Animal Development Ch 47 Section 1

The presence of yolk in an egg is a key factor influencing the pattern of cleavage. Yolk is a stored nutrient that provides nourishment to the developing embryo. The distribution and amount of yolk in the egg affects how the cells divide during cleavage. In eggs with a large amount of yolk, such as bird eggs, cleavage is typically meroblastic, meaning that only a portion of the egg cytoplasm undergoes division. This is because the yolk is not evenly distributed throughout the egg and restricts the movement of cells. In contrast, eggs with little or no yolk, like those of mammals, undergo holoblastic cleavage, where the entire egg cytoplasm is divided evenly.

During gastrulation, the blastopore is the opening that forms in the early embryo. The circular lip of the blastopore encircles a yolk plug, which is a mass of nutrient-laden cells located on the outer edge. As gastrulation progresses, the ectoderm expands, causing the blastopore to shrink further. The protruding cells of the yolk plug then move inward, contributing to the formation of the three germ layers and the development of different body structures.

The explanation for the correct answer is that during embryonic development, cells migrate inward along the midline of the blastoderm, causing a thickening known as the primitive streak. This process occurs along the anterior-posterior axis of the embryo and is crucial for the establishment of the body plan and formation of the three germ layers. The primitive streak plays a key role in gastrulation, during which the cells differentiate and organize themselves to form the various tissues and organs of the developing embryo.

Organogenesis refers to the process in which various regions of the three embryonic germ layers develop into the rudiments of organs. This process is crucial for the formation and development of organs in the body. It involves the differentiation and specialization of cells, as well as their organization into specific structures and tissues that eventually form fully functional organs. Organogenesis is a complex and highly regulated process that occurs during embryonic development, and it is essential for the proper functioning of the body's organ systems.

The trophoblast is the outer epithelium of the blastocyst, which is the early stage of development of an embryo. It does not directly contribute to the formation of the embryo, but instead plays a crucial role in providing support services. These include implantation of the blastocyst into the uterine wall, formation of the placenta, and secretion of hormones that are essential for maintaining pregnancy. The trophoblast is responsible for establishing a connection between the developing embryo and the mother's body, allowing for nutrient and gas exchange to support the growth and development of the embryo.

The allantois in mammals is a membranous sac that forms during embryonic development. It plays a crucial role in the formation of the umbilical cord, which connects the developing fetus to the placenta. The allantois acts as a conduit for blood vessels, allowing for the exchange of nutrients, oxygen, and waste products between the fetus and the mother's bloodstream. Therefore, the allantois is incorporated into the umbilical cord, facilitating the necessary connections for fetal development and survival.

During organogenesis, the three layers of cells formed during fertilization interact and move, leading to the development of rudimentary organs. These rudimentary organs serve as the foundation for the growth and formation of adult structures in the organism. This stage is crucial for the development of the various organs and systems in the body.

When the head of a sea urchin sperm comes into contact with the jelly coat of a sea urchin egg, certain molecules present in the egg's coat stimulate a process known as the acrosomal reaction in the sperm. This reaction involves the release of enzymes from the acrosome, a structure at the tip of the sperm, which helps the sperm penetrate the jelly coat and reach the egg for fertilization.

The yolk concentration decreases significantly toward the opposite pole called the animal pole. This is because the animal pole is the site where the polar bodies of oogenesis bud from the cell. The polar bodies are small, non-functional cells that are produced during oogenesis and contain very little yolk. Therefore, as the polar bodies bud from the cell at the animal pole, the yolk concentration decreases significantly in that area.

During cleavage, the zygote divides into multiple cells, forming a hollow ball of cells known as a blastula. This early stage of embryonic development is characterized by rapid cell division without growth, resulting in the formation of a hollow sphere. The blastula is an important stage as it precedes the formation of the gastrula, where further cell differentiation and tissue formation occur. Therefore, blastula is the correct answer that describes the hollow ball of cells during cleavage.

The correct answer is blastocoel. During the process of cleavage, the zygote undergoes rapid cell division, forming a hollow ball of cells called the blastula. The blastocoel is the fluid-filled cavity that forms within the blastula. It is important for the development of the embryo as it provides a space for further cell division and differentiation.

