Fluent Essays

Questions 1. Ninety-eight percent of an egg shell is calcite, which is calcium carbonate (CaCO3). Calcium is the major component of bone as well (in the form of calcium phosphate, or apatite). The calcium that goes into the shell comes both from the hen’s diet and from her bones. The average weight of a chicken egg shell is 7.26 grams. A truly remarkable hen can lay an egg a day. In a year, a hen can put into her eggshells over 25 times her own skeletal weight in calcium. Obviously, this must be replaced. The standard feed given to laying hens is 3 to 4\% calcium, and one hen receives about a 100 gm of feed a day. Based on the weight of the shell, is this sufficient to replace the calcium lost in a superhen laying every day? Do the calculations to support your answer.  CaCO3 = 100.9 grams / mole  Atomic weights of molecules from the periodic table.  Ca = 40.08 C = 12.01 O = 16.00 2. Why is the amniote egg considered to be an important evolutionary development? 3. What is the function of the air space in the chick egg?  4. What is the importance of chalazae? 5. Why is initial cleavage of the chick egg meroblastic rather than holoblastic? 6. What is the cavity that underlies the area pellucida? What is its importance relative to the primitive streak?  7. What is the role of the primitive streak and Hensen’s node? 8. Define the term somite.  9. What structure is found between the somites and what is its role?Questions 1. Ninety-eight percent of an egg shell is calcite, which is calcium carbonate (CaCO3). Calcium is the major component of bone as well (in the form of calcium phosphate, or apatite). The calcium that goes into the shell comes both from the hen’s diet and from her bones. The average weight of a chicken egg shell is 7.26 grams . A truly remarkable hen can lay an egg a day. In a year, a hen can put into her eggshells over 25 times her own skeletal weight in calcium. Obviously, this must be replaced. The standard feed given to laying hens is 3 to 4\% calcium, and one hen receives about a 100 gm of feed a day. Based on the weight of the shell, is this sufficient to replace the calcium lost in a superhen laying every day? Do the calculations to support your answer.  CaCO3 = 100.9 grams / mole Atomic weights of molecules from the periodic table. Ca = 40.08 C = 12.01 O = 16.00 2. Why is the amniote egg considered to be an important evolutionary development? 3. What is the function of the air space in the chick egg? 4. What is the importance of chalazae? 5. Why is initial cleavage of the chick egg meroblastic rather than holoblastic? 6. What is the cavity that underlies the area pellucida? What is its importance relative to the primitive streak? 7. What is the role of the primitive streak and Hensen’s node? 8. Define the term somite. 9. What structure is found between the somites and what is its role? Q uestions 1. Ninety - eight percent of an egg shell is calcite , which is calcium carbonate (CaCO 3 ). Calcium is the major component of bone as well (in the form of calcium phosphate, or apatite). The calcium that goes into the shell comes both from the hen’s diet and from her bones. The average weight of a chicken egg shell is 7.26 grams . A truly remarkable hen can lay an egg a day. In a year, a hen can put into her eggshells o ver 25 times her own skeletal weight in calcium. Obviously, this must be replaced. The standard feed given to laying hens is 3 to 4\% calcium, and one hen receives about a 100 gm of feed a day . Based on the weight of the shell, is this sufficient to replace the calcium lost in a superhen laying every day? Do the calcula tions to support your answer. CaCO 3 = 100.9 grams / mole Atomic weights of molecules from the periodic table. Ca = 40.08 C = 12.01 O = 16.00 2. Why is the amniote egg considered to be an important evolutionary development? 3. What is the function of the air space in the chick egg? 4. What is the importance of chalazae? 5. Why is initial cleavage of the chick egg meroblastic rather than holoblastic? 6. What is the cavity that underlies the area pellucida? What is its importance relative to the primitive streak? 7. What is the role of the primitive streak and Hensen’s node? 8. Define the term somite. 9. What structure is found between the somites and what is its role? Questions 1. Ninety-eight percent of an egg shell is calcite,c h a p t e r Early Development of the Chick Gallus domesticus The common domestic chick, Gallus domesticus, is traditionally studied in embryology classes. Its development is an international language common to all students of embryology, and this alone is reason enough to learn about it. There are other reasons as well. Living chick embryos are easily obtained. Since chickens breed in any season, chick embryos often are no further away than the nearest farm. Above all, chick embryos can teach you a great deal about vertebrate development in general and will help you understand comparative vertebrate anatomy and vertebrate evolution. You will see the vertebrate body plan being laid down, learn how the organs form, and witness