

    Which statement about cell growth is true?

    <p>Cells undergo asymmetric division resulting in different-sized cells.</p> Signup and view all the answers

    Who proposed a reconciliation between epigenesis and preformationism?

    <p>Immanuel Kant</p> Signup and view all the answers

    How does apoptosis contribute to development?

    <p>It eliminates cells that are no longer needed, such as those in webbing.</p> Signup and view all the answers

    What is a significant advancement in fate map technology?

    <p>Improved methods for generating fate maps.</p> Signup and view all the answers

    What did E.B. Wilson note about cell division during cleavage in 1923?

    <p>It is simpler than it appears but highly complex.</p> Signup and view all the answers

    What aspect of embryonic development was supported by the lack of cell theory at the time?

    <p>The idea that development did not involve the formation of new structures</p> Signup and view all the answers

    Which of the following describes a characteristic of germ cell development?

    <p>Germ cells must migrate into the developing gonad.</p> Signup and view all the answers

    What observation did Malpighi make regarding the unincubated chick egg that supported preformationism?

    <p>It exhibited complex structures already present.</p> Signup and view all the answers

    What influence do changes in cell membrane composition have?

    <p>They influence neighboring cells and their development.</p> Signup and view all the answers

    Which cells undergo significant changes in size during development?

    <p>Sperm cells decrease in size while egg cells grow larger.</p> Signup and view all the answers

    In preformationism, what does the term 'prefigured state' refer to?

    <p>The assumed position of organs before they develop.</p> Signup and view all the answers

    What is a blastomere?

    <p>A cell in the cleavage stage of embryonic development.</p> Signup and view all the answers

    Study Notes

    Importance of Developmental Biology

    • Developmental biology examines crucial issues that impact other fields like molecular biology, physiology, cell biology, genetics, and more.
    • It explores how a single cell develops into a complex organism.

    Gametogenesis

    • A group of cells designated for reproductive function are known as germ cells.
    • These cells migrate to the gonads where they differentiate during gametogenesis, the process of forming gametes (sperm and egg).

    Frog Fertilization

    • Most frog species fertilize externally.
    • The male frog holds the female's back and fertilizes the eggs as she releases them.
    • The eggs are often anchored to vegetation or float freely in a pond.

    Cleavage and Gastrulation

    • Cleavage: The zygote divides into thousands of cells, maintaining the same volume.
    • Gastrulation: Initiated at the point opposite sperm entry.   - Forms a dimple called a blastopore, marking the future dorsal side of the embryo.   - Cells migrating through the blastopore become mesoderm and endoderm.   - Cells remaining on the outside develop into ectoderm, eventually enclosing the embryo.

    Germ Layers and Their Roles

    • Ectoderm: Develops into the epidermis, brain, and nerves.
    • Endoderm: Develops into the gut lining and respiratory systems.
    • Mesoderm: Develops into connective tissue, muscle, blood, heart, skeleton, gonads, and kidneys

    Organogenesis

    • The dorsal mesoderm cells condense to form a notochord, a rod of cells that releases chemical signals influencing ectodermal cell fate.
    • This process begins when the notochord releases chemical signals that influence the fate of the ectodermal cells above them.

    Preformationism

    • Suggested by Immanuel Kant and Johann Friedrich Blumenbach.
    • This theory claimed that adult organs were in miniature within the sperm or egg.
    • Supported by Malpighi's observations of structural complexity in unincubated chick eggs.

    Support for Preformationism

    • Embryonic development was considered a growth of existing structures, not the formation of new ones.
    • A prefigured generation was believed to exist in germ cells of the current generation.
    • The lack of cell theory at the time contributed to the persistence of this view.

    Epigenesis

    • Proposed by Blumenbach, who introduced the concept of Bildungstrieb (developmental force).
    • It proposed that organisms are "constructed" rather than "unrolled."
    • Blumenbach argued this force was observable through phenomena like the regeneration of hydra after amputation.
    • Modern biology aligns with the idea that epigenetic development is directed by preformed instructions, present in the fertilized egg.

    Patterns of Cleavage

    • Blastomeres: The cells in the cleavage stage.

    Discoveries of Christian Pander

    • Studied the chick embryo and identified three germ layers: ectoderm, endoderm, and mesoderm.
    • Demonstrated that the germ layers require induction to develop properly.

    The Four Principles of Karl Ernst von Baer

    • Expanded upon Pander's work, discovering that all vertebrate embryos follow a common developmental pattern.
    • Introduced the concept of "fate mapping," a tool for identifying the adult structures that originate from specific embryonic regions.

    Importance of Fate Maps

    • They provide critical insights into the developmental lineages of embryonic cells.
    • Advanced technology allows for more precise and detailed fate mapping.

    Cell Migration

    • Critical for proper development, as cells must move to their appropriate locations.
    • Examples:   - Germ cells migrating to the developing gonad.   - Primordial heart cells meeting in the middle of the vertebrate neck and migrating to the left part of the chest.

    Cell Growth

    • Cells change in size during development, particularly evident in germ cells:   - Sperm cells eliminate most of their cytoplasm and become smaller.   - Egg cells conserve and add cytoplasm, becoming larger.   - Asymmetric division can create one larger cell and one smaller cell with distinct fates.

    Cell Death (Apoptosis)

    • Cell death is a crucial aspect of development, as it removes unnecessary or unwanted cells.
    • Examples:   - Cells forming webbing between toes and fingers die before birth.   - Cells in our tails also die.   - Apoptosis contributes to the formation of orifices in the mouth, anus, and reproductive glands.

    Changes in Cell Membrane Composition or Secreted Products

    • Influence neighboring cells during development.

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