The yolk in an egg is often concentrated towards one pole, known as the vegetal pole. This concentration is due to the process of oogenesis, where the yolk is produced and accumulates in the egg during the development of the female reproductive system. The vegetal pole is usually located opposite to the animal pole, which contains the nucleus and other cellular components. The positioning of the yolk towards the vegetal pole is important for the development of the embryo, as it provides essential nutrients and energy for growth and development.

Meroblastic cleavage refers to the incomplete division of a yolk-rich egg during embryonic development. In this type of cleavage, only a portion of the egg cytoplasm undergoes cell division, while the rest remains as yolk. This type of cleavage is commonly seen in eggs of birds, reptiles, and some fish, where the yolk serves as a source of nutrients for the developing embryo. The division of the cytoplasm creates a blastodisc, which eventually develops into the embryo.

This term refers to the biological process through which an organism develops its shape and form. It involves the movement and positioning of cells in order for them to occupy their proper locations and fulfill their specific functions. Morphogenesis is a fundamental aspect of development in all living organisms, playing a crucial role in the formation of tissues, organs, and overall body structures.

Gastrulation is the correct answer because it is the second stage of fertilization. After the sperm fertilizes the egg in the process of fertilization, gastrulation occurs. During gastrulation, the single-celled zygote undergoes a series of cell divisions and movements to form three distinct germ layers: ectoderm, mesoderm, and endoderm. These germ layers eventually give rise to different tissues and organs in the developing embryo. Therefore, gastrulation is a crucial stage in embryonic development and occurs after fertilization.

Gastrulation is the stage of fertilization where the blastula, a hollow ball of cells, is rearranged into a three-layered embryo called the gastrula. During gastrulation, cells migrate and differentiate to form the three germ layers: ectoderm, mesoderm, and endoderm. This process is crucial for the development of different tissues and organs in the embryo.

Invagination is the correct answer because it refers to the process described in the question. During invagination, the cells near the vegetal pole flatten and form a vegetal plate that buckles inward due to changes in cell shape. This process is commonly observed during embryonic development, particularly in the formation of certain tissue layers and organs. Invagination is an essential step in the morphogenesis of various organisms and plays a crucial role in shaping the body plan.

During gastrulation, the frog embryo undergoes a process where the cells move and rearrange to form the three germ layers. The part above the crease, known as the dorsal side, gives rise to the dorsal lip of the blastopore. The blastopore is a structure that forms during gastrulation and eventually develops into the anus or the mouth of the organism. The dorsal lip plays a crucial role in organizing the development of the embryo and is responsible for initiating the formation of the neural tube.

The notochord is a skeletal rod that is found in the embryos of all chordates. It is one of the first organs to develop and take shape in the embryo. The notochord provides support and structure to the developing embryo, and later on, it serves as a basis for the formation of the vertebral column in vertebrates.

The allantois in mammals is a structure that develops during embryonic development and is incorporated into the umbilical cord. It plays a crucial role in waste disposal and gas exchange, as well as nutrient transport between the developing fetus and the mother. The allantois eventually fuses with the chorion to form the placenta, which is responsible for providing oxygen and nutrients to the fetus and removing waste products.

Organogenesis is the process in which the organs of an organism develop from the three germ layers - ectoderm, mesoderm, and endoderm. It occurs during the third stage of fertilization, where the fertilized egg undergoes rapid cell division and differentiation to form the basic structures of the organs. This stage is crucial for the formation and development of various organ systems, including the nervous system, cardiovascular system, and digestive system. Organogenesis lays the foundation for the overall body plan and structure of the organism.

The zona pellucida is a glycoprotein-rich extracellular matrix that surrounds the egg. It plays a crucial role in fertilization by protecting the egg and facilitating sperm binding and penetration. The zona pellucida also helps in preventing polyspermy, which is the entry of multiple sperm into the egg. It is formed by the secretions of the oocyte and surrounding follicle cells.

The trophoblast is responsible for initiating implantation by secreting enzymes that break down molecules of the endometrium, the lining of the uterus. This process allows the fertilized egg to implant and establish a connection with the maternal blood supply, essential for the development of the embryo. The trophoblast plays a crucial role in the early stages of pregnancy by facilitating implantation and supporting the growth and development of the embryo.

The specialized vesicle at the tip of the sperm in a sea urchin is called the acrosome. The acrosome plays a crucial role in fertilization by containing enzymes that help the sperm penetrate the outer layer of the egg. It releases these enzymes upon contact with the egg, allowing the sperm to enter and fertilize the egg. The acrosome is therefore essential for successful reproduction in sea urchins.