how they relate developmentally to one another. You will see the structures form that are diagnostic characters of the phylum Chordata and subphylum Vertebrata. And you can extrapolate from chick to human development and suddenly know a tremendous amount about what must go right for a normal baby to be born and what can go wrong that causes birth defects. Learn chick developmental anatomy well, and I promise it will serve you well. Throughout the chapter, you will find a number of questions (easy ones). Remember to record answers to these questions in your laboratory notebook. The Chick Egg The female chicken lays an amniote egg, the same type of egg laid by other birds, reptiles, and monotreme mammals. An evolutionary invention of the early reptiles, it is one of the major changes that freed vertebrates from the water, allowing them to lay eggs on land. The design is an engineering masterpiece. An outer shell protects against physical damage and dehydration while still allowing for gas exchange. Packed within is enough food and water to survive the long journey to hatching—and a long journey it is. In the chick, it takes 21 days. Stranded out on land, the embryo cannot rely on an aquatic feeding larval stage, as do, for example, most amphibian embryos. The provisions packed within the shell must be enough to nourish all of development through to the hatching of the juvenile. In a medium-size chick egg (about 60 gm), these provisions include more protein (7.2 gm) than there is in a frankfurter; as much fat (6 gm) as is in 2 teaspoons of butter but with about seven times the cholesterol (300 mg); and about 8.5 teaspoons of water (40 gm). Despite the bad reputation of its cholesterol, the egg truly is an excellent food source. In order to permanently alter the way you look at an egg in the kitchen, you will be dissecting one in the laboratory. Obtain an egg that was collected from the wilds of a local grocery store. Examine the shell and see that one end is blunt. This marks the region of an air space that you will see upon opening the egg. Prior to opening your egg, put it briefly into hot water (water that has been brought to a boil, 9 Early Development of the Chick 9 - 2 Bird Early Development https://www.youtube.com/watch?v=w-M33PtwtM4 https://www.youtube.com/watch?v=PedajVADLGw https://www.youtube.com/watch?v=vBGumRAWaa0 https://www.youtube.com/watch?v=uP7IHXAaJq4 https://embryology.med.unsw.edu.au/embryology/index.php/Hamburger_Hamilton_Stages Parts of the Egg A hen requires about 24 to 26 hours to produce an egg. The Shell The shell, is a hard, protective covering / made almost entirely of calcium carbonate (CaCO3) crystals. The shell is porous (about 7,000 pores) / allow for the transfer of gases Carbon dioxide and moisture are given off through the pores and are replaced by atmospheric gases, including oxygen. The shell also has a thin outermost coating called the bloom or cuticle that helps keep out bacteria and dust. Parts of the Egg Immediately beneath the shell are two membranes: outer shell membrane inner shell membranes Protect the contents of the egg from bacteria and prevent moisture from leaving the egg too quickly. While the embryo is growing, the shell membranes surround and contain the white or albumen of the egg. The albumen provides the liquid medium in which the embryo develops, and it also contains a large amount of the protein necessary for proper development. Parts of the Egg Because the body temperature of a hen is approximately 106° F, eggs are very warm at the time they are laid. The temperature of the air is usually much lower than 106° F, and the egg cools to the temperature of its surroundings. As cooling takes place, the contents of the egg contract more than does the shell of the egg. This creates a vacuum and air is drawn through the pores of the egg. Parts of the Egg Chalazae - are made of twisted strands of mucin fibers. The chalazae hold the yolk in the center of the egg. The yolk is the source of food for the embryo and contains all the fat in the egg. The small white spot on the yolk is call the germinal disc. The germinal disc is where the females genetic material is found. Early Development of Vertebrates: Birds Cleavage in Bird Eggs Fertilization of chick egg occurs in the oviduct, before albumen and shell are secreted to cover it. Telolecithal egg – small disc of cytoplasm sitting atop a large yolk. Discoidal meroblastic cleavage. Cleavage only in blastodisc. Initially get a single-layered blastoderm, eventually 5 to 6 layered blastoderm. Cells linked by tight junctions. Early Development of Vertebrates: Birds Subgerminal cavity – space between the blastoderm and the yolk. Cells absorb water from the albumen and secrete the fluid between themselves and the yolk. Early Development Birds At this point deep cells in the center of blastoderm are shed and die, leaving behind a one cell thick area pellucida. This area forms most of embryo. At sides get the area opaca –peripheral ring of blastoderm cells that have not shed their deep cells. Between two areas have marginal zon