Module 4
1. Module 4
1.5. Page 3
Module 4—From Fertilization to Birth
Lab—Comparing Embryonic Structures
Looking at images will help you understand the differences between the stages of embryonic development and the structures that support the embryo. In this lab you will examine microscope slides showing various stages of embryonic development in a sea urchin and you will compare the support structures of an embryonic chick to those of an embryonic human.
© 2008 Jupiterimages Corporation
Early embryonic development is similar in many species. In the beginning, formation of the embryonic cells and the supporting structure cells cannot be distinguished between different species of organisms. Embryos in the early stages of development of a fish, reptile, amphibian, bird, and mammal all seem to be very similar.
In this investigation you will compare embryonic stages of development using a microscope. The images will be provided.
The lab is similar to the one on page 519 of the textbook; however, since you may not have a microscope, various microscope images will be provided for you.
Module 4: Lesson 1 Assignment
Retrieve the copy of the Module 4: Lesson 1 Assignment that you saved to your computer earlier in this lesson. Complete Lab—Comparing Embryonic Structures. Save your completed assignment in your course folder. You will receive instructions about when to submit your assignment to your teacher later in this lesson.
Self-Check
SC 1. To review the developmental stages of the embryo, complete this drag-and-drop activity about fertilization.
SC 2. Complete this drag-and-drop activity to check your understanding of the events from ovulation to implantation
SC 3. Label the diagram showing the extra-embryonic membranes supporting the developing embryo.
Self-Check Answers
SC 3.
- chorion
- amniotic cavity
- allantois
- maternal blood vessels
- endometrium
- amnion
- yolk sac
- developing placenta
The extra-embryonic membranes are structures that are external to (extra-) the embryo.
Discuss
In your course discussion area, respond to one, some, or all of the following questions:
D 1. Do you think that there should be special schools for pregnant teens, or should all schools do more to try to accommodate the various needs of these expectant mothers?
D 2. Does an embryo have the use of all its senses in utero?
D 3. How is it possible that different mammalian species develop all of the same organ systems in different time periods? What regulates this process?
D 4. Is it possible for the fetus to learn in utero? If so, what is the possible extent of the learning?
D 5. To what extent can or should humans control and change the characteristics of an embryo?
D 6. How is it possible that the development of litters of four or more offspring happens?
Self-Check
SC 4. Many important processes, structures, and functions were presented in this lesson. Check your mastery of this information by completing the following questions from your textbook.
- questions 1 to 4, page 509
- questions 5 to 9, page 511
- questions 10 to 14, page 512
- questions 15 to 19, page 515
- questions 20 to 23, page 517
Check the following link to see how well you answered the questions and consult with your teacher about any concerns that you may have.
Self-Check Answers
SC 4.
- There are 46 chromosomes that make up the zygote (fertilized egg): 23 from the sperm and 23 from the egg.
- The egg must be fertilized within 12 to 24 hours of release because it loses its capacity to develop further after 24 hours.
- The sperm must survive the acidic environment of the female reproductive tract. In addition, only one oviduct contains an egg each month; many of the sperm may enter the "wrong" oviduct.
- It takes the actions of several sperm and their acrosome enzymes to break through the protective jelly-like layer of the egg, so a sperm that arrives after the first few have breached the barrier is able to utilize its own acrosome enzymes to enter successfully.
- Cleavage is cell division without growth. This is the initial stage of mitotic divisions after the formation of the zygote in the oviduct. The cleavage divisions do not increase the size of the zygote. They only increase the number of cells within it.
- The morula reaches the uterus within 3-5 days of fertilization, and upon arrival it begins to fill with fluid that diffuses from the uterus. Within the fluid-filled space inside the morula, two different groups of cells characterize the blastocyst: ones that nourish the embryo and ones that become the embyro.
- It is the inner cell mass that develops into the embryo.