The neural tube is the precursor to the central nervous system in animals. During embryonic development, the neural tube forms from the ectoderm and eventually gives rise to the brain and spinal cord. It is a hollow structure that develops into the complex network of neurons and glial cells that make up the central nervous system. The neural tube plays a crucial role in the development and functioning of the animal's nervous system, making it the correct answer in this context.

The term "cortex" refers to the outer layer or rim of the cytoplasm. It is the region of the cytoplasm that is located just beneath the cell membrane. The cortex plays a crucial role in maintaining the shape and structure of the cell. It is involved in various cellular processes, such as cell movement, cell division, and the organization of cellular components. The cortex contains a network of cytoskeletal elements, including actin filaments, which provide mechanical support and help in cell motility.

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During the formation of the blastoderm, the future endoderm and mesoderm cell layers move from the surface of the embryo and roll over the edge of the lip, entering the interior of the embryo. This process is known as involution.

During the embryonic stage, mammals develop a structure called a blastocyst. This is the mammalian version of a blastula, which is an early stage of embryonic development characterized by a hollow ball of cells. The blastocyst consists of an outer layer of cells called the trophoblast, which will eventually form the placenta, and an inner mass of cells called the inner cell mass, which will develop into the embryo itself. The blastocyst is an important stage in mammalian development as it marks the beginning of implantation into the uterus.

The trophoblast is a layer of cells that forms during early pregnancy and plays a crucial role in the development of the placenta. It thickens through cell division and extends fingerlike projections into the surrounding maternal tissue, which is rich in blood vessels. This allows for the exchange of nutrients and waste products between the mother and the developing embryo. The trophoblast also helps to anchor the embryo to the uterine wall and produces hormones that support the pregnancy.

The open end of the archenteron, which will become the anus, is called the blastopore. The blastopore is the initial opening in the early embryo, formed during gastrulation. It is the site where the endoderm and ectoderm layers meet. As development progresses, the blastopore gives rise to the digestive system, with the opening eventually becoming the anus. This process occurs in organisms such as sea urchins and amphibians during embryonic development.

During embryonic development, the ectoderm, which is the outermost germ layer, undergoes a process called neural induction. This occurs in response to signaling molecules secreted by mesodermal and other tissues. The neural plate is formed from the ectoderm above the notochord as a result of this induction. The neural plate is the precursor to the central nervous system and eventually gives rise to the brain and spinal cord.

Cortical granules are vesicles located near the egg plasma membrane in the cytoplasm. They play a crucial role in preventing polyspermy, which is the fertilization of an egg by multiple sperm. These granules are responsible for a longer-lasting block against polyspermy, ensuring that only one sperm can successfully fertilize the egg.

After sperm binds to the egg, cortical granules fuse with the egg plasma membrane, initiating the cortical reaction. This reaction involves the release of enzymes and other substances from the cortical granules into the space between the egg plasma membrane and the zona pellucida (outer layer of the egg). These substances create a barrier that prevents other sperm from binding to the egg, ensuring that only one sperm can fertilize the egg. Additionally, the cortical reaction helps to activate the egg and initiate the process of embryonic development.

Holoblastic cleavage refers to a pattern of cell division in animal embryos where the entire embryo undergoes complete division. In this pattern, the blastocoel (the fluid-filled cavity) is centrally located, and the cleavage furrow passes all the way through the cells. This type of cleavage is typically observed in animals whose eggs contain relatively little yolk. During holoblastic cleavage, the cells divide completely and evenly, resulting in the formation of a multicellular embryo. This pattern allows for the development of a well-organized and symmetrical organism.

During gastrulation, the process by which the three primary germ layers are formed, the embryonic tissues differentiate into three distinct layers known as the germ layers. These layers, namely the ectoderm, mesoderm, and endoderm, give rise to different structures and organs in the developing embryo. The ectoderm forms the skin, nervous system, and sensory organs, the mesoderm gives rise to muscles, bones, and the circulatory system, while the endoderm develops into the digestive and respiratory systems. Collectively, these three germ layers play a crucial role in the early development of an embryo.