- Implantation occurs when the blastocyst nestles in the endometrium (lining of the uterus). This happens between about the 10th and 14th day after fertilization. The blastocyst attaches to the endometrium by secreting enzymes from the trophoblast cells within to digest some of the tissues and blood vessels.
- hCG is human chorionic gonadotropin hormone, which is secreted to maintain the corpus luteum once implantation has taken place. It is secreted at a high level for the first two months, declining to a low level by the end of four months, when there is a fully functional placenta to take over the production of estrogen and progesterone from the corpus luteum. At this point, the hormone production of the corpus luteum is no longer important, although it continues to exist throughout the pregnancy.
- The amniotic cavity is a space that forms between the inner cell mass and the trophoblast. This space fills with fluid, and this is where the embryo will develop, within the sac known as the amnion.
- The embryonic disk is composed of three layers: the ectoderm, mesoderm, and endoderm.
- The creation of the primary germ layers is called gastrulation. The developing embryo at this point is called the gastrula.
- Morphogenesis, which begins with gastrulation, is a series of events that form the distinct structures of the developing embryo. It depends on the ability of embryonic cells to change into different types of cells.
- The development of the primary germ layers creates three distinct layers of cells: the endoderm, mesoderm, or the ectoderm. The cells in the primary germ layers are the source of all of the organs and tissues of the body. The process of the development of these cells into particular shapes and able to perform particular functions is called differentiation.
- Neurulation is the development of the neural tube (found just above the notochord), which develops into the brain and the spinal cord. Cells along the surface of the notochord begin to thicken. As the cells thicken, folds develop along each side of a groove along this surface. As the folds fuse, they become the neural tube.
- During the third week, a thickened band of mesoderm cells (a primary germ layer) develops along the back of the embryonic disk. These cells lie along what will become the baby's back and come together to form the notochord (the basic framework of the skeleton). In addition, a small reddish bulge that contains the heart forms; the heart begins to beat on the 18th day.
- During the fourth week, the blood cells are forming and beginning to fill the developing blood vessels; the lungs and kidneys are taking shape; small buds which will become limbs form; a distinct head, with early evidence of eyes, ears, and a nose, is visible.
- Students will list any four of the following: In the fifth week, the lidless eyes are open, and the cells of the brain are differentiating very quickly. At the sixth week, the brain is continuing to develop; the limbs are lengthening and can flex; the gonads produce hormones to influence the development of the external genitalia. In the seventh and eighth weeks, the organs are fully formed; the nervous system is coordinating the body activity; a skeleton of cartilage has formed; eyes are well developed, but not open; nostrils are developed but are plugged with mucus; external genitalia are developing, but are undifferentiated at this point. Upon completion of the eighth week, approximately 90 percent of the organs and structures are established, and continue to enlarge and mature.
- The embryo is identified as a fetus ("offspring") after the eighth week of pregnancy, when the organs and structures are established.
- The extra-embryonic membranes are: the allantois, the amnion, the chorion, and the yolk sac.
- One portion of the placenta develops from the chorion. The allantois is the foundation of the umbilical cord.
- The placenta has nutritional, excretory, respiratory, endocrine, and immune functions.
Nutritional: transports nutrients such as glucose, amino acids, and fatty acids; it also stores nutrients (protein, fats, and carbohydrates, minerals) to be released later in the pregnancy.
Excretory: transports wastes such as urea, ammonia, and creatinine from the fetal blood to the mother's blood.
Respiratory: transports oxygen from mother to fetus, and carbon dioxide from fetus to mother.
Endocrine: secretes hormones such as estrogen, progesterone, and human chorionic gonadotropin; allows these hormones to diffuse from mother to fetus and fetus to mother.
Immune: provides passive immunity by transporting antibodies from the mother to the fetus's blood.
- The umbilical cord contains one vein and two arteries; the arteries transport oxygen-depleted blood from the fetus to the placenta. The vein transports oxygen-rich blood to the fetus. (Students can diagram the pathway to summarize the role).
Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), TRG Pg 6-42 & 6-43. Reproduced by permission