The allantois is a membranous sac that forms as an outgrowth of the embryo's hindgut. It serves multiple functions during embryonic development, including disposing of waste products such as nitrogenous waste and contributing to gas exchange. The allantois is involved in the exchange of gases, allowing for the diffusion of oxygen and carbon dioxide between the embryo and the surrounding environment. Additionally, it plays a role in the storage and transfer of nutrients to the developing embryo.

The acrosomal reaction refers to the process where a specialized vesicle at the tip of the sperm releases hydrolytic enzymes. These enzymes help the sperm penetrate the protective layers surrounding the egg, allowing fertilization to occur. This reaction is crucial for successful fertilization as it enables the sperm to reach and fuse with the egg.

Gastrulation is the process by which cells in an embryo rearrange themselves to form three primary germ layers, which later give rise to different tissues and organs in the body. During gastrulation, cells migrate and differentiate into specific cell types, establishing the basic body plan of the organism. This process is crucial for the development of complex multicellular organisms and is essential for the formation of tissues and organs. Therefore, the given explanation aligns with the concept of gastrulation as it describes the morphogenic process that allows the later formation of tissues and organs.

The blastoderm is the outer layer of cells that forms on top of the yolk mass during embryonic development. Within the blastoderm, there are two distinct layers called the epiblast and the hypoblast. The epiblast is the upper layer of cells, while the hypoblast is the lower layer. These layers play important roles in the formation of the embryo and the development of different tissues and organs.

Development involves morphogenesis, which refers to the process by which cells and tissues are organized into specific structures and shapes during the growth and development of an organism. This process includes cell movements, changes in cell shape, and the formation of specialized tissues and organs. Morphogenesis is essential for the proper formation of body structures and organs, and it is regulated by various molecular and cellular mechanisms.

Cleavage is the correct answer because it refers to the first stage of fertilization in which the zygote undergoes rapid cell division, resulting in the formation of a multicellular embryo. During cleavage, the zygote divides into smaller cells called blastomeres, which continue to divide and form a solid ball of cells called a morula. Cleavage is an essential process for the development of an embryo and is crucial for the formation of different cell types and tissues.

Cytoplasmic determinants refer to molecules, such as proteins and RNA's, that are present in the cytoplasm of the egg and are placed there by the mother. These determinants play a crucial role in the early development of the embryo, as they provide instructions for various cellular processes and help determine the fate of different cells. Therefore, the presence of proteins and RNA's in the egg that are contributed by the mother can be referred to as cytoplasmic determinants.

The yolk sac is responsible for enclosing the yolk and providing nutrients to the developing embryo until it hatches. It serves as a temporary source of nourishment, allowing the embryo to grow and develop before it can obtain nutrients from its environment. The yolk sac is an essential structure in the early stages of embryonic development.

The zona pellucida is a layer surrounding the oocyte (egg cell) in the ovary. It acts as a barrier that a sperm must penetrate in order to reach and fertilize the egg. Before reaching the zona pellucida, the sperm must first travel through a layer of follicle cells that surround the oocyte. These follicle cells provide protection and support to the developing egg.

The buckled vegetal plate undergoes extensive rearrangement of its cells, resulting in the transformation of the shallow invagination into a deeper, narrower, blind-ended tube called the archenteron. This process is a crucial step in the development of certain organisms, as the archenteron eventually gives rise to the digestive cavity or gut.

As a zygote divides, differences arise between early embryonic cells due to the uneven distribution of cytoplasmic determinants. These determinants are molecules or substances that are unequally distributed within the cytoplasm of the zygote. This uneven distribution leads to the activation or repression of specific genes in different cells, causing them to develop different characteristics and functions. This process is crucial for the development of different cell types and the formation of distinct tissues and organs in the growing embryo.

During fertilization, the zygote undergoes cell division, known as cleavage. This process leads to the formation of a hollow ball of cells called the blastula. Cleavage is a crucial stage in early embryonic development, as it allows for the rapid division of cells and the formation of specialized cell types. The blastula serves as the foundation for further development and eventually gives rise to the formation of tissues and organs.

The amnion is a membrane that eventually encloses the embryo in a protective, fluid-filled amniotic cavity. This cavity provides a cushioning and protective environment for the developing embryo, allowing it to grow and develop without being exposed to external forces or harmful substances. The amnion is essential for the survival and well-being of the embryo during gestation.

In the late gastrula, the ectoderm forms the outer layer of the embryo. The endoderm lines the embryonic digestive tract. The mesoderm partly fills the space between the ectoderm and endoderm.